Moved the code to spring-5-reactive-2

README.md

@@ -1,12 +1,16 @@
 
-The "REST with Spring" Classes
+The Courses
 ==============================
 
-Here's the Master Class of REST With Spring (along with the newly announced Boot 2 material): <br/>
-**[>> THE REST WITH SPRING - MASTER CLASS](http://www.baeldung.com/rest-with-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=rws#master-class)**
 
-And here's the Master Class of Learn Spring Security: <br/>
-**[>> LEARN SPRING SECURITY - MASTER CLASS](http://www.baeldung.com/learn-spring-security-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=lss#master-class)**
+Here's the new "Learn Spring" course: <br/>
+**[>> LEARN SPRING - THE MASTER CLASS](https://www.baeldung.com/learn-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=ls#master-class)**
+
+Here's the Master Class of "REST With Spring" (along with the new announced Boot 2 material): <br/>
+**[>> THE REST WITH SPRING - MASTER CLASS](https://www.baeldung.com/rest-with-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=rws#master-class)**
+
+And here's the Master Class of "Learn Spring Security": <br/>
+**[>> LEARN SPRING SECURITY - MASTER CLASS](https://www.baeldung.com/learn-spring-security-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=lss#master-class)**
 
 
 
@@ -15,7 +19,7 @@ Java and Spring Tutorials
 
 This project is **a collection of small and focused tutorials** - each covering a single and well defined area of development in the Java ecosystem. 
 A strong focus of these is, of course, the Spring Framework - Spring, Spring Boot and Spring Security. 
-In additional to Spring, the following technologies are in focus: `core Java`, `Jackson`, `HttpClient`, `Guava`. 
+In additional to Spring, the modules here are covering a number of aspects in Java. 
 
 
 Building the project
@@ -32,8 +36,15 @@ Running a Spring Boot module
 ====================
 To run a Spring Boot module run the command: `mvn spring-boot:run` in the module directory
 
-#Running Tests
 
+Working with the IDE
+====================
+This repo contains a large number of modules. 
+When you're working with an individual module, there's no need to import all of them (or build all of them) - you can simply import that particular module in either Eclipse or IntelliJ. 
+
+
+Running Tests
+=============
 The command `mvn clean install` will run the unit tests in a module.
 To run the integration tests, use the command `mvn clean install -Pintegration-lite-first`
 

algorithms-miscellaneous-3/README.md

@@ -6,4 +6,4 @@
 - [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
 - [Checking If a List Is Sorted in Java](https://www.baeldung.com/java-check-if-list-sorted)
 - [Checking if a Java Graph has a Cycle](https://www.baeldung.com/java-graph-has-a-cycle)
-- [A Guide to the Folding Technique](https://www.baeldung.com/folding-hashing-technique)
+- [A Guide to the Folding Technique in Java](https://www.baeldung.com/folding-hashing-technique)

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java

@@ -0,0 +1,30 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import java.util.Comparator;
+
+public final class NaturalOrderComparators {
+
+    private static final String DIGIT_AND_DECIMAL_REGEX = "[^\\d.]";
+
+    private NaturalOrderComparators() {
+        throw new AssertionError("Let's keep this static");
+    }
+
+    public static Comparator<String> createNaturalOrderRegexComparator() {
+        return Comparator.comparingDouble(NaturalOrderComparators::parseStringToNumber);
+    }
+
+    private static double parseStringToNumber(String input){
+
+        final String digitsOnly = input.replaceAll(DIGIT_AND_DECIMAL_REGEX, "");
+
+        if("".equals(digitsOnly)) return 0;
+
+        try{
+            return Double.parseDouble(digitsOnly);
+        }catch (NumberFormatException nfe){
+            return 0;
+        }
+    }
+
+}

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import com.baeldung.algorithms.stringsortingbynumber.NaturalOrderComparators;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class NaturalOrderComparatorsUnitTest {
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoubles_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("a1", "d2.2", "d2.3d", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoublesWithAnInvalidNumber_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenAllForseenProblems_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.f4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.f4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenComplexStringsContainingSeparatedNumbers_whenSortedByRegex_checkNumbersCondensedAndSorted() {
+
+        List<String> testStrings = Arrays.asList("a1b2c5", "b3ght3.2", "something65.thensomething5"); //125, 33.2, 65.5
+
+        List<String> expected = Arrays.asList("b3ght3.2", "something65.thensomething5", "a1b2c5" );
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+
+    }
+
+    @Test
+    public void givenStringsNotContainingNumbers_whenSortedByRegex_checkOrderNotChanged() {
+
+        List<String> testStrings = Arrays.asList("a", "c", "d", "e");
+        List<String> expected = new ArrayList<>(testStrings);
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+    }
+}

algorithms-sorting/src/main/java/com/baeldung/algorithms/shellsort/ShellSort.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.shellsort;
+
+public class ShellSort {
+
+    public static void sort(int arrayToSort[]) {
+        int n = arrayToSort.length;
+
+        for (int gap = n / 2; gap > 0; gap /= 2) {
+            for (int i = gap; i < n; i++) {
+                int key = arrayToSort[i];
+                int j = i;
+                while (j >= gap && arrayToSort[j - gap] > key) {
+                    arrayToSort[j] = arrayToSort[j - gap];
+                    j -= gap;
+                }
+                arrayToSort[j] = key;
+            }
+        }
+    }
+}

algorithms-sorting/src/test/java/com/baeldung/algorithms/shellsort/ShellSortUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.algorithms.shellsort;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class ShellSortUnitTest {
+
+    @Test
+    public void givenUnsortedArray_whenShellSort_thenSortedAsc() {
+        int[] input = {41, 15, 82, 5, 65, 19, 32, 43, 8};
+        ShellSort.sort(input);
+        int[] expected = {5, 8, 15, 19, 32, 41, 43, 65, 82};
+        assertArrayEquals("the two arrays are not equal", expected, input);
+    }
+}

axon/pom.xml

@@ -18,12 +18,6 @@
             <groupId>org.axonframework</groupId>
             <artifactId>axon-spring-boot-starter</artifactId>
             <version>${axon.version}</version>
-            <exclusions>
-                <exclusion>
-                    <groupId>org.axonframework</groupId>
-                    <artifactId>axon-server-connector</artifactId>
-                </exclusion>
-            </exclusions>
         </dependency>
 
         <dependency>
@@ -58,7 +52,7 @@
     </dependencies>
 
     <properties>
-        <axon.version>4.0.3</axon.version>
+        <axon.version>4.1.2</axon.version>
     </properties>
 
 </project>

axon/src/main/java/com/baeldung/axon/commandmodel/OrderAggregate.java

@@ -13,6 +13,7 @@ import com.baeldung.axon.coreapi.commands.ShipOrderCommand;
 import com.baeldung.axon.coreapi.events.OrderConfirmedEvent;
 import com.baeldung.axon.coreapi.events.OrderPlacedEvent;
 import com.baeldung.axon.coreapi.events.OrderShippedEvent;
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
 
 @Aggregate
 public class OrderAggregate {
@@ -34,7 +35,7 @@ public class OrderAggregate {
     @CommandHandler
     public void handle(ShipOrderCommand command) {
         if (!orderConfirmed) {
-            throw new IllegalStateException("Cannot ship an order which has not been confirmed yet.");
+            throw new UnconfirmedOrderException();
         }
 
         apply(new OrderShippedEvent(orderId));
@@ -43,12 +44,12 @@ public class OrderAggregate {
     @EventSourcingHandler
     public void on(OrderPlacedEvent event) {
         this.orderId = event.getOrderId();
-        orderConfirmed = false;
+        this.orderConfirmed = false;
     }
 
     @EventSourcingHandler
     public void on(OrderConfirmedEvent event) {
-        orderConfirmed = true;
+        this.orderConfirmed = true;
     }
 
     protected OrderAggregate() {

axon/src/main/java/com/baeldung/axon/coreapi/exceptions/UnconfirmedOrderException.java

@@ -0,0 +1,8 @@
+package com.baeldung.axon.coreapi.exceptions;
+
+public class UnconfirmedOrderException extends IllegalStateException {
+
+    public UnconfirmedOrderException() {
+        super("Cannot ship an order which has not been confirmed yet.");
+    }
+}

axon/src/main/java/com/baeldung/axon/querymodel/OrderedProductsEventHandler.java

@@ -5,6 +5,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.axonframework.config.ProcessingGroup;
 import org.axonframework.eventhandling.EventHandler;
 import org.axonframework.queryhandling.QueryHandler;
 import org.springframework.stereotype.Service;
@@ -16,6 +17,7 @@ import com.baeldung.axon.coreapi.queries.FindAllOrderedProductsQuery;
 import com.baeldung.axon.coreapi.queries.OrderedProduct;
 
 @Service
+@ProcessingGroup("ordered-products")
 public class OrderedProductsEventHandler {
 
     private final Map<String, OrderedProduct> orderedProducts = new HashMap<>();

axon/src/main/resources/application.properties

@@ -0,0 +1 @@
+spring.application.name=Order Management Service

axon/src/test/java/com/baeldung/axon/commandmodel/OrderAggregateUnitTest.java

@@ -2,6 +2,7 @@ package com.baeldung.axon.commandmodel;
 
 import java.util.UUID;
 
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
 import org.axonframework.test.aggregate.AggregateTestFixture;
 import org.axonframework.test.aggregate.FixtureConfiguration;
 import org.junit.*;
@@ -41,12 +42,12 @@ public class OrderAggregateUnitTest {
     }
 
