Merge branch 'master' into BAEL-3760_Introduction_to_Takes

# Conflicts:
#	libraries-3/pom.xml

algorithms-miscellaneous-5/README.md

@@ -16,4 +16,8 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Maximum Subarray Problem](https://www.baeldung.com/java-maximum-subarray)
 - [How to Merge Two Sorted Arrays](https://www.baeldung.com/java-merge-sorted-arrays)
 - [Median of Stream of Integers using Heap](https://www.baeldung.com/java-stream-integers-median-using-heap)
+- [Kruskal’s Algorithm for Spanning Trees](https://www.baeldung.com/java-spanning-trees-kruskal)
+- [Balanced Brackets Algorithm in Java](https://www.baeldung.com/java-balanced-brackets-algorithm)
+- [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
+- [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-4)

algorithms-sorting-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Partitioning and Sorting Arrays with Many Repeated Entries](https://www.baeldung.com/java-sorting-arrays-with-repeated-entries)

apache-poi/README.md

@@ -6,3 +6,6 @@ This module contains articles about Apache POI
 - [Microsoft Word Processing in Java with Apache POI](https://www.baeldung.com/java-microsoft-word-with-apache-poi)
 - [Working with Microsoft Excel in Java](https://www.baeldung.com/java-microsoft-excel)
 - [Creating a MS PowerPoint Presentation in Java](https://www.baeldung.com/apache-poi-slideshow)
+- [Merge Cells in Excel Using Apache POI](https://www.baeldung.com/java-apache-poi-merge-cells)
+- [Get String Value of Excel Cell with Apache POI](https://www.baeldung.com/java-apache-poi-cell-string-value)
+- [Read Excel Cell Value Rather Than Formula With Apache POI](https://github.com/eugenp/tutorials/tree/master/apache-poi)

apache-poi/src/test/java/com/baeldung/poi/excel/merge/ExcelCellMergerUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.poi.excel;
+package com.baeldung.poi.excel.merge;
 
 import static org.junit.Assert.assertEquals;
 

apache-rocketmq/README.md

@@ -3,3 +3,5 @@
 This module contains articles about Apache RocketMQ
 
 ### Relevant Articles: 
+
+- [Apache RocketMQ with Spring Boot](https://www.baeldung.com/apache-rocketmq-spring-boot)

blade/pom.xml

@@ -106,7 +106,7 @@
                             <arguments>
                                 <argument>java</argument>
                                 <argument>-jar</argument>
-                                <argument>sample-blade-app.jar</argument>
+                                <argument>blade.jar</argument>
                             </arguments>
                         </configuration>
                     </execution>

core-java-modules/core-java-13/README.md

@@ -1,3 +1,4 @@
 ### Relevant articles:
 
 - [Java Switch Statement](https://www.baeldung.com/java-switch)
+- [New Java 13 Features](https://www.baeldung.com/java-13-new-features)

core-java-modules/core-java-arrays-2/README.md

@@ -13,4 +13,5 @@ This module contains articles about Java arrays
 - [Removing an Element from an Array in Java](https://www.baeldung.com/java-array-remove-element)
 - [Removing the First Element of an Array](https://www.baeldung.com/java-array-remove-first-element)
 - [Adding an Element to a Java Array vs an ArrayList](https://www.baeldung.com/java-add-element-to-array-vs-list)
+- [Arrays.sort vs Arrays.parallelSort](https://www.baeldung.com/java-arrays-sort-vs-parallelsort)
 - [[<-- Prev]](/core-java-modules/core-java-arrays)

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/arraysort/SortComparisonUnitTest.java

@@ -69,7 +69,7 @@ public class SortComparisonUnitTest {
     }
 
     @Test
-    public void givenArrayOfIntegers_whenUsingArraysSortMethodWithRange_thenSortRangeOfArrayInAscendingOrder() {
+    public void givenArrayOfIntegers_whenUsingArraysSortWithRange_thenSortRangeOfArrayAsc() {
         int[] array = { 10, 4, 6, 2, 1, 9, 7, 8, 3, 5 };
         int[] expected = { 10, 4, 1, 2, 6, 7, 8, 9, 3, 5 };
 
@@ -89,7 +89,7 @@ public class SortComparisonUnitTest {
     }
 
     @Test
-    public void givenArrayOfIntegers_whenUsingArraysParallelSortMethodWithRange_thenSortRangeOfArrayInAscendingOrder() {
+    public void givenArrayOfIntegers_whenUsingArraysParallelSortWithRange_thenSortRangeOfArrayAsc() {
         int[] array = { 10, 4, 6, 2, 1, 9, 7, 8, 3, 5 };
         int[] expected = { 10, 4, 1, 2, 6, 7, 8, 9, 3, 5 };
 

core-java-modules/core-java-arrays-3/README.md

@@ -0,0 +1,5 @@
+## Core Java Arrays (Part 3)
+
+This module contains articles about Java arrays
+
+## Relevant Articles

core-java-modules/core-java-arrays-3/pom.xml

@@ -0,0 +1,31 @@
+<?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>core-java-arrays-3</artifactId>
+	<version>0.1.0-SNAPSHOT</version>
+	<name>core-java-arrays-3</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.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>${assertj.version}</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<properties>
+		<assertj.version>3.14.0</assertj.version>
+	</properties>
+
+</project>

core-java-modules/core-java-arrays-3/src/test/java/com/baeldung/arrays/deepequals/ArraysDeepEqualsUnitTest.java

@@ -0,0 +1,96 @@
+package com.baeldung.arrays.deepequals;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Arrays;
+import java.util.Objects;
+import org.junit.jupiter.api.Test;
+
+public class ArraysDeepEqualsUnitTest {
+
+    class Person {
+        private int id;
+        private String name;
+        private int age;
+
+        Person(int id, String name, int age) {
+            this.id = id;
+            this.name = name;
+            this.age = age;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (this == obj) {
+                return true;
+            }
+            if (obj == null) {
+                return false;
+            }
+            if (!(obj instanceof Person))
+                return false;
+            Person person = (Person) obj;
+            return id == person.id && name.equals(person.name) && age == person.age;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(id, name, age);
+        }
+    }
+
+    @Test
+    void givenTwoUnidimensionalObjectTypeArrays_whenUsingEqualsAndDeepEquals_thenBothShouldReturnTrue() {
+        Object[] anArray = new Object[] { "string1", "string2", "string3" };
+        Object[] anotherArray = new Object[] { "string1", "string2", "string3" };
+
+        assertTrue(Arrays.equals(anArray, anotherArray));
+        assertTrue(Arrays.deepEquals(anArray, anotherArray));
+    }
+
+    @Test
+    void givenTwoUnidimensionalObjectTypeArraysWithNullElements_whenUsingEqualsAndDeepEquals_thenBothShouldReturnTrue() {
+        Object[] anArray = new Object[] { "string1", null, "string3" };
+        Object[] anotherArray = new Object[] { "string1", null, "string3" };
+
+        assertTrue(Arrays.equals(anArray, anotherArray));
+        assertTrue(Arrays.deepEquals(anArray, anotherArray));
+    }
+
+    @Test
+    void givenTwoUnidimensionalObjectTypeArraysWithNestedElements_whenUsingEqualsAndDeepEquals_thenShouldReturnDifferently() {
+        Object[] anArray = new Object[] { "string1", null, new String[] { "nestedString1", "nestedString2" } };
+        Object[] anotherArray = new Object[] { "string1", null, new String[] { "nestedString1", "nestedString2" } };
+
+        assertFalse(Arrays.equals(anArray, anotherArray));
+        assertTrue(Arrays.deepEquals(anArray, anotherArray));
+    }
+
+    @Test
+    void givenTwoMultidimensionalPrimitiveTypeArrays_whenUsingEqualsAndDeepEquals_thenBothShouldReturnDifferently() {
+        int[][] anArray = { { 1, 2, 3 }, { 4, 5, 6, 9 }, { 7 } };
+        int[][] anotherArray = { { 1, 2, 3 }, { 4, 5, 6, 9 }, { 7 } };
+
+        assertFalse(Arrays.equals(anArray, anotherArray));
+        assertTrue(Arrays.deepEquals(anArray, anotherArray));
+    }
+
+    @Test
+    void givenTwoMultidimensionalObjectTypeArrays_whenUsingEqualsAndDeepEquals_thenBothShouldReturnDifferently() {
+        Person personArray1[][] = { { new Person(1, "John", 22), new Person(2, "Mike", 23) }, { new Person(3, "Steve", 27), new Person(4, "Gary", 28) } };
+        Person personArray2[][] = { { new Person(1, "John", 22), new Person(2, "Mike", 23) }, { new Person(3, "Steve", 27), new Person(4, "Gary", 28) } };
+
+        assertFalse(Arrays.equals(personArray1, personArray2));
+        assertTrue(Arrays.deepEquals(personArray1, personArray2));
+    }
+
+    @Test
+    void givenTwoMultidimensionalObjectTypeArrays_whenUsingDeepEqualsFromObjectsAndArraysClasses_thenBothShouldReturnTrue() {
+        Person personArray1[][] = { { new Person(1, "John", 22), new Person(2, "Mike", 23) }, { new Person(3, "Steve", 27), new Person(4, "Gary", 28) } };
+        Person personArray2[][] = { { new Person(1, "John", 22), new Person(2, "Mike", 23) }, { new Person(3, "Steve", 27), new Person(4, "Gary", 28) } };
+
+        assertTrue(Objects.deepEquals(personArray1, personArray2));
+        assertTrue(Arrays.deepEquals(personArray1, personArray2));
+    }
+}

core-java-modules/core-java-arrays/src/main/java/com/baeldung/array/Find2ndLargestInArray.java

@@ -1,20 +0,0 @@
-package com.baeldung.array;
-
-public class Find2ndLargestInArray {
-
-    public static int find2ndLargestElement(int[] array) {
-        int maxElement = array[0];
-        int secondLargestElement = -1;
-
-        for (int index = 0; index < array.length; index++) {
-            if (maxElement <= array[index]) {
-                secondLargestElement = maxElement;
-                maxElement = array[index];
-            } else if (secondLargestElement < array[index]) {
-                secondLargestElement = array[index];
-            }
-        }
-        return secondLargestElement;
-    }
-
-}

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

@@ -1,22 +0,0 @@
-package com.baeldung.array;
-
-import java.util.Arrays;
-
-public class FindElementInArray {
-
-    public static boolean findGivenElementInArrayWithoutUsingStream(int[] array, int element) {
-        boolean actualResult = false;
-
-        for (int index = 0; index < array.length; index++) {
-            if (element == array[index]) {
-                actualResult = true;
-                break;
-            }
-        }
-        return actualResult;
-    }
-
-    public static boolean findGivenElementInArrayUsingStream(int[] array, int element) {
-        return Arrays.stream(array).filter(x -> element == x).findFirst().isPresent();
-    }
-}

core-java-modules/core-java-arrays/src/test/java/com/baeldung/array/Find2ndLargestInArrayUnitTest.java

