Merge branch 'master' of https://github.com/eugenp/tutorials

algorithms-searching/src/main/java/com/baeldung/algorithms/suffixtree/Node.java

@@ -0,0 +1,57 @@
+package com.baeldung.algorithms.suffixtree;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Node {
+    private String text;
+    private List<Node> children;
+    private int position;
+
+    public Node(String word, int position) {
+        this.text = word;
+        this.position = position;
+        this.children = new ArrayList<>();
+    }
+
+    public String getText() {
+        return text;
+    }
+
+    public void setText(String text) {
+        this.text = text;
+    }
+
+    public int getPosition() {
+        return position;
+    }
+
+    public void setPosition(int position) {
+        this.position = position;
+    }
+
+    public List<Node> getChildren() {
+        return children;
+    }
+
+    public void setChildren(List<Node> children) {
+        this.children = children;
+    }
+
+    public String printTree(String depthIndicator) {
+        String str = "";
+        String positionStr = position > -1 ? "[" + String.valueOf(position) + "]" : "";
+        str += depthIndicator + text + positionStr + "\n";
+
+        for (int i = 0; i < children.size(); i++) {
+            str += children.get(i)
+                .printTree(depthIndicator + "\t");
+        }
+        return str;
+    }
+
+    @Override
+    public String toString() {
+        return printTree("");
+    }
+}

algorithms-searching/src/main/java/com/baeldung/algorithms/suffixtree/SuffixTree.java

@@ -0,0 +1,175 @@
+package com.baeldung.algorithms.suffixtree;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class SuffixTree {
+    private static final Logger LOGGER = LoggerFactory.getLogger(SuffixTree.class);
+    private static final String WORD_TERMINATION = "$";
+    private static final int POSITION_UNDEFINED = -1;
+    private Node root;
+    private String fullText;
+
+    public SuffixTree(String text) {
+        root = new Node("", POSITION_UNDEFINED);
+        for (int i = 0; i < text.length(); i++) {
+            addSuffix(text.substring(i) + WORD_TERMINATION, i);
+        }
+        fullText = text;
+    }
+
+    public List<String> searchText(String pattern) {
+        LOGGER.info("Searching for pattern \"{}\"", pattern);
+        List<String> result = new ArrayList<>();
+        List<Node> nodes = getAllNodesInTraversePath(pattern, root, false);
+
+        if (nodes.size() > 0) {
+            Node lastNode = nodes.get(nodes.size() - 1);
+            if (lastNode != null) {
+                List<Integer> positions = getPositions(lastNode);
+                positions = positions.stream()
+                    .sorted()
+                    .collect(Collectors.toList());
+                positions.forEach(m -> result.add((markPatternInText(m, pattern))));
+            }
+        }
+        return result;
+    }
+
+    private void addSuffix(String suffix, int position) {
+        LOGGER.info(">>>>>>>>>>>> Adding new suffix {}", suffix);
+        List<Node> nodes = getAllNodesInTraversePath(suffix, root, true);
+        if (nodes.size() == 0) {
+            addChildNode(root, suffix, position);
+            LOGGER.info("{}", printTree());
+        } else {
+            Node lastNode = nodes.remove(nodes.size() - 1);
+            String newText = suffix;
+            if (nodes.size() > 0) {
+                String existingSuffixUptoLastNode = nodes.stream()
+                    .map(a -> a.getText())
+                    .reduce("", String::concat);
+
+                // Remove prefix from newText already included in parent
+                newText = newText.substring(existingSuffixUptoLastNode.length());
+            }
+            extendNode(lastNode, newText, position);
+            LOGGER.info("{}", printTree());
+        }
+    }
+
+    private List<Integer> getPositions(Node node) {
+        List<Integer> positions = new ArrayList<>();
+        if (node.getText()
+            .endsWith(WORD_TERMINATION)) {
+            positions.add(node.getPosition());
+        }
+        for (int i = 0; i < node.getChildren()
+            .size(); i++) {
+            positions.addAll(getPositions(node.getChildren()
+                .get(i)));
+        }
+        return positions;
+    }
+
+    private String markPatternInText(Integer startPosition, String pattern) {
+        String matchingTextLHS = fullText.substring(0, startPosition);
+        String matchingText = fullText.substring(startPosition, startPosition + pattern.length());
+        String matchingTextRHS = fullText.substring(startPosition + pattern.length());
+        return matchingTextLHS + "[" + matchingText + "]" + matchingTextRHS;
+    }
+
+    private void addChildNode(Node parentNode, String text, int position) {
+        parentNode.getChildren()
+            .add(new Node(text, position));
+    }
+
+    private void extendNode(Node node, String newText, int position) {
+        String currentText = node.getText();
+        String commonPrefix = getLongestCommonPrefix(currentText, newText);
+
+        if (commonPrefix != currentText) {
+            String parentText = currentText.substring(0, commonPrefix.length());
+            String childText = currentText.substring(commonPrefix.length());
+            splitNodeToParentAndChild(node, parentText, childText);
+        }
+
+        String remainingText = newText.substring(commonPrefix.length());
+        addChildNode(node, remainingText, position);
+    }
+
+    private void splitNodeToParentAndChild(Node parentNode, String parentNewText, String childNewText) {
+        Node childNode = new Node(childNewText, parentNode.getPosition());
+
+        if (parentNode.getChildren()
+            .size() > 0) {
+            while (parentNode.getChildren()
+                .size() > 0) {
+                childNode.getChildren()
+                    .add(parentNode.getChildren()
+                        .remove(0));
+            }
+        }
+
+        parentNode.getChildren()
+            .add(childNode);
+        parentNode.setText(parentNewText);
+        parentNode.setPosition(POSITION_UNDEFINED);
+    }
+
+    private String getLongestCommonPrefix(String str1, String str2) {
+        int compareLength = Math.min(str1.length(), str2.length());
+        for (int i = 0; i < compareLength; i++) {
+            if (str1.charAt(i) != str2.charAt(i)) {
+                return str1.substring(0, i);
+            }
+        }
+        return str1.substring(0, compareLength);
+    }
+
+    private List<Node> getAllNodesInTraversePath(String pattern, Node startNode, boolean isAllowPartialMatch) {
+        List<Node> nodes = new ArrayList<>();
+        for (int i = 0; i < startNode.getChildren()
+            .size(); i++) {
+            Node currentNode = startNode.getChildren()
+                .get(i);
+            String nodeText = currentNode.getText();
+            if (pattern.charAt(0) == nodeText.charAt(0)) {
+                if (isAllowPartialMatch && pattern.length() <= nodeText.length()) {
+                    nodes.add(currentNode);
+                    return nodes;
+                }
+
+                int compareLength = Math.min(nodeText.length(), pattern.length());
+                for (int j = 1; j < compareLength; j++) {
+                    if (pattern.charAt(j) != nodeText.charAt(j)) {
+                        if (isAllowPartialMatch) {
+                            nodes.add(currentNode);
+                        }
+                        return nodes;
+                    }
+                }
+
+                nodes.add(currentNode);
+                if (pattern.length() > compareLength) {
+                    List<Node> nodes2 = getAllNodesInTraversePath(pattern.substring(compareLength), currentNode, isAllowPartialMatch);
+                    if (nodes2.size() > 0) {
+                        nodes.addAll(nodes2);
+                    } else if (!isAllowPartialMatch) {
+                        nodes.add(null);
+                    }
+                }
+                return nodes;
+            }
+        }
+        return nodes;
+    }
+
+    public String printTree() {
+        return root.printTree("");
+    }
+}