     @Test
-    public void givenOrderPlacedEvent_whenShipOrderCommand_thenShouldThrowIllegalStateException() {
+    public void givenOrderPlacedEvent_whenShipOrderCommand_thenShouldThrowUnconfirmedOrderException() {
         String orderId = UUID.randomUUID().toString();
         String product = "Deluxe Chair";
         fixture.given(new OrderPlacedEvent(orderId, product))
                .when(new ShipOrderCommand(orderId))
-               .expectException(IllegalStateException.class);
+               .expectException(UnconfirmedOrderException.class);
     }
 
     @Test

core-groovy-2/src/main/groovy/com/baeldung/concatenate/Wonder.groovy

@@ -0,0 +1,52 @@
+package com.baeldung.concatenate
+
+class Wonder {
+
+    String numOfWonder = 'seven'
+
+    String operator_plus() {
+        return 'The ' + numOfWonder + ' wonders of the world'
+    }
+
+    String operator_left() {
+        return 'The ' << numOfWonder << ' wonders of ' << 'the world'
+    }
+
+    String interpolation_one() {
+        return "The $numOfWonder wonders of the world"
+
+    }
+
+    String interpolation_two() {
+        return "The ${numOfWonder} wonders of the world"
+    }
+
+    String multilineString() {
+        return """
+            There are $numOfWonder wonders of the world.
+            Can you name them all? 
+            1. The Great Pyramid of Giza
+            2. Hanging Gardens of Babylon
+            3. Colossus of Rhode
+            4. Lighthouse of Alexendra
+            5. Temple of Artemis
+            6. Status of Zeus at Olympia
+            7. Mausoleum at Halicarnassus
+        """
+    }
+
+    String method_concat() {
+        return 'The '.concat(numOfWonder).concat(' wonders of the world')
+
+    }
+
+    String method_builder() {
+        return new StringBuilder()
+                .append('The ').append(numOfWonder).append(' wonders of the world')
+    }
+
+    String method_buffer() {
+        return new StringBuffer()
+                .append('The ').append(numOfWonder).append(' wonders of the world')
+    }
+}

core-groovy-2/src/test/groovy/com/baeldung/concatenate/WonderUnitTest.groovy

@@ -0,0 +1,69 @@
+package com.baeldung.concatenate
+
+import org.junit.Before
+import org.junit.Test
+
+import static org.junit.Assert.*
+
+class WonderUnitTest {
+
+    static final String EXPECTED_SINGLE_LINE = "The seven wonders of the world"
+
+    Wonder wonder
+
+    @Before
+    void before() {
+        wonder = new Wonder()
+    }
+
+    @Test
+    void whenUsingOperatorPlus_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.operator_plus())
+    }
+
+    @Test
+    void whenUsingOperatorLeft_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.operator_left())
+    }
+
+    @Test
+    void whenUsingInterpolationOne_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.interpolation_one())
+    }
+
+    @Test
+    void whenUsingInterpolationTwo_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.interpolation_two())
+    }
+
+    @Test
+    void whenUsingMultiline_thenConcatCorrectly() {
+        def expectedMultiline = """
+            There are seven wonders of the world.
+            Can you name them all? 
+            1. The Great Pyramid of Giza
+            2. Hanging Gardens of Babylon
+            3. Colossus of Rhode
+            4. Lighthouse of Alexendra
+            5. Temple of Artemis
+            6. Status of Zeus at Olympia
+            7. Mausoleum at Halicarnassus
+        """
+        assertEquals(expectedMultiline, wonder.multilineString())
+    }
+
+    @Test
+    void whenUsingMethodConcat_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.method_concat())
+    }
+
+    @Test
+    void whenUsingMethodBuilder_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.method_builder())
+    }
+
+    @Test
+    void whenUsingMethodBuffer_thenConcatCorrectly() {
+        assertEquals(EXPECTED_SINGLE_LINE, wonder.method_buffer())
+    }
+}

core-java-modules/core-java-11/src/main/java/com/baeldung/predicate/not/README.md

@@ -0,0 +1,3 @@
+## Relevant articles:
+
+- [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

core-java-modules/core-java-12/README.md

@@ -0,0 +1,4 @@
+## Relevant Articles:
+
+
+- [String API Updates in Java 12](https://www.baeldung.com/java12-string-api)

core-java-modules/core-java-8/src/main/java/com/baeldung/java_8_features/groupingby/Tuple.java

@@ -0,0 +1,34 @@
+package com.baeldung.java_8_features.groupingby;
+
+public class Tuple {
+
+    private BlogPostType type;
+    private String author;
+    
+    public Tuple(BlogPostType type, String author) {
+        super();
+        this.type = type;
+        this.author = author;
+    }
+
+    public BlogPostType getType() {
+        return type;
+    }
+
+    public void setType(BlogPostType type) {
+        this.type = type;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public void setAuthor(String author) {
+        this.author = author;
+    }
+
+    @Override
+    public String toString() {
+        return "Tuple [type=" + type + ", author=" + author + ", getType()=" + getType() + ", getAuthor()=" + getAuthor() + ", getClass()=" + getClass() + ", hashCode()=" + hashCode() + ", toString()=" + super.toString() + "]";
+    }
+}

core-java-modules/core-java-8/src/test/java/com/baeldung/java8/optional/OptionalUnitTest.java

@@ -259,4 +259,15 @@ public class OptionalUnitTest {
         LOG.debug("Getting default value...");
         return "Default Value";
     }
+    
+//    Uncomment code when code base is compatiable with Java 11     
+//    @Test
+//    public void givenAnEmptyOptional_thenIsEmptyBehavesAsExpected() {
+//        Optional<String> opt = Optional.of("Baeldung");
+//        assertFalse(opt.isEmpty());
+//     
+//        opt = Optional.ofNullable(null);
+//        assertTrue(opt.isEmpty());
+//    }
+
 }

core-java-modules/core-java-arrays-2/.gitignore

@@ -0,0 +1,25 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-arrays-2/pom.xml

@@ -0,0 +1,50 @@
+<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</groupId>
+    <artifactId>core-java-arrays-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-arrays-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-arrays-2</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+
+        <!-- util -->
+        <commons-lang3.version>3.9</commons-lang3.version>
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-arrays-2/src/main/java/com/baeldung/array/looping/LoopDiagonally.java

@@ -0,0 +1,45 @@
+package com.baeldung.array.looping;
+
+public class LoopDiagonally {
+
+
+    public String loopDiagonally(String[][] twoDArray) {
+
+        int length = twoDArray.length;
+        int diagonalLines = (length + length) - 1;
+        int itemsInDiagonal = 0;
+        int midPoint = (diagonalLines / 2) + 1;
+        StringBuilder output = new StringBuilder();
+
+        for (int i = 1; i <= diagonalLines; i++) {
+
+            StringBuilder items = new StringBuilder();
+            int rowIndex;
+            int columnIndex;
+
+            if (i <= midPoint) {
+                itemsInDiagonal++;
+                for (int j = 0; j < itemsInDiagonal; j++) {
+                    rowIndex = (i - j) - 1;
+                    columnIndex = j;
+                    items.append(twoDArray[rowIndex][columnIndex]);
+                }
+            } else {
+                itemsInDiagonal--;
+                for (int j = 0; j < itemsInDiagonal; j++) {
+                    rowIndex = (length - 1) - j;
+                    columnIndex = (i - length) + j;
+                    items.append(twoDArray[rowIndex][columnIndex]);
+                }
+            }
+
+            if (i != diagonalLines) {
+                output.append(items).append(" ");
+            } else {
+                output.append(items);
+            }
+        }
+
+        return output.toString();
+    }
+}

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/array/looping/LoopDiagonallyUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.array.looping;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class LoopDiagonallyUnitTest {
+
+    @Test
+    public void twoArrayIsLoopedDiagonallyAsExpected() {
+
+        LoopDiagonally loopDiagonally = new LoopDiagonally();
+        String[][] twoDArray = {{"a", "b", "c"},
+                                {"d", "e", "f"},
+                                {"g", "h", "i"}};
+
+        String output = loopDiagonally.loopDiagonally(twoDArray);
+        assertEquals("a db gec hf i", output);
+    }
+}

core-java-modules/core-java-arrays/src/main/java/com/baeldung/array/SortedArrayChecker.java

@@ -2,7 +2,10 @@ package com.baeldung.array;
 
 import com.baeldung.arraycopy.model.Employee;
 
+import java.util.Comparator;
+
 public class SortedArrayChecker {
+
     boolean isSorted(int[] array, int length) {
         if (array == null || length < 2)
             return true;
@@ -22,7 +25,7 @@ public class SortedArrayChecker {
         return true;
     }
 
-    boolean isSorted(String[] array, int length) {
+    boolean isSorted(Comparable[] array, int length) {
         if (array == null || length < 2)
             return true;
 
@@ -32,40 +35,31 @@ public class SortedArrayChecker {
         return isSorted(array, length - 1);
     }
 