@@ -1,16 +0,0 @@
-package com.baeldung.array;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-public class Find2ndLargestInArrayUnitTest {
-    @Test
-    public void givenAnIntArray_thenFind2ndLargestElement() {
-        int[] array = { 1, 3, 24, 16, 87, 20 };
-        int expected2ndLargest = 24;
-
-        int actualSecondLargestElement = Find2ndLargestInArray.find2ndLargestElement(array);
-
-        Assert.assertEquals(expected2ndLargest, actualSecondLargestElement);
-    }
-}

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

@@ -1,35 +0,0 @@
-package com.baeldung.array;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-public class FindElementInArrayUnitTest {
-    @Test
-    public void givenAnIntArray_whenNotUsingStream_thenFindAnElement() {
-        int[] array = { 1, 3, 4, 8, 19, 20 };
-        int element = 19;
-        boolean expectedResult = true;
-        boolean actualResult = FindElementInArray.findGivenElementInArrayWithoutUsingStream(array, element);
-        Assert.assertEquals(expectedResult, actualResult);
-
-        element = 78;
-        expectedResult = false;
-        actualResult = FindElementInArray.findGivenElementInArrayWithoutUsingStream(array, element);
-        Assert.assertEquals(expectedResult, actualResult);
-    }
-
-    @Test
-    public void givenAnIntArray_whenUsingStream_thenFindAnElement() {
-        int[] array = { 15, 16, 12, 18 };
-        int element = 16;
-        boolean expectedResult = true;
-        boolean actualResult = FindElementInArray.findGivenElementInArrayUsingStream(array, element);
-        Assert.assertEquals(expectedResult, actualResult);
-
-        element = 20;
-        expectedResult = false;
-        actualResult = FindElementInArray.findGivenElementInArrayUsingStream(array, element);
-        Assert.assertEquals(expectedResult, actualResult);
-    }
-
-}

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -8,4 +8,6 @@ This module contains articles about advanced topics about multithreading with co
 
 - [Common Concurrency Pitfalls in Java](https://www.baeldung.com/java-common-concurrency-pitfalls)
 - [Guide to RejectedExecutionHandler](https://www.baeldung.com/java-rejectedexecutionhandler)
-[[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)
+- [Guide to Work Stealing in Java](https://www.baeldung.com/java-work-stealing)
+- [Asynchronous Programming in Java](https://www.baeldung.com/java-asynchronous-programming)
+- [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-date-operations-2/README.md

@@ -6,4 +6,5 @@ This module contains articles about date operations in Java.
 - [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)
 - [Checking If Two Java Dates Are on the Same Day](https://www.baeldung.com/java-check-two-dates-on-same-day)
 - [Converting Java Date to OffsetDateTime](https://www.baeldung.com/java-convert-date-to-offsetdatetime)
+- [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

core-java-modules/core-java-datetime-java8-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Creating a LocalDate with Values in Java](https://www.baeldung.com/java-creating-localdate-with-values)

core-java-modules/core-java-exceptions-2/README.md

@@ -6,3 +6,4 @@ This module contains articles about core java exceptions
 
 - [Is It a Bad Practice to Catch Throwable?](https://www.baeldung.com/java-catch-throwable-bad-practice)
 - [Wrapping vs Rethrowing Exceptions in Java](https://www.baeldung.com/java-wrapping-vs-rethrowing-exceptions)
+- [java.net.UnknownHostException: Invalid Hostname for Server](https://www.baeldung.com/java-unknownhostexception)

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/socketexception/SocketClient.java

@@ -0,0 +1,32 @@
+package com.baeldung.socketexception;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+
+public class SocketClient {
+
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void startConnection(String ip, int port) throws IOException {
+        clientSocket = new Socket(ip, port);
+        out = new PrintWriter(clientSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+    }
+
+    public String sendMessage(String msg) throws IOException {
+        out.println(msg);
+        return in.readLine();
+    }
+
+    public void stopConnection() throws IOException {
+        in.close();
+        out.close();
+        clientSocket.close();
+    }
+
+}

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/socketexception/SocketServer.java

@@ -0,0 +1,45 @@
+package com.baeldung.socketexception;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class SocketServer {
+
+    private ServerSocket serverSocket;
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void start(int port) {
+        try {
+            serverSocket = new ServerSocket(port);
+            clientSocket = serverSocket.accept();
+            out = new PrintWriter(clientSocket.getOutputStream(), true);
+            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+            String msg = in.readLine();
+            if (msg.contains("hi"))
+                out.println("hi");
+            else
+                out.println("didn't understand");
+            close();
+            stop();
+        } catch (IOException e) {
+            
+        }
+    }
+
+    private void close() throws IOException {
+        in.close();
+        out.close();
+    }
+
+    private void stop() throws IOException {
+        clientSocket.close();
+        serverSocket.close();
+    }
+
+}

core-java-modules/core-java-exceptions-2/src/test/java/com/baeldung/socketexception/SocketExceptionHandlingUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.socketexception;
+
+import java.io.IOException;
+import java.net.SocketException;
+import java.util.concurrent.Executors;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class SocketExceptionHandlingUnitTest {
+
+    @BeforeClass
+    public static void runServer() throws IOException, InterruptedException {
+        Executors.newSingleThreadExecutor()
+            .submit(() -> new SocketServer().start(6699));
+        Thread.sleep(100);
+    }
+
+    @Test
+    public void givenRunningServer_whenConnectToClosedSocket_thenHandleException() throws IOException {
+        SocketClient client = new SocketClient();
+        client.startConnection("127.0.0.1", 6699);
+        try {
+            client.sendMessage("hi");
+            client.sendMessage("hi again");
+        } catch (SocketException e) {
+            client.stopConnection();
+        }
+    }
+
+}

core-java-modules/core-java-io/src/test/java/com/baeldung/readfile/FileOperationsManualTest.java

@@ -1,134 +0,0 @@
-package com.baeldung.readfile;
-
-import org.apache.commons.io.FileUtils;
-import org.apache.commons.io.IOUtils;
-import org.hamcrest.CoreMatchers;
-import org.hamcrest.Matchers;
-import org.junit.Test;
-
-import java.io.BufferedReader;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.net.URISyntaxException;
-import java.net.URL;
-import java.net.URLConnection;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.nio.file.Paths;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertThat;
-
-public class FileOperationsManualTest {
-
-    @Test
-    public void givenFileName_whenUsingClassloader_thenFileData() throws IOException {
-        String expectedData = "Hello World from fileTest.txt!!!";
-
-        ClassLoader classLoader = getClass().getClassLoader();
-        File file = new File(classLoader.getResource("fileTest.txt").getFile());
-        InputStream inputStream = new FileInputStream(file);
-        String data = readFromInputStream(inputStream);
-
-        assertEquals(expectedData, data.trim());
-    }
-
-    @Test
-    public void givenFileNameAsAbsolutePath_whenUsingClasspath_thenFileData() throws IOException {
-        String expectedData = "Hello World from fileTest.txt!!!";
-
-        Class clazz = FileOperationsManualTest.class;
-        InputStream inputStream = clazz.getResourceAsStream("/fileTest.txt");
-        String data = readFromInputStream(inputStream);
-
-        assertEquals(expectedData, data.trim());
-    }
-
-    @Test
-    public void givenFileName_whenUsingJarFile_thenFileData() throws IOException {
-        String expectedData = "MIT License";
-
-        Class clazz = Matchers.class;
-        InputStream inputStream = clazz.getResourceAsStream("/LICENSE.txt");
-        String data = readFromInputStream(inputStream);
-
-        assertThat(data.trim(), CoreMatchers.containsString(expectedData));
-    }
-
-    @Test
-    public void givenURLName_whenUsingURL_thenFileData() throws IOException {
-        String expectedData = "Example Domain";
-
-        URL urlObject = new URL("http://www.example.com/");
-
-        URLConnection urlConnection = urlObject.openConnection();
-
-        InputStream inputStream = urlConnection.getInputStream();
-        String data = readFromInputStream(inputStream);
-
-        assertThat(data.trim(), CoreMatchers.containsString(expectedData));
-    }
-
-    @Test
-    public void givenFileName_whenUsingFileUtils_thenFileData() throws IOException {
-        String expectedData = "Hello World from fileTest.txt!!!";
-
-        ClassLoader classLoader = getClass().getClassLoader();
-        File file = new File(classLoader.getResource("fileTest.txt").getFile());
-        String data = FileUtils.readFileToString(file, "UTF-8");
-
-        assertEquals(expectedData, data.trim());
-    }
-
-    @Test
-    public void givenFilePath_whenUsingFilesReadAllBytes_thenFileData() throws IOException, URISyntaxException {
-        String expectedData = "Hello World from fileTest.txt!!!";
-
-        Path path = Paths.get(getClass().getClassLoader().getResource("fileTest.txt").toURI());
-
-        byte[] fileBytes = Files.readAllBytes(path);
-        String data = new String(fileBytes);
-
-        assertEquals(expectedData, data.trim());
-    }
-
-    @Test
-    public void givenFilePath_whenUsingFilesLines_thenFileData() throws IOException, URISyntaxException {
-        String expectedData = "Hello World from fileTest.txt!!!";
-
-        Path path = Paths.get(getClass().getClassLoader().getResource("fileTest.txt").toURI());
-
-        Stream<String> lines = Files.lines(path);
-        String data = lines.collect(Collectors.joining("\n"));
-        lines.close();
-
-        assertEquals(expectedData, data.trim());
-    }
-
-    private String readFromInputStream(InputStream inputStream) throws IOException {
-        StringBuilder resultStringBuilder = new StringBuilder();
-        try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {
-            String line;
-            while ((line = bufferedReader.readLine()) != null) {
-                resultStringBuilder.append(line).append("\n");
-            }
-        }
-
-        return resultStringBuilder.toString();
-    }
-    
-    @Test
-    public void givenFileName_whenUsingIOUtils_thenFileData() throws IOException {
-        String expectedData = "This is a content of the file";
-
-        FileInputStream fis = new FileInputStream("src/test/resources/fileToRead.txt");
-        String data = IOUtils.toString(fis, "UTF-8");
-        
-        assertEquals(expectedData, data.trim());
-    }
-}

core-java-modules/core-java-io/src/test/java/com/baeldung/readfile/JavaReadFromFileUnitTest.java