algorithms-searching/src/test/java/com/baeldung/algorithms/suffixtree/SuffixTreeUnitTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.algorithms.suffixtree;
+
+import java.util.List;
+
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class SuffixTreeUnitTest {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(SuffixTreeUnitTest.class);
+
+    private static SuffixTree suffixTree;
+
+    @BeforeClass
+    public static void setUp() {
+        suffixTree = new SuffixTree("havanabanana");
+        printTree();
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForA_thenReturn6Matches() {
+        List<String> matches = suffixTree.searchText("a");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] { "h[a]vanabanana", "hav[a]nabanana", "havan[a]banana", "havanab[a]nana", "havanaban[a]na", "havanabanan[a]" }, matches.toArray());
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForNab_thenReturn1Match() {
+        List<String> matches = suffixTree.searchText("nab");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] { "hava[nab]anana" }, matches.toArray());
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForNag_thenReturnNoMatches() {
+        List<String> matches = suffixTree.searchText("nag");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] {}, matches.toArray());
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForBanana_thenReturn2Matches() {
+        List<String> matches = suffixTree.searchText("ana");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] { "hav[ana]banana", "havanab[ana]na", "havanaban[ana]" }, matches.toArray());
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForNa_thenReturn4Matches() {
+        List<String> matches = suffixTree.searchText("na");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] { "hava[na]banana", "havanaba[na]na", "havanabana[na]" }, matches.toArray());
+    }
+
+    @Test
+    public void givenSuffixTree_whenSearchingForX_thenReturnNoMatches() {
+        List<String> matches = suffixTree.searchText("x");
+        matches.stream()
+            .forEach(m -> LOGGER.info(m));
+        Assert.assertArrayEquals(new String[] {}, matches.toArray());
+    }
+
+    private static void printTree() {
+        suffixTree.printTree();
+
+        LOGGER.info("\n" + suffixTree.printTree());
+        LOGGER.info("==============================================");
+    }
+}

