Merge remote-tracking branch 'eugenp/master'

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "testgitrepo"]
-	path = testgitrepo
-	url = /home/prd/Development/projects/idea/tutorials/spring-boot/src/main/resources/testgitrepo/

algorithms/README.md

@@ -22,3 +22,6 @@
 - [Displaying Money Amounts in Words](http://www.baeldung.com/java-money-into-words)
 - [A Collaborative Filtering Recommendation System in Java](http://www.baeldung.com/java-collaborative-filtering-recommendations)
 - [Find All Pairs of Numbers in an Array That Add Up to a Given Sum](http://www.baeldung.com/java-algorithm-number-pairs-sum)
+- [Converting Between Roman and Arabic Numerals in Java](http://www.baeldung.com/java-convert-roman-arabic)
+- [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
+- [Find the Middle Element of a Linked List](http://www.baeldung.com/java-linked-list-middle-element)

algorithms/src/main/java/com/baeldung/algorithms/mcts/montecarlo/MonteCarloTreeSearch.java

@@ -10,7 +10,7 @@ public class MonteCarloTreeSearch {
 
     private static final int WIN_SCORE = 10;
     private int level;
-    private int oponent;
+    private int opponent;
 
     public MonteCarloTreeSearch() {
         this.level = 3;
@@ -32,11 +32,11 @@ public class MonteCarloTreeSearch {
         long start = System.currentTimeMillis();
         long end = start + 60 * getMillisForCurrentLevel();
 
-        oponent = 3 - playerNo;
+        opponent = 3 - playerNo;
         Tree tree = new Tree();
         Node rootNode = tree.getRoot();
         rootNode.getState().setBoard(board);
-        rootNode.getState().setPlayerNo(oponent);
+        rootNode.getState().setPlayerNo(opponent);
 
         while (System.currentTimeMillis() < end) {
             // Phase 1 - Selection
@@ -93,7 +93,7 @@ public class MonteCarloTreeSearch {
         State tempState = tempNode.getState();
         int boardStatus = tempState.getBoard().checkStatus();
 
-        if (boardStatus == oponent) {
+        if (boardStatus == opponent) {
             tempNode.getParent().getState().setWinScore(Integer.MIN_VALUE);
             return boardStatus;
         }

antlr/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles: 
+
+- [Java with ANTLR](http://www.baeldung.com/java-antlr)

aws-lambda/sam-templates/template-implicit.yaml

@@ -0,0 +1,60 @@
+AWSTemplateFormatVersion: '2010-09-09'
+Transform: 'AWS::Serverless-2016-10-31'
+Description: Baeldung Serverless Application Model Example with Implicit API Definition
+Globals:
+  Api:
+    EndpointConfiguration: REGIONAL
+    Name: "TestAPI"
+Resources:
+  PersonTable:
+    Type: AWS::Serverless::SimpleTable
+    Properties:
+      PrimaryKey:
+          Name: id
+          Type: Number
+      TableName: Person
+  StorePersonFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      Handler: com.baeldung.lambda.apigateway.APIDemoHandler::handleRequest
+      Runtime: java8
+      Timeout: 15
+      MemorySize: 512
+      CodeUri: ../target/aws-lambda-0.1.0-SNAPSHOT.jar
+      Policies:
+        - DynamoDBCrudPolicy:
+            TableName: !Ref PersonTable
+      Environment:
+        Variables:
+          TABLE_NAME: !Ref PersonTable
+      Events:
+        StoreApi:
+          Type: Api
+          Properties:
+            Path: /persons
+            Method: PUT
+  GetPersonByHTTPParamFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      Handler: com.baeldung.lambda.apigateway.APIDemoHandler::handleGetByParam
+      Runtime: java8
+      Timeout: 15
+      MemorySize: 512
+      CodeUri: ../target/aws-lambda-0.1.0-SNAPSHOT.jar
+      Policies:
+        - DynamoDBReadPolicy:
+            TableName: !Ref PersonTable
+      Environment:
+        Variables:
+          TABLE_NAME: !Ref PersonTable
+      Events:
+        GetByPathApi:
+          Type: Api
+          Properties:
+            Path: /persons/{id}
+            Method: GET
+        GetByQueryApi:
+          Type: Api
+          Properties:
+            Path: /persons
+            Method: GET

aws-lambda/sam-templates/template-inline-swagger.yaml

@@ -0,0 +1,112 @@
+AWSTemplateFormatVersion: '2010-09-09'
+Transform: 'AWS::Serverless-2016-10-31'
+Description: Baeldung Serverless Application Model Example with Inline Swagger API Definition
+Resources:
+  PersonTable:
+    Type: AWS::Serverless::SimpleTable
+    Properties:
+      PrimaryKey:
+          Name: id
+          Type: Number
+      TableName: Person
+  StorePersonFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      Handler: com.baeldung.lambda.apigateway.APIDemoHandler::handleRequest
+      Runtime: java8
+      Timeout: 15
+      MemorySize: 512
+      CodeUri: ../target/aws-lambda-0.1.0-SNAPSHOT.jar
+      Policies:
+        - DynamoDBCrudPolicy:
+            TableName: !Ref PersonTable
+      Environment:
+        Variables:
+          TABLE_NAME: !Ref PersonTable
+      Events:
+        StoreApi:
+          Type: Api
+          Properties:
+            Path: /persons
+            Method: PUT
+            RestApiId:
+                Ref: MyApi
+  GetPersonByHTTPParamFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      Handler: com.baeldung.lambda.apigateway.APIDemoHandler::handleGetByParam
+      Runtime: java8
+      Timeout: 15
+      MemorySize: 512
+      CodeUri: ../target/aws-lambda-0.1.0-SNAPSHOT.jar
+      Policies:
+        - DynamoDBReadPolicy:
+            TableName: !Ref PersonTable
+      Environment:
+        Variables:
+          TABLE_NAME: !Ref PersonTable
+      Events:
+        GetByPathApi:
+          Type: Api
+          Properties:
+            Path: /persons/{id}
+            Method: GET
+            RestApiId:
+                Ref: MyApi
+        GetByQueryApi:
+          Type: Api
+          Properties:
+            Path: /persons
+            Method: GET
+            RestApiId:
+                Ref: MyApi
+  MyApi:
+    Type: AWS::Serverless::Api
+    Properties:
+      StageName: test
+      EndpointConfiguration: REGIONAL
+      DefinitionBody:
+        swagger: "2.0"
+        info:
+          title: "TestAPI"
+        paths:
+          /persons:
+            get:
+              parameters:
+              - name: "id"
+                in: "query"
+                required: true
+                type: "string"
+              x-amazon-apigateway-request-validator: "Validate query string parameters and\
+                \ headers"
+              x-amazon-apigateway-integration:
+                uri:
+                  Fn::Sub: arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${GetPersonByHTTPParamFunction.Arn}/invocations
+                responses: {}
+                httpMethod: "POST"
+                type: "aws_proxy"
+            put:
+              x-amazon-apigateway-integration:
+                uri:
+                  Fn::Sub: arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${StorePersonFunction.Arn}/invocations
+                responses: {}
+                httpMethod: "POST"
+                type: "aws_proxy"
+          /persons/{id}:
+            get:
+              parameters:
+              - name: "id"
+                in: "path"
+                required: true
+                type: "string"
+              responses: {}
+              x-amazon-apigateway-integration:
+                uri:
+                  Fn::Sub: arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${GetPersonByHTTPParamFunction.Arn}/invocations
+                responses: {}
+                httpMethod: "POST"
+                type: "aws_proxy"
+        x-amazon-apigateway-request-validators:
+          Validate query string parameters and headers:
+            validateRequestParameters: true
+            validateRequestBody: false

aws-lambda/src/main/java/com/baeldung/lambda/apigateway/APIDemoHandler.java

@@ -36,9 +36,7 @@ public class APIDemoHandler implements RequestStreamHandler {
 
                 dynamoDb.getTable(DYNAMODB_TABLE_NAME)
                     .putItem(new PutItemSpec().withItem(new Item().withNumber("id", person.getId())
-								.withString("firstName", person.getFirstName())
+                        .withString("name", person.getName())));
-								.withString("lastName", person.getLastName()).withNumber("age", person.getAge())
-								.withString("address", person.getAddress())));
             }
 
             JSONObject responseBody = new JSONObject();
@@ -61,8 +59,7 @@ public class APIDemoHandler implements RequestStreamHandler {
         writer.close();
     }
 
-	public void handleGetByPathParam(InputStream inputStream, OutputStream outputStream, Context context)
+    public void handleGetByParam(InputStream inputStream, OutputStream outputStream, Context context) throws IOException {
-			throws IOException {
 
         BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
         JSONObject responseJson = new JSONObject();
@@ -81,61 +78,20 @@ public class APIDemoHandler implements RequestStreamHandler {
                 if (pps.get("id") != null) {
 
                     int id = Integer.parseInt((String) pps.get("id"));
-					result = dynamoDb.getTable(DYNAMODB_TABLE_NAME).getItem("id", id);
+                    result = dynamoDb.getTable(DYNAMODB_TABLE_NAME)
+                        .getItem("id", id);
                 }
 
-			}
+            } else if (event.get("queryStringParameters") != null) {
-			if (result != null) {
-
-				Person person = new Person(result.toJSON());
-				responseBody.put("Person", person);
-				responseJson.put("statusCode", 200);
-			} else {
-
-				responseBody.put("message", "No item found");
-				responseJson.put("statusCode", 404);
-			}
-
-			JSONObject headerJson = new JSONObject();
-			headerJson.put("x-custom-header", "my custom header value");
-
-			responseJson.put("headers", headerJson);
-			responseJson.put("body", responseBody.toString());
-
-		} catch (ParseException pex) {
-			responseJson.put("statusCode", 400);
-			responseJson.put("exception", pex);
-		}
-
-		OutputStreamWriter writer = new OutputStreamWriter(outputStream, "UTF-8");
-		writer.write(responseJson.toString());
-		writer.close();
-	}
-
-	public void handleGetByQueryParam(InputStream inputStream, OutputStream outputStream, Context context)
-			throws IOException {
-
-		BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
-		JSONObject responseJson = new JSONObject();
-
-		AmazonDynamoDB client = AmazonDynamoDBClientBuilder.defaultClient();
-		DynamoDB dynamoDb = new DynamoDB(client);
-
-		Item result = null;
-		try {
-			JSONObject event = (JSONObject) parser.parse(reader);
-			JSONObject responseBody = new JSONObject();
-
-			if (event.get("queryStringParameters") != null) {
 
                 JSONObject qps = (JSONObject) event.get("queryStringParameters");
                 if (qps.get("id") != null) {
 
                     int id = Integer.parseInt((String) qps.get("id"));
-					result = dynamoDb.getTable(DYNAMODB_TABLE_NAME).getItem("id", id);
+                    result = dynamoDb.getTable(DYNAMODB_TABLE_NAME)
+                        .getItem("id", id);
                 }
             }
-
             if (result != null) {
 
                 Person person = new Person(result.toJSON());
@@ -162,5 +118,4 @@ public class APIDemoHandler implements RequestStreamHandler {
         writer.write(responseJson.toString());
         writer.close();
     }
-
 }

aws-lambda/src/main/java/com/baeldung/lambda/apigateway/model/Person.java

@@ -6,19 +6,13 @@ import com.google.gson.GsonBuilder;
 public class Person {
 
     private int id;
-	private String firstName;
+    private String name;
-	private String lastName;
-	private int age;
-	private String address;
 
     public Person(String json) {
         Gson gson = new Gson();
         Person request = gson.fromJson(json, Person.class);
         this.id = request.getId();
-		this.firstName = request.getFirstName();
+        this.name = request.getName();
-		this.lastName = request.getLastName();
-		this.age = request.getAge();
-		this.address = request.getAddress();
     }
 
     public String toString() {
@@ -34,35 +28,11 @@ public class Person {
         this.id = id;
     }
 
-	public String getFirstName() {
+    public String getName() {
-		return firstName;
+        return name;
     }
 