@@ -1,11 +1,15 @@
 package com.baeldung.readfile;
 
+import org.apache.commons.io.FileUtils;
+import org.apache.commons.io.IOUtils;
+import org.hamcrest.CoreMatchers;
+import org.hamcrest.Matchers;
 import org.junit.Test;
-import org.junit.Ignore;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.io.*;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.net.URLConnection;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.charset.Charset;
@@ -13,55 +17,148 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.Scanner;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 public class JavaReadFromFileUnitTest {
 
-    private static final Logger LOG = LoggerFactory.getLogger(JavaReadFromFileUnitTest.class);
-
     @Test
     public void whenReadWithBufferedReader_thenCorrect() throws IOException {
-        final String expected_value = "Hello world";
+        final String expected_value = "Hello, world!";
 
-        final BufferedReader reader = new BufferedReader(new FileReader("src/test/resources/test_read.in"));
+        final BufferedReader reader = new BufferedReader(new FileReader("src/test/resources/fileTest.txt"));
         final String currentLine = reader.readLine();
         reader.close();
 
         assertEquals(expected_value, currentLine);
     }
 
+    @Test
+    public void givenFileName_whenUsingClassloader_thenFileData() throws IOException {
+        String expectedData = "Hello, world!";
+
+        ClassLoader classLoader = getClass().getClassLoader();
+        File file = new File(classLoader.getResource("fileTest.txt").getFile());
+        InputStream inputStream = new FileInputStream(file);
+        String data = readFromInputStream(inputStream);
+
+        assertEquals(expectedData, data.trim());
+    }
+
+    @Test
+    public void givenFileNameAsAbsolutePath_whenUsingClasspath_thenFileData() throws IOException {
+        String expectedData = "Hello, world!";
+
+        Class clazz = JavaReadFromFileUnitTest.class;
+        InputStream inputStream = clazz.getResourceAsStream("/fileTest.txt");
+        String data = readFromInputStream(inputStream);
+
+        assertEquals(expectedData, data.trim());
+    }
+
+    @Test
+    public void givenFileName_whenUsingJarFile_thenFileData() throws IOException {
+        String expectedData = "BSD License";
+
+        Class clazz = Matchers.class;
+        InputStream inputStream = clazz.getResourceAsStream("/LICENSE.txt");
+        String data = readFromInputStream(inputStream);
+
+        assertThat(data.trim(), CoreMatchers.containsString(expectedData));
+    }
+
+    @Test
+    public void givenURLName_whenUsingURL_thenFileData() throws IOException {
+        String expectedData = "Example Domain";
+
+        URL urlObject = new URL("http://www.example.com/");
+
+        URLConnection urlConnection = urlObject.openConnection();
+
+        InputStream inputStream = urlConnection.getInputStream();
+        String data = readFromInputStream(inputStream);
+
+        assertThat(data.trim(), CoreMatchers.containsString(expectedData));
+    }
+
+    @Test
+    public void givenFileName_whenUsingFileUtils_thenFileData() throws IOException {
+        String expectedData = "Hello, world!";
+
+        ClassLoader classLoader = getClass().getClassLoader();
+        File file = new File(classLoader.getResource("fileTest.txt").getFile());
+        String data = FileUtils.readFileToString(file, "UTF-8");
+
+        assertEquals(expectedData, data.trim());
+    }
+
+    @Test
+    public void givenFilePath_whenUsingFilesReadAllBytes_thenFileData() throws IOException, URISyntaxException {
+        String expectedData = "Hello, world!";
+
+        Path path = Paths.get(getClass().getClassLoader().getResource("fileTest.txt").toURI());
+
+        byte[] fileBytes = Files.readAllBytes(path);
+        String data = new String(fileBytes);
+
+        assertEquals(expectedData, data.trim());
+    }
+
+    @Test
+    public void givenFilePath_whenUsingFilesLines_thenFileData() throws IOException, URISyntaxException {
+        String expectedData = "Hello, world!";
+
+        Path path = Paths.get(getClass().getClassLoader().getResource("fileTest.txt").toURI());
+
+        Stream<String> lines = Files.lines(path);
+        String data = lines.collect(Collectors.joining("\n"));
+        lines.close();
+
+        assertEquals(expectedData, data.trim());
+    }
+
+    @Test
+    public void givenFileName_whenUsingIOUtils_thenFileData() throws IOException {
+        String expectedData = "Hello, world!";
+
+        FileInputStream fis = new FileInputStream("src/test/resources/fileTest.txt");
+        String data = IOUtils.toString(fis, "UTF-8");
+
+        assertEquals(expectedData, data.trim());
+    }
+
     @Test
     public void whenReadWithScanner_thenCorrect() throws IOException {
-        final Scanner scanner = new Scanner(new File("src/test/resources/test_read1.in"));
+        final Scanner scanner = new Scanner(new File("src/test/resources/fileTest.txt"));
         scanner.useDelimiter(" ");
 
         assertTrue(scanner.hasNext());
-        assertEquals("Hello", scanner.next());
+        assertEquals("Hello,", scanner.next());
-        assertEquals("world", scanner.next());
+        assertEquals("world!", scanner.next());
-        assertEquals(1, scanner.nextInt());
 
         scanner.close();
-
     }
 
     @Test
     public void whenReadWithScannerTwoDelimiters_thenCorrect() throws IOException {
-        final Scanner scanner = new Scanner(new File("src/test/resources/test_read2.in"));
+        final Scanner scanner = new Scanner(new File("src/test/resources/fileTest.txt"));
-        scanner.useDelimiter(",| ");
+        scanner.useDelimiter("\\s|,");
 
-        assertTrue(scanner.hasNextInt());
+        assertTrue(scanner.hasNext());
-        assertEquals(2, scanner.nextInt());
+        assertEquals("Hello", scanner.next());
-        assertEquals(3, scanner.nextInt());
+        assertEquals("", scanner.next());
-        assertEquals(4, scanner.nextInt());
+        assertEquals("world!", scanner.next());
 
         scanner.close();
     }
 
     @Test
     public void whenReadWithStreamTokenizer_thenCorrectTokens() throws IOException {
-        final FileReader reader = new FileReader("src/test/resources/test_read3.in");
+        final FileReader reader = new FileReader("src/test/resources/fileTestTokenizer.txt");
         final StreamTokenizer tokenizer = new StreamTokenizer(reader);
 
         tokenizer.nextToken();
@@ -78,49 +175,36 @@ public class JavaReadFromFileUnitTest {
 
     @Test
     public void whenReadWithDataInputStream_thenCorrect() throws IOException {
-        final String expected_value = "Hello";
+        String expectedValue = "Hello, world!";
+        String file ="src/test/resources/fileTest.txt";
 
-        String result;
+        String result = null;
-        final DataInputStream reader = new DataInputStream(new FileInputStream("src/test/resources/test_read4.in"));
-        result = reader.readUTF();
-        reader.close();
 
-        assertEquals(expected_value, result);
+        DataInputStream reader = new DataInputStream(new FileInputStream(file));
-    }
+        int nBytesToRead = reader.available();
+        if(nBytesToRead > 0) {
+            byte[] bytes = new byte[nBytesToRead];
+            reader.read(bytes);
+            result = new String(bytes);
+        }
 
-    public void whenReadTwoFilesWithSequenceInputStream_thenCorrect() throws IOException {
+        assertEquals(expectedValue, result);
-        final int expected_value1 = 2000;
-        final int expected_value2 = 5000;
-
-        final FileInputStream stream1 = new FileInputStream("src/test/resources/test_read5.in");
-        final FileInputStream stream2 = new FileInputStream("src/test/resources/test_read6.in");
-
-        final SequenceInputStream sequence = new SequenceInputStream(stream1, stream2);
-        final DataInputStream reader = new DataInputStream(sequence);
-
-        assertEquals(expected_value1, reader.readInt());
-        assertEquals(expected_value2, reader.readInt());
-
-        reader.close();
-        stream2.close();
     }
 
     @Test
-    @Ignore // TODO
     public void whenReadUTFEncodedFile_thenCorrect() throws IOException {
         final String expected_value = "青空";
-        final BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("src/test/resources/test_read7.in"), "UTF-8"));
+        final BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("src/test/resources/fileTestUtf8.txt"), "UTF-8"));
         final String currentLine = reader.readLine();
         reader.close();
-        LOG.debug(currentLine);
+
-        
         assertEquals(expected_value, currentLine);
     }
 
     @Test
     public void whenReadFileContentsIntoString_thenCorrect() throws IOException {
-        final String expected_value = "Hello world \n Test line \n";
+        final String expected_value = "Hello, world!\n";
-        final BufferedReader reader = new BufferedReader(new FileReader("src/test/resources/test_read8.in"));
+        final BufferedReader reader = new BufferedReader(new FileReader("src/test/resources/fileTest.txt"));
         final StringBuilder builder = new StringBuilder();
         String currentLine = reader.readLine();
         while (currentLine != null) {
@@ -136,8 +220,8 @@ public class JavaReadFromFileUnitTest {
 
     @Test
     public void whenReadWithFileChannel_thenCorrect() throws IOException {
-        final String expected_value = "Hello world";
+        final String expected_value = "Hello, world!";
-        final RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r");
+        final RandomAccessFile reader = new RandomAccessFile("src/test/resources/fileTest.txt", "r");
         final FileChannel channel = reader.getChannel();
 
         int bufferSize = 1024;
@@ -154,8 +238,8 @@ public class JavaReadFromFileUnitTest {
 
     @Test
     public void whenReadSmallFileJava7_thenCorrect() throws IOException {
-        final String expected_value = "Hello world";
+        final String expected_value = "Hello, world!";
-        final Path path = Paths.get("src/test/resources/test_read.in");
+        final Path path = Paths.get("src/test/resources/fileTest.txt");
 
         final String read = Files.readAllLines(path, Charset.defaultCharset()).get(0);
         assertEquals(expected_value, read);
@@ -163,12 +247,24 @@ public class JavaReadFromFileUnitTest {
 
     @Test
     public void whenReadLargeFileJava7_thenCorrect() throws IOException {
-        final String expected_value = "Hello world";
+        final String expected_value = "Hello, world!";
 
-        final Path path = Paths.get("src/test/resources/test_read.in");
+        final Path path = Paths.get("src/test/resources/fileTest.txt");
         final BufferedReader reader = Files.newBufferedReader(path, Charset.defaultCharset());
         final String line = reader.readLine();
         assertEquals(expected_value, line);
     }
 
