Merge branch 'master' of https://github.com/eugenp/tutorials into BAEL-14776

README.md

@@ -20,17 +20,22 @@ In additional to Spring, the following technologies are in focus: `core Java`, `
 
 Building the project
 ====================
-To do the full build, do: `mvn install -Pdefault -Dgib.enabled=false`
+To do the full build, do: `mvn clean install`
 
 
 Building a single module
 ====================
-To build a specific module run the command: `mvn clean install -Dgib.enabled=false` in the module directory
+To build a specific module run the command: `mvn clean install` in the module directory
 
 
 Running a Spring Boot module
 ====================
-To run a Spring Boot module run the command: `mvn spring-boot:run -Dgib.enabled=false` in the module directory
+To run a Spring Boot module run the command: `mvn spring-boot:run` in the module directory
+
+#Running Tests
+
+The command `mvn clean install` will run the unit tests in a module.
+To run the integration tests, use the command `mvn clean install -Pintegration-lite-first`
 
 
 

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/graphcycledetection/domain/Graph.java

@@ -0,0 +1,51 @@
+package com.baeldung.algorithms.graphcycledetection.domain;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Graph {
+
+    private List<Vertex> vertices;
+
+    public Graph() {
+        this.vertices = new ArrayList<>();
+    }
+
+    public Graph(List<Vertex> vertices) {
+        this.vertices = vertices;
+    }
+
+    public void addVertex(Vertex vertex) {
+        this.vertices.add(vertex);
+    }
+
+    public void addEdge(Vertex from, Vertex to) {
+        from.addNeighbour(to);
+    }
+
+    public boolean hasCycle() {
+        for (Vertex vertex : vertices) {
+            if (!vertex.isVisited() && hasCycle(vertex)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public boolean hasCycle(Vertex sourceVertex) {
+        sourceVertex.setBeingVisited(true);
+
+        for (Vertex neighbour : sourceVertex.getAdjacencyList()) {
+            if (neighbour.isBeingVisited()) {
+                // backward edge exists
+                return true;
+            } else if (!neighbour.isVisited() && hasCycle(neighbour)) {
+                return true;
+            }
+        }
+
+        sourceVertex.setBeingVisited(false);
+        sourceVertex.setVisited(true);
+        return false;
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/graphcycledetection/domain/Vertex.java

@@ -0,0 +1,56 @@
+package com.baeldung.algorithms.graphcycledetection.domain;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Vertex {
+
+    private String label;
+
+    private boolean visited;
+
+    private boolean beingVisited;
+
+    private List<Vertex> adjacencyList;
+
+    public Vertex(String label) {
+        this.label = label;
+        this.adjacencyList = new ArrayList<>();
+    }
+
+    public String getLabel() {
+        return label;
+    }
+
+    public void setLabel(String label) {
+        this.label = label;
+    }
+
+    public boolean isVisited() {
+        return visited;
+    }
+
+    public void setVisited(boolean visited) {
+        this.visited = visited;
+    }
+
+    public boolean isBeingVisited() {
+        return beingVisited;
+    }
+
+    public void setBeingVisited(boolean beingVisited) {
+        this.beingVisited = beingVisited;
+    }
+
+    public List<Vertex> getAdjacencyList() {
+        return adjacencyList;
+    }
+
+    public void setAdjacencyList(List<Vertex> adjacencyList) {
+        this.adjacencyList = adjacencyList;
+    }
+
+    public void addNeighbour(Vertex adjacent) {
+        this.adjacencyList.add(adjacent);
+    }
+}

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/graphcycledetection/GraphCycleDetectionUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.algorithms.graphcycledetection;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+import com.baeldung.algorithms.graphcycledetection.domain.Graph;
+import com.baeldung.algorithms.graphcycledetection.domain.Vertex;
+
+public class GraphCycleDetectionUnitTest {
+
+    @Test
+    public void givenGraph_whenCycleExists_thenReturnTrue() {
+
+        Vertex vertexA = new Vertex("A");
+        Vertex vertexB = new Vertex("B");
+        Vertex vertexC = new Vertex("C");
+        Vertex vertexD = new Vertex("D");
+
+        Graph graph = new Graph();
+        graph.addVertex(vertexA);
+        graph.addVertex(vertexB);
+        graph.addVertex(vertexC);
+        graph.addVertex(vertexD);
+
+        graph.addEdge(vertexA, vertexB);
+        graph.addEdge(vertexB, vertexC);
+        graph.addEdge(vertexC, vertexA);
+        graph.addEdge(vertexD, vertexC);
+
+        assertTrue(graph.hasCycle());
+    }
+
+    @Test
+    public void givenGraph_whenNoCycleExists_thenReturnFalse() {
+
+        Vertex vertexA = new Vertex("A");
+        Vertex vertexB = new Vertex("B");
+        Vertex vertexC = new Vertex("C");
+        Vertex vertexD = new Vertex("D");
+
+        Graph graph = new Graph();
+        graph.addVertex(vertexA);
+        graph.addVertex(vertexB);
+        graph.addVertex(vertexC);
+        graph.addVertex(vertexD);
+
+        graph.addEdge(vertexA, vertexB);
+        graph.addEdge(vertexB, vertexC);
+        graph.addEdge(vertexA, vertexC);
+        graph.addEdge(vertexD, vertexC);
+
+        assertFalse(graph.hasCycle());
+    }
+}