-	public void setFirstName(String firstName) {
+    public void setName(String name) {
-		this.firstName = firstName;
+        this.name = name;
-	}
-
-	public String getLastName() {
-		return lastName;
-	}
-
-	public void setLastName(String lastName) {
-		this.lastName = lastName;
-	}
-
-	public int getAge() {
-		return age;
-	}
-
-	public void setAge(int age) {
-		this.age = age;
-	}
-
-	public String getAddress() {
-		return address;
-	}
-
-	public void setAddress(String address) {
-		this.address = address;
     }
 }

cdi/README.md

@@ -1,2 +1,3 @@
 ### Relevant Articles:
 - [CDI Interceptor vs Spring AspectJ](http://www.baeldung.com/cdi-interceptor-vs-spring-aspectj)
+- [An Introduction to CDI (Contexts and Dependency Injection) in Java](http://www.baeldung.com/java-ee-cdi)

core-java-8/README.md

@@ -54,3 +54,5 @@
 - [An Introduction to Java.util.Hashtable Class](http://www.baeldung.com/java-hash-table)
 - [Method Parameter Reflection in Java](http://www.baeldung.com/java-parameter-reflection)
 - [Java 8 Unsigned Arithmetic Support](http://www.baeldung.com/java-unsigned-arithmetic)
+- [How to Get the Start and the End of a Day using Java](http://www.baeldung.com/java-day-start-end)
+- [Generalized Target-Type Inference in Java](http://www.baeldung.com/java-generalized-target-type-inference)

core-java-8/src/test/java/com/baeldung/fileToBase64StringConversion/FileToBase64StringConversionUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.fileToBase64StringConversion;
+
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Base64;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.Test;
+
+public class FileToBase64StringConversionUnitTest {
+
+    private String inputFilePath = "test_image.jpg";
+    private String outputFilePath = "test_image_copy.jpg";
+
+    @Test
+    public void fileToBase64StringConversion() throws IOException {
+        //load file from /src/test/resources
+        ClassLoader classLoader = getClass().getClassLoader();
+        File inputFile = new File(classLoader
+          .getResource(inputFilePath)
+          .getFile());
+
+        byte[] fileContent = FileUtils.readFileToByteArray(inputFile);
+        String encodedString = Base64
+          .getEncoder()
+          .encodeToString(fileContent);
+
+        //create output file
+        File outputFile = new File(inputFile
+          .getParentFile()
+          .getAbsolutePath() + File.pathSeparator + outputFilePath);
+
+        // decode the string and write to file
+        byte[] decodedBytes = Base64
+          .getDecoder()
+          .decode(encodedString);
+        FileUtils.writeByteArrayToFile(outputFile, decodedBytes);
+
+        assertTrue(FileUtils.contentEquals(inputFile, outputFile));
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/list/ReverseIterator.java

@@ -0,0 +1,80 @@
+package com.baeldung.java.list;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.ListIterator;
+
+import org.apache.commons.collections4.iterators.ReverseListIterator;
+
+import com.google.common.collect.Lists;
+
+/**
+ * Provides methods for iterating backward over a list.
+ */
+public class ReverseIterator {
+
+    /**
+     * Iterate using the for loop.
+     *
+     * @param list the list
+     */
+    public void iterateUsingForLoop(final List<String> list) {
+
+        for (int i = list.size(); i-- > 0; ) {
+            System.out.println(list.get(i));
+        }
+    }
+
+    /**
+     * Iterate using the Java {@link ListIterator}.
+     *
+     * @param list the list
+     */
+    public void iterateUsingListIterator(final List<String> list) {
+
+        final ListIterator listIterator = list.listIterator(list.size());
+        while (listIterator.hasPrevious()) {
+            System.out.println(listIterator.previous());
+        }
+    }
+
+    /**
+     * Iterate using Java {@link Collections} API.
+     *
+     * @param list the list
+     */
+    public void iterateUsingCollections(final List<String> list) {
+
+        Collections.reverse(list);
+        for (final String item : list) {
+            System.out.println(item);
+        }
+    }
+
+    /**
+     * Iterate using Apache Commons {@link ReverseListIterator}.
+     *
+     * @param list the list
+     */
+    public void iterateUsingApacheReverseListIterator(final List<String> list) {
+
+        final ReverseListIterator listIterator = new ReverseListIterator(list);
+        while (listIterator.hasNext()) {
+            System.out.println(listIterator.next());
+        }
+    }
+
+    /**
+     * Iterate using Guava {@link Lists} API.
+     *
+     * @param list the list
+     */
+    public void iterateUsingGuava(final List<String> list) {
+
+        final List<String> reversedList = Lists.reverse(list);
+        for (final String item : reversedList) {
+            System.out.println(item);
+        }
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/java/list/ReverseIteratorUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.java.list;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.ListIterator;
+
+import org.apache.commons.collections4.iterators.ReverseListIterator;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import com.google.common.collect.Lists;
+
+public class ReverseIteratorUnitTest {
+
+    private final ReverseIterator reverseIterator = new ReverseIterator();
+
+    private List<String> list;
+
+    private final String originalString = "ABCDE";
+
+    @BeforeEach
+    void setUp() {
+
+        list = Lists.newArrayList("A", "B", "C", "D", "E");
+    }
+
+    @Test
+    void whenIteratingUsingForLoop_thenCorrect() {
+
+        String reverseString = "";
+        for (int i = list.size(); i-- > 0; ) {
+            reverseString += list.get(i);
+        }
+        assertEquals(reverseString, StringUtils.reverse(originalString));
+    }
+
+    @Test
+    void whenIteratingUsingListIterator_thenCorrect() {
+
+        String reverseString = "";
+        final ListIterator listIterator = list.listIterator(list.size());
+        while (listIterator.hasPrevious()) {
+            reverseString += listIterator.previous();
+        }
+        assertEquals(reverseString, StringUtils.reverse(originalString));
+    }
+
+    @Test
+    void whenIteratingUsingCollections_thenCorrect() {
+
+        String reverseString = "";
+        Collections.reverse(list);
+        for (final String item : list) {
+            reverseString += item;
+        }
+        assertEquals(reverseString, StringUtils.reverse(originalString));
+
+        assertEquals("E", list.get(0));
+    }
+
+    @Test
+    void whenIteratingUsingApacheReverseListIterator_thenCorrect() {
+
+        String reverseString = "";
+        final ReverseListIterator listIterator = new ReverseListIterator(list);
+        while (listIterator.hasNext()) {
+            reverseString += listIterator.next();
+        }
+        assertEquals(reverseString, StringUtils.reverse(originalString));
+    }
+
+    @Test
+    void whenIteratingUsingGuava_thenCorrect() {
+
+        String reverseString = "";
+        final List<String> reversedList = Lists.reverse(list);
+        for (final String item : reversedList) {
+            reverseString += item;
+        }
+        assertEquals(reverseString, StringUtils.reverse(originalString));
+
+        assertEquals("A", list.get(0));
+    }
+}

core-java-io/src/main/java/com/baeldung/symlink/SymLinkExample.java

@@ -0,0 +1,54 @@
+package com.baeldung.symlink;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import static java.nio.file.StandardOpenOption.*;
+import java.util.stream.IntStream;
+
+public class SymLinkExample {
+
+    public void createSymbolicLink(Path link, Path target) throws IOException {
+        if (Files.exists(link)) {
+            Files.delete(link);
+        }
+        Files.createSymbolicLink(link, target);
+    }
+
+    public void createHardLink(Path link, Path target) throws IOException {
+        if (Files.exists(link)) {
+            Files.delete(link);
+        }
+        Files.createLink(link, target);
+    }
+
+    public Path createTextFile() throws IOException {
+        byte[] content = IntStream.range(0, 10000)
+            .mapToObj(i -> i + System.lineSeparator())
+            .reduce("", String::concat)
+            .getBytes(StandardCharsets.UTF_8);
+        Path filePath = Paths.get(".", "target_link.txt");
+        Files.write(filePath, content, CREATE, TRUNCATE_EXISTING);
+        return filePath;
+    }
+
+    public void printLinkFiles(Path path) throws IOException {
+        try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
+            for (Path file : stream) {
+                if (Files.isDirectory(file)) {
+                    printLinkFiles(file);
+                } else if (Files.isSymbolicLink(file)) {
+                    System.out.format("File link '%s' with target '%s'%n", file, Files.readSymbolicLink(file));
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        new SymLinkExample().printLinkFiles(Paths.get("."));
+    }
+
+}

core-java-io/src/test/java/com/baeldung/symlink/SymLinkExampleUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.symlink;
+
+import static org.junit.Assert.*;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.junit.Test;
+
+public class SymLinkExampleUnitTest {
+
+    @Test
+    public void whenUsingFiles_thenCreateSymbolicLink() throws IOException {
+        SymLinkExample example = new SymLinkExample();
+        Path filePath = example.createTextFile();
+        Path linkPath = Paths.get(".", "symbolic_link.txt");
+        example.createSymbolicLink(linkPath, filePath);
+        assertTrue(Files.isSymbolicLink(linkPath));
+    }
+
+    @Test
+    public void whenUsingFiles_thenCreateHardLink() throws IOException {
+        SymLinkExample example = new SymLinkExample();
+        Path filePath = example.createTextFile();
+        Path linkPath = Paths.get(".", "hard_link.txt");
+        example.createHardLink(linkPath, filePath);
+        assertFalse(Files.isSymbolicLink(linkPath));
+        assertEquals(filePath.toFile()
+            .length(),
+            linkPath.toFile()
+                .length());
+    }
+
+}

core-java/README.md

@@ -160,3 +160,9 @@
 - [Guide to the super Java Keyword](http://www.baeldung.com/java-super)
 - [Guide to the this Java Keyword](http://www.baeldung.com/java-this)
 - [Jagged Arrays In Java](http://www.baeldung.com/java-jagged-arrays)
+- [Importance of Main Manifest Attribute in a Self-Executing JAR](http://www.baeldung.com/java-jar-executable-manifest-main-class)
+- [Extracting Year, Month and Day from Date in Java](http://www.baeldung.com/java-year-month-day)
+- [Get Date Without Time in Java](http://www.baeldung.com/java-date-without-time)
+- [Convert a String to Title Case](http://www.baeldung.com/java-string-title-case)
+- [How to Get the File Extension of a File in Java](http://www.baeldung.com/java-file-extension)
+- [Immutable Objects in Java](http://www.baeldung.com/java-immutable-object)

core-java/pom.xml

@@ -198,11 +198,6 @@
             <artifactId>mail</artifactId>
             <version>${javax.mail.version}</version>
       </dependency>
-        <dependency>
-            <groupId>javax.mail</groupId>
-            <artifactId>mail</artifactId>
-            <version>1.5.0-b01</version>
-        </dependency>
         <dependency>
             <groupId>com.ibm.icu</groupId>
             <artifactId>icu4j</artifactId>
@@ -255,6 +250,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-jar-plugin</artifactId>
+                <version>${maven-jar-plugin.version}</version>
                 <configuration>
                     <archive>
                         <manifest>
@@ -293,6 +289,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-shade-plugin</artifactId>
+                <version>${maven-shade-plugin.version}</version>
                 <executions>
                     <execution>
                         <goals>
@@ -314,6 +311,7 @@
             <plugin>
                 <groupId>com.jolira</groupId>
                 <artifactId>onejar-maven-plugin</artifactId>
+                <version>${onejar-maven-plugin.version}</version>
                 <executions>
                     <execution>
                         <configuration>
@@ -331,6 +329,7 @@
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
+                <version>${spring-boot-maven-plugin.version}</version>
                 <executions>
                     <execution>
                         <goals>
@@ -478,6 +477,10 @@
         <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
         <exec-maven-plugin.version>1.6.0</exec-maven-plugin.version>
         <javax.mail.version>1.5.0-b01</javax.mail.version>
+        <maven-jar-plugin.version>3.0.2</maven-jar-plugin.version>
+        <onejar-maven-plugin.version>1.4.4</onejar-maven-plugin.version>
+        <maven-shade-plugin.version>3.1.1</maven-shade-plugin.version>
+        <spring-boot-maven-plugin.version>2.0.3.RELEASE</spring-boot-maven-plugin.version>
         <icu4j.version>61.1</icu4j.version>
     </properties>
 

core-java/src/main/java/com/baeldung/console/ConsoleConsoleClass.java

@@ -0,0 +1,26 @@
+package com.baeldung.console;
+
+import java.io.Console;
+
+public class ConsoleConsoleClass {
+
+    public static void main(String[] args) {
+        Console console = System.console();
+
+        if (console == null) {
+            System.out.print("No console available");
+            return;
+        }
+
+        String progLanguauge = console.readLine("Enter your favourite programming language: ");
+        console.printf(progLanguauge + " is very interesting!");
+
+        char[] pass = console.readPassword("To finish, enter password: ");
+        
+        if ("BAELDUNG".equals(pass.toString().toUpperCase()))
+            console.printf("Good! Regards!");
+        else 
+            console.printf("Nice try. Regards.");
+
+    }
+}