+    private String readFromInputStream(InputStream inputStream) throws IOException {
+        StringBuilder resultStringBuilder = new StringBuilder();
+        try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {
+            String line;
+            while ((line = bufferedReader.readLine()) != null) {
+                resultStringBuilder.append(line).append("\n");
+            }
+        }
+
+        return resultStringBuilder.toString();
+    }
+
 }

core-java-modules/core-java-io/src/test/resources/fileTest.txt

@@ -1 +1 @@
-Hello World from fileTest.txt!!!
+Hello, world!

core-java-modules/core-java-io/src/test/resources/test_read1.in

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

core-java-modules/core-java-io/src/test/resources/test_read2.in

@@ -1 +0,0 @@
-2,3 4

core-java-modules/core-java-io/src/test/resources/test_read8.in

@@ -1,2 +0,0 @@
-Hello world 
- Test line 

core-java-modules/core-java-lang-2/README.md

@@ -7,4 +7,6 @@ This module contains articles about core features in the Java language
 - [Command-Line Arguments in Java](https://www.baeldung.com/java-command-line-arguments)
 - [What is a POJO Class?](https://www.baeldung.com/java-pojo-class)
 - [Java Default Parameters Using Method Overloading](https://www.baeldung.com/java-default-parameters-method-overloading)
+- [How to Return Multiple Values From a Java Method](https://www.baeldung.com/java-method-return-multiple-values)
+- [Guide to the Java finally Keyword](https://www.baeldung.com/java-finally-keyword)
 - [[<-- Prev]](/core-java-modules/core-java-lang)

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/headlessmode/FlexibleApp.java

@@ -0,0 +1,27 @@
+package com.baeldung.headlessmode;
+
+import java.awt.GraphicsEnvironment;
+
+import javax.swing.JOptionPane;
+
+public class FlexibleApp {
+    public static final int HEADLESS = 0;
+    public static final int HEADED = 1;
+    public FlexibleApp() {
+
+        if (GraphicsEnvironment.isHeadless()) {
+            System.out.println("Hello World");
+        } else {
+            JOptionPane.showMessageDialog(null, "Hello World");
+        }
+
+    }
+    
+    public static int iAmFlexible() {
+        if (GraphicsEnvironment.isHeadless()) {
+            return HEADLESS;
+        } else {
+            return HEADED;
+        }
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/headlessmode/HeadlessModeUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.headlessmode;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+import java.awt.Canvas;
+import java.awt.Font;
+import java.awt.FontMetrics;
+import java.awt.Frame;
+import java.awt.GraphicsEnvironment;
+import java.awt.HeadlessException;
+import java.awt.image.BufferedImage;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+
+import javax.imageio.ImageIO;
+
+import org.junit.Assume;
+import org.junit.Before;
+import org.junit.Test;
+
+public class HeadlessModeUnitTest {
+
+    private static final String IN_FILE = "/product.png";
+    private static final String OUT_FILE = System.getProperty("java.io.tmpdir") + "/product.jpg";
+    private static final String FORMAT = "jpg";
+
+    @Before
+    public void setUpHeadlessMode() {
+        System.setProperty("java.awt.headless", "true");
+    }
+
+    @Test
+    public void whenJavaAwtHeadlessSetToTrue_thenIsHeadlessReturnsTrue() {
+        assertThat(GraphicsEnvironment.isHeadless()).isTrue();
+    }
+
+    @Test
+    public void whenHeadlessMode_thenFontsWork() {
+        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
+
+        String fonts[] = ge.getAvailableFontFamilyNames();
+
+        assertThat(fonts).isNotEmpty();
+
+        Font font = new Font(fonts[0], Font.BOLD, 14);
+
+        FontMetrics fm = (new Canvas()).getFontMetrics(font);
+
+        assertThat(fm.getHeight()).isGreaterThan(0);
+        assertThat(fm.getAscent()).isGreaterThan(0);
+        assertThat(fm.getDescent()).isGreaterThan(0);
+    }
+
+    @Test
+    public void whenHeadlessMode_thenImagesWork() throws IOException {
+        boolean result = false;
+        try (InputStream inStream = HeadlessModeUnitTest.class.getResourceAsStream(IN_FILE); FileOutputStream outStream = new FileOutputStream(OUT_FILE)) {
+            BufferedImage inputImage = ImageIO.read(inStream);
+            result = ImageIO.write(inputImage, FORMAT, outStream);
+        }
+
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void whenHeadlessmode_thenFrameThrowsHeadlessException() {
+        assertThatExceptionOfType(HeadlessException.class).isThrownBy(() -> {
+            Frame frame = new Frame();
+            frame.setVisible(true);
+            frame.setSize(120, 120);
+        });
+    }    
+
+    @Test
+    public void whenHeadless_thenFlexibleAppAdjustsItsBehavior() {
+        assertThat(FlexibleApp.iAmFlexible()).isEqualTo(FlexibleApp.HEADLESS);
+    }
+
+    @Test
+    public void whenHeaded_thenFlexibleAppAdjustsItsBehavior() {
+        Assume.assumeFalse(GraphicsEnvironment.isHeadless());
+        assertThat(FlexibleApp.iAmFlexible()).isEqualTo(FlexibleApp.HEADED);
+    }
+
+}

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

@@ -9,3 +9,4 @@
 - [The strictfp Keyword in Java](https://www.baeldung.com/java-strictfp)
 - [Basic Calculator in Java](https://www.baeldung.com/java-basic-calculator)
 - [Overflow and Underflow in Java](https://www.baeldung.com/java-overflow-underflow)
+- [Obtaining a Power Set of a Set in Java](https://www.baeldung.com/java-power-set-of-a-set)

core-java-modules/core-java-lang-syntax-2/README.md

@@ -12,4 +12,5 @@ This module contains articles about Java syntax
 - [Variable Scope in Java](https://www.baeldung.com/java-variable-scope)
 - [Introduction to Basic Syntax in Java](https://www.baeldung.com/java-syntax)
 - [Java ‘protected’ Access Modifier](https://www.baeldung.com/java-protected-access-modifier)
+- [Using the Not Operator in If Conditions in Java](https://www.baeldung.com/java-using-not-in-if-conditions)
 - [[<-- Prev]](/core-java-modules/core-java-lang-syntax)

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

@@ -13,4 +13,7 @@ This module contains articles about Java syntax
 - [Infinite Loops in Java](https://www.baeldung.com/infinite-loops-java)
 - [Java Switch Statement](https://www.baeldung.com/java-switch)
 - [Breaking Out of Nested Loops](https://www.baeldung.com/java-breaking-out-nested-loop)
+- [Java Do-While Loop](https://www.baeldung.com/java-do-while-loop)
+- [Java While Loop](https://www.baeldung.com/java-while-loop)
+- [Java For Loop](https://www.baeldung.com/java-for-loop)
 - [[More -->]](/core-java-modules/core-java-lang-syntax-2)

core-java-modules/core-java-reflection/README.MD

@@ -6,4 +6,5 @@
 - [Guide to Java Reflection](http://www.baeldung.com/java-reflection)
 - [Call Methods at Runtime Using Java Reflection](http://www.baeldung.com/java-method-reflection)
 - [Changing Annotation Parameters At Runtime](http://www.baeldung.com/java-reflection-change-annotation-params)
-- [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
+- [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
+- [What Causes java.lang.reflect.InvocationTargetException?](https://www.baeldung.com/java-lang-reflect-invocationtargetexception)

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

@@ -5,4 +5,6 @@
 ### Relevant Articles: 
 - [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
 - [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
-- [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
+- [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
+- [Pre-compile Regex Patterns Into Pattern Objects](https://www.baeldung.com/java-regex-pre-compile)
+- [Difference Between Java Matcher find() and matches()](https://www.baeldung.com/java-matcher-find-vs-matches)

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

@@ -1,7 +0,0 @@
-=========
-
-## Core Java 8 Cookbooks and Examples
-
-### Relevant Articles: 
-- [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
-- [Pre-compile Regex Patterns Into Pattern Objects](https://www.baeldung.com/java-regex-pre-compile)

core-java-modules/pom.xml

@@ -31,6 +31,7 @@
         <module>core-java-annotations</module>
         <module>core-java-arrays</module>
         <module>core-java-arrays-2</module>
+        <module>core-java-arrays-3</module>
 
         <module>core-java-collections</module>
         <module>core-java-collections-2</module>

core-kotlin-modules/core-kotlin-2/README.md

@@ -4,5 +4,5 @@ This module contains articles about Kotlin core features.
 
 ### Relevant articles:
 - [Working with Dates in Kotlin](https://www.baeldung.com/kotlin-dates)
-- [Kotlin Ternary Conditional Operator](https://www.baeldung.com/kotlin-ternary-conditional-operator)
+- [Kotlin Ternary Conditional Operator](https://www.baeldung.com/kotlin-ternary-operator)
 - [[<-- Prev]](/core-kotlin-modules/core-kotlin)

core-kotlin-modules/core-kotlin/README.md

@@ -3,7 +3,7 @@
 This module contains articles about Kotlin core features.
 
 ### Relevant articles:
-- [Introduction to the Kotlin Language](https://www.baeldung.com/kotlin)
+- [Introduction to the Kotlin Language](https://www.baeldung.com/kotlin-intro)
 - [Kotlin Java Interoperability](https://www.baeldung.com/kotlin-java-interoperability)
 - [Get a Random Number in Kotlin](https://www.baeldung.com/kotlin-random-number)
 - [Create a Java and Kotlin Project with Maven](https://www.baeldung.com/kotlin-maven-java-project)

data-structures/README.md

@@ -8,3 +8,4 @@ This module contains articles about data structures in Java
 - [Implementing a Binary Tree in Java](https://www.baeldung.com/java-binary-tree)
 - [Circular Linked List Java Implementation](https://www.baeldung.com/java-circular-linked-list)
 - [How to Print a Binary Tree Diagram](https://www.baeldung.com/java-print-binary-tree-diagram)
+- [Introduction to Big Queue](https://www.baeldung.com/java-big-queue)

ddd/pom.xml

@@ -20,6 +20,10 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-data-mongodb</artifactId>
         </dependency>
+        <dependency>
+        	<groupId>org.springframework.boot</groupId>
+        	<artifactId>spring-boot-starter-data-cassandra</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>

ddd/src/main/java/com/baeldung/dddhexagonalspring/DomainLayerApplication.java

@@ -1,13 +1,37 @@
 package com.baeldung.dddhexagonalspring;
 
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
 import org.springframework.boot.SpringApplication;
+import org.springframework.boot.WebApplicationType;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.PropertySource;
 