-boolean isSorted(String[] array) {
-    for (int i = 0; i < array.length - 1; ++i) {
-        if (array[i].compareTo(array[i + 1]) > 0)
-            return false;
-    }
-
-    return true;
-}
-
-    boolean isSortedByName(Employee[] array) {
+    boolean isSorted(Comparable[] array) {
         for (int i = 0; i < array.length - 1; ++i) {
-            if (array[i].getName().compareTo(array[i + 1].getName()) > 0)
+            if (array[i].compareTo(array[i + 1]) > 0)
                 return false;
         }
 
         return true;
     }
 
-boolean isSortedByAge(Employee[] array) {
-    for (int i = 0; i < array.length - 1; ++i) {
-        if (array[i].getAge() > (array[i + 1].getAge()))
-            return false;
+    boolean isSorted(Object[] array, Comparator comparator) {
+        for (int i = 0; i < array.length - 1; ++i) {
+            if (comparator.compare(array[i], (array[i + 1])) > 0)
+                return false;
+        }
+
+        return true;
     }
 
-    return true;
-}
-
-    boolean isSortedByAge(Employee[] array, int length) {
+    boolean isSorted(Object[] array, Comparator comparator, int length) {
         if (array == null || length < 2)
             return true;
 
-        if (array[length - 2].getAge() > array[length - 1].getAge())
+        if (comparator.compare(array[length - 2], array[length - 1]) > 0)
             return false;
 
-        return isSortedByAge(array, length - 1);
+        return isSorted(array, comparator, length - 1);
     }
 }

core-java-modules/core-java-arrays/src/test/java/com/baeldung/array/SortedArrayCheckerUnitTest.java

@@ -4,32 +4,33 @@ import com.baeldung.arraycopy.model.Employee;
 import org.junit.Before;
 import org.junit.Test;
 
+import java.util.Comparator;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
-class SortedArrayCheckerUnitTest {
-
+public class SortedArrayCheckerUnitTest {
     private static final int[] INTEGER_SORTED = {1, 3, 5, 7, 9};
     private static final int[] INTEGER_NOT_SORTED = {1, 3, 11, 7};
 
     private static final String[] STRING_SORTED = {"abc", "cde", "fgh"};
     private static final String[] STRING_NOT_SORTED = {"abc", "fgh", "cde", "ijk"};
 
-    private final Employee[] EMPLOYEES_SORTED_BY_NAME = {
+    private static final Employee[] EMPLOYEES_SORTED_BY_NAME = {
             new Employee(1, "Carlos", 26),
             new Employee(2, "Daniel", 31),
             new Employee(3, "Marta", 27)};
 
-    private final Employee[] EMPLOYEES_NOT_SORTED_BY_NAME = {
+    private static final Employee[] EMPLOYEES_NOT_SORTED_BY_NAME = {
             new Employee(1, "Daniel", 31),
             new Employee(2, "Carlos", 26),
             new Employee(3, "Marta", 27)};
 
-    private final Employee[] EMPLOYEES_SORTED_BY_AGE = {
+    private static final Employee[] EMPLOYEES_SORTED_BY_AGE = {
             new Employee(1, "Carlos", 26),
             new Employee(2, "Marta", 27),
             new Employee(3, "Daniel", 31)};
 
-    private final Employee[] EMPLOYEES_NOT_SORTED_BY_AGE = {
+    private static final Employee[] EMPLOYEES_NOT_SORTED_BY_AGE = {
             new Employee(1, "Marta", 27),
             new Employee(2, "Carlos", 26),
             new Employee(3, "Daniel", 31)};
@@ -61,13 +62,18 @@ class SortedArrayCheckerUnitTest {
 
     @Test
     public void givenEmployeeArray_thenReturnIfItIsSortedOrNot() {
-        assertThat(sortedArrayChecker.isSortedByName(EMPLOYEES_SORTED_BY_NAME)).isEqualTo(true);
-        assertThat(sortedArrayChecker.isSortedByName(EMPLOYEES_NOT_SORTED_BY_NAME)).isEqualTo(false);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_SORTED_BY_NAME, Comparator.comparing(Employee::getName))).isEqualTo(true);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_NOT_SORTED_BY_NAME, Comparator.comparing(Employee::getName))).isEqualTo(false);
 
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_SORTED_BY_AGE)).isEqualTo(true);
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_NOT_SORTED_BY_AGE)).isEqualTo(false);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge))).isEqualTo(true);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_NOT_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge))).isEqualTo(false);
 
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_SORTED_BY_AGE, EMPLOYEES_SORTED_BY_AGE.length)).isEqualTo(true);
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_NOT_SORTED_BY_AGE, EMPLOYEES_NOT_SORTED_BY_AGE.length)).isEqualTo(false);
+        assertThat(sortedArrayChecker
+                .isSorted(EMPLOYEES_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge), EMPLOYEES_SORTED_BY_AGE.length))
+                .isEqualTo(true);
+        assertThat(sortedArrayChecker
+                .isSorted(EMPLOYEES_NOT_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge), EMPLOYEES_NOT_SORTED_BY_AGE.length))
+                .isEqualTo(false);
     }
+
 }

core-java-modules/core-java-collections-array-list/src/test/java/org/baeldung/java/collections/CoreJavaCollectionsUnitTest.java

@@ -42,7 +42,7 @@ public class CoreJavaCollectionsUnitTest {
     @Test(expected = UnsupportedOperationException.class)
     public final void givenUsingGuavaBuilder_whenUnmodifiableListIsCreatedFromOriginal_thenNoLongerModifiable() {
         final List<String> list = new ArrayList<String>(Arrays.asList("one", "two", "three"));
-        final ImmutableList<Object> unmodifiableList = ImmutableList.builder().addAll(list).build();
+        final ImmutableList<String> unmodifiableList = ImmutableList.<String>builder().addAll(list).build();
         unmodifiableList.add("four");
     }
 

core-java-modules/core-java-concurrency-basic/README.md

@@ -17,3 +17,4 @@
 - [Runnable vs. Callable in Java](http://www.baeldung.com/java-runnable-callable)
 - [What is Thread-Safety and How to Achieve it?](https://www.baeldung.com/java-thread-safety)
 - [How to Start a Thread in Java](https://www.baeldung.com/java-start-thread)
+- [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)

core-java-modules/core-java-exceptions/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles:
+
+- [Will an Error Be Caught by Catch Block in Java?](https://www.baeldung.com/java-error-catch)

core-java-modules/core-java-lambdas/README.md

@@ -0,0 +1,3 @@
+## Relevant articles:
+
+- [Why Do Local Variables Used in Lambdas Have to Be Final or Effectively Final?](https://www.baeldung.com/java-lambda-effectively-final-local-variables)

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/Car.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.aggregation;
+
+import java.util.List;
+
+public class Car {
+
+    private List<Wheel> wheels;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/CarWithStaticInnerWheel.java

@@ -0,0 +1,13 @@
+package com.baeldung.relationships.aggregation;
+
+import java.util.List;
+
+public class CarWithStaticInnerWheel {
+
+    private List<Wheel> wheels;
+
+    public static class Wheel {
+
+    }
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/Wheel.java

@@ -0,0 +1,7 @@
+package com.baeldung.relationships.aggregation;
+
+public class Wheel {
+
+    private Car car;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/association/Child.java

@@ -0,0 +1,7 @@
+package com.baeldung.relationships.association;
+
+public class Child {
+
+    private Mother mother;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/association/Mother.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.association;
+
+import java.util.List;
+
+public class Mother {
+
+    private List<Child> children;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/composition/Building.java

@@ -0,0 +1,18 @@
+package com.baeldung.relationships.composition;
+
+import java.util.List;
+
+public class Building {
+
+    private String address;
+    private List<Room> rooms;
+    
+    public class Room {
+        
+        public String getBuildingAddress() {
+            return Building.this.address;
+        }
+        
+    }
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/composition/BuildingWithDefinitionRoomInMethod.java

@@ -0,0 +1,28 @@
+package com.baeldung.relationships.composition;
+
+public class BuildingWithDefinitionRoomInMethod {
+
+    public Room createAnonymousRoom() {
+        return new Room() {
+            @Override
+            public void doInRoom() {}
+        };
+    }
+
+    public Room createInlineRoom() {
+        class InlineRoom implements Room {
+            @Override
+            public void doInRoom() {}
+        }
+        return new InlineRoom();
+    }
+    
+    public Room createLambdaRoom() {
+        return () -> {};
+    }
+
+    public interface Room {
+        void doInRoom();
+    }
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/Department.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class Department {
+
+    private List<Professor> professors;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/Professor.java

@@ -0,0 +1,10 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class Professor {
+
+    private List<Department> department;
+    private List<Professor> friends;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/University.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class University {
+
+    private List<Department> department;
+    
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/constructors/BankAccount.java

@@ -54,3 +54,15 @@ class BankAccountCopyConstructor extends BankAccount {
         this.balance = 0.0f;
     }
 }
+
+class BankAccountChainedConstructors extends BankAccount {
+    public BankAccountChainedConstructors(String name, LocalDateTime opened, double balance) {
+        this.name = name;
+        this.opened = opened;
+        this.balance = balance;
+    }
+
+    public BankAccountChainedConstructors(String name) {
+        this(name, LocalDateTime.now(), 0.0f);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/constructors/ConstructorUnitTest.java

@@ -1,15 +1,14 @@
 package com.baeldung.constructors;
 
-import com.baeldung.constructors.*;
+import com.google.common.collect.Comparators;
+import org.junit.Test;
 
-import java.util.logging.Logger;
 import java.time.LocalDateTime;
 import java.time.Month;
+import java.util.ArrayList;
+import java.util.logging.Logger;
 