apache-geode/src/test/java/com/baeldung/geode/GeodeSamplesLiveTest.java

@@ -21,7 +21,7 @@ import java.util.stream.Stream;
 
 import static org.junit.Assert.assertEquals;
 
-public class GeodeSamplesIntegrationTest {
+public class GeodeSamplesLiveTest {
 
     ClientCache cache = null;
     Region<String, String> region = null;

apache-olingo/README.md

@@ -0,0 +1,3 @@
+## Relevant articles:
+
+- [OData Protocol Guide](https://www.baeldung.com/odata)

core-groovy-2/README.md

@@ -3,5 +3,6 @@
 ## Relevant articles:
 
 - [String Matching in Groovy](http://www.baeldung.com/)
+- [Template Engines in Groovy](https://www.baeldung.com/groovy-template-engines)
 - [Groovy def Keyword](https://www.baeldung.com/groovy-def-keyword)
-- [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)
+- [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)

core-groovy-2/gmavenplus-pom.xml

@@ -0,0 +1,178 @@
+<?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-groovy-2</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <name>core-groovy-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>${logback.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-all</artifactId>
+            <version>${groovy.version}</version>
+            <type>pom</type>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hsqldb</groupId>
+            <artifactId>hsqldb</artifactId>
+            <version>${hsqldb.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.spockframework</groupId>
+            <artifactId>spock-core</artifactId>
+            <version>${spock-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <scriptSourceDirectory>src/main/groovy</scriptSourceDirectory>
+        <sourceDirectory>src/main/java</sourceDirectory>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.gmavenplus</groupId>
+                <artifactId>gmavenplus-plugin</artifactId>
+                <version>1.7.0</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>execute</goal>
+                            <goal>addSources</goal>
+                            <goal>addTestSources</goal>
+                            <goal>generateStubs</goal>
+                            <goal>compile</goal>
+                            <goal>generateTestStubs</goal>
+                            <goal>compileTests</goal>
+                            <goal>removeStubs</goal>
+                            <goal>removeTestStubs</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.codehaus.groovy</groupId>
+                        <artifactId>groovy-all</artifactId>
+                        <!-- any version of Groovy \>= 1.5.0 should work here -->
+                        <version>${groovy.version}</version>
+                        <scope>runtime</scope>
+                        <type>pom</type>
+                    </dependency>
+                </dependencies>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+            </plugin>
+            <plugin>
+                <artifactId>maven-failsafe-plugin</artifactId>
+                <version>${maven-failsafe-plugin.version}</version>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.junit.platform</groupId>
+                        <artifactId>junit-platform-surefire-provider</artifactId>
+                        <version>${junit.platform.version}</version>
+                    </dependency>
+                </dependencies>
+                <executions>
+                    <execution>
+                        <id>junit5</id>
+                        <goals>
+                            <goal>integration-test</goal>
+                            <goal>verify</goal>
+                        </goals>
+                        <configuration>
+                            <includes>
+                                <include>**/*Test5.java</include>
+                            </includes>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.20.1</version>
+                <configuration>
+                <useFile>false</useFile>
+                <includes>
+                    <include>**/*Test.java</include>
+                    <include>**/*Spec.java</include>
+                </includes>
+                </configuration>
+            </plugin>
+            <!-- Maven Assembly Plugin: needed to run the jar through command line -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>3.1.0</version>
+                <configuration>
+                    <!-- get all project dependencies -->
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <!-- MainClass in mainfest make a executable jar -->
+                    <archive>
+                        <manifest>
+                            <mainClass>com.baeldung.MyJointCompilationApp</mainClass>
+                        </manifest>
+                    </archive>
+
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id>
+                        <!-- bind to the packaging phase -->
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <repositories>
+        <repository>
+            <id>central</id>
+            <url>http://jcenter.bintray.com</url>
+        </repository>
+    </repositories>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <junit.platform.version>1.0.0</junit.platform.version>
+        <hsqldb.version>2.4.0</hsqldb.version>
+        <spock-core.version>1.1-groovy-2.4</spock-core.version>
+        <commons-lang3.version>3.9</commons-lang3.version>
+        <java.version>1.8</java.version>
+        <logback.version>1.2.3</logback.version>
+        <groovy.version>2.5.7</groovy.version>
+        <gmavenplus-plugin.version>1.6</gmavenplus-plugin.version>
+    </properties>
+</project>
+