+import com.baeldung.dddhexagonalspring.application.cli.CliOrderController;
+
 @SpringBootApplication
 @PropertySource(value = { "classpath:ddd-layers.properties" })
-public class DomainLayerApplication {
+public class DomainLayerApplication implements CommandLineRunner {
+
     public static void main(final String[] args) {
-        SpringApplication.run(DomainLayerApplication.class, args);
+        SpringApplication application = new SpringApplication(DomainLayerApplication.class);
+        // uncomment to run just the console application
+        // application.setWebApplicationType(WebApplicationType.NONE);
+        application.run(args);
+    }
+
+    @Autowired
+    public CliOrderController orderController;
+
+    @Autowired
+    public ConfigurableApplicationContext context;
+
+    @Override
+    public void run(String... args) throws Exception {
+        orderController.createCompleteOrder();
+        orderController.createIncompleteOrder();
+        // uncomment to stop the context when execution is done
+        // context.close();
     }
 }

ddd/src/main/java/com/baeldung/dddhexagonalspring/application/cli/CliOrderController.java

@@ -0,0 +1,47 @@
+package com.baeldung.dddhexagonalspring.application.cli;
+
+import java.math.BigDecimal;
+import java.util.UUID;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import com.baeldung.dddhexagonalspring.domain.Product;
+import com.baeldung.dddhexagonalspring.domain.service.OrderService;
+
+@Component
+public class CliOrderController {
+
+    private static final Logger LOG = LoggerFactory.getLogger(CliOrderController.class);
+
+    private final OrderService orderService;
+
+    @Autowired
+    public CliOrderController(OrderService orderService) {
+        this.orderService = orderService;
+    }
+
+    public void createCompleteOrder() {
+        LOG.info("<<Create complete order>>");
+        UUID orderId = createOrder();
+        orderService.completeOrder(orderId);
+    }
+
+    public void createIncompleteOrder() {
+        LOG.info("<<Create incomplete order>>");
+        UUID orderId = createOrder();
+    }
+
+    private UUID createOrder() {
+        LOG.info("Placing a new order with two products");
+        Product mobilePhone = new Product(UUID.randomUUID(), BigDecimal.valueOf(200), "mobile");
+        Product razor = new Product(UUID.randomUUID(), BigDecimal.valueOf(50), "razor");
+        LOG.info("Creating order with mobile phone");
+        UUID orderId = orderService.createOrder(mobilePhone);
+        LOG.info("Adding a razor to the order");
+        orderService.addProduct(orderId, razor);
+        return orderId;
+    }
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/application/rest/OrderController.java

@@ -1,4 +1,4 @@
-package com.baeldung.dddhexagonalspring.application.controller;
+package com.baeldung.dddhexagonalspring.application.rest;
 
 import com.baeldung.dddhexagonalspring.application.request.AddProductRequest;
 import com.baeldung.dddhexagonalspring.application.request.CreateOrderRequest;

ddd/src/main/java/com/baeldung/dddhexagonalspring/domain/Order.java

@@ -4,6 +4,7 @@ import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.UUID;
 
 public class Order {
@@ -40,13 +41,11 @@ public class Order {
     }
 
     private OrderItem getOrderItem(final UUID id) {
-        return orderItems
+        return orderItems.stream()
-          .stream()
+            .filter(orderItem -> orderItem.getProductId()
-          .filter(orderItem -> orderItem
+                .equals(id))
-            .getProductId()
+            .findFirst()
-            .equals(id))
+            .orElseThrow(() -> new DomainException("Product with " + id + " doesn't exist."));
-          .findFirst()
-          .orElseThrow(() -> new DomainException("Product with " + id + " doesn't exist."));
     }
 
     private void validateState() {
@@ -77,6 +76,21 @@ public class Order {
         return Collections.unmodifiableList(orderItems);
     }
 
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, orderItems, price, status);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (!(obj instanceof Order))
+            return false;
+        Order other = (Order) obj;
+        return Objects.equals(id, other.id) && Objects.equals(orderItems, other.orderItems) && Objects.equals(price, other.price) && status == other.status;
+    }
+
     private Order() {
     }
 }

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/configuration/CassandraConfiguration.java

@@ -0,0 +1,10 @@
+package com.baeldung.dddhexagonalspring.infrastracture.configuration;
+
+import org.springframework.data.cassandra.repository.config.EnableCassandraRepositories;
+
+import com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra.SpringDataCassandraOrderRepository;
+
+@EnableCassandraRepositories(basePackageClasses = SpringDataCassandraOrderRepository.class)
+public class CassandraConfiguration {
+
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/configuration/MongoDBConfiguration.java

@@ -1,8 +1,9 @@
 package com.baeldung.dddhexagonalspring.infrastracture.configuration;
 
-import com.baeldung.dddhexagonalspring.infrastracture.repository.SpringDataOrderRepository;
 import org.springframework.data.mongodb.repository.config.EnableMongoRepositories;
 
-@EnableMongoRepositories(basePackageClasses = SpringDataOrderRepository.class)
+import com.baeldung.dddhexagonalspring.infrastracture.repository.mongo.SpringDataMongoOrderRepository;
+
+@EnableMongoRepositories(basePackageClasses = SpringDataMongoOrderRepository.class)
 public class MongoDBConfiguration {
 }

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/cassandra/CassandraDbOrderRepository.java

@@ -0,0 +1,38 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra;
+
+import java.util.Optional;
+import java.util.UUID;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import com.baeldung.dddhexagonalspring.domain.Order;
+import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
+
+@Component
+public class CassandraDbOrderRepository implements OrderRepository {
+
+    private final SpringDataCassandraOrderRepository orderRepository;
+
+    @Autowired
+    public CassandraDbOrderRepository(SpringDataCassandraOrderRepository orderRepository) {
+        this.orderRepository = orderRepository;
+    }
+
+    @Override
+    public Optional<Order> findById(UUID id) {
+        Optional<OrderEntity> orderEntity = orderRepository.findById(id);
+        if (orderEntity.isPresent()) {
+            return Optional.of(orderEntity.get()
+                .toOrder());
+        } else {
+            return Optional.empty();
+        }
+    }
+
+    @Override
+    public void save(Order order) {
+        orderRepository.save(new OrderEntity(order));
+    }
+
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/cassandra/OrderEntity.java

@@ -0,0 +1,75 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra;
+
+import java.math.BigDecimal;
+import java.util.List;
+import java.util.UUID;
+import java.util.stream.Collectors;
+
+import org.springframework.data.cassandra.core.mapping.PrimaryKey;
+
+import com.baeldung.dddhexagonalspring.domain.Order;
+import com.baeldung.dddhexagonalspring.domain.OrderItem;
+import com.baeldung.dddhexagonalspring.domain.OrderStatus;
+import com.baeldung.dddhexagonalspring.domain.Product;
+
+public class OrderEntity {
+
+    @PrimaryKey
+    private UUID id;
+    private OrderStatus status;
+    private List<OrderItemEntity> orderItemEntities;
+    private BigDecimal price;
+
+    public OrderEntity(UUID id, OrderStatus status, List<OrderItemEntity> orderItemEntities, BigDecimal price) {
+        this.id = id;
+        this.status = status;
+        this.orderItemEntities = orderItemEntities;
+        this.price = price;
+    }
+
+    public OrderEntity() {
+    }
+
+    public OrderEntity(Order order) {
+        this.id = order.getId();
+        this.price = order.getPrice();
+        this.status = order.getStatus();
+        this.orderItemEntities = order.getOrderItems()
+            .stream()
+            .map(OrderItemEntity::new)
+            .collect(Collectors.toList());
+
+    }
+
+    public Order toOrder() {
+        List<OrderItem> orderItems = orderItemEntities.stream()
+            .map(OrderItemEntity::toOrderItem)
+            .collect(Collectors.toList());
+        List<Product> namelessProducts = orderItems.stream()
+            .map(orderItem -> new Product(orderItem.getProductId(), orderItem.getPrice(), ""))
+            .collect(Collectors.toList());
+        Order order = new Order(id, namelessProducts.remove(0));
+        namelessProducts.forEach(product -> order.addOrder(product));
+        if (status == OrderStatus.COMPLETED) {
+            order.complete();
+        }
+        return order;
+    }
+
+    public UUID getId() {
+        return id;
+    }
+
+    public OrderStatus getStatus() {
+        return status;
+    }
+
+    public List<OrderItemEntity> getOrderItems() {
+        return orderItemEntities;
+    }
+
+    public BigDecimal getPrice() {
+        return price;
+    }
+
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/cassandra/OrderItemEntity.java

@@ -0,0 +1,44 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra;
+
+import java.math.BigDecimal;
+import java.util.UUID;
+
+import org.springframework.data.cassandra.core.mapping.UserDefinedType;
+
+import com.baeldung.dddhexagonalspring.domain.OrderItem;
+import com.baeldung.dddhexagonalspring.domain.Product;
+
+@UserDefinedType
+public class OrderItemEntity {
+
+    private UUID productId;
+    private BigDecimal price;
+
+    public OrderItemEntity() {
+    }
+
+    public OrderItemEntity(final OrderItem orderItem) {
+        this.productId = orderItem.getProductId();
+        this.price = orderItem.getPrice();
+    }
+
+    public OrderItem toOrderItem() {
+        return new OrderItem(new Product(productId, price, ""));
+    }
+
+    public UUID getProductId() {
+        return productId;
+    }
+
+    public void setProductId(UUID productId) {
+        this.productId = productId;
+    }
+
+    public BigDecimal getPrice() {
+        return price;
+    }
+
+    public void setPrice(BigDecimal price) {
+        this.price = price;
+    }
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/cassandra/SpringDataCassandraOrderRepository.java

@@ -0,0 +1,10 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra;
+
+import java.util.UUID;
+
+import org.springframework.data.cassandra.repository.CassandraRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface SpringDataCassandraOrderRepository extends CassandraRepository<OrderEntity, UUID> {
+}

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/mongo/MongoDbOrderRepository.java

@@ -1,20 +1,23 @@
-package com.baeldung.dddhexagonalspring.infrastracture.repository;
+package com.baeldung.dddhexagonalspring.infrastracture.repository.mongo;
-
-import com.baeldung.dddhexagonalspring.domain.Order;
-import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
-import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.stereotype.Component;
 
 import java.util.Optional;
 import java.util.UUID;
 
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Primary;
+import org.springframework.stereotype.Component;
+
+import com.baeldung.dddhexagonalspring.domain.Order;
+import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
+
 @Component
+@Primary
 public class MongoDbOrderRepository implements OrderRepository {
 
-    private final SpringDataOrderRepository orderRepository;
+    private final SpringDataMongoOrderRepository orderRepository;
 
     @Autowired
-    public MongoDbOrderRepository(final SpringDataOrderRepository orderRepository) {
+    public MongoDbOrderRepository(final SpringDataMongoOrderRepository orderRepository) {
         this.orderRepository = orderRepository;
     }
 

ddd/src/main/java/com/baeldung/dddhexagonalspring/infrastracture/repository/mongo/SpringDataMongoOrderRepository.java