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

@@ -11,5 +11,5 @@ This module contains articles about core Java input and output (IO)
 - [List Files in a Directory in Java](https://www.baeldung.com/java-list-directory-files)
 - [Java – Append Data to a File](https://www.baeldung.com/java-append-to-file)
 - [How to Copy a File with Java](https://www.baeldung.com/java-copy-file)
-- [Create a Directory in Java](https://www.baeldung.com/java-create-directory)
+- [Create a Directory in Java](https://www.baeldung.com/java-create-directory) 
 - [[<-- Prev]](/core-java-modules/core-java-io)

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/lock/FileLocks.java

@@ -0,0 +1,148 @@
+package com.baeldung.lock;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.channels.NonReadableChannelException;
+import java.nio.channels.NonWritableChannelException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+
+public class FileLocks {
+
+    private static final Logger LOG = LoggerFactory.getLogger(FileLocks.class);
+
+    // Write locks
+
+    /**
+     * Trying to get an exclusive lock on a read-only FileChannel won't work.
+     */
+    static void getExclusiveLockFromInputStream() throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (FileInputStream fis = new FileInputStream(path.toFile());
+            FileLock lock = fis.getChannel()
+                .lock()) {
+            LOG.debug("This won't happen");
+        } catch (NonWritableChannelException e) {
+            LOG.error("The channel obtained through a FileInputStream isn't writable. You can't obtain an exclusive lock on it!");
+            throw e;
+        }
+    }
+
+    /**
+     * Gets an exclusive lock from a RandomAccessFile. Works because the file is writable.
+     * @param from beginning of the locked region
+     * @param size how many bytes to lock
+     * @return A lock object representing the newly-acquired lock
+     * @throws IOException if there is a problem creating the temporary file
+     */
+    static FileLock getExclusiveLockFromRandomAccessFile(long from, long size) throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (RandomAccessFile file = new RandomAccessFile(path.toFile(), "rw");
+            FileLock lock = file.getChannel()
+                .lock(from, size, false)) {
+            if (lock.isValid()) {
+                LOG.debug("This is a valid exclusive lock");
+                return lock;
+            }
+            return null;
+        } catch (Exception e) {
+            LOG.error(e.getMessage());
+        }
+        return null;
+    }
+
+    /**
+     * Acquires an exclusive lock on a file region.
+     * @param from beginning of the locked region
+     * @param size how many bytes to lock
+     * @return A lock object representing the newly-acquired lock
+     * @throws IOException if there is a problem creating the temporary file
+     */
+    static FileLock getExclusiveLockFromFileChannelOpen(long from, long size) throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (FileChannel channel = FileChannel.open(path, StandardOpenOption.APPEND); FileLock lock = channel.lock(from, size, false)) {
+            String text = "Hello, world.";
+            ByteBuffer buffer = ByteBuffer.allocate(text.length() + System.lineSeparator()
+                .length());
+            buffer.put((text + System.lineSeparator()).getBytes(StandardCharsets.UTF_8));
+            buffer.flip();
+            while (buffer.hasRemaining()) {
+                channel.write(buffer, channel.size());
+            }
+            LOG.debug("This was written to the file");
+            Files.lines(path)
+                .forEach(LOG::debug);
+            return lock;
+        }
+    }
+
+    // Read locks
+
+    /**
+     * Trying to get a shared lock on a write-only FileChannel won't work.
+     */
+    static void getReadLockFromOutputStream() throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (FileOutputStream fis = new FileOutputStream(path.toFile());
+            FileLock lock = fis.getChannel()
+                .lock(0, Long.MAX_VALUE, true)) {
+            LOG.debug("This won't happen");
+        } catch (NonReadableChannelException e) {
+            LOG.error("The channel obtained through a FileOutputStream isn't readable. " + "You can't obtain an shared lock on it!");
+            throw e;
+        }
+    }
+
+    /**
+     * Gets a lock from an <tt>InputStream</tt>.
+     * @param from beginning of the locked region
+     * @param size how many bytes to lock
+     * @return A lock object representing the newly-acquired lock
+     * @throws IOException if there is a problem creating the temporary file
+     */
+    static FileLock getReadLockFromInputStream(long from, long size) throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (FileInputStream fis = new FileInputStream(path.toFile());
+            FileLock lock = fis.getChannel()
+                .lock(from, size, true)) {
+            if (lock.isValid()) {
+                LOG.debug("This is a valid shared lock");
+                return lock;
+            }
+            return null;
+        }
+    }
+
+    /**
+     * Gets an exclusive lock from a RandomAccessFile. Works because the file is readable.
+     * @param from beginning of the locked region
+     * @param size how many bytes to lock
+     * @return A lock object representing the newly-acquired lock
+     * @throws IOException if there is a problem creating the temporary file
+     */
+    static FileLock getReadLockFromRandomAccessFile(long from, long size) throws IOException {
+        Path path = Files.createTempFile("foo", "txt");
+        try (RandomAccessFile file = new RandomAccessFile(path.toFile(), "r"); // could also be "rw", but "r" is sufficient for reading
+            FileLock lock = file.getChannel()
+                .lock(from, size, true)) {
+            if (lock.isValid()) {
+                LOG.debug("This is a valid shared lock");
+                return lock;
+            }
+        } catch (Exception e) {
+            LOG.error(e.getMessage());
+        }
+        return null;
+    }
+
+}