-import org.junit.Test;
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatCode;
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.*;
 
 public class ConstructorUnitTest {
     final static Logger LOGGER = Logger.getLogger(ConstructorUnitTest.class.getName());
@@ -17,26 +16,28 @@ public class ConstructorUnitTest {
     @Test
     public void givenNoExplicitContructor_whenUsed_thenFails() {
         BankAccount account = new BankAccount();
-        assertThatThrownBy(() -> { account.toString(); }).isInstanceOf(Exception.class);
+        assertThatThrownBy(() -> {
+            account.toString();
+        }).isInstanceOf(Exception.class);
     }
 
     @Test
     public void givenNoArgumentConstructor_whenUsed_thenSucceeds() {
         BankAccountEmptyConstructor account = new BankAccountEmptyConstructor();
         assertThatCode(() -> {
-                account.toString();
-            }).doesNotThrowAnyException();
+            account.toString();
+        }).doesNotThrowAnyException();
     }
 
     @Test
     public void givenParameterisedConstructor_whenUsed_thenSucceeds() {
         LocalDateTime opened = LocalDateTime.of(2018, Month.JUNE, 29, 06, 30, 00);
         BankAccountParameterizedConstructor account =
-            new BankAccountParameterizedConstructor("Tom", opened, 1000.0f);
-        
+                new BankAccountParameterizedConstructor("Tom", opened, 1000.0f);
+
         assertThatCode(() -> {
-                account.toString();
-            }).doesNotThrowAnyException();
+            account.toString();
+        }).doesNotThrowAnyException();
     }
 
     @Test
@@ -47,7 +48,16 @@ public class ConstructorUnitTest {
 
         assertThat(account.getName()).isEqualTo(newAccount.getName());
         assertThat(account.getOpened()).isNotEqualTo(newAccount.getOpened());
-        
+
         assertThat(newAccount.getBalance()).isEqualTo(0.0f);
     }
+
+    @Test
+    public void givenChainedConstructor_whenUsed_thenMaintainsLogic() {
+        BankAccountChainedConstructors account = new BankAccountChainedConstructors("Tim");
+        BankAccountChainedConstructors newAccount = new BankAccountChainedConstructors("Tim", LocalDateTime.now(), 0.0f);
+
+        assertThat(account.getName()).isEqualTo(newAccount.getName());
+        assertThat(account.getBalance()).isEqualTo(newAccount.getBalance());
+    }
 }

core-java-modules/core-java-lang/README.md

@@ -18,7 +18,6 @@
 - [A Guide to Inner Interfaces in Java](http://www.baeldung.com/java-inner-interfaces)
 - [Recursion In Java](http://www.baeldung.com/java-recursion)
 - [A Guide to the finalize Method in Java](http://www.baeldung.com/java-finalize)
-- [A Guide to Java Enums](http://www.baeldung.com/a-guide-to-java-enums)
 - [Infinite Loops in Java](http://www.baeldung.com/infinite-loops-java)
 - [Quick Guide to java.lang.System](http://www.baeldung.com/java-lang-system)
 - [Using Java Assertions](http://www.baeldung.com/java-assert)

core-java-modules/core-java-networking-2/.gitignore

@@ -0,0 +1,25 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-networking-2/pom.xml

@@ -0,0 +1,20 @@
+<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>
+    <artifactId>core-java-networking-2</artifactId>
+    <name>core-java-networking-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-networking-2</finalName>
+    </build>	
+</project>

core-java-modules/core-java-networking-2/src/main/java/com/baeldung/url/UrlChecker.java

@@ -0,0 +1,25 @@
+package com.baeldung.url;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+public class UrlChecker {
+
+    public int getResponseCodeForURL(String address) throws IOException {
+        return getResponseCodeForURLUsing(address, "GET");
+    }
+
+    public int getResponseCodeForURLUsingHead(String address) throws IOException {
+        return getResponseCodeForURLUsing(address, "HEAD");
+    }
+
+    private int getResponseCodeForURLUsing(String address, String method) throws IOException {
+        HttpURLConnection.setFollowRedirects(false); // Set follow redirects to false
+        final URL url = new URL(address);
+        HttpURLConnection huc = (HttpURLConnection) url.openConnection();
+        huc.setRequestMethod(method);
+        return huc.getResponseCode();
+    }
+
+}

core-java-modules/core-java-networking-2/src/test/java/com/baeldung/url/UrlCheckerUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.url;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+
+import org.junit.Test;
+
+public class UrlCheckerUnitTest {
+
+    @Test
+    public void givenValidUrl_WhenUsingHEAD_ThenReturn200() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURLUsingHead("http://www.example.com");
+        assertEquals(200, responseCode);
+    }
+    
+    @Test
+    public void givenInvalidIUrl_WhenUsingHEAD_ThenReturn404() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURLUsingHead("http://www.example.com/unkownurl");
+        assertEquals(404, responseCode);
+    }
+    
+    @Test
+    public void givenValidUrl_WhenUsingGET_ThenReturn200() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURL("http://www.example.com");
+        assertEquals(200, responseCode);
+    }
+    
+    @Test
+    public void givenInvalidIUrl_WhenUsingGET_ThenReturn404() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURL("http://www.example.com/unkownurl");
+        assertEquals(404, responseCode);
+    }
+    
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/core/pwd/CurrentDirectoryFetcher.java

@@ -0,0 +1,40 @@
+package com.baeldung.core.pwd;
+
+import java.io.File;
+import java.nio.file.FileSystems;
+import java.nio.file.Paths;
+
+public final class CurrentDirectoryFetcher {
+
+    public static void main(String[] args) {
+        System.out.printf("Current Directory Using Java System API: %s%n", currentDirectoryUsingSystemProperties());
+
+        System.out.printf("Current Directory Using Java IO File API: %s%n", currentDirectoryUsingFile());
+
+        System.out.printf("Current Directory Using Java NIO FileSystems API: %s%n", currentDirectoryUsingFileSystems());
+
+        System.out.printf("Current Directory Using Java NIO Paths API: %s%n", currentDirectoryUsingPaths());
+    }
+
+    public static String currentDirectoryUsingSystemProperties() {
+        return System.getProperty("user.dir");
+    }
+
+    public static String currentDirectoryUsingPaths() {
+        return Paths.get("")
+            .toAbsolutePath()
+            .toString();
+    }
+
+    public static String currentDirectoryUsingFileSystems() {
+        return FileSystems.getDefault()
+            .getPath("")
+            .toAbsolutePath()
+            .toString();
+    }
+
+    public static String currentDirectoryUsingFile() {
+        return new File("").getAbsolutePath();
+    }
+
+}

core-java-modules/core-java-os/src/test/java/com/baeldung/core/pwd/CurrentDirectoryFetcherTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.core.pwd;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class CurrentDirectoryFetcherTest {
+
+    private static final String CURRENT_DIR = "core-java-os";
+
+    @Test
+    public void whenUsingSystemProperties_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingSystemProperties()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaNioPaths_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingPaths()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaNioFileSystems_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingFileSystems()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaIoFile_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingFile()
+            .endsWith(CURRENT_DIR));
+    }
+}

core-java-modules/core-java/README.md

@@ -37,7 +37,6 @@
 - [Common Java Exceptions](http://www.baeldung.com/java-common-exceptions)
 - [Throw Exception in Optional in Java 8](https://www.baeldung.com/java-optional-throw-exception)
 - [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
-- [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)
 - [Guide to Character Encoding](https://www.baeldung.com/java-char-encoding)

core-java-modules/multimodulemavenproject/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Multi-Module Maven Application with Java Modules](https://www.baeldung.com/maven-multi-module-project-java-jpms)

core-java-modules/pom.xml

@@ -17,6 +17,7 @@
         <module>pre-jpms</module>
         <module>core-java-exceptions</module>
         <module>core-java-optional</module>
+        <module>core-java-networking-2</module>
     </modules>
     
 </project>

custom-pmd/src/main/java/org/baeldung/pmd/UnitTestNamingConventionRule.java

@@ -22,6 +22,10 @@ public class UnitTestNamingConventionRule extends AbstractJavaRule {
         String className = node.getImage();
         Objects.requireNonNull(className);
 
+        if (className.endsWith("SpringContextTest")) {
+            return data;
+        }
+        
         if (className.endsWith("Tests")
                 || (className.endsWith("Test") && allowedEndings.stream().noneMatch(className::endsWith))) {
             addViolation(data, node);

data-structures/src/main/java/com/baeldung/graph/Graph.java

@@ -0,0 +1,72 @@
+package com.baeldung.graph;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Stack;
+
+public class Graph {
+
+    private Map<Integer, List<Integer>> adjVertices;
+
+    public Graph() {
+        this.adjVertices = new HashMap<Integer, List<Integer>>();
+    }
+
+    public void addVertex(int vertex) {
+        adjVertices.putIfAbsent(vertex, new ArrayList<>());
+    }
+
+    public void addEdge(int src, int dest) {
+        adjVertices.get(src).add(dest);
+    }
+
+    public void dfsWithoutRecursion(int start) {
+        Stack<Integer> stack = new Stack<Integer>();
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        stack.push(start);
+        while (!stack.isEmpty()) {
+            int current = stack.pop();
+            isVisited[current] = true;
+            System.out.print(" " + current);
+            for (int dest : adjVertices.get(current)) {
+                if (!isVisited[dest])
+                    stack.push(dest);
+            }
+        }
+    }
+
+    public void dfs(int start) {
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        dfsRecursive(start, isVisited);
+    }
+
+    private void dfsRecursive(int current, boolean[] isVisited) {
+        isVisited[current] = true;
+        System.out.print(" " + current);
+        for (int dest : adjVertices.get(current)) {
+            if (!isVisited[dest])
+                dfsRecursive(dest, isVisited);
+        }
+    }
+
+    public void topologicalSort(int start) {
+        Stack<Integer> result = new Stack<Integer>();
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        topologicalSortRecursive(start, isVisited, result);
+        while (!result.isEmpty()) {
+            System.out.print(" " + result.pop());
+        }
+    }
+
+    private void topologicalSortRecursive(int current, boolean[] isVisited, Stack<Integer> result) {
+        isVisited[current] = true;
+        for (int dest : adjVertices.get(current)) {
+            if (!isVisited[dest])
+                topologicalSortRecursive(dest, isVisited, result);
+        }
+        result.push(current);
+    }
+
+}