core-java/src/main/java/com/baeldung/console/ConsoleScannerClass.java

@@ -0,0 +1,76 @@
+package com.baeldung.console;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Scanner;
+import java.util.regex.Pattern;
+
+public class ConsoleScannerClass {
+
+    public static void main(String[] args) {
+        System.out.println("Please enter your name and surname: ");
+
+        Scanner scanner = new Scanner(System.in);
+
+        String nameSurname = scanner.nextLine();
+
+        System.out.println("Please enter your gender: ");
+
+        char gender = scanner.next().charAt(0);
+
+        System.out.println("Please enter your age: ");
+
+        int age = scanner.nextInt();
+
+        System.out.println("Please enter your height in meters: ");
+
+        double height = scanner.nextDouble();
+
+        System.out.println(nameSurname + ", " + age + ", is a great " + (gender == 'm' ? "guy" : "girl") + " with " + height + " meters height" + " and " + (gender == 'm' ? "he" : "she") + " reads Baeldung.");
+
+        System.out.print("Have a good");
+        System.out.print(" one!");
+
+        System.out.println("\nPlease enter number of years of experience as a developer: ");
+
+        BufferedReader buffReader = new BufferedReader(new InputStreamReader(System.in));
+
+        int i = 0;
+
+        try {
+            i = Integer.parseInt(buffReader.readLine());
+        } catch (NumberFormatException e) {
+            // TODO Auto-generated catch block
+            e.printStackTrace();
+        } catch (IOException e) {
+            // TODO Auto-generated catch block
+            e.printStackTrace();
+        }
+
+        System.out.println("You are a " + (i > 5 ? "great" : "good") + " developer!");
+
+        int sum = 0, count = 0;
+
+        System.out.println("Please enter your college degrees. To finish, enter baeldung website url");
+
+        while (scanner.hasNextInt()) {
+            int nmbr = scanner.nextInt();
+            sum += nmbr;
+            count++;
+        }
+        int mean = sum / count;
+
+        System.out.println("Your average degree is " + mean);
+
+        if (scanner.hasNext(Pattern.compile("www.baeldung.com")))
+            System.out.println("Correct!");
+        else
+            System.out.println("Baeldung website url is www.baeldung.com");
+
+        if (scanner != null)
+            scanner.close();
+
+    }
+
+}

core-java/src/main/java/com/baeldung/customexception/FileManager.java

@@ -0,0 +1,43 @@
+package com.baeldung.customexception;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.util.Scanner;
+
+public class FileManager {
+
+    public static String getFirstLine(String fileName) throws IncorrectFileNameException {
+        try (Scanner file = new Scanner(new File(fileName))) {
+            if (file.hasNextLine()) {
+                return file.nextLine();
+            } else {
+                throw new IllegalArgumentException("Non readable file");
+            }
+        } catch (FileNotFoundException err) {
+            if (!isCorrectFileName(fileName)) {
+                throw new IncorrectFileNameException("Incorrect filename : " + fileName, err);
+            }
+            // Logging etc
+        } catch (IllegalArgumentException err) {
+            if (!containsExtension(fileName)) {
+                throw new IncorrectFileExtensionException("Filename does not contain extension : " + fileName, err);
+            }
+            // Other error cases and logging
+        }
+        return "Default First Line";
+    }
+
+    private static boolean containsExtension(String fileName) {
+        if (fileName.contains(".txt") || fileName.contains(".doc"))
+            return true;
+        return false;
+    }
+
+    private static boolean isCorrectFileName(String fileName) {
+        if (fileName.equals("wrongFileName.txt"))
+            return false;
+        else
+            return true;
+    }
+
+}

core-java/src/main/java/com/baeldung/customexception/IncorrectFileExtensionException.java

@@ -0,0 +1,9 @@
+package com.baeldung.customexception;
+
+public class IncorrectFileExtensionException extends RuntimeException{
+    private static final long serialVersionUID = 1L;
+
+    public IncorrectFileExtensionException(String errorMessage, Throwable err) {
+        super(errorMessage, err);
+    }
+}

core-java/src/main/java/com/baeldung/customexception/IncorrectFileNameException.java

@@ -0,0 +1,9 @@
+package com.baeldung.customexception;
+
+public class IncorrectFileNameException extends Exception {
+    private static final long serialVersionUID = 1L;
+    
+    public IncorrectFileNameException(String errorMessage, Throwable err) {
+        super(errorMessage, err);
+    }
+}

core-java/src/main/java/com/baeldung/encrypt/FileEncrypterDecrypter.java

@@ -0,0 +1,60 @@
+package com.baeldung.encrypt;
+
+import javax.crypto.*;
+import javax.crypto.spec.IvParameterSpec;
+import java.io.*;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+class FileEncrypterDecrypter {
+
+    private SecretKey secretKey;
+    private Cipher cipher;
+
+    FileEncrypterDecrypter(SecretKey secretKey, String cipher) throws NoSuchPaddingException, NoSuchAlgorithmException {
+        this.secretKey = secretKey;
+        this.cipher = Cipher.getInstance(cipher);
+    }
+
+    void encrypt(String content, String fileName) throws InvalidKeyException, IOException {
+        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
+        byte[] iv = cipher.getIV();
+
+        try (
+                FileOutputStream fileOut = new FileOutputStream(fileName);
+                CipherOutputStream cipherOut = new CipherOutputStream(fileOut, cipher)
+        ) {
+            fileOut.write(iv);
+            cipherOut.write(content.getBytes());
+        }
+
+    }
+
+    String decrypt(String fileName) throws InvalidAlgorithmParameterException, InvalidKeyException, IOException {
+
+        String content;
+
+        try (FileInputStream fileIn = new FileInputStream(fileName)) {
+            byte[] fileIv = new byte[16];
+            fileIn.read(fileIv);
+            cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(fileIv));
+
+            try (
+                    CipherInputStream cipherIn = new CipherInputStream(fileIn, cipher);
+                    InputStreamReader inputReader = new InputStreamReader(cipherIn);
+                    BufferedReader reader = new BufferedReader(inputReader)
+                ) {
+
+                StringBuilder sb = new StringBuilder();
+                String line;
+                while ((line = reader.readLine()) != null) {
+                    sb.append(line);
+                }
+                content = sb.toString();
+            }
+
+        }
+        return content;
+    }
+}

core-java/src/test/java/com/baeldung/customexception/IncorrectFileExtensionExceptionUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.customexception;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.File;
+
+import org.junit.Test;
+
+public class IncorrectFileExtensionExceptionUnitTest {
+
+    @Test
+    public void testWhenCorrectFileExtensionGiven_ReceivesNoException() throws IncorrectFileNameException {
+        assertThat(FileManager.getFirstLine("correctFileNameWithProperExtension.txt")).isEqualTo("Default First Line");
+    }
+
+    @Test(expected = IncorrectFileExtensionException.class)
+    public void testWhenCorrectFileNameExceptionThrown_ReceivesNoException() throws IncorrectFileNameException {
+        StringBuffer sBuffer = new StringBuffer();
+        sBuffer.append("src");
+        sBuffer.append(File.separator);
+        sBuffer.append("test");
+        sBuffer.append(File.separator);
+        sBuffer.append("resources");
+        sBuffer.append(File.separator);
+        sBuffer.append("correctFileNameWithoutProperExtension");
+        FileManager.getFirstLine(sBuffer.toString());
+    }
+
+}

core-java/src/test/java/com/baeldung/customexception/IncorrectFileNameExceptionUnitTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.customexception;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class IncorrectFileNameExceptionUnitTest {
+
+    @Test(expected = IncorrectFileNameException.class)
+    public void testWhenIncorrectFileNameExceptionThrown_ReceivesIncorrectFileNameException() throws IncorrectFileNameException {
+        FileManager.getFirstLine("wrongFileName.txt");
+    }
+
+    @Test
+    public void testWhenCorrectFileNameExceptionThrown_ReceivesNoException() throws IncorrectFileNameException {
+        assertThat(FileManager.getFirstLine("correctFileName.txt")).isEqualTo("Default First Line");
+    }
+
+}

core-java/src/test/java/com/baeldung/encrypt/FileEncrypterDecrypterIntegrationTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.encrypt;
+
+import org.junit.Test;
+
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
+import java.io.File;
+import java.io.IOException;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
+public class FileEncrypterDecrypterIntegrationTest {
+
+    @Test
+    public void givenStringAndFilename_whenEncryptingIntoFile_andDecryptingFileAgain_thenOriginalStringIsReturned() throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IOException, InvalidAlgorithmParameterException {
+        String originalContent = "foobar";
+        SecretKey secretKey = KeyGenerator.getInstance("AES").generateKey();
+
+        FileEncrypterDecrypter fileEncrypterDecrypter = new FileEncrypterDecrypter(secretKey, "AES/CBC/PKCS5Padding");
+        fileEncrypterDecrypter.encrypt(originalContent, "baz.enc");
+
+        String decryptedContent = fileEncrypterDecrypter.decrypt("baz.enc");
+        assertThat(decryptedContent, is(originalContent));
+
+        new File("baz.enc").delete(); // cleanup
+    }
+}

core-java/src/test/java/com/baeldung/thread/join/ThreadJoinUnitTest.java

@@ -0,0 +1,95 @@
+package com.baeldung.thread.join;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.logging.Logger;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+/**
+ * Demonstrates Thread.join behavior.
+ *
+ */
+public class ThreadJoinUnitTest {
+
+    final static Logger LOGGER = Logger.getLogger(ThreadJoinUnitTest.class.getName());
+
+    class SampleThread extends Thread {
+        public int processingCount = 0;
+
+        SampleThread(int processingCount) {
+            this.processingCount = processingCount;
+            LOGGER.info("Thread " + this.getName() + " created");
+        }
+
+        @Override
+        public void run() {
+            LOGGER.info("Thread " + this.getName() + " started");
+            while (processingCount > 0) {
+                try {
+                    Thread.sleep(1000); // Simulate some work being done by thread
+                } catch (InterruptedException e) {
+                    LOGGER.info("Thread " + this.getName() + " interrupted.");
+                }
+                processingCount--;
+                LOGGER.info("Inside Thread " + this.getName() + ", processingCount = " + processingCount);
+            }
+            LOGGER.info("Thread " + this.getName() + " exiting");
+        }
+    }
+
+    @Test
+    public void givenNewThread_whenJoinCalled_returnsImmediately() throws InterruptedException {
+        Thread t1 = new SampleThread(0);
+        LOGGER.info("Invoking join.");
+        t1.join();
+        LOGGER.info("Returned from join");
+        LOGGER.info("Thread state is" + t1.getState());
+        assertFalse(t1.isAlive());
+    }
+
+    @Test
+    public void givenStartedThread_whenJoinCalled_waitsTillCompletion() 
+      throws InterruptedException {
+        Thread t2 = new SampleThread(1);
+        t2.start();
+        LOGGER.info("Invoking join.");
+        t2.join();
+        LOGGER.info("Returned from join");
+        assertFalse(t2.isAlive());
+    }
+
+    @Test
+    public void givenStartedThread_whenTimedJoinCalled_waitsUntilTimedout() 
+      throws InterruptedException {
+        Thread t3 = new SampleThread(10);
+        t3.start();
+        t3.join(1000);
+        assertTrue(t3.isAlive());
+    }
+
+    @Test
+    @Ignore
+    public void givenThreadTerminated_checkForEffect_notGuaranteed() 
+      throws InterruptedException {
+        SampleThread t4 = new SampleThread(10);
+        t4.start();
+      //not guaranteed to stop even if t4 finishes.
+        do {
+            
+        } while (t4.processingCount > 0);  
+    }
+
+    @Test
+    public void givenJoinWithTerminatedThread_checkForEffect_guaranteed() 
+      throws InterruptedException {
+        SampleThread t4 = new SampleThread(10);
+        t4.start();
+        do {
+            t4.join(100);
+        } while (t4.processingCount > 0);
+    }
+
+}

core-kotlin/.gitignore

@@ -1 +1,14 @@
 /bin/
+
+#ignore gradle
+.gradle/
+
+
+#ignore build and generated files
+build/
+node/
+out/
+
+#ignore installed node modules and package lock file
+node_modules/
+package-lock.json

core-kotlin/README.md

@@ -30,3 +30,5 @@
 - [Lambda Expressions in Kotlin](http://www.baeldung.com/kotlin-lambda-expressions)
 - [Writing Specifications with Kotlin and Spek](http://www.baeldung.com/kotlin-spek)
 - [Processing JSON with Kotlin and Klaxson](http://www.baeldung.com/kotlin-json-klaxson)
+- [Kotlin String Templates](http://www.baeldung.com/kotlin-string-template)
+- [Java EE 8 Security API](http://www.baeldung.com/java-ee-8-security)