core-java-modules/core-java-nio-2/src/test/java/com/baeldung/lock/FileLocksUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.lock;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.channels.FileLock;
+import java.nio.channels.NonReadableChannelException;
+import java.nio.channels.NonWritableChannelException;
+
+import org.junit.jupiter.api.Test;
+
+class FileLocksUnitTest {
+
+    @Test
+    void givenAnInputStream_whenGetWriteLock_thenThrowNonWritableChannelException() {
+        assertThrows(NonWritableChannelException.class, () -> FileLocks.getExclusiveLockFromInputStream());
+    }
+
+    @Test
+    void givenARandomAccessFileWithReadWriteAccess_whenGetWriteLock_thenLock() throws IOException {
+        FileLock lock = FileLocks.getExclusiveLockFromRandomAccessFile(0, 10);
+        assertNotNull(lock);
+        assertFalse(lock.isShared());
+    }
+
+    @Test
+    void givenAPath_whenGetExclusiveLock_thenLock() throws IOException {
+        FileLock lock = FileLocks.getExclusiveLockFromFileChannelOpen(0, 10);
+        assertNotNull(lock);
+        assertFalse(lock.isShared());
+    }
+
+    @Test
+    void givenAFileOutputStream_whenGetSharedLock_thenThrowNonReadableChannelException() {
+        assertThrows(NonReadableChannelException.class, FileLocks::getReadLockFromOutputStream);
+    }
+
+    @Test
+    void givenAnInputStream_whenGetSharedLock_thenLock() throws IOException {
+        FileLock lock = FileLocks.getReadLockFromInputStream(0, 10);
+        assertNotNull(lock);
+        assertTrue(lock.isShared());
+    }
+
+    @Test
+    void givenARandomAccessFile_whenGetSharedLock_thenLock() throws IOException {
+        FileLock lock = FileLocks.getReadLockFromRandomAccessFile(0, 10);
+        assertNotNull(lock);
+        assertTrue(lock.isShared());
+    }
+}

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

@@ -11,7 +11,7 @@
 - [Introduction to Java Serialization](http://www.baeldung.com/java-serialization)
 - [Guide to UUID in Java](http://www.baeldung.com/java-uuid)
 - [Creating a Java Compiler Plugin](http://www.baeldung.com/java-build-compiler-plugin)
-- [Quick Guide to Java Stack](http://www.baeldung.com/java-stack)
+- [Quick Guide to the Java Stack](http://www.baeldung.com/java-stack)
 - [Compiling Java *.class Files with javac](http://www.baeldung.com/javac)
 - [Introduction to Javadoc](http://www.baeldung.com/javadoc)
 - [Guide to the Externalizable Interface in Java](http://www.baeldung.com/java-externalizable)

core-java-modules/core-java/src/test/java/com/baeldung/timer/JavaTimerLongRunningUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.timer;
 
 import org.junit.Test;
 import org.slf4j.Logger;

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

@@ -5,4 +5,5 @@ 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-operator)
+- [Sequences in Kotlin](https://www.baeldung.com/kotlin/sequences)
 - [[<-- Prev]](/core-kotlin-modules/core-kotlin)

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

@@ -13,4 +13,7 @@ This module contains articles about Kotlin core features.
 - [Implementing a Binary Tree in Kotlin](https://www.baeldung.com/kotlin-binary-tree)
 - [JUnit 5 for Kotlin Developers](https://www.baeldung.com/junit-5-kotlin)
 - [Converting Kotlin Data Class from JSON using GSON](https://www.baeldung.com/kotlin-json-convert-data-class)
+- [Fuel HTTP Library with Kotlin](https://www.baeldung.com/kotlin-fuel)
+- [Introduction to Kovenant Library for Kotlin](https://www.baeldung.com/kotlin-kovenant)
+- [Dependency Injection for Kotlin with Injekt](https://www.baeldung.com/kotlin-dependency-injection-with-injekt)
 - [[More --> ]](/core-kotlin-modules/core-kotlin-2)

core-scala/README.md

@@ -5,3 +5,4 @@ This module contains articles about Scala's core features
 ### Relevant Articles: 
 