data-structures/src/main/java/com/baeldung/tree/BinaryTree.java

@@ -2,6 +2,7 @@ package com.baeldung.tree;
 
 import java.util.LinkedList;
 import java.util.Queue;
+import java.util.Stack;
 
 public class BinaryTree {
 
@@ -147,6 +148,68 @@ public class BinaryTree {
         }
     }
 
+    
+    public void traverseInOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node current = root;
+        stack.push(root);
+        while(! stack.isEmpty()) {
+            while(current.left != null) {
+                current = current.left;                
+                stack.push(current);                
+            }
+            current = stack.pop();
+            System.out.print(" " + current.value);
+            if(current.right != null) {
+                current = current.right;                
+                stack.push(current);
+            }
+        }
+    }
+    
+    public void traversePreOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node current = root;
+        stack.push(root);
+        while(! stack.isEmpty()) {
+            current = stack.pop();
+            System.out.print(" " + current.value);
+            
+            if(current.right != null)
+                stack.push(current.right);
+                
+            if(current.left != null)
+                stack.push(current.left);
+        }        
+    }
+    
+    public void traversePostOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node prev = root;
+        Node current = root;
+        stack.push(root);
+
+        while (!stack.isEmpty()) {
+            current = stack.peek();
+            boolean hasChild = (current.left != null || current.right != null);
+            boolean isPrevLastChild = (prev == current.right || (prev == current.left && current.right == null));
+
+            if (!hasChild || isPrevLastChild) {
+                current = stack.pop();
+                System.out.print(" " + current.value);
+                prev = current;
+            } else {
+                if (current.right != null) {
+                    stack.push(current.right);
+                }
+                if (current.left != null) {
+                    stack.push(current.left);
+                }
+            }
+        }   
+    }    
+    
+    
     class Node {
         int value;
         Node left;

data-structures/src/test/java/com/baeldung/graph/GraphUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.graph;
+
+import org.junit.Test;
+
+public class GraphUnitTest {
+
+    @Test
+    public void givenDirectedGraph_whenDFS_thenPrintAllValues() {
+        Graph graph = createDirectedGraph();
+        graph.dfs(0);
+        System.out.println();
+        graph.dfsWithoutRecursion(0);
+    }
+
+    @Test
+    public void givenDirectedGraph_whenGetTopologicalSort_thenPrintValuesSorted() {
+        Graph graph = createDirectedGraph();
+        graph.topologicalSort(0);
+    }
+
+    private Graph createDirectedGraph() {
+        Graph graph = new Graph();
+        graph.addVertex(0);
+        graph.addVertex(1);
+        graph.addVertex(2);
+        graph.addVertex(3);
+        graph.addVertex(4);
+        graph.addVertex(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(0, 2);
+        graph.addEdge(1, 3);
+        graph.addEdge(2, 3);
+        graph.addEdge(3, 4);
+        graph.addEdge(4, 5);
+        return graph;
+    }
+}

data-structures/src/test/java/com/baeldung/tree/BinaryTreeUnitTest.java

@@ -87,6 +87,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traverseInOrder(bt.root);
+        System.out.println();
+        bt.traverseInOrderWithoutRecursion();
     }
 
     @Test
@@ -95,6 +97,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traversePreOrder(bt.root);
+        System.out.println();
+        bt.traversePreOrderWithoutRecursion();
     }
 
     @Test
@@ -103,6 +107,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traversePostOrder(bt.root);
+        System.out.println();
+        bt.traversePostOrderWithoutRecursion();
     }
 
     @Test

jackson-simple/src/test/java/com/baeldung/jackson/test/JacksonSerializationIgnoreUnitTest.java

@@ -165,7 +165,7 @@ public class JacksonSerializationIgnoreUnitTest {
     }
 
     @Test
-    public final void givenIgnoringNullFieldsOnClass_whenWritingObjectWithNullField_thenFieldIsIgnored() throws JsonProcessingException {
+    public final void givenNullsIgnoredOnClass_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
         final ObjectMapper mapper = new ObjectMapper();
         final MyDtoIgnoreNull dtoObject = new MyDtoIgnoreNull();
 
@@ -178,7 +178,7 @@ public class JacksonSerializationIgnoreUnitTest {
     }
 
     @Test
-    public final void givenIgnoringNullFieldsGlobally_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
+    public final void givenNullsIgnoredGlobally_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
         final ObjectMapper mapper = new ObjectMapper();
         mapper.setSerializationInclusion(Include.NON_NULL);
         final MyDto dtoObject = new MyDto();

java-strings-2/README.MD

@@ -4,3 +4,4 @@
 - [Check If a String Contains a Substring](https://www.baeldung.com/java-string-contains-substring)
 - [Removing Stopwords from a String in Java](https://www.baeldung.com/java-string-remove-stopwords)
 - [Blank and Empty Strings in Java](https://www.baeldung.com/java-blank-empty-strings)
+- [String Initialization in Java](https://www.baeldung.com/java-string-initialization)

java-strings-2/src/test/java/com/baeldung/string/changecase/ToLowerCaseUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToLowerCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignUppercase = "\u0049";
+
+    @Test
+    public void givenMixedCaseString_WhenToLowerCase_ThenResultIsLowerCase() {
+        assertEquals("john doe", name.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithoutLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0069", foreignUppercase.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0131", foreignUppercase.toLowerCase(TURKISH));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/changecase/ToUpperCaseUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToUpperCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignLowercase = "\u0069";
+
+    @Test
+    public void givenMixedCaseString_WhenToUpperCase_ThenResultIsUpperCase() {
+        assertEquals("JOHN DOE", name.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithoutLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0049", foreignLowercase.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0130", foreignLowercase.toUpperCase(TURKISH));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/multiline/MultiLineStringUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.string;
+package com.baeldung.string.multiline;
 
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;

javaxval/src/main/java/org/baeldung/javabeanconstraints/bigdecimal/Invoice.java

@@ -0,0 +1,19 @@
+package org.baeldung.javabeanconstraints.bigdecimal;
+
+import java.math.BigDecimal;
+
+import javax.validation.constraints.DecimalMin;
+import javax.validation.constraints.Digits;
+
+public class Invoice {
+	
+	@DecimalMin(value = "0.0", inclusive = false)
+	@Digits(integer=3, fraction=2)
+    private BigDecimal price;
+    private String description;
+    
+	public Invoice(BigDecimal price, String description) {
+		this.price = price;
+		this.description = description;
+	}
+}

javaxval/src/test/java/org/baeldung/javabeanconstraints/bigdecimal/InvoiceUnitTest.java

@@ -0,0 +1,62 @@
+package org.baeldung.javabeanconstraints.bigdecimal;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.math.BigDecimal;
+import java.util.Set;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class InvoiceUnitTest {
+	
+	private static Validator validator;
+
+    @BeforeClass
+    public static void setupValidatorInstance() {
+        validator = Validation.buildDefaultValidatorFactory().getValidator();
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitLessThanThreeWithDecimalValue_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(10.21), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("numeric value out of bounds (<3 digits>.<2 digits> expected)"));
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitLessThanThreeWithIntegerValue_thenShouldNotGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(10), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(0);
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitGreaterThanThree_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(1021.21), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("numeric value out of bounds (<3 digits>.<2 digits> expected)"));
+    }
+    
+    @Test
+    public void whenPriceIsZero_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(000.00), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("must be greater than 0.0"));
+    }
+    
+    @Test
+    public void whenPriceIsGreaterThanZero_thenShouldNotGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(100.50), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(0);
+    }
+
+}

jhipster/README.md

@@ -1,6 +0,0 @@
-## Relevant articles:
-
-- [JHipster with a Microservice Architecture](http://www.baeldung.com/jhipster-microservices)
-- [Intro to JHipster](http://www.baeldung.com/jhipster)
-- [Building a Basic UAA-Secured JHipster Microservice](https://www.baeldung.com/jhipster-uaa-secured-micro-service)
-- [Creating New Roles and Authorities in JHipster](https://www.baeldung.com/jhipster-new-roles)

jhipster/jhipster-microservice/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [JHipster with a Microservice Architecture](https://www.baeldung.com/jhipster-microservices)

jhipster/jhipster-monolithic/README.md

@@ -1,4 +1,6 @@
-### Relevant articles
+## Relevant Articles
+
+- [Intro to JHipster](https://www.baeldung.com/jhipster)
 