core-kotlin/build.gradle

@@ -0,0 +1,57 @@
+
+
+group 'com.baeldung.ktor'
+version '1.0-SNAPSHOT'
+
+
+buildscript {
+    ext.kotlin_version = '1.2.41'
+    ext.ktor_version = '0.9.2'
+
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
+apply plugin: 'java'
+apply plugin: 'kotlin'
+apply plugin: 'application'
+
+mainClassName = 'APIServer.kt'
+
+sourceCompatibility = 1.8
+compileKotlin { kotlinOptions.jvmTarget = "1.8" }
+compileTestKotlin { kotlinOptions.jvmTarget = "1.8" }
+
+kotlin { experimental { coroutines "enable" } }
+
+repositories {
+    mavenCentral()
+    jcenter()
+    maven { url "https://dl.bintray.com/kotlin/ktor" }
+}
+sourceSets {
+    main{
+        kotlin{
+            srcDirs 'com/baeldung/ktor'
+        }
+    }
+
+}
+
+dependencies {
+    compile "io.ktor:ktor-server-netty:$ktor_version"
+    compile "ch.qos.logback:logback-classic:1.2.1"
+    compile "io.ktor:ktor-gson:$ktor_version"
+    testCompile group: 'junit', name: 'junit', version: '4.12'
+    implementation 'com.beust:klaxon:3.0.1'
+
+}
+task runServer(type: JavaExec) {
+    main = 'APIServer'
+   classpath = sourceSets.main.runtimeClasspath
+}

core-kotlin/kotlin-ktor/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-bin.zip

core-kotlin/kotlin-ktor/gradlew

@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

core-kotlin/kotlin-ktor/gradlew.bat

@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

core-kotlin/kotlin-ktor/src/main/kotlin/APIServer.kt

@@ -33,7 +33,7 @@ fun main(args: Array<String>) {
             header("X-Developer", "Baeldung")
         }
         install(CallLogging) {
-            level = Level.INFO
+            level = Level.DEBUG
             filter { call -> call.request.path().startsWith("/todo") }
             filter { call -> call.request.path().startsWith("/author") }
         }

core-kotlin/resources/logback.xml

@@ -0,0 +1,11 @@
+<configuration>
+  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+    </encoder>
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="STDOUT"/>
+  </root>
+</configuration>

core-kotlin/settings.gradle

@@ -0,0 +1,2 @@
+rootProject.name = 'KtorWithKotlin'
+

core-kotlin/src/main/kotlin/com/baeldung/ktor/APIServer.kt

@@ -0,0 +1,73 @@
+@file:JvmName("APIServer")
+
+
+import io.ktor.application.call
+import io.ktor.application.install
+import io.ktor.features.CallLogging
+import io.ktor.features.ContentNegotiation
+import io.ktor.features.DefaultHeaders
+import io.ktor.gson.gson
+import io.ktor.request.path
+import io.ktor.request.receive
+import io.ktor.response.respond
+import io.ktor.routing.*
+import io.ktor.server.engine.embeddedServer
+import io.ktor.server.netty.Netty
+import org.slf4j.event.Level
+
+data class Author(val name: String, val website: String)
+data class ToDo(var id: Int, val name: String, val description: String, val completed: Boolean)
+
+fun main(args: Array<String>) {
+
+    val toDoList = ArrayList<ToDo>();
+    val jsonResponse = """{
+            "id": 1,
+            "task": "Pay waterbill",
+            "description": "Pay water bill today",
+        }"""
+
+
+    embeddedServer(Netty, 8080) {
+        install(DefaultHeaders) {
+            header("X-Developer", "Baeldung")
+        }
+        install(CallLogging) {
+            level = Level.DEBUG
+            filter { call -> call.request.path().startsWith("/todo") }
+            filter { call -> call.request.path().startsWith("/author") }
+        }
+        install(ContentNegotiation) {
+            gson {
+                setPrettyPrinting()
+            }
+        }
+        routing() {
+            route("/todo") {
+                post {
+                    var toDo = call.receive<ToDo>();
+                    toDo.id = toDoList.size;
+                    toDoList.add(toDo);
+                    call.respond("Added")
+
+                }
+                delete("/{id}") {
+                    call.respond(toDoList.removeAt(call.parameters["id"]!!.toInt()));
+                }
+                get("/{id}") {
+
+                    call.respond(toDoList[call.parameters["id"]!!.toInt()]);
+                }
+                get {
+                    call.respond(toDoList);
+                }
+            }
+        get("/author"){
+            call.respond(Author("Baeldung","baeldung.com"));
+
+        }
+
+
+        }
+    }.start(wait = true)
+}

deltaspike/README.md

@@ -1 +1,3 @@
 ## Relevant articles:
+
+- [A Guide to DeltaSpike Data Module](http://www.baeldung.com/deltaspike-data-module)

ethereum/README.md

@@ -1,4 +1,4 @@
-## EthereumJ
+## Ethereum
 
 ### Relevant Articles:
 - [Introduction to EthereumJ](http://www.baeldung.com/ethereumj)

ethereum/pom.xml

@@ -0,0 +1,242 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung.ethereum</groupId>
+    <artifactId>ethereum</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>ethereum</name>
+
+    <!-- Don't Use This - Use the BOM or direct dependency rather than parent -->
+    <!--<parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>1.5.6.RELEASE</version>
+    </parent>-->
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <java.version>1.8</java.version>
+        <tomcat.version>8.5.4</tomcat.version>
+        <ethereumj-core.version>1.5.0-RELEASE</ethereumj-core.version>
+        <web3j.core.version>3.3.1</web3j.core.version>
+        <springframework.version>5.0.5.RELEASE</springframework.version>
+        <spring.boot.version>1.5.6.RELEASE</spring.boot.version>
+        <maven-surefire.version>2.18.1</maven-surefire.version>
+        <mockito.version>1.10.19</mockito.version>
+        <jackson-databind.version>2.5.0</jackson-databind.version>
+        <hamcrest.version>1.3</hamcrest.version>
+        <jackson.version>2.9.3</jackson.version>
+        <javax-jsp.version>2.3.1</javax-jsp.version>
+        <javax-servlet.version>3.1.0</javax-servlet.version>
+        <jsonpath.version>2.4.0</jsonpath.version>
+        <jstl.version>1.2</jstl.version>
+        <junit.version>4.12</junit.version>
+        <logback.version>1.2.3</logback.version>
+        <slf4j.version>1.7.25</slf4j.version>
+    </properties>
+
+    <repositories>
+        <repository>
+            <id>Ethereum</id>
+            <name>Ethereum</name>
+            <url>https://dl.bintray.com/ethereum/maven/</url>
+        </repository>
+    </repositories>
+
+    <dependencies>
+
+        <!-- Spring Boot Dependencies -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+            <version>${spring.boot.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+            <version>${spring.boot.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-tomcat</artifactId>
+            <version>${spring.boot.version}</version>
+        </dependency>
+
+        <!-- Spring Dependencies -->
+       <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-core</artifactId>
+            <version>${springframework.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-web</artifactId>
+            <version>${springframework.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-webmvc</artifactId>
+            <version>${springframework.version}</version>
+        </dependency>
+
+        <!-- Ethereum -->
+        <dependency>
+            <groupId>org.ethereum</groupId>
+            <artifactId>ethereumj-core</artifactId>
+            <version>${ethereumj-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.web3j</groupId>
+            <artifactId>core</artifactId>
+            <version>${web3j.core.version}</version>
+        </dependency>
+
+        <!-- Jackson Dependencies -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+
+        <!-- Servlet -->
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>jstl</artifactId>
+            <version>${jstl.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>javax.servlet-api</artifactId>
+            <version>${javax-servlet.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet.jsp.jstl</groupId>
+            <artifactId>jstl-api</artifactId>
+            <version>${jstl.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet.jsp</groupId>
+            <artifactId>javax.servlet.jsp-api</artifactId>
+            <version>${javax-jsp.version}</version>
+        </dependency>
+
+        <!-- Logging -->
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>jcl-over-slf4j</artifactId>
+            <version>${slf4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>${logback.version}</version>
+        </dependency>
+
+        <!-- Spring Testing -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+            <version>${spring.boot.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-context</artifactId>
+            <version>${springframework.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <version>${springframework.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- Testing -->
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>${mockito.version}</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.hamcrest</groupId>
+                    <artifactId>hamcrest-core</artifactId>
+                </exclusion>
+            </exclusions>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.hamcrest</groupId>
+                    <artifactId>hamcrest-core</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-library</artifactId>
+            <version>${hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.jayway.jsonpath</groupId>
+            <artifactId>json-path</artifactId>
+            <version>${jsonpath.version}</version>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.1</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-war-plugin</artifactId>
+                <version>3.0.0</version>
+                <configuration>
+                    <warSourceDirectory>src/main/webapp</warSourceDirectory>
+                    <failOnMissingWebXml>false</failOnMissingWebXml>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>${maven-surefire.version}</version>
+                <executions>
+                    <execution>
+                        <id>install</id>
+                        <phase>install</phase>
+                        <goals>
+                            <goal>test</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+        <finalName>ethereum</finalName>
+    </build>
+</project>

ethereum/src/main/java/com/baeldung/web3j/config/AppConfig.java

@@ -0,0 +1,68 @@
+package com.baeldung.web3j.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.scheduling.annotation.EnableAsync;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+import org.springframework.web.servlet.config.annotation.EnableWebMvc;
+import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
+import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+import org.springframework.web.servlet.resource.PathResourceResolver;
+import org.springframework.web.servlet.view.JstlView;
+import org.springframework.web.servlet.view.UrlBasedViewResolver;
+
+import java.util.concurrent.Executor;
+
+@Configuration
+@EnableWebMvc
+@EnableAsync
+@ComponentScan("com.baeldung.web3j")
+public class AppConfig implements WebMvcConfigurer {
+
+    public void addViewControllers(ViewControllerRegistry registry) {
+        registry.addViewController("/").setViewName("index");
+    }
+
+    /**
+     * Static resource locations including themes
+     */
+    @Override
+    public void addResourceHandlers(ResourceHandlerRegistry registry) {
+        registry.addResourceHandler("/resources/**/*")
+                .addResourceLocations("/", "/resources/")
+                .setCachePeriod(3600)
+                .resourceChain(true)
+                .addResolver(new PathResourceResolver());
+    }
+
+    /**
+     * View resolver for JSP
+     */
+    @Bean
+    public UrlBasedViewResolver viewResolver() {
+        UrlBasedViewResolver resolver = new UrlBasedViewResolver();
+        resolver.setPrefix("/WEB-INF/jsp/");
+        resolver.setSuffix(".jsp");
+        resolver.setViewClass(JstlView.class);
+        return resolver;
+    }
+
+    /**
+     * Configuration for async thread bean
+     *
+     * More: https://docs.spring.io/autorepo/docs/spring-framework/5.0.3.RELEASE/javadoc-api/org/springframework/scheduling/SchedulingTaskExecutor.html
+     */
+    @Bean
+    public Executor asyncExecutor() {
+        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+        executor.setCorePoolSize(2);
+        executor.setMaxPoolSize(2);
+        executor.setQueueCapacity(500);
+        executor.setThreadNamePrefix("CsvThread");
+        executor.initialize();
+        return executor;
+    }
+
+}

ethereum/src/main/java/com/baeldung/web3j/config/WebAppInitializer.java

@@ -0,0 +1,28 @@
+package com.baeldung.web3j.config;
+
+import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;
+
+public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
+
+    //AbstractDispatcherServletInitializer override DEFAULT_SERVLET_NAME
+    @Override
+    protected String getServletName() {
+        return "dispatcher";
+    }
+
+    @Override
+    protected Class<?>[] getRootConfigClasses() {
+        return new Class[]{};
+    }
+
+    @Override
+    protected Class<?>[] getServletConfigClasses() {
+        return new Class[]{AppConfig.class};
+    }
+
+    @Override
+    protected String[] getServletMappings() {
+        return new String[]{"/"};
+    }
+
+}

ethereum/src/main/java/com/baeldung/web3j/constants/Constants.java

@@ -0,0 +1,18 @@
+package com.baeldung.web3j.constants;
+
+public class Constants {
+
+    public static final String API_BLOCK = "/api/block";
+    public static final String API_ACCOUNTS = "/api/accounts";
+    public static final String API_TRANSACTIONS = "/api/transactions";
+    public static final String API_BALANCE = "/api/balance";
+
+    public static final String GENERIC_EXCEPTION = "Exception encountered!";
+    public static final String PLEASE_SUPPLY_REAL_DATA = "Please Supply Real Data!";
+
+    public static final String DEFAULT_ADDRESS = "0x281055afc982d96fab65b3a49cac8b878184cb16";
+    public static final String DEFAULT_CONTRACT_ADDRESS = "00000000000000000000";
+
+
+
+}