core-groovy-2/pom.xml

@@ -1,6 +1,6 @@
 <?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">
+         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-groovy-2</artifactId>
     <version>1.0-SNAPSHOT</version>
@@ -15,25 +15,20 @@
 
     <dependencies>
         <dependency>
-            <groupId>org.codehaus.groovy</groupId>
-            <artifactId>groovy</artifactId>
-            <version>${groovy.version}</version>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>${logback.version}</version>
         </dependency>
         <dependency>
             <groupId>org.codehaus.groovy</groupId>
             <artifactId>groovy-all</artifactId>
-            <version>${groovy-all.version}</version>
-            <type>pom</type>
-        </dependency>
-        <dependency>
-            <groupId>org.codehaus.groovy</groupId>
-            <artifactId>groovy-dateutil</artifactId>
             <version>${groovy.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>org.codehaus.groovy</groupId>
-            <artifactId>groovy-sql</artifactId>
-            <version>${groovy-sql.version}</version>
+            <type>pom</type>
         </dependency>
         <dependency>
             <groupId>org.junit.platform</groupId>
@@ -56,21 +51,35 @@
     </dependencies>
 
     <build>
+        <scriptSourceDirectory>src/main/groovy</scriptSourceDirectory>
+        <sourceDirectory>src/main/java</sourceDirectory>
         <plugins>
             <plugin>
-                <groupId>org.codehaus.gmavenplus</groupId>
-                <artifactId>gmavenplus-plugin</artifactId>
-                <version>${gmavenplus-plugin.version}</version>
-                <executions>
-                    <execution>
-                        <goals>
-                            <goal>addSources</goal>
-                            <goal>addTestSources</goal>
-                            <goal>compile</goal>
-                            <goal>compileTests</goal>
-                        </goals>
-                    </execution>
-                </executions>
+                <groupId>org.codehaus.groovy</groupId>
+                <artifactId>groovy-eclipse-compiler</artifactId>
+                <version>3.3.0-01</version>
+                <extensions>true</extensions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.0</version>
+                <configuration>
+                    <compilerId>groovy-eclipse-compiler</compilerId>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
+                </configuration>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.codehaus.groovy</groupId>
+                        <artifactId>groovy-eclipse-compiler</artifactId>
+                        <version>3.3.0-01</version>
+                    </dependency>
+                    <dependency>
+                        <groupId>org.codehaus.groovy</groupId>
+                        <artifactId>groovy-eclipse-batch</artifactId>
+                        <version>${groovy.version}-01</version>
+                    </dependency>
+                </dependencies>
             </plugin>
             <plugin>
                 <artifactId>maven-failsafe-plugin</artifactId>
@@ -101,13 +110,42 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>2.20.1</version>
                 <configuration>
-                <useFile>false</useFile>
-                <includes>
-                    <include>**/*Test.java</include>
-                    <include>**/*Spec.java</include>
-                </includes>
+                    <useFile>false</useFile>
+                    <includes>
+                        <include>**/*Test.java</include>
+                        <include>**/*Spec.java</include>
+                    </includes>
                 </configuration>
             </plugin>
+            <!-- Maven Assembly Plugin: needed to run the jar through command line -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>3.1.0</version>
+                <configuration>
+                    <!-- get all project dependencies -->
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <!-- MainClass in mainfest make a executable jar -->
+                    <archive>
+                        <manifest>
+                            <mainClass>com.baeldung.MyJointCompilationApp</mainClass>
+                        </manifest>
+                    </archive>
+
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id>
+                        <!-- bind to the packaging phase -->
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
 