 
 # baeldung

jhipster/jhipster-uaa/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Building a Basic UAA-Secured JHipster Microservice](https://www.baeldung.com/jhipster-uaa-secured-micro-service)

libraries-io/README.md

@@ -0,0 +1,5 @@
+
+### Relevant Articles: 
+
+- [Transferring a File Through SFTP in Java](https://www.baeldung.com/java-file-sftp)
+

libraries-io/pom.xml

@@ -0,0 +1,40 @@
+<?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/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>libraries-io</artifactId>
+    <name>libraries-io</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <!-- sftp file transfer -->
+        <dependency>
+            <groupId>com.jcraft</groupId>
+            <artifactId>jsch</artifactId>
+            <version>${jsch.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.hierynomus</groupId>
+            <artifactId>sshj</artifactId>
+            <version>${sshj.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-vfs2</artifactId>
+            <version>${vfs.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <!-- sftp -->
+        <jsch.version>0.1.55</jsch.version>
+        <sshj.version>0.27.0</sshj.version>
+        <vfs.version>2.4</vfs.version>
+    </properties>
+</project>

libraries-io/src/main/resources/input.txt

@@ -0,0 +1 @@
+This is a sample text content

libraries-io/src/test/java/org/baeldung/java/io/remote/SftpFileTransferLiveTest.java

@@ -0,0 +1,106 @@
+package org.baeldung.java.io.remote;
+
+import java.io.IOException;
+
+import org.apache.commons.vfs2.FileObject;
+import org.apache.commons.vfs2.FileSystemManager;
+import org.apache.commons.vfs2.Selectors;
+import org.apache.commons.vfs2.VFS;
+import org.junit.Test;
+
+import com.jcraft.jsch.ChannelSftp;
+import com.jcraft.jsch.JSch;
+import com.jcraft.jsch.JSchException;
+import com.jcraft.jsch.Session;
+import com.jcraft.jsch.SftpException;
+
+import net.schmizz.sshj.SSHClient;
+import net.schmizz.sshj.sftp.SFTPClient;
+import net.schmizz.sshj.transport.verification.PromiscuousVerifier;
+
+public class SftpFileTransferLiveTest {
+
+    private String remoteHost = "HOST_NAME_HERE";
+    private String username = "USERNAME_HERE";
+    private String password = "PASSWORD_HERE";
+    private String localFile = "src/main/resources/input.txt";
+    private String remoteFile = "welcome.txt";
+    private String localDir = "src/main/resources/";
+    private String remoteDir = "remote_sftp_test/";
+    private String knownHostsFileLoc = "/Users/USERNAME/known_hosts_sample";
+
+    @Test
+    public void whenUploadFileUsingJsch_thenSuccess() throws JSchException, SftpException {
+        ChannelSftp channelSftp = setupJsch();
+        channelSftp.connect();
+        channelSftp.put(localFile, remoteDir + "jschFile.txt");
+        channelSftp.exit();
+    }
+
+    @Test
+    public void whenDownloadFileUsingJsch_thenSuccess() throws JSchException, SftpException {
+        ChannelSftp channelSftp = setupJsch();
+        channelSftp.connect();
+        channelSftp.get(remoteFile, localDir + "jschFile.txt");
+        channelSftp.exit();
+    }
+
+    @Test
+    public void whenUploadFileUsingSshj_thenSuccess() throws IOException {
+        SSHClient sshClient = setupSshj();
+        SFTPClient sftpClient = sshClient.newSFTPClient();
+        sftpClient.put(localFile, remoteDir + "sshjFile.txt");
+        sftpClient.close();
+        sshClient.disconnect();
+    }
+
+    @Test
+    public void whenDownloadFileUsingSshj_thenSuccess() throws IOException {
+        SSHClient sshClient = setupSshj();
+        SFTPClient sftpClient = sshClient.newSFTPClient();
+        sftpClient.get(remoteFile, localDir + "sshjFile.txt");
+        sftpClient.close();
+        sshClient.disconnect();
+    }
+
+    @Test
+    public void whenUploadFileUsingApacheVfs_thenSuccess() throws IOException {
+        FileSystemManager manager = VFS.getManager();
+        FileObject local = manager.resolveFile(System.getProperty("user.dir") + "/" + localFile);
+        FileObject remote = manager.resolveFile("sftp://" + username + ":" + password + "@" + remoteHost + "/" + remoteDir + "vfsFile.txt");
+        remote.copyFrom(local, Selectors.SELECT_SELF);
+        local.close();
+        remote.close();
+    }
+
+    @Test
+    public void whenDownloadFileUsingApacheVfs_thenSuccess() throws IOException {
+        FileSystemManager manager = VFS.getManager();
+        FileObject local = manager.resolveFile(System.getProperty("user.dir") + "/" + localDir + "vfsFile.txt");
+        FileObject remote = manager.resolveFile("sftp://" + username + ":" + password + "@" + remoteHost + "/" + remoteFile);
+        local.copyFrom(remote, Selectors.SELECT_SELF);
+        local.close();
+        remote.close();
+    }
+
+    // ====== ssh-keyscan -H -t rsa remoteHost >> known_hosts_sample
+
+    private ChannelSftp setupJsch() throws JSchException {
+        JSch jsch = new JSch();
+        jsch.setKnownHosts(knownHostsFileLoc);
+        Session jschSession = jsch.getSession(username, remoteHost);
+        jschSession.setPassword(password);
+        //jschSession.setConfig("StrictHostKeyChecking", "no");
+        jschSession.connect();
+        return (ChannelSftp) jschSession.openChannel("sftp");
+    }
+
+    private SSHClient setupSshj() throws IOException {
+        SSHClient client = new SSHClient();
+        client.addHostKeyVerifier(new PromiscuousVerifier());
+        client.connect(remoteHost);
+        client.authPassword(username, password);
+        return client;
+    }
+
+}

libraries/README.md

@@ -42,7 +42,6 @@
 - [Introduction to Akka Actors in Java](http://www.baeldung.com/akka-actors-java)
 - [Introduction to Smooks](http://www.baeldung.com/smooks)
 - [A Guide to Infinispan in Java](http://www.baeldung.com/infinispan)
-- [Introduction to OpenCSV](http://www.baeldung.com/opencsv)
 - [A Guide to Unirest](http://www.baeldung.com/unirest)
 - [Introduction to Akka Actors in Java](http://www.baeldung.com/akka-actors-java)
 - [A Guide to Byte Buddy](http://www.baeldung.com/byte-buddy)

lombok/src/main/java/com/baeldung/lombok/getter/GetterLazy.java

@@ -13,9 +13,9 @@ public class GetterLazy {
     private static final String DELIMETER = ",";
 
     @Getter(lazy = true)
-    private final Map<String, Long> transactions = readTxnsFromFile();
+    private final Map<String, Long> transactions = getTransactions();
 
-    private Map<String, Long> readTxnsFromFile() {
+    private Map<String, Long> getTransactions() {
 
         final Map<String, Long> cache = new HashMap<>();
         List<String> txnRows = readTxnListFromFile();

lombok/src/main/java/com/baeldung/lombok/intro/Utility.java

@@ -0,0 +1,26 @@
+package com.baeldung.lombok.intro;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.stream.Collectors;
+
+import lombok.SneakyThrows;
+import lombok.Synchronized;
+
+public class Utility {
+
+    @SneakyThrows
+    public String resourceAsString() throws IOException {
+        try (InputStream is = this.getClass().getResourceAsStream("sure_in_my_jar.txt")) {
+            BufferedReader br = new BufferedReader(new InputStreamReader(is, "UTF-8"));
+            return br.lines().collect(Collectors.joining("\n"));
+        } 
+    }
+
+    @Synchronized
+    public void putValueInCache(String key, String value) {
+        System.out.println("Thread safe here with key : [" + key + "] and value[" + value + "]");
+    }
+}

lombok/src/main/resources/sure_in_my_jar.txt

@@ -0,0 +1 @@
+Hello

morphia/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-
-- [Intro to Morphia](http://www.baeldung.com/intro-to-morphia)

morphia/pom.xml

@@ -1,43 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xmlns="http://maven.apache.org/POM/4.0.0"
-	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.morphia</groupId>
-	<artifactId>morphia</artifactId>
-	<name>morphia</name>
-
-	<parent>
-		<groupId>com.baeldung</groupId>
-		<artifactId>parent-modules</artifactId>
-		<version>1.0.0-SNAPSHOT</version>
-		<relativePath>..</relativePath>
-	</parent>
-
-	<dependencies>
-		<dependency>
-			<groupId>dev.morphia.morphia</groupId>
-			<artifactId>core</artifactId>
-			<version>${morphia.version}</version>
-		</dependency>
-
-	</dependencies>
-
-	<build>
-		<pluginManagement>
-			<plugins>
-				<plugin>
-					<groupId>org.springframework.boot</groupId>
-					<artifactId>spring-boot-maven-plugin</artifactId>
-					<version>${spring-boot-maven-plugin.version}</version>
-				</plugin>
-			</plugins>
-		</pluginManagement>
-	</build>
-
-	<properties>
-		<spring-boot-maven-plugin.version>1.4.2.RELEASE</spring-boot-maven-plugin.version>
-		<morphia.version>1.5.3</morphia.version>
-	</properties>
-
-</project>

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/api/AuthorizationEndpoint.java

@@ -121,8 +121,8 @@ public class AuthorizationEndpoint {
         String redirectUri = originalParams.getFirst("resolved_redirect_uri");
         StringBuilder sb = new StringBuilder(redirectUri);
 
-        String approbationStatus = params.getFirst("approbation_status");
-        if ("NO".equals(approbationStatus)) {
+        String approvalStatus = params.getFirst("approval_status");
+        if ("NO".equals(approvalStatus)) {
             URI location = UriBuilder.fromUri(sb.toString())
                     .queryParam("error", "User doesn't approved the request.")
                     .queryParam("error_description", "User doesn't approved the request.")