 - [Introduction to Scala](https://www.baeldung.com/scala-intro)
+- [Regular Expressions in Scala](https://www.baeldung.com/scala/regular-expressions)

core-scala/src/test/scala/com/baeldung/scala/HigherOrderFunctionsExamplesUnitTest.scala

@@ -0,0 +1,82 @@
+package com.baeldung.scala
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+
+class HigherOrderFunctionsExamplesUnitTest {
+
+  @Test
+  def whenCallingMapWithAnonymousFunction_thenTransformationIsApplied() = {
+    val expected = Seq("sir Alex Ferguson", "sir Bobby Charlton", "sir Frank Lampard")
+
+    val names = Seq("Alex Ferguson", "Bobby Charlton", "Frank Lampard")
+    val sirNames = names.map(name => "sir " + name)
+
+    assertEquals(expected, sirNames)
+  }
+
+  @Test
+  def whenCallingMapWithDefined_thenTransformationIsApplied() = {
+    val expected = Seq("sir Alex Ferguson", "sir Bobby Charlton", "sir Frank Lampard")
+
+    val names = Seq("Alex Ferguson", "Bobby Charlton", "Frank Lampard")
+
+    def prefixWithSir(name: String) = "sir " + name
+    val sirNames = names.map(prefixWithSir)
+
+    assertEquals(expected, sirNames)
+  }
+
+  @Test
+  def whenCallingFilter_thenUnecessaryElementsAreRemoved() = {
+    val expected = Seq("John O'Shea", "John Hartson")
+
+    val names = Seq("John O'Shea", "Aiden McGeady", "John Hartson")
+    val johns = names.filter(name => name.matches("^John .*"))
+
+    assertEquals(expected, johns)
+  }
+
+  @Test
+  def whenCallingReduce_thenProperSumIsCalculated() = {
+    val expected = 2750
+
+    val earnings = Seq(1000, 1300, 450)
+    val sumEarnings = earnings.reduce((acc, x) => acc + x)
+
+    assertEquals(expected, sumEarnings)
+  }
+
+  @Test
+  def whenCallingFold_thenNumberOfWordsShouldBeCalculated() = {
+    val expected = 6
+
+    val strings = Seq("bunch of words", "just me", "it")
+    val sumEarnings = strings.foldLeft(0)((acc, x) => acc + x.split(" ").size)
+
+    assertEquals(expected, sumEarnings)
+  }
+
+  @Test
+  def whenCallingOwnHigherOrderFunction_thenProperFunctionIsReturned() = {
+    def mathOperation(name: String): (Int, Int) => Int = (x: Int, y: Int) => {
+      name match {
+        case "addition" => x + y
+        case "multiplication" => x * y
+        case "division" => x/y
+        case "subtraction" => x - y
+      }
+    }
+
+    def add: (Int, Int) => Int = mathOperation("addition")
+    def mul: (Int, Int) => Int = mathOperation("multiplication")
+    def div: (Int, Int) => Int = mathOperation("division")
+    def sub: (Int, Int) => Int = mathOperation("subtraction")
+
+    assertEquals(15, add(10, 5))
+    assertEquals(50, mul(10, 5))
+    assertEquals(2, div(10, 5))
+    assertEquals(5, sub(10, 5))
+  }
+}

core-scala/src/test/scala/com/baeldung/scala/regex/RegexUnitTest.scala

@@ -1,4 +1,4 @@
-package com.baeldung.scala
+package com.baeldung.scala.regex
 
 import org.junit.Test
 import org.junit.Assert.assertEquals

ddd-modules/README.md

@@ -0,0 +1 @@
+## Relevant Articles

ddd-modules/infrastructure/pom.xml

@@ -0,0 +1,53 @@
+<?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>
+    <groupId>com.baeldung.dddmodules.infrastructure</groupId>
+    <artifactId>infrastructure</artifactId>
+    <version>1.0</version>
+
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.dddmodules</groupId>
+        <artifactId>dddmodules</artifactId>
+        <version>1.0</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.baeldung.dddmodules.shippingcontext</groupId>
+            <artifactId>shippingcontext</artifactId>
+            <version>${appmodules.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.baeldung.dddmodules.ordercontext</groupId>
+            <artifactId>ordercontext</artifactId>
+            <version>${appmodules.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.baeldung.dddmodules.sharedkernel</groupId>
+            <artifactId>sharedkernel</artifactId>
+            <version>${appmodules.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>${source.version}</source>
+                    <target>${target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <source.version>9</source.version>
+        <target.version>9</target.version>
+    </properties>
+
+</project>

ddd-modules/infrastructure/src/main/java/com/baeldung/dddmodules/infrastructure/db/InMemoryOrderStore.java