@@ -118,14 +156,32 @@
         </repository>
     </repositories>
 
+    <pluginRepositories>
+                <pluginRepository>
+                    <id>bintray</id>
+                    <name>Groovy Bintray</name>
+                    <url>https://dl.bintray.com/groovy/maven</url>
+                    <releases>
+                        <!-- avoid automatic updates -->
+                        <updatePolicy>never</updatePolicy>
+                    </releases>
+                    <snapshots>
+                        <enabled>false</enabled>
+                    </snapshots>
+                </pluginRepository>
+            </pluginRepositories>
+
+
     <properties>
         <junit.platform.version>1.0.0</junit.platform.version>
-        <groovy.version>2.5.6</groovy.version>
-        <groovy-all.version>2.5.6</groovy-all.version>
-        <groovy-sql.version>2.5.6</groovy-sql.version>
         <hsqldb.version>2.4.0</hsqldb.version>
         <spock-core.version>1.1-groovy-2.4</spock-core.version>
-        <gmavenplus-plugin.version>1.6</gmavenplus-plugin.version>
+        <commons-lang3.version>3.9</commons-lang3.version>
+        <java.version>1.8</java.version>
+        <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+        <logback.version>1.2.3</logback.version>
+        <groovy.version>2.5.7</groovy.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
 </project>
 

core-groovy-2/src/main/groovy/com/baeldung/CalcMath.groovy

@@ -0,0 +1,25 @@
+package com.baeldung
+
+import org.slf4j.LoggerFactory
+
+class CalcMath {
+    def log = LoggerFactory.getLogger(this.getClass())
+
+    def calcSum(x, y) {
+        log.info "Executing $x + $y"
+        x + y
+    }
+
+    /**
+     * example of method that in java would throw error at compile time
+     * @param x
+     * @param y
+     * @return
+     */
+    def calcSum2(x, y) {
+        log.info "Executing $x + $y"
+        // DANGER! This won't throw a compilation issue and fail only at runtime!!!
+        calcSum3()
+        log.info("Logging an undefined variable: $z")
+    }
+}

core-groovy-2/src/main/groovy/com/baeldung/CalcScript.groovy

@@ -0,0 +1,16 @@
+package com.baeldung
+
+def calcSum(x, y) {
+    x + y
+}
+
+def calcSum2(x, y) {
+    // DANGER! The variable "log" may be undefined
+    log.info "Executing $x + $y"
+    // DANGER! This method doesn't exist!
+    calcSum3()
+    // DANGER! The logged variable "z" is undefined!
+    log.info("Logging an undefined variable: $z")
+}
+
+calcSum(1,5)