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/api/TokenEndpoint.java

@@ -15,15 +15,14 @@ import javax.ws.rs.core.HttpHeaders;
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.MultivaluedMap;
 import javax.ws.rs.core.Response;
+import java.util.Arrays;
 import java.util.Base64;
-import java.util.Collections;
 import java.util.List;
-import java.util.Objects;
 
 @Path("token")
 public class TokenEndpoint {
 
-    List<String> supportedGrantTypes = Collections.singletonList("authorization_code");
+    List<String> supportedGrantTypes = Arrays.asList("authorization_code", "refresh_token");
 
     @Inject
     private AppDataRepository appDataRepository;
@@ -39,36 +38,36 @@ public class TokenEndpoint {
 
         //Check grant_type params
         String grantType = params.getFirst("grant_type");
-        Objects.requireNonNull(grantType, "grant_type params is required");
-        if (!supportedGrantTypes.contains(grantType)) {
-            JsonObject error = Json.createObjectBuilder()
-                    .add("error", "unsupported_grant_type")
-                    .add("error_description", "grant type should be one of :" + supportedGrantTypes)
-                    .build();
-            return Response.status(Response.Status.BAD_REQUEST)
-                    .entity(error).build();
+        if (grantType == null || grantType.isEmpty())
+            return responseError("Invalid_request", "grant_type is required", Response.Status.BAD_REQUEST);
 
+        if (!supportedGrantTypes.contains(grantType)) {
+            return responseError("unsupported_grant_type", "grant_type should be one of :" + supportedGrantTypes, Response.Status.BAD_REQUEST);
         }
 
         //Client Authentication
         String[] clientCredentials = extract(authHeader);
+        if (clientCredentials.length != 2) {
+            return responseError("Invalid_request", "Bad Credentials client_id/client_secret", Response.Status.BAD_REQUEST);
+        }
         String clientId = clientCredentials[0];
-        String clientSecret = clientCredentials[1];
         Client client = appDataRepository.getClient(clientId);
-        if (client == null || clientSecret == null || !clientSecret.equals(client.getClientSecret())) {
-            JsonObject error = Json.createObjectBuilder()
-                    .add("error", "invalid_client")
-                    .build();
-            return Response.status(Response.Status.UNAUTHORIZED)
-                    .entity(error).build();
+        if (client == null) {
+            return responseError("Invalid_request", "Invalid client_id", Response.Status.BAD_REQUEST);
+        }
+        String clientSecret = clientCredentials[1];
+        if (!clientSecret.equals(client.getClientSecret())) {
+            return responseError("Invalid_request", "Invalid client_secret", Response.Status.UNAUTHORIZED);
         }
 
         AuthorizationGrantTypeHandler authorizationGrantTypeHandler = authorizationGrantTypeHandlers.select(NamedLiteral.of(grantType)).get();
         JsonObject tokenResponse = null;
         try {
             tokenResponse = authorizationGrantTypeHandler.createAccessToken(clientId, params);
+        } catch (WebApplicationException e) {
+            return e.getResponse();
         } catch (Exception e) {
-            e.printStackTrace();
+            return responseError("Invalid_request", "Can't get token", Response.Status.INTERNAL_SERVER_ERROR);
         }
 
         return Response.ok(tokenResponse)
@@ -81,6 +80,15 @@ public class TokenEndpoint {
         if (authHeader != null && authHeader.startsWith("Basic ")) {
             return new String(Base64.getDecoder().decode(authHeader.substring(6))).split(":");
         }
-        return null;
+        return new String[]{};
+    }
+
+    private Response responseError(String error, String errorDescription, Response.Status status) {
+        JsonObject errorResponse = Json.createObjectBuilder()
+                .add("error", error)
+                .add("error_description", errorDescription)
+                .build();
+        return Response.status(status)
+                .entity(errorResponse).build();
     }
 }

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/AbstractGrantTypeHandler.java

@@ -0,0 +1,87 @@
+package com.baeldung.oauth2.authorization.server.handler;
+
+import com.baeldung.oauth2.authorization.server.PEMKeyUtils;
+import com.nimbusds.jose.*;
+import com.nimbusds.jose.crypto.RSASSASigner;
+import com.nimbusds.jose.crypto.RSASSAVerifier;
+import com.nimbusds.jose.jwk.JWK;
+import com.nimbusds.jose.jwk.RSAKey;
+import com.nimbusds.jwt.JWTClaimsSet;
+import com.nimbusds.jwt.SignedJWT;
+import org.eclipse.microprofile.config.Config;
+
+import javax.inject.Inject;
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.UUID;
+
+public abstract class AbstractGrantTypeHandler implements AuthorizationGrantTypeHandler {
+
+    //Always RSA 256, but could be parametrized
+    protected JWSHeader jwsHeader = new JWSHeader.Builder(JWSAlgorithm.RS256).type(JOSEObjectType.JWT).build();
+
+    @Inject
+    protected Config config;
+
+    //30 min
+    protected Long expiresInMin = 30L;
+
+    protected JWSVerifier getJWSVerifier() throws Exception {
+        String verificationkey = config.getValue("verificationkey", String.class);
+        String pemEncodedRSAPublicKey = PEMKeyUtils.readKeyAsString(verificationkey);
+        RSAKey rsaPublicKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPublicKey);
+        return new RSASSAVerifier(rsaPublicKey);
+    }
+
+    protected JWSSigner getJwsSigner() throws Exception {
+        String signingkey = config.getValue("signingkey", String.class);
+        String pemEncodedRSAPrivateKey = PEMKeyUtils.readKeyAsString(signingkey);
+        RSAKey rsaKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPrivateKey);
+        return new RSASSASigner(rsaKey.toRSAPrivateKey());
+    }
+
+    protected String getAccessToken(String clientId, String subject, String approvedScope) throws Exception {
+        //4. Signing
+        JWSSigner jwsSigner = getJwsSigner();
+
+        Instant now = Instant.now();
+        //Long expiresInMin = 30L;
+        Date expirationTime = Date.from(now.plus(expiresInMin, ChronoUnit.MINUTES));
+
+        //3. JWT Payload or claims
+        JWTClaimsSet jwtClaims = new JWTClaimsSet.Builder()
+                .issuer("http://localhost:9080")
+                .subject(subject)
+                .claim("upn", subject)
+                .claim("client_id", clientId)
+                .audience("http://localhost:9280")
+                .claim("scope", approvedScope)
+                .claim("groups", Arrays.asList(approvedScope.split(" ")))
+                .expirationTime(expirationTime) // expires in 30 minutes
+                .notBeforeTime(Date.from(now))
+                .issueTime(Date.from(now))
+                .jwtID(UUID.randomUUID().toString())
+                .build();
+        SignedJWT signedJWT = new SignedJWT(jwsHeader, jwtClaims);
+        signedJWT.sign(jwsSigner);
+        return signedJWT.serialize();
+    }
+
+    protected String getRefreshToken(String clientId, String subject, String approvedScope) throws Exception {
+        JWSSigner jwsSigner = getJwsSigner();
+        Instant now = Instant.now();
+        //6.Build refresh token
+        JWTClaimsSet refreshTokenClaims = new JWTClaimsSet.Builder()
+                .subject(subject)
+                .claim("client_id", clientId)
+                .claim("scope", approvedScope)
+                //refresh token for 1 day.
+                .expirationTime(Date.from(now.plus(1, ChronoUnit.DAYS)))
+                .build();
+        SignedJWT signedRefreshToken = new SignedJWT(jwsHeader, refreshTokenClaims);
+        signedRefreshToken.sign(jwsSigner);
+        return signedRefreshToken.serialize();
+    }
+}

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/AuthorizationCodeGrantTypeHandler.java

@@ -1,18 +1,7 @@
 package com.baeldung.oauth2.authorization.server.handler;
 
-import com.baeldung.oauth2.authorization.server.PEMKeyUtils;
 import com.baeldung.oauth2.authorization.server.model.AuthorizationCode;
-import com.nimbusds.jose.JOSEObjectType;
-import com.nimbusds.jose.JWSAlgorithm;
-import com.nimbusds.jose.JWSHeader;
-import com.nimbusds.jose.crypto.RSASSASigner;
-import com.nimbusds.jose.jwk.JWK;
-import com.nimbusds.jose.jwk.RSAKey;
-import com.nimbusds.jwt.JWTClaimsSet;
-import com.nimbusds.jwt.SignedJWT;
-import org.eclipse.microprofile.config.Config;
 
-import javax.inject.Inject;
 import javax.inject.Named;
 import javax.json.Json;
 import javax.json.JsonObject;
@@ -20,22 +9,14 @@ import javax.persistence.EntityManager;
 import javax.persistence.PersistenceContext;
 import javax.ws.rs.WebApplicationException;
 import javax.ws.rs.core.MultivaluedMap;
-import java.time.Instant;
 import java.time.LocalDateTime;
-import java.time.temporal.ChronoUnit;
-import java.util.Arrays;
-import java.util.Date;
-import java.util.UUID;
 
 @Named("authorization_code")
-public class AuthorizationCodeGrantTypeHandler implements AuthorizationGrantTypeHandler {
+public class AuthorizationCodeGrantTypeHandler extends AbstractGrantTypeHandler {
 