ethereum/src/main/java/com/baeldung/web3j/contracts/Example.java

@@ -0,0 +1,74 @@
+package com.baeldung.web3j.contracts;
+
+import java.math.BigInteger;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import org.web3j.abi.TypeReference;
+import org.web3j.abi.datatypes.Function;
+import org.web3j.abi.datatypes.Type;
+import org.web3j.crypto.Credentials;
+import org.web3j.protocol.Web3j;
+import org.web3j.protocol.core.RemoteCall;
+import org.web3j.protocol.core.methods.response.TransactionReceipt;
+import org.web3j.tx.Contract;
+import org.web3j.tx.TransactionManager;
+
+/**
+ * <p>Auto generated code.
+ * <p><strong>Do not modify!</strong>
+ * <p>Please use the <a href="https://docs.web3j.io/command_line.html">web3j command line tools</a>,
+ * or the org.web3j.codegen.SolidityFunctionWrapperGenerator in the 
+ * <a href="https://github.com/web3j/web3j/tree/master/codegen">codegen module</a> to update.
+ *
+ * <p>Generated with web3j version 3.3.1.
+ */
+public class Example extends Contract {
+    private static final String BINARY = "0x60606040523415600e57600080fd5b60848061001c6000396000f300606060405260043610603f576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff168063b818dacd146044575b600080fd5b3415604e57600080fd5b60546056565b005b5600a165627a7a72305820bebcbbdf06550591bc772dfcb0eadc842f95953869feb7a9528bac91487d95240029";
+
+    protected static final HashMap<String, String> _addresses;
+
+    static {
+        _addresses = new HashMap<>();
+    }
+
+    protected Example(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
+        super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
+    }
+
+    protected Example(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
+        super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
+    }
+
+    public static RemoteCall<Example> deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
+        return deployRemoteCall(Example.class, web3j, credentials, gasPrice, gasLimit, BINARY, "");
+    }
+
+    public static RemoteCall<Example> deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
+        return deployRemoteCall(Example.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, "");
+    }
+
+    public RemoteCall<TransactionReceipt> ExampleFunction() {
+        final Function function = new Function(
+                "ExampleFunction", 
+                Arrays.<Type>asList(), 
+                Collections.<TypeReference<?>>emptyList());
+        return executeRemoteCallTransaction(function);
+    }
+
+    public static Example load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
+        return new Example(contractAddress, web3j, credentials, gasPrice, gasLimit);
+    }
+
+    public static Example load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
+        return new Example(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
+    }
+
+    protected String getStaticDeployedAddress(String networkId) {
+        return _addresses.get(networkId);
+    }
+
+    public static String getPreviouslyDeployedAddress(String networkId) {
+        return _addresses.get(networkId);
+    }
+}

ethereum/src/main/java/com/baeldung/web3j/controllers/EthereumRestController.java

@@ -0,0 +1,103 @@
+package com.baeldung.web3j.controllers;
+
+import com.baeldung.web3j.constants.Constants;
+import com.baeldung.web3j.helpers.TimeHelper;
+import com.baeldung.web3j.services.Web3Service;
+import com.baeldung.web3j.transfers.ResponseTransfer;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.RestController;
+import org.web3j.protocol.core.methods.response.EthAccounts;
+import org.web3j.protocol.core.methods.response.EthBlockNumber;
+import org.web3j.protocol.core.methods.response.EthGetBalance;
+import org.web3j.protocol.core.methods.response.EthGetTransactionCount;
+
+import java.time.Instant;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
+
+import static com.baeldung.web3j.constants.Constants.GENERIC_EXCEPTION;
+
+@RestController
+public class EthereumRestController {
+
+    @Autowired
+    Web3Service web3Service;
+
+    @RequestMapping(value = Constants.API_BLOCK, method = RequestMethod.GET)
+    public Future<ResponseTransfer> getBlock() {
+        ResponseTransfer responseTransfer = new ResponseTransfer();
+        Instant start = TimeHelper.start();
+
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                CompletableFuture<EthBlockNumber> result = web3Service.getBlockNumber();
+                responseTransfer.setMessage(result.get().toString());
+            } catch (Exception e) {
+                responseTransfer.setMessage(GENERIC_EXCEPTION);
+            }
+            return responseTransfer;
+        }).thenApplyAsync(result -> {
+            result.setPerformance(TimeHelper.stop(start));
+            return result;
+        });
+    }
+
+    @RequestMapping(value = Constants.API_ACCOUNTS, method = RequestMethod.GET)
+    public Future<ResponseTransfer> getAccounts() {
+        ResponseTransfer responseTransfer = new ResponseTransfer();
+        Instant start = TimeHelper.start();
+
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                CompletableFuture<EthAccounts> result = web3Service.getEthAccounts();
+                responseTransfer.setMessage(result.get().toString());
+            } catch (Exception e) {
+                responseTransfer.setMessage(GENERIC_EXCEPTION);
+            }
+            return responseTransfer;
+
+        }).thenApplyAsync(result -> {
+            result.setPerformance(TimeHelper.stop(start));
+            return result;
+        });
+    }
+
+    @RequestMapping(value = Constants.API_TRANSACTIONS, method = RequestMethod.GET)
+    public Future<ResponseTransfer> getTransactions() {
+        ResponseTransfer responseTransfer = new ResponseTransfer();
+        Instant start = TimeHelper.start();
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                CompletableFuture<EthGetTransactionCount> result = web3Service.getTransactionCount();
+                responseTransfer.setMessage(result.get().toString());
+            } catch (Exception e) {
+                responseTransfer.setMessage(GENERIC_EXCEPTION);
+            }
+            return responseTransfer;
+        }).thenApplyAsync(result -> {
+            result.setPerformance(TimeHelper.stop(start));
+            return result;
+        });
+    }
+
+    @RequestMapping(value = Constants.API_BALANCE, method = RequestMethod.GET)
+    public Future<ResponseTransfer> getBalance() {
+        ResponseTransfer responseTransfer = new ResponseTransfer();
+        Instant start = TimeHelper.start();
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                CompletableFuture<EthGetBalance> result = web3Service.getEthBalance();
+                responseTransfer.setMessage(result.get().toString());
+            } catch (Exception e) {
+                responseTransfer.setMessage(GENERIC_EXCEPTION);
+            }
+            return responseTransfer;
+        }).thenApplyAsync(result -> {
+            result.setPerformance(TimeHelper.stop(start));
+            return result;
+        });
+    }
+
+}

ethereum/src/main/java/com/baeldung/web3j/helpers/TimeHelper.java

@@ -0,0 +1,16 @@
+package com.baeldung.web3j.helpers;
+
+import java.time.Duration;
+import java.time.Instant;
+
+public class TimeHelper {
+
+    public static Instant start() {
+        return Instant.now();
+    }
+
+    public static Duration stop(Instant start) {
+        Instant end = Instant.now();
+        return Duration.between(start, end);
+    }
+}

ethereum/src/main/java/com/baeldung/web3j/services/Web3Service.java

@@ -0,0 +1,151 @@
+package com.baeldung.web3j.services;
+
+import com.baeldung.web3j.contracts.Example;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Service;
+import org.web3j.abi.FunctionEncoder;
+import org.web3j.abi.datatypes.Function;
+import org.web3j.crypto.Credentials;
+import org.web3j.crypto.WalletUtils;
+import org.web3j.protocol.Web3j;
+import org.web3j.protocol.core.DefaultBlockParameter;
+import org.web3j.protocol.core.methods.request.Transaction;
+import org.web3j.protocol.core.methods.response.EthAccounts;
+import org.web3j.protocol.core.methods.response.EthBlockNumber;
+import org.web3j.protocol.core.methods.response.EthGetBalance;
+import org.web3j.protocol.core.methods.response.EthGetTransactionCount;
+import org.web3j.protocol.http.HttpService;
+import org.web3j.tx.Contract;
+import org.web3j.tx.ManagedTransaction;
+
+import java.io.File;
+import java.math.BigInteger;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+
+import static com.baeldung.web3j.constants.Constants.DEFAULT_ADDRESS;
+import static com.baeldung.web3j.constants.Constants.GENERIC_EXCEPTION;
+import static com.baeldung.web3j.constants.Constants.PLEASE_SUPPLY_REAL_DATA;
+
+@Service
+public class Web3Service {
+
+    private Web3j web3j = Web3j.build(new HttpService());
+
+    //Create and Init the default Web3J connection
+    public void customInit(String provider) {
+        this.web3j = Web3j.build(new HttpService(provider));
+    }
+
+    //Convert to and from supplied contract ABI bytecode
+    public static String toBinary(String bytecode) {
+        return bytecode.replaceFirst("^0x", "");
+    }
+
+    public static String toByteCode(String binary) {
+        return "0x" + binary;
+    }
+
+    public CompletableFuture<EthBlockNumber> getBlockNumber() {
+        EthBlockNumber result = new EthBlockNumber();
+        try {
+            result = this.web3j.ethBlockNumber().sendAsync().get();
+        } catch (Exception ex) {
+            System.out.println(GENERIC_EXCEPTION);
+        }
+        return CompletableFuture.completedFuture(result);
+    }
+
+    public CompletableFuture<EthAccounts> getEthAccounts() {
+        EthAccounts result = new EthAccounts();
+        try {
+             result = this.web3j.ethAccounts().sendAsync().get();
+        } catch (Exception ex) {
+            System.out.println(GENERIC_EXCEPTION);
+        }
+        return CompletableFuture.completedFuture(result);
+    }
+
+    public CompletableFuture<EthGetTransactionCount> getTransactionCount() {
+        EthGetTransactionCount result = new EthGetTransactionCount();
+        try {
+             result = this.web3j.ethGetTransactionCount(DEFAULT_ADDRESS, DefaultBlockParameter.valueOf("latest")).sendAsync().get();
+        } catch (Exception ex) {
+            System.out.println(GENERIC_EXCEPTION);
+        }
+        return CompletableFuture.completedFuture(result);
+    }
+
+    public CompletableFuture<EthGetBalance> getEthBalance() {
+        EthGetBalance result = new EthGetBalance();
+        try {
+            result = this.web3j.ethGetBalance(DEFAULT_ADDRESS, DefaultBlockParameter.valueOf("latest")).sendAsync().get();
+        } catch (Exception ex) {
+            System.out.println(GENERIC_EXCEPTION);
+        }
+        return CompletableFuture.completedFuture(result);
+    }
+
+    public CompletableFuture<String> fromScratchContractExample() {
+
+        String contractAddress = "";
+
+        try {
+            //Create a wallet
+            WalletUtils.generateNewWalletFile("PASSWORD", new File("/path/to/destination"), true);
+            //Load the credentials from it
+            Credentials credentials = WalletUtils.loadCredentials("PASSWORD", "/path/to/walletfile");
+
+            //Deploy contract to address specified by wallet
+            Example contract = Example.deploy(this.web3j,
+                    credentials,
+                    ManagedTransaction.GAS_PRICE,
+                    Contract.GAS_LIMIT).send();
+
+            //Het the address
+            contractAddress = contract.getContractAddress();
+
+        } catch (Exception ex) {
+            System.out.println(PLEASE_SUPPLY_REAL_DATA);
+            return CompletableFuture.completedFuture(PLEASE_SUPPLY_REAL_DATA);
+        }
+        return CompletableFuture.completedFuture(contractAddress);
+    }
+
+    @Async
+    public CompletableFuture<String> sendTx() {
+        String transactionHash = "";
+
+        try {
+            List inputParams = new ArrayList();
+            List outputParams = new ArrayList();
+            Function function = new Function("fuctionName", inputParams, outputParams);
+
+            String encodedFunction = FunctionEncoder.encode(function);
+
+            BigInteger nonce = BigInteger.valueOf(100);
+            BigInteger gasprice = BigInteger.valueOf(100);
+            BigInteger gaslimit = BigInteger.valueOf(100);
+
+            Transaction transaction = Transaction.createFunctionCallTransaction("FROM_ADDRESS", nonce, gasprice, gaslimit, "TO_ADDRESS", encodedFunction);
+
+            org.web3j.protocol.core.methods.response.EthSendTransaction transactionResponse = web3j.ethSendTransaction(transaction).sendAsync().get();
+            transactionHash = transactionResponse.getTransactionHash();
+
+        } catch (Exception ex) {
+            System.out.println(PLEASE_SUPPLY_REAL_DATA);
+            return CompletableFuture.completedFuture(PLEASE_SUPPLY_REAL_DATA);
+        }
+
+        return CompletableFuture.completedFuture(transactionHash);
+    }
+}
+
+
+
+
+
+
+
+

ethereum/src/main/java/com/baeldung/web3j/transfers/ResponseTransfer.java

@@ -0,0 +1,28 @@
+package com.baeldung.web3j.transfers;
+
+import java.time.Duration;
+
+public class ResponseTransfer {
+
+    public ResponseTransfer() {}
+
+    private Duration performance;
+    private String message;
+
+    public Duration getPerformance() {
+        return performance;
+    }
+
+    public void setPerformance(Duration performance) {
+        this.performance = performance;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+}

ethereum/src/main/resources/dev_ganache/README.md

@@ -0,0 +1,23 @@
+# Ganache Readme
+
+TL:DR - To set up Ganache visit: http://truffleframework.com/ganache/
+
+# Three Ways to Install Ganache
+
+Ganache is provided in three libraries or distributions:
+
+(1) Ganache - https://github.com/trufflesuite/ganache
+
+This is a pre-built and out-of-the-box solution. Easiest to set up. It provides an interface and server shell for Ganache CLI.
+
+(2) Ganache CLI - https://www.npmjs.com/package/ganache-cli
+
+Ganache CLI abstracts Ganache Core and supplies the default options and arguments used.
+
+(3) Ganache Core - https://www.npmjs.com/package/ganache-core
+
+Basically, only use Ganache Core if you need to build a totally customized option.
+
+# Use
+
+The default port is *8545* on *localhost*

ethereum/src/main/resources/dev_truffle/README.md

@@ -0,0 +1,43 @@
+# Using Truffle
+
+Basic Truffle walkthrough readme.
+
+See also: http://truffleframework.com/docs/
+
+# Bash
+
+Truffle install
+
+```bash
+	$ npm install truffle -g
+	$ truffle version 
+```
+
+Truffle commands:
+
+```bash
+	$ truffle init
+	$ truffle compile
+	$ truffle migrate
+	$ truffle test
+```
+
+# Directory Structure
+
+The command `$ truffle init` will create a directory structure in the specified root according to the following:
+
+```
+root -|
+      |-build               (Compiled Solc JSON Output Dir)  
+      |-contracts           (Solc Contracts to be Compiled and Migrated)  
+      |-migrations          (Specify the Order and Dependencies of Contracts to Be Deployed)  
+      |-test                (Truffle Tests)  
+```
+      
+# Compile
+
+Truffle will compile the smart contracts and expose their **JSON ABI's for use with Web3.js** or **Binary ABI's for use with Web3J**.
+
+# Migration
+
+Truffle will let you deploy your Solc contracts directly to a blockchin of your choice.