@@ -1,4 +1,4 @@
-package com.baeldung.dddhexagonalspring.infrastracture.repository;
+package com.baeldung.dddhexagonalspring.infrastracture.repository.mongo;
 
 import com.baeldung.dddhexagonalspring.domain.Order;
 import org.springframework.data.mongodb.repository.MongoRepository;
@@ -7,5 +7,5 @@ import org.springframework.stereotype.Repository;
 import java.util.UUID;
 
 @Repository
-public interface SpringDataOrderRepository extends MongoRepository<Order, UUID> {
+public interface SpringDataMongoOrderRepository extends MongoRepository<Order, UUID> {
 }

ddd/src/main/resources/ddd-layers.properties

@@ -1,5 +1,12 @@
+spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
 spring.data.mongodb.host=localhost
 spring.data.mongodb.port=27017
 spring.data.mongodb.database=order-database
 spring.data.mongodb.username=order
-spring.data.mongodb.password=order
+spring.data.mongodb.password=order
+
+spring.data.cassandra.keyspaceName=order_database
+spring.data.cassandra.username=cassandra
+spring.data.cassandra.password=cassandra
+spring.data.cassandra.contactPoints=localhost
+spring.data.cassandra.port=9042

ddd/src/test/java/com/baeldung/dddhexagonalspring/infrastracture/repository/CassandraDbOrderRepositoryIntegrationTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.math.BigDecimal;
+import java.util.Optional;
+import java.util.UUID;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import com.baeldung.dddhexagonalspring.domain.Order;
+import com.baeldung.dddhexagonalspring.domain.Product;
+import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
+import com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra.SpringDataCassandraOrderRepository;
+
+@SpringJUnitConfig
+@SpringBootTest
+@TestPropertySource("classpath:ddd-layers-test.properties")
+class CassandraDbOrderRepositoryIntegrationTest {
+
+    @Autowired
+    private SpringDataCassandraOrderRepository cassandraOrderRepository;
+
+    @Autowired
+    private OrderRepository orderRepository;
+
+    @AfterEach
+    void cleanUp() {
+        cassandraOrderRepository.deleteAll();
+    }
+
+    @Test
+    void shouldFindById_thenReturnOrder() {
+
+        // given
+        final UUID id = UUID.randomUUID();
+        final Order order = createOrder(id);
+        order.addOrder(new Product(UUID.randomUUID(), BigDecimal.TEN, "second"));
+        order.complete();
+
+        // when
+        orderRepository.save(order);
+
+        final Optional<Order> result = orderRepository.findById(id);
+
+        assertEquals(order, result.get());
+    }
+
+    private Order createOrder(UUID id) {
+        return new Order(id, new Product(UUID.randomUUID(), BigDecimal.TEN, "product"));
+    }
+}

ddd/src/test/java/com/baeldung/dddhexagonalspring/infrastracture/repository/MongoDbOrderRepositoryIntegrationTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.dddhexagonalspring.infrastracture.repository;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.math.BigDecimal;
+import java.util.Optional;
+import java.util.UUID;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import com.baeldung.dddhexagonalspring.domain.Order;
+import com.baeldung.dddhexagonalspring.domain.Product;
+import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
+import com.baeldung.dddhexagonalspring.infrastracture.repository.mongo.SpringDataMongoOrderRepository;
+
+@SpringJUnitConfig
+@SpringBootTest
+@TestPropertySource("classpath:ddd-layers-test.properties")
+class MongoDbOrderRepositoryIntegrationTest {
+
+    @Autowired
+    private SpringDataMongoOrderRepository mongoOrderRepository;
+
+    @Autowired
+    private OrderRepository orderRepository;
+
+    @AfterEach
+    void cleanUp() {
+        mongoOrderRepository.deleteAll();
+    }
+
+    @Test
+    void shouldFindById_thenReturnOrder() {
+
+        // given
+        final UUID id = UUID.randomUUID();
+        final Order order = createOrder(id);
+
+        // when
+        orderRepository.save(order);
+
+        final Optional<Order> result = orderRepository.findById(id);
+
+        assertEquals(order, result.get());
+    }
+
+    private Order createOrder(UUID id) {
+        return new Order(id, new Product(UUID.randomUUID(), BigDecimal.TEN, "product"));
+    }
+}

ddd/src/test/java/com/baeldung/dddhexagonalspring/infrastracture/repository/MongoDbOrderRepositoryUnitTest.java

@@ -2,6 +2,9 @@ package com.baeldung.dddhexagonalspring.infrastracture.repository;
 
 import com.baeldung.dddhexagonalspring.domain.Order;
 import com.baeldung.dddhexagonalspring.domain.Product;
+import com.baeldung.dddhexagonalspring.infrastracture.repository.mongo.MongoDbOrderRepository;
+import com.baeldung.dddhexagonalspring.infrastracture.repository.mongo.SpringDataMongoOrderRepository;
+
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -14,12 +17,12 @@ import static org.mockito.Mockito.*;
 
 class MongoDbOrderRepositoryUnitTest {
 
-    private SpringDataOrderRepository springDataOrderRepository;
+    private SpringDataMongoOrderRepository springDataOrderRepository;
     private MongoDbOrderRepository tested;
 
     @BeforeEach
-    void setUp(){
+    void setUp() {
-        springDataOrderRepository = mock(SpringDataOrderRepository.class);
+        springDataOrderRepository = mock(SpringDataMongoOrderRepository.class);
 
         tested = new MongoDbOrderRepository(springDataOrderRepository);
     }

ddd/src/test/resources/com/baeldung/dddhexagonalspring/README.md

@@ -4,4 +4,6 @@ To run this project, follow these steps:
 
 * Run the application database by executing `docker-compose up` in this directory.
 * Launch the Spring Boot Application (DomainLayerApplication). 
-* By default, application will connect to this database (configuration in *ddd-layers.properties*)
+* By default, the application will connect to the one of the two databases (configuration in *ddd-layers.properties*)
+     * check `CassandraDbOrderRepository.java` and `MongoDbOrderRepository.java` 
+     * switch between the databases by making one of the above beans primary using the `@Primary` annotation  

ddd/src/test/resources/com/baeldung/dddhexagonalspring/cassandra-init.cql

@@ -0,0 +1,12 @@
+CREATE KEYSPACE IF NOT exists order_database
+WITH replication = {'class':'SimpleStrategy', 'replication_factor':1};
+
+CREATE TYPE IF NOT EXISTS order_database.orderitementity (productid uuid, price decimal); 
+
+CREATE TABLE IF NOT EXISTS order_database.orderentity(
+   id uuid,
+   status text,
+   orderitementities list<frozen<orderitementity>>,
+   price decimal,
+   primary key(id)
+);

ddd/src/test/resources/com/baeldung/dddhexagonalspring/docker-compose.yml

@@ -3,6 +3,7 @@ version: '3'
 services:
   order-mongo-database:
     image: mongo:3.4.13
+    container_name: order-mongo-db
     restart: always
     ports:
       - 27017:27017
@@ -11,4 +12,19 @@ services:
       MONGO_INITDB_ROOT_PASSWORD: admin
       MONGO_INITDB_DATABASE: order-database
     volumes:
-      - ./mongo-init.js:/docker-entrypoint-initdb.d/mongo-init.js:ro
+      - ./mongo-init.js:/docker-entrypoint-initdb.d/mongo-init.js:ro
+  order-cassandra-database:
+    image: cassandra:3.11.5
+    container_name: order-cassandra-db
+    restart: always
+    ports: 
+      - 9042:9042
+  order-cassandra-init:
+    image: cassandra:3.11.5
+    container_name: order-cassandra-db-init
+    depends_on:
+      - order-cassandra-database
+    volumes:
+      - ./cassandra-init.cql:/cassandra-init.cql:ro
+    command: bin/bash -c "echo Initializing cassandra schema... && sleep 30 && cqlsh -u cassandra -p cassandra -f cassandra-init.cql order-cassandra-db" 
+      

ddd/src/test/resources/ddd-layers-test.properties

@@ -0,0 +1,12 @@
+spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration 
+spring.data.mongodb.host=127.0.0.1
+spring.data.mongodb.port=27017
+spring.data.mongodb.database=order-database
+spring.data.mongodb.username=order
+spring.data.mongodb.password=order
+
+spring.data.cassandra.keyspaceName=order_database
+spring.data.cassandra.username=cassandra
+spring.data.cassandra.password=cassandra
+spring.data.cassandra.contactPoints=127.0.0.1
+spring.data.cassandra.port=9042

dropwizard/README.md

@@ -1 +1,5 @@
-# Dropwizard
+# Dropwizard
+
+### Relevant Articles:
+
+- [Introduction to Dropwizard](https://www.baeldung.com/java-dropwizard)

gradle-6/.gitignore

@@ -0,0 +1,18 @@
+
+# Gradle
+
+.gradle
+build
+
+# Ignore Gradle GUI config
+gradle-app.setting
+
+# Avoid ignoring Gradle wrapper jar file (.jar files are usually ignored)
+!gradle-wrapper.jar
+
+# Cache of project
+.gradletasknamecache
+
+# # Work around https://youtrack.jetbrains.com/issue/IDEA-116898
+# gradle/wrapper/gradle-wrapper.properties
+

gradle-6/build.gradle.kts

@@ -0,0 +1,5 @@
+subprojects {
+    repositories {
+        mavenCentral()
+    }
+}

gradle-6/configuration-avoidance/build.gradle.kts

@@ -0,0 +1,37 @@
+plugins {
+    base
+}
+
+description = """
+    Demonstrates Gradle Configuraiton Avoidance API. Creates a new configuration "extralibs" to 
+    which we add dependencies. The custom task "copyExtraLibs" copies those dependencies to a new 
+    build directory "extra-libs". This build uses the Task Configuraion Avoidance APIs which have 
+    been marked stable in Gradle 6.0
+""".trimIndent()
+
+// extraLibs is a NamedDomainObjectProvider<Configuration!> - the Configuration object will not be
+// realized until it is needed. In the meantime, the build may reference it by name
+val extralibs by configurations.registering
+
+dependencies {
+    // we can call extralibs.name without causing the extralibs to be realized
+    add(extralibs.name, "junit:junit:4.12")
+}
+
+// extraLibsDir is a Provider<Directory!> - the Directory object will not be realized until it is
+// needed
+val extraLibsDir = project.layout.buildDirectory.dir("extra-libs")
+
+// copyExtraLibs is a TaskProvider<Copy!> - the task will not be realized until it is needed
+val copyExtraLibs by tasks.registering(Copy::class) {
+    // the copy task's "from" and "into" APIs accept Provider types to support configuration
+    // avoidance
+    from(extralibs)
+    into(extraLibsDir)
+}
+
+// configures the "build" task only if it needs to be
+tasks.build {
+    // dependsOn accepts a TaskProvider to avoid realizing the copyExtraLibs needlessly
+    dependsOn(copyExtraLibs)
+}

gradle-6/dependency-constraints/build.gradle.kts

@@ -0,0 +1,29 @@
+plugins {
+    `java-library`
+}
+
+group = "com.baeldung"
+version = "1.0.0"
+
+dependencies {
+    api("io.reactivex.rxjava2:rxjava:2.2.16")
+    implementation("com.google.guava:guava") {
+        version {
+            require("10.0")
+            prefer("28.1-jre")
+            because("Only uses ImmutableList type, so any version since 2.0 will do, but tested with 28.1-jre")
+        }
+    }
+
+    testImplementation("org.junit.jupiter:junit-jupiter-api:5.5.2")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.5.2")
+}
+
+tasks.compileJava {
+    sourceCompatibility = "1.8"
+    targetCompatibility = "1.8"
+}
+
+tasks.test {
+    useJUnitPlatform()
+}

gradle-6/dependency-constraints/src/main/java/com/baeldung/gradle/RxHelloWorld.java