@@ -0,0 +1,79 @@
+package com.baeldung.dddmodules.infrastructure.db;
+
+import com.baeldung.dddmodules.ordercontext.model.CustomerOrder;
+import com.baeldung.dddmodules.ordercontext.repository.CustomerOrderRepository;
+import com.baeldung.dddmodules.shippingcontext.model.PackageItem;
+import com.baeldung.dddmodules.shippingcontext.model.ShippableOrder;
+import com.baeldung.dddmodules.shippingcontext.repository.ShippingOrderRepository;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+public class InMemoryOrderStore implements CustomerOrderRepository, ShippingOrderRepository {
+    private Map<Integer, PersistenceOrder> ordersDb = new HashMap<>();
+    private volatile static InMemoryOrderStore instance = new InMemoryOrderStore();
+
+    @Override
+    public void saveCustomerOrder(CustomerOrder order) {
+        this.ordersDb.put(order.getOrderId(), new PersistenceOrder(order.getOrderId(),
+          order.getPaymentMethod(),
+          order.getAddress(),
+          order
+            .getOrderItems()
+            .stream()
+            .map(orderItem ->
+              new PersistenceOrder.OrderItem(orderItem.getProductId(),
+                orderItem.getQuantity(),
+                orderItem.getUnitWeight(),
+                orderItem.getUnitPrice()))
+            .collect(Collectors.toList())
+        ));
+    }
+
+    @Override
+    public Optional<ShippableOrder> findShippableOrder(int orderId) {
+        if (!this.ordersDb.containsKey(orderId)) return Optional.empty();
+        PersistenceOrder orderRecord = this.ordersDb.get(orderId);
+        return Optional.of(
+          new ShippableOrder(orderRecord.orderId, orderRecord.orderItems
+            .stream().map(orderItem -> new PackageItem(orderItem.productId,
+              orderItem.itemWeight,
+              orderItem.quantity * orderItem.unitPrice)
+            ).collect(Collectors.toList())));
+    }
+
+    public static InMemoryOrderStore provider() {
+        return instance;
+    }
+
+    public static class PersistenceOrder {
+        public int orderId;
+        public String paymentMethod;
+        public String address;
+        public List<OrderItem> orderItems;
+
+        public PersistenceOrder(int orderId, String paymentMethod, String address, List<OrderItem> orderItems) {
+            this.orderId = orderId;
+            this.paymentMethod = paymentMethod;
+            this.address = address;
+            this.orderItems = orderItems;
+        }
+
+        public static class OrderItem {
+            public int productId;
+            public float unitPrice;
+            public float itemWeight;
+            public int quantity;
+
+            public OrderItem(int productId, int quantity, float unitWeight, float unitPrice) {
+                this.itemWeight = unitWeight;
+                this.quantity = quantity;
+                this.unitPrice = unitPrice;
+                this.productId = productId;
+            }
+        }
+    }
+}

ddd-modules/infrastructure/src/main/java/com/baeldung/dddmodules/infrastructure/events/SimpleEventBus.java

@@ -0,0 +1,39 @@
+package com.baeldung.dddmodules.infrastructure.events;
+
+import com.baeldung.dddmodules.sharedkernel.events.ApplicationEvent;
+import com.baeldung.dddmodules.sharedkernel.events.EventBus;
+import com.baeldung.dddmodules.sharedkernel.events.EventSubscriber;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArraySet;
+
+public class SimpleEventBus implements EventBus {
+    private final Map<String, Set<EventSubscriber>> subscribers = new ConcurrentHashMap<>();
+
+    @Override
+    public <E extends ApplicationEvent> void publish(E event) {
+        if (subscribers.containsKey(event.getType())) {
+            subscribers.get(event.getType())
+              .forEach(subscriber -> subscriber.onEvent(event));
+        }
+    }
+
+    @Override
+    public <E extends ApplicationEvent> void subscribe(String eventType, EventSubscriber subscriber) {
+        Set<EventSubscriber> eventSubscribers = subscribers.get(eventType);
+        if (eventSubscribers == null) {
+            eventSubscribers = new CopyOnWriteArraySet<>();
+            subscribers.put(eventType, eventSubscribers);
+        }
+        eventSubscribers.add(subscriber);
+    }
+
+    @Override
+    public <E extends ApplicationEvent> void unsubscribe(String eventType, EventSubscriber subscriber) {
+        if (subscribers.containsKey(eventType)) {
+            subscribers.get(eventType).remove(subscriber);
+        }
+    }
+}