     @PersistenceContext
     private EntityManager entityManager;
 
-    @Inject
-    private Config config;
-
     @Override
     public JsonObject createAccessToken(String clientId, MultivaluedMap<String, String> params) throws Exception {
         //1. code is required
@@ -58,42 +39,16 @@ public class AuthorizationCodeGrantTypeHandler implements AuthorizationGrantType
             throw new WebApplicationException("invalid_grant");
         }
 
-        //JWT Header
-        JWSHeader jwsHeader = new JWSHeader.Builder(JWSAlgorithm.RS256).type(JOSEObjectType.JWT).build();
-
-        Instant now = Instant.now();
-        Long expiresInMin = 30L;
-        Date expiresIn = Date.from(now.plus(expiresInMin, ChronoUnit.MINUTES));
-
         //3. JWT Payload or claims
-        JWTClaimsSet jwtClaims = new JWTClaimsSet.Builder()
-                .issuer("http://localhost:9080")
-                .subject(authorizationCode.getUserId())
-                .claim("upn", authorizationCode.getUserId())
-                .audience("http://localhost:9280")
-                .claim("scope", authorizationCode.getApprovedScopes())
-                .claim("groups", Arrays.asList(authorizationCode.getApprovedScopes().split(" ")))
-                .expirationTime(expiresIn) // expires in 30 minutes
-                .notBeforeTime(Date.from(now))
-                .issueTime(Date.from(now))
-                .jwtID(UUID.randomUUID().toString())
-                .build();
-        SignedJWT signedJWT = new SignedJWT(jwsHeader, jwtClaims);
-
-        //4. Signing
-        String signingkey = config.getValue("signingkey", String.class);
-        String pemEncodedRSAPrivateKey = PEMKeyUtils.readKeyAsString(signingkey);
-        RSAKey rsaKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPrivateKey);
-        signedJWT.sign(new RSASSASigner(rsaKey.toRSAPrivateKey()));
-
-        //5. Finally the JWT access token
-        String accessToken = signedJWT.serialize();
+        String accessToken = getAccessToken(clientId, authorizationCode.getUserId(), authorizationCode.getApprovedScopes());
+        String refreshToken = getRefreshToken(clientId, authorizationCode.getUserId(), authorizationCode.getApprovedScopes());
 
         return Json.createObjectBuilder()
                 .add("token_type", "Bearer")
                 .add("access_token", accessToken)
                 .add("expires_in", expiresInMin * 60)
                 .add("scope", authorizationCode.getApprovedScopes())
+                .add("refresh_token", refreshToken)
                 .build();
     }
 }

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/RefreshTokenGrantTypeHandler.java

@@ -0,0 +1,72 @@
+package com.baeldung.oauth2.authorization.server.handler;
+
+import com.nimbusds.jose.JWSVerifier;
+import com.nimbusds.jwt.SignedJWT;
+
+import javax.inject.Named;
+import javax.json.Json;
+import javax.json.JsonObject;
+import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.MultivaluedMap;
+import javax.ws.rs.core.Response;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.HashSet;
+import java.util.Set;
+
+@Named("refresh_token")
+public class RefreshTokenGrantTypeHandler extends AbstractGrantTypeHandler {
+
+    @Override
+    public JsonObject createAccessToken(String clientId, MultivaluedMap<String, String> params) throws Exception {
+        String refreshToken = params.getFirst("refresh_token");
+        if (refreshToken == null || "".equals(refreshToken)) {
+            throw new WebApplicationException("invalid_grant");
+        }
+
+        //Decode refresh token
+        SignedJWT signedRefreshToken = SignedJWT.parse(refreshToken);
+        JWSVerifier verifier = getJWSVerifier();
+
+        if (!signedRefreshToken.verify(verifier)) {
+            throw new WebApplicationException("Invalid refresh token.");
+        }
+        if (!(new Date().before(signedRefreshToken.getJWTClaimsSet().getExpirationTime()))) {
+            throw new WebApplicationException("Refresh token expired.");
+        }
+        String refreshTokenClientId = signedRefreshToken.getJWTClaimsSet().getStringClaim("client_id");
+        if (!clientId.equals(refreshTokenClientId)) {
+            throw new WebApplicationException("Invalid client_id.");
+        }
+
+        //At this point, the refresh token is valid and not yet expired
+        //So create a new access token from it.
+        String subject = signedRefreshToken.getJWTClaimsSet().getSubject();
+        String approvedScopes = signedRefreshToken.getJWTClaimsSet().getStringClaim("scope");
+
+        String requestedScopes = params.getFirst("scope");
+        if (requestedScopes != null && !requestedScopes.isEmpty()) {
+            Set<String> rScopes = new HashSet(Arrays.asList(requestedScopes.split(" ")));
+            Set<String> aScopes = new HashSet(Arrays.asList(approvedScopes.split(" ")));
+            if (!aScopes.containsAll(rScopes)) {
+                JsonObject error = Json.createObjectBuilder()
+                        .add("error", "Invalid_request")
+                        .add("error_description", "Requested scopes should be a subset of the original scopes.")
+                        .build();
+                Response response = Response.status(Response.Status.BAD_REQUEST).entity(error).build();
+                throw new WebApplicationException(response);
+            }
+        } else {
+            requestedScopes = approvedScopes;
+        }
+
+        String accessToken = getAccessToken(clientId, subject, requestedScopes);
+        return Json.createObjectBuilder()
+                .add("token_type", "Bearer")
+                .add("access_token", accessToken)
+                .add("expires_in", expiresInMin * 60)
+                .add("scope", requestedScopes)
+                .add("refresh_token", refreshToken)
+                .build();
+    }
+}

oauth2-framework-impl/oauth2-authorization-server/src/main/webapp/authorize.jsp

@@ -41,8 +41,8 @@
 
             <tr>
                 <td colspan="2">
-                    <input type="submit" name="approbation_status" value="YES"/>
-                    <input type="submit" name="approbation_status" value="NO"/>
+                    <input type="submit" name="approval_status" value="YES"/>
+                    <input type="submit" name="approval_status" value="NO"/>
                 </td>
             </tr>
         </table>

oauth2-framework-impl/oauth2-client/src/main/java/com/baeldung/oauth2/client/AbstractServlet.java

@@ -0,0 +1,23 @@
+package com.baeldung.oauth2.client;
+
+import javax.servlet.RequestDispatcher;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.util.Base64;
+
+public abstract class AbstractServlet extends HttpServlet {
+
+    protected void dispatch(String location, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+        RequestDispatcher requestDispatcher = request.getRequestDispatcher(location);
+        requestDispatcher.forward(request, response);
+    }
+
+    protected String getAuthorizationHeaderValue(String clientId, String clientSecret) {
+        String token = clientId + ":" + clientSecret;
+        String encodedString = Base64.getEncoder().encodeToString(token.getBytes());
+        return "Basic " + encodedString;
+    }
+}

oauth2-framework-impl/oauth2-client/src/main/java/com/baeldung/oauth2/client/CallbackServlet.java

@@ -4,10 +4,8 @@ import org.eclipse.microprofile.config.Config;
 
 import javax.inject.Inject;
 import javax.json.JsonObject;
-import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebServlet;
-import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.ws.rs.client.Client;
@@ -18,10 +16,9 @@ import javax.ws.rs.core.Form;
 import javax.ws.rs.core.HttpHeaders;
 import javax.ws.rs.core.MediaType;
 import java.io.IOException;
-import java.util.Base64;
 
 @WebServlet(urlPatterns = "/callback")
-public class CallbackServlet extends HttpServlet {
+public class CallbackServlet extends AbstractServlet {
 
     @Inject
     private Config config;
@@ -29,6 +26,9 @@ public class CallbackServlet extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
+        String clientId = config.getValue("client.clientId", String.class);
+        String clientSecret = config.getValue("client.clientSecret", String.class);
+
         //Error:
         String error = request.getParameter("error");
         if (error != null) {
@@ -53,24 +53,15 @@ public class CallbackServlet extends HttpServlet {
         form.param("code", code);
         form.param("redirect_uri", config.getValue("client.redirectUri", String.class));
 
-        JsonObject tokenResponse = target.request(MediaType.APPLICATION_JSON_TYPE)
-                .header(HttpHeaders.AUTHORIZATION, getAuthorizationHeaderValue())
-                .post(Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), JsonObject.class);
-
-        request.getSession().setAttribute("tokenResponse", tokenResponse);
+        try {
+            JsonObject tokenResponse = target.request(MediaType.APPLICATION_JSON_TYPE)
+                    .header(HttpHeaders.AUTHORIZATION, getAuthorizationHeaderValue(clientId, clientSecret))
+                    .post(Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), JsonObject.class);
+            request.getSession().setAttribute("tokenResponse", tokenResponse);
+        } catch (Exception ex) {
+            System.out.println(ex.getMessage());
+            request.setAttribute("error", ex.getMessage());
+        }
         dispatch("/", request, response);
     }
-
-    private void dispatch(String location, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
-        RequestDispatcher requestDispatcher = request.getRequestDispatcher(location);
-        requestDispatcher.forward(request, response);
-    }
-
-    private String getAuthorizationHeaderValue() {
-        String clientId = config.getValue("client.clientId", String.class);
-        String clientSecret = config.getValue("client.clientSecret", String.class);
-        String token = clientId + ":" + clientSecret;
-        String encodedString = Base64.getEncoder().encodeToString(token.getBytes());
-        return "Basic " + encodedString;
-    }
 }