@@ -0,0 +1,24 @@
+package com.baeldung.gradle;
+
+import com.google.common.collect.ImmutableList;
+import io.reactivex.Observable;
+
+import java.util.List;
+
+/**
+ * Demonstrates a library type that returns an RxJava type.
+ */
+public class RxHelloWorld {
+
+    /**
+     * @return an {@link Observable} that emits events "hello" and "world" before completing.
+     */
+    public static Observable<String> hello() {
+        // Guava ImmutableList class is an implementation detail.
+        List<String> values = ImmutableList.of("hello", "world");
+        return Observable.fromIterable(values);
+    }
+
+    private RxHelloWorld() {
+    }
+}

gradle-6/dependency-constraints/src/test/java/com/baeldung/gradle/RxHelloWorldUnitTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.gradle;
+
+import org.junit.jupiter.api.Test;
+
+import static com.baeldung.gradle.RxHelloWorld.hello;
+
+/**
+ * Unit test for {@link RxHelloWorld}.
+ */
+final class RxHelloWorldUnitTest {
+    @Test void it_emits_hello_world_values() {
+        hello().test().assertValues("hello", "world").assertComplete();
+    }
+}

gradle-6/fibonacci-recursive/build.gradle.kts

@@ -0,0 +1,17 @@
+plugins {
+    `java-library`
+}
+
+dependencies {
+    api(project(":fibonacci-spi"))
+    compileOnly("com.google.auto.service:auto-service-annotations:1.0-rc6")
+    annotationProcessor("com.google.auto.service:auto-service:1.0-rc6")
+
+    testImplementation(testFixtures(project(":fibonacci-spi")))
+    testImplementation("org.junit.jupiter:junit-jupiter-api:5.5.2")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.5.2")
+}
+
+tasks.test {
+    useJUnitPlatform()
+}

gradle-6/fibonacci-recursive/src/main/java/com/baeldung/fibonacci/impl/RecursiveFibonacci.java

@@ -0,0 +1,20 @@
+package com.baeldung.fibonacci.impl;
+
+import com.baeldung.fibonacci.FibonacciSequenceGenerator;
+import com.google.auto.service.AutoService;
+
+/**
+ * Recursive implementation of the {@link FibonacciSequenceGenerator}.
+ */
+@AutoService(FibonacciSequenceGenerator.class) public final class RecursiveFibonacci implements FibonacciSequenceGenerator {
+
+    @Override public int generate(int nth) {
+        if (nth < 0) {
+            throw new IllegalArgumentException("sequence number must be 0 or greater");
+        }
+        if (nth <= 1) {
+            return nth;
+        }
+        return generate(nth - 1) + generate(nth - 2);
+    }
+}

gradle-6/fibonacci-recursive/src/test/java/com/baeldung/fibonacci/impl/RecursiveFibonacciUnitTest.java

@@ -0,0 +1,13 @@
+package com.baeldung.fibonacci.impl;
+
+import com.baeldung.fibonacci.FibonacciSequenceGenerator;
+import com.baeldung.fibonacci.FibonacciSequenceGeneratorFixture;
+
+/**
+ * Unit test which reuses the {@link FibonacciSequenceGeneratorFixture} test mix-in exported from the fibonacci-spi project.
+ */
+final class RecursiveFibonacciUnitTest implements FibonacciSequenceGeneratorFixture {
+    @Override public FibonacciSequenceGenerator provide() {
+        return new RecursiveFibonacci();
+    }
+}

gradle-6/fibonacci-spi/build.gradle.kts

@@ -0,0 +1,13 @@
+plugins {
+    `java-library`
+    `java-test-fixtures`
+}
+
+dependencies {
+    testFixturesApi("org.junit.jupiter:junit-jupiter-api:5.5.2")
+    testFixturesImplementation("org.junit.jupiter:junit-jupiter-engine:5.5.2")
+}
+
+tasks.test {
+    useJUnitPlatform()
+}

gradle-6/fibonacci-spi/src/main/java/com/baeldung/fibonacci/FibonacciSequenceGenerator.java

@@ -0,0 +1,13 @@
+package com.baeldung.fibonacci;
+
+/**
+ * Describes an SPI for a Fibonacci sequence generator function.
+ */
+public interface FibonacciSequenceGenerator {
+
+    /**
+     * @param nth the index of the number in the fibonacci sequence
+     * @return the nth number in the fibonacci sequence
+     */
+    int generate(int nth);
+}

gradle-6/fibonacci-spi/src/testFixtures/java/com/baeldung/fibonacci/FibonacciSequenceGeneratorFixture.java

@@ -0,0 +1,30 @@
+package com.baeldung.fibonacci;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+/**
+ * Reusable test fixture for {@link FibonacciSequenceGenerator} implementations. Tests will be skipped if no such implementation exists.
+ */
+public interface FibonacciSequenceGeneratorFixture {
+
+    /**
+     * @return the implementation of {@link FibonacciSequenceGenerator} to test. Must not be null
+     */
+    FibonacciSequenceGenerator provide();
+
+    @Test default void when_sequence_index_is_negative_then_throws() {
+        final FibonacciSequenceGenerator generator = provide();
+        assertThrows(IllegalArgumentException.class, () -> generator.generate(-1));
+    }
+
+    @Test default void when_given_index_then_generates_fibonacci_number() {
+        final FibonacciSequenceGenerator generator = provide();
+        final int[] sequence = { 0, 1, 1, 2, 3, 5, 8 };
+        for (int i = 0; i < sequence.length; i++) {
+            assertEquals(sequence[i], generator.generate(i));
+        }
+    }
+}

gradle-6/gradle.properties

@@ -0,0 +1,2 @@
+org.gradle.parallel=true
+org.gradle.configureondemand=true

gradle-6/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradle-6/gradlew

@@ -0,0 +1,183 @@
+#!/usr/bin/env sh
+
+#
+# Copyright 2015 the original author or authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+##
+##  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 "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+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 or MSYS, switch paths to Windows format before running java
+if [ "$cygwin" = "true" -o "$msys" = "true" ] ; 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=`expr $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"
+
+exec "$JAVACMD" "$@"

gradle-6/gradlew.bat

@@ -0,0 +1,100 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@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="-Xmx64m" "-Xms64m"
+
+@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

gradle-6/httpclient-platform/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+    `java-platform`
+}
+
+dependencies {
+    constraints {
+        api("org.apache.httpcomponents:fluent-hc:4.5.10")
+        api("org.apache.httpcomponents:httpclient:4.5.10")
+        runtime("commons-logging:commons-logging:1.2")
+    }
+}

gradle-6/module-metadata-publishing/build.gradle.kts

@@ -0,0 +1,12 @@
+plugins {
+    java
+    `maven-publish`
+}
+
+publishing {
+    publications {
+        register<MavenPublication>("mavenJava") {
+            from(components["java"])
+        }
+    }
+}

gradle-6/person-rest-client/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+    `java-library`
+}
+
+dependencies {
+    api(platform(project(":httpclient-platform")))
+    implementation("org.apache.httpcomponents:fluent-hc")
+}

gradle-6/settings.gradle.kts

@@ -0,0 +1,10 @@
+rootProject.name = "gradle-6"
+
+include("configuration-avoidance")
+include("dependency-constraints")
+include("fibonacci-spi")
+include("fibonacci-recursive")
+include("httpclient-platform")
+include("module-metadata-publishing")
+include("person-rest-client")
+include("widget-rest-client")

gradle-6/widget-rest-client/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+    `java-library`
+}
+
+dependencies {
+    api(platform(project(":httpclient-platform")))
+    implementation("org.apache.httpcomponents:httpclient")
+}

java-numbers-3/README.md

@@ -0,0 +1,4 @@
+### Relevant Articles:
+
+- [Generating Random Numbers](https://www.baeldung.com/java-generating-random-numbers)
+- [Convert Double to Long in Java](https://www.baeldung.com/java-convert-double-long)

json-2/README.md

@@ -3,3 +3,4 @@
 This module contains articles about JSON.
 