ethereum/src/main/resources/dev_truffle/build/contracts/ConvertLib.json

@@ -0,0 +1,455 @@
+{
+  "contractName": "ConvertLib",
+  "abi": [
+    {
+      "constant": false,
+      "inputs": [
+        {
+          "name": "amount",
+          "type": "uint256"
+        },
+        {
+          "name": "conversionRate",
+          "type": "uint256"
+        }
+      ],
+      "name": "convert",
+      "outputs": [
+        {
+          "name": "convertedAmount",
+          "type": "uint256"
+        }
+      ],
+      "payable": false,
+      "stateMutability": "nonpayable",
+      "type": "function"
+    }
+  ],
+  "bytecode": "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",
+  "deployedBytecode": "0x73000000000000000000000000000000000000000030146060604052600436106056576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806396e4ee3d14605b575b600080fd5b8115606557600080fd5b608260048080359060200190919080359060200190919050506098565b6040518082815260200191505060405180910390f35b60008183029050929150505600a165627a7a72305820ab84b2740847d7b84a33de9738ae9cf9aabac1b68e6a64d60bd5020b9b6235e40029",
+  "sourceMap": "28:148:0:-;;132:2:-1;166:7;155:9;146:7;137:37;252:7;246:14;243:1;238:23;232:4;229:33;270:1;265:20;;;;222:63;;265:20;274:9;222:63;;298:9;295:1;288:20;328:4;319:7;311:22;352:7;343;336:24",
+  "deployedSourceMap": "28:148:0:-;;;;;;;;;;;;;;;;;;;;;;;;;;;50:123;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;109:20;154:14;145:6;:23;138:30;;50:123;;;;:::o",
+  "source": "pragma solidity ^0.4.17;\r\n\r\nlibrary ConvertLib{\r\n\tfunction convert(uint amount,uint conversionRate) returns (uint convertedAmount)\r\n\t{\r\n\t\treturn amount * conversionRate;\r\n\t}\r\n}\r\n",
+  "sourcePath": "C:\\workspace\\current_workspace\\web3java\\dev_truffle\\contracts\\ConvertLib.sol",
+  "ast": {
+    "absolutePath": "/C/workspace/current_workspace/web3java/dev_truffle/contracts/ConvertLib.sol",
+    "exportedSymbols": {
+      "ConvertLib": [
+        16
+      ]
+    },
+    "id": 17,
+    "nodeType": "SourceUnit",
+    "nodes": [
+      {
+        "id": 1,
+        "literals": [
+          "solidity",
+          "^",
+          "0.4",
+          ".17"
+        ],
+        "nodeType": "PragmaDirective",
+        "src": "0:24:0"
+      },
+      {
+        "baseContracts": [],
+        "contractDependencies": [],
+        "contractKind": "library",
+        "documentation": null,
+        "fullyImplemented": true,
+        "id": 16,
+        "linearizedBaseContracts": [
+          16
+        ],
+        "name": "ConvertLib",
+        "nodeType": "ContractDefinition",
+        "nodes": [
+          {
+            "body": {
+              "id": 14,
+              "nodeType": "Block",
+              "src": "133:40:0",
+              "statements": [
+                {
+                  "expression": {
+                    "argumentTypes": null,
+                    "commonType": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    },
+                    "id": 12,
+                    "isConstant": false,
+                    "isLValue": false,
+                    "isPure": false,
+                    "lValueRequested": false,
+                    "leftExpression": {
+                      "argumentTypes": null,
+                      "id": 10,
+                      "name": "amount",
+                      "nodeType": "Identifier",
+                      "overloadedDeclarations": [],
+                      "referencedDeclaration": 3,
+                      "src": "145:6:0",
+                      "typeDescriptions": {
+                        "typeIdentifier": "t_uint256",
+                        "typeString": "uint256"
+                      }
+                    },
+                    "nodeType": "BinaryOperation",
+                    "operator": "*",
+                    "rightExpression": {
+                      "argumentTypes": null,
+                      "id": 11,
+                      "name": "conversionRate",
+                      "nodeType": "Identifier",
+                      "overloadedDeclarations": [],
+                      "referencedDeclaration": 5,
+                      "src": "154:14:0",
+                      "typeDescriptions": {
+                        "typeIdentifier": "t_uint256",
+                        "typeString": "uint256"
+                      }
+                    },
+                    "src": "145:23:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "functionReturnParameters": 9,
+                  "id": 13,
+                  "nodeType": "Return",
+                  "src": "138:30:0"
+                }
+              ]
+            },
+            "documentation": null,
+            "id": 15,
+            "implemented": true,
+            "isConstructor": false,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "convert",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 6,
+              "nodeType": "ParameterList",
+              "parameters": [
+                {
+                  "constant": false,
+                  "id": 3,
+                  "name": "amount",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "67:11:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 2,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "67:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                },
+                {
+                  "constant": false,
+                  "id": 5,
+                  "name": "conversionRate",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "79:19:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 4,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "79:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                }
+              ],
+              "src": "66:33:0"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 9,
+              "nodeType": "ParameterList",
+              "parameters": [
+                {
+                  "constant": false,
+                  "id": 8,
+                  "name": "convertedAmount",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "109:20:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 7,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "109:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                }
+              ],
+              "src": "108:22:0"
+            },
+            "scope": 16,
+            "src": "50:123:0",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          }
+        ],
+        "scope": 17,
+        "src": "28:148:0"
+      }
+    ],
+    "src": "0:178:0"
+  },
+  "legacyAST": {
+    "absolutePath": "/C/workspace/current_workspace/web3java/dev_truffle/contracts/ConvertLib.sol",
+    "exportedSymbols": {
+      "ConvertLib": [
+        16
+      ]
+    },
+    "id": 17,
+    "nodeType": "SourceUnit",
+    "nodes": [
+      {
+        "id": 1,
+        "literals": [
+          "solidity",
+          "^",
+          "0.4",
+          ".17"
+        ],
+        "nodeType": "PragmaDirective",
+        "src": "0:24:0"
+      },
+      {
+        "baseContracts": [],
+        "contractDependencies": [],
+        "contractKind": "library",
+        "documentation": null,
+        "fullyImplemented": true,
+        "id": 16,
+        "linearizedBaseContracts": [
+          16
+        ],
+        "name": "ConvertLib",
+        "nodeType": "ContractDefinition",
+        "nodes": [
+          {
+            "body": {
+              "id": 14,
+              "nodeType": "Block",
+              "src": "133:40:0",
+              "statements": [
+                {
+                  "expression": {
+                    "argumentTypes": null,
+                    "commonType": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    },
+                    "id": 12,
+                    "isConstant": false,
+                    "isLValue": false,
+                    "isPure": false,
+                    "lValueRequested": false,
+                    "leftExpression": {
+                      "argumentTypes": null,
+                      "id": 10,
+                      "name": "amount",
+                      "nodeType": "Identifier",
+                      "overloadedDeclarations": [],
+                      "referencedDeclaration": 3,
+                      "src": "145:6:0",
+                      "typeDescriptions": {
+                        "typeIdentifier": "t_uint256",
+                        "typeString": "uint256"
+                      }
+                    },
+                    "nodeType": "BinaryOperation",
+                    "operator": "*",
+                    "rightExpression": {
+                      "argumentTypes": null,
+                      "id": 11,
+                      "name": "conversionRate",
+                      "nodeType": "Identifier",
+                      "overloadedDeclarations": [],
+                      "referencedDeclaration": 5,
+                      "src": "154:14:0",
+                      "typeDescriptions": {
+                        "typeIdentifier": "t_uint256",
+                        "typeString": "uint256"
+                      }
+                    },
+                    "src": "145:23:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "functionReturnParameters": 9,
+                  "id": 13,
+                  "nodeType": "Return",
+                  "src": "138:30:0"
+                }
+              ]
+            },
+            "documentation": null,
+            "id": 15,
+            "implemented": true,
+            "isConstructor": false,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "convert",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 6,
+              "nodeType": "ParameterList",
+              "parameters": [
+                {
+                  "constant": false,
+                  "id": 3,
+                  "name": "amount",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "67:11:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 2,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "67:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                },
+                {
+                  "constant": false,
+                  "id": 5,
+                  "name": "conversionRate",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "79:19:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 4,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "79:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                }
+              ],
+              "src": "66:33:0"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 9,
+              "nodeType": "ParameterList",
+              "parameters": [
+                {
+                  "constant": false,
+                  "id": 8,
+                  "name": "convertedAmount",
+                  "nodeType": "VariableDeclaration",
+                  "scope": 15,
+                  "src": "109:20:0",
+                  "stateVariable": false,
+                  "storageLocation": "default",
+                  "typeDescriptions": {
+                    "typeIdentifier": "t_uint256",
+                    "typeString": "uint256"
+                  },
+                  "typeName": {
+                    "id": 7,
+                    "name": "uint",
+                    "nodeType": "ElementaryTypeName",
+                    "src": "109:4:0",
+                    "typeDescriptions": {
+                      "typeIdentifier": "t_uint256",
+                      "typeString": "uint256"
+                    }
+                  },
+                  "value": null,
+                  "visibility": "internal"
+                }
+              ],
+              "src": "108:22:0"
+            },
+            "scope": 16,
+            "src": "50:123:0",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          }
+        ],
+        "scope": 17,
+        "src": "28:148:0"
+      }
+    ],
+    "src": "0:178:0"
+  },
+  "compiler": {
+    "name": "solc",
+    "version": "0.4.21+commit.dfe3193c.Emscripten.clang"
+  },
+  "networks": {},
+  "schemaVersion": "2.0.0",
+  "updatedAt": "2018-04-14T03:37:39.678Z"
+}