ddd-modules/infrastructure/src/main/java/module-info.java

@@ -0,0 +1,11 @@
+module com.baeldung.dddmodules.infrastructure {
+    requires transitive com.baeldung.dddmodules.sharedkernel;
+    requires transitive com.baeldung.dddmodules.ordercontext;
+    requires transitive com.baeldung.dddmodules.shippingcontext;
+    provides com.baeldung.dddmodules.sharedkernel.events.EventBus
+      with com.baeldung.dddmodules.infrastructure.events.SimpleEventBus;
+    provides com.baeldung.dddmodules.ordercontext.repository.CustomerOrderRepository
+      with com.baeldung.dddmodules.infrastructure.db.InMemoryOrderStore;
+    provides com.baeldung.dddmodules.shippingcontext.repository.ShippingOrderRepository
+      with com.baeldung.dddmodules.infrastructure.db.InMemoryOrderStore;
+}

ddd-modules/mainapp/pom.xml

@@ -0,0 +1,51 @@
+<?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>
+    <groupId>com.baeldung.dddmodules.mainapp</groupId>
+    <artifactId>mainapp</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.dddmodules</groupId>
+        <artifactId>dddmodules</artifactId>
+        <version>1.0</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.baeldung.dddmodules.infrastructure</groupId>
+            <artifactId>infrastructure</artifactId>
+            <version>${appmodules.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.16</version>
+                <configuration>
+                    <enableAssertions>true</enableAssertions>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${compiler.plugin.version}</version>
+                <configuration>
+                    <source>${source.version}</source>
+                    <target>${target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <source.version>9</source.version>
+        <target.version>9</target.version>
+    </properties>
+
+</project>

ddd-modules/mainapp/src/main/java/com/baeldung/dddmodules/mainapp/Application.java

@@ -0,0 +1,54 @@
+package com.baeldung.dddmodules.mainapp;
+
+import com.baeldung.dddmodules.ordercontext.model.CustomerOrder;
+import com.baeldung.dddmodules.ordercontext.model.OrderItem;
+import com.baeldung.dddmodules.ordercontext.repository.CustomerOrderRepository;
+import com.baeldung.dddmodules.ordercontext.service.OrderService;
+import com.baeldung.dddmodules.sharedkernel.events.EventBus;
+import com.baeldung.dddmodules.shippingcontext.repository.ShippingOrderRepository;
+import com.baeldung.dddmodules.shippingcontext.service.ShippingService;
+
+import java.util.*;
+
+public class Application {
+
+    public static void main(String args[]) {
+        Map<Class<?>, Object> container = createContainer();
+        OrderService orderService = (OrderService) container.get(OrderService.class);
+        ShippingService shippingService = (ShippingService) container.get(ShippingService.class);
+        shippingService.listenToOrderEvents();
+
+        CustomerOrder customerOrder = new CustomerOrder();
+        int orderId = 1;
+        customerOrder.setOrderId(orderId);
+        List<OrderItem> orderItems = new ArrayList<OrderItem>();
+        orderItems.add(new OrderItem(1, 2, 3, 1));
+        orderItems.add(new OrderItem(2, 1, 1, 1));
+        orderItems.add(new OrderItem(3, 4, 11, 21));
+        customerOrder.setOrderItems(orderItems);
+        customerOrder.setPaymentMethod("PayPal");
+        customerOrder.setAddress("Full address here");
+        orderService.placeOrder(customerOrder);
+
+        if (orderId == shippingService.getParcelByOrderId(orderId).get().getOrderId()) {
+            System.out.println("Order has been processed and shipped successfully");
+        }
+    }
+
+    public static Map<Class<?>, Object> createContainer() {
+        EventBus eventBus = ServiceLoader.load(EventBus.class).findFirst().get();
+        CustomerOrderRepository customerOrderRepository = ServiceLoader.load(CustomerOrderRepository.class).findFirst().get();
+        ShippingOrderRepository shippingOrderRepository = ServiceLoader.load(ShippingOrderRepository.class).findFirst().get();
+        ShippingService shippingService = ServiceLoader.load(ShippingService.class).findFirst().get();
+        shippingService.setEventBus(eventBus);
+        shippingService.setOrderRepository(shippingOrderRepository);
+        OrderService orderService = ServiceLoader.load(OrderService.class).findFirst().get();
+        orderService.setEventBus(eventBus);
+        orderService.setOrderRepository(customerOrderRepository);
+        HashMap<Class<?>, Object> container = new HashMap<>();
+        container.put(OrderService.class, orderService);
+        container.put(ShippingService.class, shippingService);
+        return container;
+    }
+
+}