 ### Relevant Articles:
+- [Introduction to Jsoniter](https://www.baeldung.com/java-jsoniter)

libraries-3/README.md

@@ -9,3 +9,5 @@ Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-m
 
 ### Relevant Articles:
 - [Parsing Command-Line Parameters with JCommander](https://www.baeldung.com/jcommander-parsing-command-line-parameters)
+- [Guide to the Cactoos Library](https://www.baeldung.com/java-cactoos)
+- [Parsing Command-Line Parameters with Airline](https://www.baeldung.com/java-airline)

libraries-3/pom.xml

@@ -73,6 +73,17 @@
             <version>${cache2k.version}</version>
             <type>pom</type>
         </dependency>
+        <dependency>
+            <groupId>com.jcabi</groupId>
+            <artifactId>jcabi-aspects</artifactId>
+            <version>${jcabi-aspects.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.aspectj</groupId>
+            <artifactId>aspectjrt</artifactId>
+            <version>${aspectjrt.version}</version>
+            <scope>runtime</scope>
+        </dependency>
         <dependency>
             <groupId>org.takes</groupId>
             <artifactId>takes</artifactId>
@@ -122,6 +133,36 @@
         </resources>
     </build>
     
+    <build>
+        <finalName>libraries-3</finalName>
+        <plugins>
+            <plugin>
+                <groupId>com.jcabi</groupId>
+                <artifactId>jcabi-maven-plugin</artifactId>
+                <version>${jcabi-maven-plugin.version}</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>ajc</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.aspectj</groupId>
+                        <artifactId>aspectjtools</artifactId>
+                        <version>${aspectjtools.version}</version>
+                    </dependency>
+                    <dependency>
+                        <groupId>org.aspectj</groupId>
+                        <artifactId>aspectjweaver</artifactId>
+                        <version>${aspectjweaver.version}</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
+        </plugins>
+    </build>
+    
     <profiles>
         <profile>
             <id>hit-refresh</id>
@@ -170,5 +211,11 @@
         <cactoos.version>0.43</cactoos.version>
         <airline.version>2.7.2</airline.version>
         <cache2k.version>1.2.3.Final</cache2k.version>
+        
+        <jcabi-aspects.version>0.22.6</jcabi-aspects.version>
+        <aspectjrt.version>1.9.2</aspectjrt.version>
+        <jcabi-maven-plugin.version>0.14.1</jcabi-maven-plugin.version>
+        <aspectjtools.version>1.9.2</aspectjtools.version>
+        <aspectjweaver.version>1.9.2</aspectjweaver.version>
     </properties>
 </project>

libraries-3/src/main/java/com/baeldung/cache2k/ProductHelper.java

@@ -4,38 +4,33 @@ import java.util.Objects;
 
 import org.cache2k.Cache;
 import org.cache2k.Cache2kBuilder;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 public class ProductHelper {
 
-    final Logger LOGGER = LoggerFactory.getLogger(ProductHelper.class);
-
     private Cache<String, Integer> cachedDiscounts;
 
+    private int cacheMissCount = 0;
+
     public ProductHelper() {
         cachedDiscounts = Cache2kBuilder.of(String.class, Integer.class)
             .name("discount")
             .eternal(true)
             .entryCapacity(100)
             .build();
-
-        initDiscountCache("Sports", 20);
-    }
-
-    public void initDiscountCache(String productType, Integer value) {
-        cachedDiscounts.put(productType, value);
     }
 
     public Integer getDiscount(String productType) {
         Integer discount = cachedDiscounts.get(productType);
         if (Objects.isNull(discount)) {
-            LOGGER.info("Discount for {} not found.", productType);
+            cacheMissCount++;
-            discount = 0;
+            discount = "Sports".equalsIgnoreCase(productType) ? 20 : 10;
-        } else {
+            cachedDiscounts.put(productType, discount);
-            LOGGER.info("Discount for {} found.", productType);
         }
         return discount;
     }
 
+    public int getCacheMissCount() {
+        return cacheMissCount;
+    }
+
 }

libraries-3/src/main/java/com/baeldung/cache2k/ProductHelperUsingLoader.java

@@ -1,6 +1,5 @@
 package com.baeldung.cache2k;
 
-import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
 import org.cache2k.Cache;
@@ -14,28 +13,26 @@ public class ProductHelperUsingLoader {
 
     private Cache<String, Integer> cachedDiscounts;
 
+    private int cacheMissCount = 0;
+
     public ProductHelperUsingLoader() {
         cachedDiscounts = Cache2kBuilder.of(String.class, Integer.class)
             .name("discount-loader")
-            .eternal(false)
             .expireAfterWrite(10, TimeUnit.MILLISECONDS)
             .entryCapacity(100)
             .loader((key) -> {
-                LOGGER.info("Calculating discount for {}.", key);
+                cacheMissCount++;
                 return "Sports".equalsIgnoreCase(key) ? 20 : 10;
             })
             .build();
     }
 
     public Integer getDiscount(String productType) {
-        Integer discount = cachedDiscounts.get(productType);
+        return cachedDiscounts.get(productType);
-        if (Objects.isNull(discount)) {
+    }
-            LOGGER.info("Discount for {} not found.", productType);
+
-            discount = 0;
+    public int getCacheMissCount() {
-        } else {
+        return cacheMissCount;
-            LOGGER.info("Discount for {} found.", productType);
-        }
-        return discount;
     }
 
 }

libraries-3/src/main/java/com/baeldung/cache2k/ProductHelperWithEventListener.java

@@ -1,6 +1,5 @@
 package com.baeldung.cache2k;
 
-import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
 import org.cache2k.Cache;
@@ -16,14 +15,15 @@ public class ProductHelperWithEventListener {
 
     private Cache<String, Integer> cachedDiscounts;
 
+    private int cacheMissCount = 0;
+
     public ProductHelperWithEventListener() {
         cachedDiscounts = Cache2kBuilder.of(String.class, Integer.class)
             .name("discount-listener")
-            .eternal(false)
             .expireAfterWrite(10, TimeUnit.MILLISECONDS)
             .entryCapacity(100)
             .loader((key) -> {
-                LOGGER.info("Calculating discount for {}.", key);
+                cacheMissCount++;
                 return "Sports".equalsIgnoreCase(key) ? 20 : 10;
             })
             .addListener(new CacheEntryCreatedListener<String, Integer>() {
@@ -36,14 +36,11 @@ public class ProductHelperWithEventListener {
     }
 
     public Integer getDiscount(String productType) {
-        Integer discount = cachedDiscounts.get(productType);
+        return cachedDiscounts.get(productType);
-        if (Objects.isNull(discount)) {
+    }
-            LOGGER.info("Discount for {} not found.", productType);
+
-            discount = 0;
+    public int getCacheMissCount() {
-        } else {
+        return cacheMissCount;
-            LOGGER.info("Discount for {} found.", productType);
-        }
-        return discount;
     }
 
 }

libraries-3/src/main/java/com/baeldung/cache2k/ProductHelperWithExpiry.java

@@ -5,39 +5,34 @@ import java.util.concurrent.TimeUnit;
 
 import org.cache2k.Cache;
 import org.cache2k.Cache2kBuilder;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 public class ProductHelperWithExpiry {
 
-    final Logger LOGGER = LoggerFactory.getLogger(ProductHelperWithExpiry.class);
-
     private Cache<String, Integer> cachedDiscounts;
 
+    private int cacheMissCount = 0;
+
     public ProductHelperWithExpiry() {
         cachedDiscounts = Cache2kBuilder.of(String.class, Integer.class)
             .name("discount-expiry")
-            .eternal(false)
             .expireAfterWrite(5, TimeUnit.MILLISECONDS)
             .entryCapacity(100)
             .build();
 
-        initDiscountCache("Sports", 20);
-    }
-
-    public void initDiscountCache(String productType, Integer value) {
-        cachedDiscounts.put(productType, value);
     }
 
     public Integer getDiscount(String productType) {
         Integer discount = cachedDiscounts.get(productType);
         if (Objects.isNull(discount)) {
-            LOGGER.info("Discount for {} not found.", productType);
+            cacheMissCount++;
-            discount = 0;
+            discount = "Sports".equalsIgnoreCase(productType) ? 20 : 10;
-        } else {
+            cachedDiscounts.put(productType, discount);
-            LOGGER.info("Discount for {} found.", productType);
         }
         return discount;
     }
 
+    public int getCacheMissCount() {
+        return cacheMissCount;
+    }
+
 }

libraries-3/src/main/java/com/baeldung/jcabi/JcabiAspectJ.java

@@ -0,0 +1,112 @@
+package com.baeldung.jcabi;
+
+
+import java.io.BufferedReader;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+import com.jcabi.aspects.Async;
+import com.jcabi.aspects.Cacheable;
+import com.jcabi.aspects.LogExceptions;
+import com.jcabi.aspects.Loggable;
+import com.jcabi.aspects.Quietly;
+import com.jcabi.aspects.RetryOnFailure;
+import com.jcabi.aspects.UnitedThrow;
+
+public class JcabiAspectJ {
+
+    public static void main(String[] args) {
+        try {
+            displayFactorial(10);
+            getFactorial(10).get();
+
+            String result = cacheExchangeRates();
+            if (result != cacheExchangeRates()) {
+                System.out.println(result);
+            }
+
+            divideByZero();
+        } catch(Exception e) {
+            e.printStackTrace();
+        }
+
+        divideByZeroQuietly();
+        try {
+            processFile();  
+        } catch(Exception e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Loggable
+    @Async
+    public static void displayFactorial(int number) {
+        long result = factorial(number);
+        System.out.println(result);
+    }
+
+    @Loggable
+    @Async
+    public static Future<Long> getFactorial(int number) {
+        Future<Long> factorialFuture = CompletableFuture.supplyAsync(() -> factorial(number));
+        return factorialFuture;
+    }
+
+    /**
+     * Finds factorial of a number
+     * @param number
+     * @return
+     */
+    public static long factorial(int number) {
+        long result = 1; 
+        for(int i=number;i>0;i--) {
+            result *= i; 
+        } 
+        return result; 
+    }
+
+    @Loggable
+    @Cacheable(lifetime = 2, unit = TimeUnit.SECONDS)
+    public static String cacheExchangeRates() {
+        String result = null;
+        try {
+            URL exchangeRateUrl = new URL("https://api.exchangeratesapi.io/latest");
+            URLConnection con = exchangeRateUrl.openConnection();
+            BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
+            result = in.readLine();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return result;
+    }
+
+    @LogExceptions
+    public static void divideByZero() {
+        int x = 1/0;
+    }
+
+    @RetryOnFailure(attempts = 2, types = {java.lang.NumberFormatException.class})
+    @Quietly
+    public static void divideByZeroQuietly() {
+        int x = 1/0;
+    }
+
+    @UnitedThrow(IllegalStateException.class)
+    public static void processFile() throws IOException, InterruptedException {
+        BufferedReader reader = new BufferedReader(new FileReader("baeldung.txt"));
+        reader.readLine();
+        
+        Thread thread = new Thread();
+        thread.wait(2000);
+    }
+
+}

libraries-3/src/test/java/com/baeldung/cache2k/ProductHelperUnitTest.java

@@ -6,12 +6,13 @@ import org.junit.Test;
 
 public class ProductHelperUnitTest {
 
-    ProductHelper productHelper = new ProductHelper();
-
     @Test
-    public void whenInvokedGetDiscount_thenGetItFromCache() {
+    public void whenInvokedGetDiscountTwice_thenGetItFromCache() {
+        ProductHelper productHelper = new ProductHelper();
+        assertTrue(productHelper.getCacheMissCount() == 0);
         assertTrue(productHelper.getDiscount("Sports") == 20);
-        assertTrue(productHelper.getDiscount("Electronics") == 0);
+        assertTrue(productHelper.getDiscount("Sports") == 20);
+        assertTrue(productHelper.getCacheMissCount() == 1);
     }
 
 }