ethereum/src/main/resources/dev_truffle/build/contracts/Example.json

@@ -0,0 +1,251 @@
+{
+  "contractName": "Example",
+  "abi": [
+    {
+      "inputs": [],
+      "payable": false,
+      "stateMutability": "nonpayable",
+      "type": "constructor"
+    },
+    {
+      "constant": false,
+      "inputs": [],
+      "name": "ExampleFunction",
+      "outputs": [],
+      "payable": false,
+      "stateMutability": "nonpayable",
+      "type": "function"
+    }
+  ],
+  "bytecode": "0x60606040523415600e57600080fd5b60848061001c6000396000f300606060405260043610603f576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff168063b818dacd146044575b600080fd5b3415604e57600080fd5b60546056565b005b5600a165627a7a72305820bebcbbdf06550591bc772dfcb0eadc842f95953869feb7a9528bac91487d95240029",
+  "deployedBytecode": "0x606060405260043610603f576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff168063b818dacd146044575b600080fd5b3415604e57600080fd5b60546056565b005b5600a165627a7a72305820bebcbbdf06550591bc772dfcb0eadc842f95953869feb7a9528bac91487d95240029",
+  "sourceMap": "28:134:1:-;;;50:45;;;;;;;;28:134;;;;;;",
+  "deployedSourceMap": "28:134:1:-;;;;;;;;;;;;;;;;;;;;;;;;101:58;;;;;;;;;;;;;;;:::o",
+  "source": "pragma solidity ^0.4.17;\r\n\r\ncontract Example {\r\n  function Example() {\r\n    // constructor\r\n  }\r\n\r\n  function ExampleFunction() {\r\n    // example function\r\n  }\r\n}",
+  "sourcePath": "C:\\workspace\\current_workspace\\web3java\\dev_truffle\\contracts\\Example.sol",
+  "ast": {
+    "absolutePath": "/C/workspace/current_workspace/web3java/dev_truffle/contracts/Example.sol",
+    "exportedSymbols": {
+      "Example": [
+        27
+      ]
+    },
+    "id": 28,
+    "nodeType": "SourceUnit",
+    "nodes": [
+      {
+        "id": 18,
+        "literals": [
+          "solidity",
+          "^",
+          "0.4",
+          ".17"
+        ],
+        "nodeType": "PragmaDirective",
+        "src": "0:24:1"
+      },
+      {
+        "baseContracts": [],
+        "contractDependencies": [],
+        "contractKind": "contract",
+        "documentation": null,
+        "fullyImplemented": true,
+        "id": 27,
+        "linearizedBaseContracts": [
+          27
+        ],
+        "name": "Example",
+        "nodeType": "ContractDefinition",
+        "nodes": [
+          {
+            "body": {
+              "id": 21,
+              "nodeType": "Block",
+              "src": "69:26:1",
+              "statements": []
+            },
+            "documentation": null,
+            "id": 22,
+            "implemented": true,
+            "isConstructor": true,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "Example",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 19,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "66:2:1"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 20,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "69:0:1"
+            },
+            "scope": 27,
+            "src": "50:45:1",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          },
+          {
+            "body": {
+              "id": 25,
+              "nodeType": "Block",
+              "src": "128:31:1",
+              "statements": []
+            },
+            "documentation": null,
+            "id": 26,
+            "implemented": true,
+            "isConstructor": false,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "ExampleFunction",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 23,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "125:2:1"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 24,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "128:0:1"
+            },
+            "scope": 27,
+            "src": "101:58:1",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          }
+        ],
+        "scope": 28,
+        "src": "28:134:1"
+      }
+    ],
+    "src": "0:162:1"
+  },
+  "legacyAST": {
+    "absolutePath": "/C/workspace/current_workspace/web3java/dev_truffle/contracts/Example.sol",
+    "exportedSymbols": {
+      "Example": [
+        27
+      ]
+    },
+    "id": 28,
+    "nodeType": "SourceUnit",
+    "nodes": [
+      {
+        "id": 18,
+        "literals": [
+          "solidity",
+          "^",
+          "0.4",
+          ".17"
+        ],
+        "nodeType": "PragmaDirective",
+        "src": "0:24:1"
+      },
+      {
+        "baseContracts": [],
+        "contractDependencies": [],
+        "contractKind": "contract",
+        "documentation": null,
+        "fullyImplemented": true,
+        "id": 27,
+        "linearizedBaseContracts": [
+          27
+        ],
+        "name": "Example",
+        "nodeType": "ContractDefinition",
+        "nodes": [
+          {
+            "body": {
+              "id": 21,
+              "nodeType": "Block",
+              "src": "69:26:1",
+              "statements": []
+            },
+            "documentation": null,
+            "id": 22,
+            "implemented": true,
+            "isConstructor": true,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "Example",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 19,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "66:2:1"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 20,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "69:0:1"
+            },
+            "scope": 27,
+            "src": "50:45:1",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          },
+          {
+            "body": {
+              "id": 25,
+              "nodeType": "Block",
+              "src": "128:31:1",
+              "statements": []
+            },
+            "documentation": null,
+            "id": 26,
+            "implemented": true,
+            "isConstructor": false,
+            "isDeclaredConst": false,
+            "modifiers": [],
+            "name": "ExampleFunction",
+            "nodeType": "FunctionDefinition",
+            "parameters": {
+              "id": 23,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "125:2:1"
+            },
+            "payable": false,
+            "returnParameters": {
+              "id": 24,
+              "nodeType": "ParameterList",
+              "parameters": [],
+              "src": "128:0:1"
+            },
+            "scope": 27,
+            "src": "101:58:1",
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          }
+        ],
+        "scope": 28,
+        "src": "28:134:1"
+      }
+    ],
+    "src": "0:162:1"
+  },
+  "compiler": {
+    "name": "solc",
+    "version": "0.4.21+commit.dfe3193c.Emscripten.clang"
+  },
+  "networks": {},
+  "schemaVersion": "2.0.0",
+  "updatedAt": "2018-04-14T03:37:39.710Z"
+}

ethereum/src/main/resources/dev_truffle/contracts/ConvertLib.sol

@@ -0,0 +1,8 @@
+pragma solidity ^0.4.17;
+
+library ConvertLib{
+	function convert(uint amount,uint conversionRate) returns (uint convertedAmount)
+	{
+		return amount * conversionRate;
+	}
+}

ethereum/src/main/resources/dev_truffle/contracts/Example.sol

@@ -0,0 +1,11 @@
+pragma solidity ^0.4.17;
+
+contract Example {
+  function Example() {
+    // constructor
+  }
+
+  function ExampleFunction() {
+    // example function
+  }
+}

ethereum/src/main/resources/dev_truffle/contracts/Migrations.sol

@@ -0,0 +1,23 @@
+pragma solidity ^0.4.17;
+
+contract Migrations {
+  address public owner;
+  uint public last_completed_migration;
+
+  modifier restricted() {
+    if (msg.sender == owner) _;
+  }
+
+  function Migrations() public {
+    owner = msg.sender;
+  }
+
+  function setCompleted(uint completed) public restricted {
+    last_completed_migration = completed;
+  }
+
+  function upgrade(address new_address) public restricted {
+    Migrations upgraded = Migrations(new_address);
+    upgraded.setCompleted(last_completed_migration);
+  }
+}

ethereum/src/main/resources/dev_truffle/migrations/1_initial_migration.js

@@ -0,0 +1,3 @@
+module.exports = deployer => {
+  deployer.deploy(artifacts.require("./Migrations.sol"));
+};

ethereum/src/main/resources/dev_truffle/migrations/2_deploy_contracts.js

@@ -0,0 +1,8 @@
+const  Example = artifacts.require("./Example.sol"),
+  ConvertLib = artifacts.require("./ConvertLib.sol");
+
+module.exports = deployer => {
+  deployer.deploy(ConvertLib);
+  deployer.link(ConvertLib, Example);
+  deployer.deploy(Example);
+};

ethereum/src/main/resources/dev_truffle/truffle.js

@@ -0,0 +1,20 @@
+module.exports = {
+  contracts_build_directory: "./build/contracts",
+  networks: {
+    live: {
+      network_id: 1, // Ethereum public network
+      host: 'localhost',
+      port: 8545
+    },
+    testnet: {
+      network_id: 3, // Official Ethereum test network (Ropsten)
+      host: 'localhost',
+      port: 8545
+    },
+    development: {
+      host: 'localhost',
+      port: 8545,
+      network_id: '*'
+    }
+  }
+}

ethereum/src/test/java/com/baeldung/web3j/controllers/EthereumRestControllerIntegrationTest.java

@@ -0,0 +1,78 @@
+package com.baeldung.web3j.controllers;
+
+
+import com.baeldung.web3j.config.AppConfig;
+import com.baeldung.web3j.constants.Constants;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.WebAppConfiguration;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.context.WebApplicationContext;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.asyncDispatch;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = {AppConfig.class})
+@WebAppConfiguration
+public class EthereumRestControllerIntegrationTest {
+
+    private MockMvc mockMvc;
+
+    private void constructAsyncTest(String endpoint) {
+        try {
+            MvcResult asyncResult = mockMvc
+                    .perform(get(endpoint))
+                    .andReturn();
+
+            mockMvc.perform(asyncDispatch(asyncResult))
+                    .andDo(print())
+                    .andExpect(status().isOk());
+
+        } catch (Exception e) {
+            System.out.println("Exception: " + e);
+        }
+    }
+
+    @Autowired
+    private WebApplicationContext wac;
+
+    @Before
+    public void preTest() throws Exception {
+        mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
+    }
+
+    @Test
+    public void accounts() {
+        constructAsyncTest(Constants.API_ACCOUNTS);
+    }
+
+    @Test
+    public void transactions() {
+        constructAsyncTest(Constants.API_TRANSACTIONS);
+    }
+
+    @Test
+    public void block() {
+        constructAsyncTest(Constants.API_BLOCK);
+    }
+
+    @Test
+    public void balance() {
+        constructAsyncTest(Constants.API_BALANCE);
+    }
+
+    @After
+    public void postTest() {
+        mockMvc = null;
+    }
+}

ethereum/src/test/java/com/baeldung/web3j/controllers/EthereumRestControllerUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.web3j.controllers;
+
+import com.baeldung.web3j.constants.Constants;
+import com.baeldung.web3j.services.Web3Service;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.asyncDispatch;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+public class EthereumRestControllerUnitTest {
+
+    private MockMvc mockMvc;
+
+    private void constructAsyncTest(String endpoint) {
+        try {
+            MvcResult asyncResult = mockMvc
+                    .perform(get(endpoint))
+                    .andReturn();
+
+            mockMvc.perform(asyncDispatch(asyncResult))
+                    .andDo(print())
+                    .andExpect(status().isOk());
+
+        } catch (Exception e) {
+            System.out.println("Exception: " + e);
+        }
+    }
+
+    @Mock
+    private Web3Service web3Service;
+
+    @InjectMocks
+    private EthereumRestController ethereumRestController;
+
+    @Before
+    public void preTest() {
+        MockitoAnnotations.initMocks(this);
+        mockMvc = MockMvcBuilders.standaloneSetup(ethereumRestController).build();
+    }
+
+    @Test
+    public void accounts() {
+        constructAsyncTest(Constants.API_ACCOUNTS);
+    }
+
+    @Test
+    public void transactions() {
+        constructAsyncTest(Constants.API_TRANSACTIONS);
+    }
+
+    @Test
+    public void block() {
+        constructAsyncTest(Constants.API_BLOCK);
+    }
+
+    @Test
+    public void balance() {
+        constructAsyncTest(Constants.API_BALANCE);
+    }
+
+    @After
+    public void postTest() {
+        mockMvc = null;
+    }
+
+}

ethereum/src/test/java/com/baeldung/web3j/services/EthereumContractUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.web3j.services;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.concurrent.CompletableFuture;
+
+public class EthereumContractUnitTest {
+
+    private Web3Service web3Service;
+
+    @Before
+    public void setup() {
+        web3Service = new Web3Service();
+    }
+
+    @Test
+    public void testContract() {
+        CompletableFuture<String> result = web3Service.fromScratchContractExample();
+        assert (result instanceof CompletableFuture);
+    }
+
+    @Test
+    public void sendTx() {
+        CompletableFuture<String> result = web3Service.sendTx();
+        assert (result instanceof CompletableFuture);
+    }
+
+    @After
+    public void cleanup() {
+    }
+}

ethereumj/pom.xml

@@ -1,86 +0,0 @@
-<?xml version="1.0"?>
-<project
-        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
-        xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
-    <modelVersion>4.0.0</modelVersion>
-    <groupId>com.baeldung.ethereumj</groupId>
-    <artifactId>ethereumj</artifactId>
-    <packaging>war</packaging>
-    <version>1.0.0</version>
-    <name>ethereumj</name>
-
-    <parent>
-        <artifactId>parent-boot-1</artifactId>
-        <groupId>com.baeldung</groupId>
-        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../parent-boot-1</relativePath>
-    </parent>
-
-    <repositories>
-        <repository>
-            <id>Ethereum</id>
-            <name>Ethereum</name>
-            <url>https://dl.bintray.com/ethereum/maven/</url>
-        </repository>
-    </repositories>
-
-    <dependencies>
-        <!-- Spring Boot Dependencies -->
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-web</artifactId>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-tomcat</artifactId>
-        </dependency>
-        <!-- Unit Testing -->
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-test</artifactId>
-            <scope>test</scope>
-        </dependency>
-        <!-- Ethereum -->
-        <dependency>
-            <groupId>org.ethereum</groupId>
-            <artifactId>ethereumj-core</artifactId>
-            <version>${ethereumj-core.version}</version>
-        </dependency>
-        <!-- Web3j -->
-        <dependency>
-            <groupId>org.web3j</groupId>
-            <artifactId>core</artifactId>
-            <version>${web3j.core.version}</version>
-        </dependency>
-        <!-- JSTL/JSP -->
-        <dependency>
-            <groupId>javax.servlet</groupId>
-            <artifactId>jstl</artifactId>
-        </dependency>
-        <dependency>
-            <groupId>com.fasterxml.jackson.core</groupId>
-            <artifactId>jackson-databind</artifactId>
-            <version>${jackson-databind.version}</version>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.springframework.boot</groupId>
-                <artifactId>spring-boot-maven-plugin</artifactId>
-            </plugin>
-        </plugins>
-        <finalName>ethereumj</finalName>
-    </build>
-
-    <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <java.version>1.8</java.version>
-        <tomcat.version>8.5.4</tomcat.version>
-        <ethereumj-core.version>1.5.0-RELEASE</ethereumj-core.version>
-        <web3j.core.version>3.3.1</web3j.core.version>
-        <jackson-databind.version>2.5.0</jackson-databind.version>
-    </properties>
-
-</project>