ddd-modules/mainapp/src/main/java/module-info.java

@@ -0,0 +1,8 @@
+module com.baeldung.dddmodules.mainapp {
+    uses com.baeldung.dddmodules.sharedkernel.events.EventBus;
+    uses com.baeldung.dddmodules.ordercontext.service.OrderService;
+    uses com.baeldung.dddmodules.ordercontext.repository.CustomerOrderRepository;
+    uses com.baeldung.dddmodules.shippingcontext.repository.ShippingOrderRepository;
+    uses com.baeldung.dddmodules.shippingcontext.service.ShippingService;
+    requires transitive com.baeldung.dddmodules.infrastructure;
+}

ddd-modules/ordercontext/pom.xml

@@ -0,0 +1,44 @@
+<?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>
+    <groupId>com.baeldung.dddmodules.ordercontext</groupId>
+    <artifactId>ordercontext</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.dddmodules</groupId>
+        <artifactId>dddmodules</artifactId>
+        <version>1.0</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.baeldung.dddmodules.sharedkernel</groupId>
+            <artifactId>sharedkernel</artifactId>
+            <version>${appmodules.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>${source.version}</source>
+                    <target>${target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <source.version>9</source.version>
+        <target.version>9</target.version>
+        <entitymodule.version>1.0</entitymodule.version>
+        <daomodule.version>1.0</daomodule.version>
+    </properties>
+
+</project>

ddd-modules/ordercontext/src/main/java/com/baeldung/dddmodules/ordercontext/model/CustomerOrder.java

@@ -0,0 +1,51 @@
+package com.baeldung.dddmodules.ordercontext.model;
+
+import java.util.List;
+
+public class CustomerOrder {
+    private int orderId;
+    private String paymentMethod;
+    private String address;
+    private List<OrderItem> orderItems;
+
+    public CustomerOrder() {
+
+    }
+
+    public float calculateTotalPrice() {
+        return orderItems.stream().map(OrderItem::getTotalPrice)
+          .reduce(0F, Float::sum);
+    }
+
+    public void setOrderItems(List<OrderItem> orderItems) {
+        this.orderItems = orderItems;
+    }
+
+    public int getOrderId() {
+        return orderId;
+    }
+
+    public List<OrderItem> getOrderItems() {
+        return orderItems;
+    }
+
+    public void setOrderId(int orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getPaymentMethod() {
+        return paymentMethod;
+    }
+
+    public void setPaymentMethod(String paymentMethod) {
+        this.paymentMethod = paymentMethod;
+    }
+
+    public String getAddress() {
+        return address;
+    }
+
+    public void setAddress(String address) {
+        this.address = address;
+    }
+}

ddd-modules/ordercontext/src/main/java/com/baeldung/dddmodules/ordercontext/model/OrderItem.java

@@ -0,0 +1,51 @@
+package com.baeldung.dddmodules.ordercontext.model;
+
+public class OrderItem {
+    private int productId;
+    private int quantity;
+    private float unitPrice;
+    private float unitWeight;
+
+    public OrderItem(int productId, int quantity, float unitPrice, float unitWeight) {
+        this.productId = productId;
+        this.quantity = quantity;
+        this.unitPrice = unitPrice;
+        this.unitWeight = unitWeight;
+    }
+
+    public int getProductId() {
+        return productId;
+    }
+
+    public void setProductId(int productId) {
+        this.productId = productId;
+    }
+
+    public int getQuantity() {
+        return quantity;
+    }
+
+    public void setQuantity(int quantity) {
+        this.quantity = quantity;
+    }
+
+    public float getTotalPrice() {
+        return this.quantity * this.unitPrice;
+    }
+
+    public void setUnitPrice(float unitPrice) {
+        this.unitPrice = unitPrice;
+    }
+
+    public float getUnitWeight() {
+        return unitWeight;
+    }
+
+    public float getUnitPrice() {
+        return unitPrice;
+    }
+
+    public void setUnitWeight(float unitWeight) {
+        this.unitWeight = unitWeight;
+    }
+}

ddd-modules/ordercontext/src/main/java/com/baeldung/dddmodules/ordercontext/repository/CustomerOrderRepository.java

@@ -0,0 +1,7 @@
+package com.baeldung.dddmodules.ordercontext.repository;
+
+import com.baeldung.dddmodules.ordercontext.model.CustomerOrder;
+
+public interface CustomerOrderRepository {
+    void saveCustomerOrder(CustomerOrder order);
+}