google-web-toolkit/pom.xml

@@ -0,0 +1,116 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+
+  <!-- POM file generated with GWT webAppCreator -->
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.baeldung</groupId>
+  <artifactId>google_web_toolkit</artifactId>
+  <packaging>war</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <name>com.baeldung.Google_web_toolkit</name>
+
+  <properties>
+
+    <!-- Setting maven.compiler.source to something different to 1.8
+         needs that you configure the sourceLevel in gwt-maven-plugin since
+         GWT compiler 2.8 requires 1.8 (see gwt-maven-plugin block below) -->
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+
+    <!-- Don't let your Mac use a crazy non-standard encoding -->
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+  </properties>
+
+  <dependencyManagement>
+    <dependencies>
+      <!-- ensure all GWT deps use the same version (unless overridden) -->
+      <dependency>
+        <groupId>com.google.gwt</groupId>
+        <artifactId>gwt</artifactId>
+        <version>2.8.2</version>
+        <type>pom</type>
+        <scope>import</scope>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.google.gwt</groupId>
+      <artifactId>gwt-servlet</artifactId>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.gwt</groupId>
+      <artifactId>gwt-user</artifactId>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.gwt</groupId>
+      <artifactId>gwt-dev</artifactId>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <!-- Output classes directly into the webapp, so that IDEs and "mvn process-classes" update them in DevMode -->
+    <outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>
+
+    <plugins>
+
+      <!-- GWT Maven Plugin-->
+      <plugin>
+        <groupId>net.ltgt.gwt.maven</groupId>
+        <artifactId>gwt-maven-plugin</artifactId>
+        <version>1.0-rc-8</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>compile</goal>
+              <goal>test</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <moduleName>com.baeldung.Google_web_toolkit</moduleName>
+          <moduleShortName>Google_web_toolkit</moduleShortName>
+          <failOnError>true</failOnError>
+          <!-- GWT compiler 2.8 requires 1.8, hence define sourceLevel here if you use
+               a different source language for java compilation -->
+          <sourceLevel>1.8</sourceLevel>
+          <!-- Compiler configuration -->
+          <compilerArgs>
+            <!-- Ask GWT to create the Story of Your Compile (SOYC) (gwt:compile) -->
+            <arg>-compileReport</arg>
+            <arg>-XcompilerMetrics</arg>
+          </compilerArgs>
+          <!-- DevMode configuration -->
+          <warDir>${project.build.directory}/${project.build.finalName}</warDir>
+          <classpathScope>compile+runtime</classpathScope>
+          <!-- URL(s) that should be opened by DevMode (gwt:devmode). -->
+          <startupUrls>
+            <startupUrl>Google_web_toolkit.html</startupUrl>
+          </startupUrls>
+        </configuration>
+      </plugin>
+
+      <!-- Skip normal test execution, we use gwt:test instead -->
+      <plugin>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>2.17</version>
+        <configuration>
+          <skip>true</skip>
+        </configuration>
+      </plugin>
+
+    </plugins>
+  </build>
+</project>

google-web-toolkit/src/main/java/com/baeldung/Google_web_toolkit.gwt.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  When updating your version of GWT, you should also update this DTD reference,
+  so that your app can take advantage of the latest GWT module capabilities.
+-->
+<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.8.2//EN"
+  "http://gwtproject.org/doctype/2.8.2/gwt-module.dtd">
+<module rename-to='google_web_toolkit'>
+  <!-- Inherit the core Web Toolkit stuff.                        -->
+  <inherits name='com.google.gwt.user.User'/>
+
+  <!-- Inherit the default GWT style sheet.  You can change       -->
+  <!-- the theme of your GWT application by uncommenting          -->
+  <!-- any one of the following lines.                            -->
+  <inherits name='com.google.gwt.user.theme.clean.Clean'/>
+  <!-- <inherits name='com.google.gwt.user.theme.standard.Standard'/> -->
+  <!-- <inherits name='com.google.gwt.user.theme.chrome.Chrome'/> -->
+  <!-- <inherits name='com.google.gwt.user.theme.dark.Dark'/>     -->
+
+  <!-- Other module inherits                                      -->
+
+  <!-- Specify the app entry point class.                         -->
+  <entry-point class='com.baeldung.client.Google_web_toolkit'/>
+
+  <!-- Specify the paths for translatable code                    -->
+  <source path='client'/>
+  <source path='shared'/>
+
+  <!-- allow Super Dev Mode -->
+  <add-linker name="xsiframe"/>
+</module>

google-web-toolkit/src/main/java/com/baeldung/client/Google_web_toolkit.java

@@ -0,0 +1,108 @@
+package com.baeldung.client;
+
+import com.baeldung.shared.MessageService;
+import com.baeldung.shared.MessageServiceAsync;
+import com.google.gwt.core.client.EntryPoint;
+import com.google.gwt.core.client.GWT;
+import com.google.gwt.event.dom.client.ClickEvent;
+import com.google.gwt.event.dom.client.ClickHandler;
+import com.google.gwt.event.dom.client.KeyCodes;
+import com.google.gwt.event.dom.client.KeyUpEvent;
+import com.google.gwt.event.dom.client.KeyUpHandler;
+import com.google.gwt.user.client.rpc.AsyncCallback;
+import com.google.gwt.user.client.ui.Button;
+import com.google.gwt.user.client.ui.DialogBox;
+import com.google.gwt.user.client.ui.HTML;
+import com.google.gwt.user.client.ui.Label;
+import com.google.gwt.user.client.ui.RootPanel;
+import com.google.gwt.user.client.ui.TextBox;
+import com.google.gwt.user.client.ui.VerticalPanel;
+
+/**
+ * Entry point classes define <code>onModuleLoad()</code>.
+ */
+public class Google_web_toolkit implements EntryPoint {
+    private final MessageServiceAsync messageServiceAsync = GWT.create(MessageService.class);
+
+    public void onModuleLoad() {
+        Button sendButton = new Button("Submit");
+        TextBox nameField = new TextBox();
+        nameField.setText("Hi there");
+
+        Label warningLabel = new Label();
+
+        sendButton.addStyleName("sendButton");
+
+        RootPanel.get("nameFieldContainer").add(nameField);
+        RootPanel.get("sendButtonContainer").add(sendButton);
+        RootPanel.get("errorLabelContainer").add(warningLabel);
+
+        Button closeButton = new Button("Thanks");
+        closeButton.getElement().setId("closeButton");
+
+        Label textToServerLabel = new Label();
+        HTML serverResponseLabel = new HTML();
+        VerticalPanel vPanel = new VerticalPanel();
+        vPanel.addStyleName("vPanel");
+        vPanel.add(new HTML("Sending message to the server:"));
+        vPanel.add(textToServerLabel);
+        vPanel.add(new HTML("<br><b>Server replies:</b>"));
+        vPanel.add(serverResponseLabel);
+        vPanel.setHorizontalAlignment(VerticalPanel.ALIGN_RIGHT);
+        vPanel.add(closeButton);
+        vPanel.setVisible(false);
+        RootPanel.get("serverResponseContainer").add(vPanel);
+
+        closeButton.addClickHandler(event -> {
+            sendButton.setEnabled(true);
+            sendButton.setFocus(true);
+            vPanel.setVisible(false);
+        });
+
+        class MyHandler implements ClickHandler, KeyUpHandler {
+
+            public void onClick(ClickEvent event) {
+                sendMessageToServer();
+            }
+
+            public void onKeyUp(KeyUpEvent event) {
+                if (event.getNativeKeyCode() == KeyCodes.KEY_ENTER) {
+                    sendMessageToServer();
+                }
+            }
+
+            private void sendMessageToServer() {
+
+                warningLabel.setText("");
+                String textToServer = nameField.getText();
+                if (textToServer == null || textToServer.isEmpty()) {
+                    warningLabel.setText("Please enter the message");
+                    return;
+                }
+
+                sendButton.setEnabled(false);
+                textToServerLabel.setText(textToServer);
+                serverResponseLabel.setText("");
+                messageServiceAsync.sendMessage(textToServer, new AsyncCallback<String>() {
+                    public void onFailure(Throwable caught) {
+                        serverResponseLabel.addStyleName("serverResponseLabelError");
+                        serverResponseLabel.setHTML("server error occurred");
+                        closeButton.setFocus(true);
+                    }
+
+                    public void onSuccess(String result) {
+                        serverResponseLabel.removeStyleName("serverResponseLabelError");
+                        serverResponseLabel.setHTML(result);
+                        closeButton.setFocus(true);
+                        vPanel.setVisible(true);
+                    }
+                });
+            }
+        }
+
+        // Add a handler to send the name to the server
+        MyHandler handler = new MyHandler();
+        sendButton.addClickHandler(handler);
+        nameField.addKeyUpHandler(handler);
+    }
+}

google-web-toolkit/src/main/java/com/baeldung/server/MessageServiceImpl.java

@@ -0,0 +1,22 @@
+package com.baeldung.server;
+
+import com.baeldung.shared.MessageService;
+import com.google.gwt.user.server.rpc.RemoteServiceServlet;
+
+import java.time.LocalDateTime;
+
+/**
+ * The server-side implementation of the RPC service.
+ */
+@SuppressWarnings("serial")
+public class MessageServiceImpl extends RemoteServiceServlet implements MessageService {
+
+    public String sendMessage(String message) throws IllegalArgumentException {
+        if (message == null) {
+            throw new IllegalArgumentException("message is null");
+        }
+
+        return "Hello, " + message + "!<br><br> Time received: " + LocalDateTime.now();
+    }
+
+}

google-web-toolkit/src/main/java/com/baeldung/shared/MessageService.java

@@ -0,0 +1,12 @@
+package com.baeldung.shared;
+
+import com.google.gwt.user.client.rpc.RemoteService;
+import com.google.gwt.user.client.rpc.RemoteServiceRelativePath;
+
+/**
+ * The client-side stub for the RPC service.
+ */
+@RemoteServiceRelativePath("greet")
+public interface MessageService extends RemoteService {
+    String sendMessage(String message) throws IllegalArgumentException;
+}

google-web-toolkit/src/main/java/com/baeldung/shared/MessageServiceAsync.java

@@ -0,0 +1,10 @@
+package com.baeldung.shared;
+
+import com.google.gwt.user.client.rpc.AsyncCallback;
+
+/**
+ * The async counterpart of <code>MessageService</code>.
+ */
+public interface MessageServiceAsync {
+    void sendMessage(String input, AsyncCallback<String> callback) throws IllegalArgumentException;
+}

google-web-toolkit/src/main/webapp/Google_web_toolkit.css

@@ -0,0 +1,31 @@
+/** Add css rules here for your application. */
+h1 {
+  font-size: 2em;
+  font-weight: bold;
+  color: #777777;
+  margin: 40px 0px 70px;
+  text-align: center;
+}
+
+.sendButton {
+  display: block;
+  font-size: 16pt;
+}
+
+/** Most GWT widgets already have a style name defined */
+.gwt-DialogBox {
+  width: 400px;
+}
+
+.vPanel {
+  margin: 5px;
+}
+
+.serverResponseLabelError {
+  color: red;
+}
+
+/** Set ids using widget.getElement().setId("idOfElement") */
+#closeButton {
+  margin: 15px 6px 6px;
+}

google-web-toolkit/src/main/webapp/Google_web_toolkit.html

@@ -0,0 +1,35 @@
+<!doctype html>
+<!-- The DOCTYPE declaration above will set the     -->
+<!-- browser's rendering engine into                -->
+<!-- "Standards Mode". Replacing this declaration   -->
+<!-- with a "Quirks Mode" doctype is not supported. -->
+<html>
+<head>
+  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
+
+  <link type="text/css" rel="stylesheet" href="Google_web_toolkit.css">
+
+  <title>Sample GWT Application</title>
+
+  <script type="text/javascript" language="javascript" src="google_web_toolkit/google_web_toolkit.nocache.js"></script>
+</head>
+
+<body>
+<h1>Sample GWT Application</h1>
+<table align="center">
+  <tr>
+    <td colspan="2" style="font-weight:bold;">Please enter your message:</td>
+  </tr>
+  <tr>
+    <td id="nameFieldContainer"></td>
+    <td id="sendButtonContainer"></td>
+  </tr>
+  <tr>
+    <td colspan="2" style="color:red;" id="errorLabelContainer"></td>
+  </tr>
+  <tr>
+    <td colspan="2" style="color:red;" id="serverResponseContainer"></td>
+  </tr>
+</table>
+</body>
+</html>