core-groovy-2/src/main/java/com/baeldung/MyJointCompilationApp.java

@@ -0,0 +1,120 @@
+package com.baeldung;
+
+import groovy.lang.*;
+import groovy.util.GroovyScriptEngine;
+import groovy.util.ResourceException;
+import groovy.util.ScriptException;
+import org.codehaus.groovy.jsr223.GroovyScriptEngineFactory;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import javax.script.ScriptEngine;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.net.URL;
+
+/**
+ * Hello world!
+ *
+ */
+public class MyJointCompilationApp {
+    private final static Logger LOG = LoggerFactory.getLogger(MyJointCompilationApp.class);
+    private final GroovyClassLoader loader;
+    private final GroovyShell shell;
+    private final GroovyScriptEngine engine;
+    private final ScriptEngine engineFromFactory;
+
+    public MyJointCompilationApp() {
+        loader = new GroovyClassLoader(this.getClass().getClassLoader());
+        shell = new GroovyShell(loader, new Binding());
+
+        URL url = null;
+        try {
+            url = new File("src/main/groovy/com/baeldung/").toURI().toURL();
+        } catch (MalformedURLException e) {
+            LOG.error("Exception while creating url", e);
+        }
+        engine = new GroovyScriptEngine(new URL[] {url}, this.getClass().getClassLoader());
+        engineFromFactory = new GroovyScriptEngineFactory().getScriptEngine();
+    }
+
+    private void addWithCompiledClasses(int x, int y) {
+        LOG.info("Executing {} + {}", x, y);
+        Object result1 = new CalcScript().calcSum(x, y);
+        LOG.info("Result of CalcScript.calcSum() method is {}", result1);
+
+        Object result2 = new CalcMath().calcSum(x, y);
+        LOG.info("Result of CalcMath.calcSum() method is {}", result2);
+    }
+
+    private void addWithGroovyShell(int x, int y) throws IOException {
+        Script script = shell.parse(new File("src/main/groovy/com/baeldung/", "CalcScript.groovy"));
+        LOG.info("Executing {} + {}", x, y);
+        Object result = script.invokeMethod("calcSum", new Object[] { x, y });
+        LOG.info("Result of CalcScript.calcSum() method is {}", result);
+    }
+
+    private void addWithGroovyShellRun() throws IOException {
+        Script script = shell.parse(new File("src/main/groovy/com/baeldung/", "CalcScript.groovy"));
+        LOG.info("Executing script run method");
+        Object result = script.run();
+        LOG.info("Result of CalcScript.run() method is {}", result);
+    }
+
+    private void addWithGroovyClassLoader(int x, int y) throws IllegalAccessException, InstantiationException, IOException {
+        Class calcClass = loader.parseClass(
+          new File("src/main/groovy/com/baeldung/", "CalcMath.groovy"));
+        GroovyObject calc = (GroovyObject) calcClass.newInstance();
+        Object result = calc.invokeMethod("calcSum", new Object[] { x + 14, y + 14 });
+        LOG.info("Result of CalcMath.calcSum() method is {}", result);
+    }
+
+    private void addWithGroovyScriptEngine(int x, int y) throws IllegalAccessException,
+      InstantiationException, ResourceException, ScriptException {
+        Class<GroovyObject> calcClass = engine.loadScriptByName("CalcMath.groovy");
+        GroovyObject calc = calcClass.newInstance();
+        //WARNING the following will throw a ClassCastException
+        //((CalcMath)calc).calcSum(1,2);
+        Object result = calc.invokeMethod("calcSum", new Object[] { x, y });
+        LOG.info("Result of CalcMath.calcSum() method is {}", result);
+    }
+
+    private void addWithEngineFactory(int x, int y) throws IllegalAccessException,
+      InstantiationException, javax.script.ScriptException, FileNotFoundException {
+        Class calcClass = (Class) engineFromFactory.eval(
+          new FileReader(new File("src/main/groovy/com/baeldung/", "CalcMath.groovy")));
+        GroovyObject calc = (GroovyObject) calcClass.newInstance();
+        Object result = calc.invokeMethod("calcSum", new Object[] { x, y });
+        LOG.info("Result of CalcMath.calcSum() method is {}", result);
+    }
+
+    private void addWithStaticCompiledClasses() {
+        LOG.info("Running the Groovy classes compiled statically...");
+        addWithCompiledClasses(5, 10);
+
+    }
+
+    private void addWithDynamicCompiledClasses() throws IOException, IllegalAccessException, InstantiationException,
+      ResourceException, ScriptException, javax.script.ScriptException {
+        LOG.info("Invocation of a dynamic groovy script...");
+        addWithGroovyShell(5, 10);
+        LOG.info("Invocation of the run method of a dynamic groovy script...");
+        addWithGroovyShellRun();
+        LOG.info("Invocation of a dynamic groovy class loaded with GroovyClassLoader...");
+        addWithGroovyClassLoader(10, 30);
+        LOG.info("Invocation of a dynamic groovy class loaded with GroovyScriptEngine...");
+        addWithGroovyScriptEngine(15, 0);
+        LOG.info("Invocation of a dynamic groovy class loaded with GroovyScriptEngine JSR223...");
+        addWithEngineFactory(5, 6);
+    }
+
+    public static void main(String[] args) throws InstantiationException, IllegalAccessException,
+      ResourceException, ScriptException, IOException, javax.script.ScriptException {
+        MyJointCompilationApp myJointCompilationApp = new MyJointCompilationApp();
+        LOG.info("Example of addition operation via Groovy scripts integration with Java.");
+        myJointCompilationApp.addWithStaticCompiledClasses();
+        myJointCompilationApp.addWithDynamicCompiledClasses();
+    }
+}

core-groovy-2/src/test/groovy/com/baeldung/xml/MarkupBuilderUnitTest.groovy

@@ -0,0 +1,40 @@
+package com.baeldung.xml
+
+import groovy.xml.MarkupBuilder
+import groovy.xml.XmlUtil
+import spock.lang.Specification
+
+class MarkupBuilderUnitTest extends Specification {
+
+    def xmlFile = getClass().getResource("articles_short_formatted.xml")
+
+def "Should create XML properly"() {
+    given: "Node structures"
+
+    when: "Using MarkupBuilderUnitTest to create com.baeldung.xml structure"
+    def writer = new StringWriter()
+    new MarkupBuilder(writer).articles {
+        article {
+            title('First steps in Java')
+            author(id: '1') {
+                firstname('Siena')
+                lastname('Kerr')
+            }
+            'release-date'('2018-12-01')
+        }
+        article {
+            title('Dockerize your SpringBoot application')
+            author(id: '2') {
+                firstname('Jonas')
+                lastname('Lugo')
+            }
+            'release-date'('2018-12-01')
+        }
+    }
+
+    then: "Xml is created properly"
+    XmlUtil.serialize(writer.toString()) == XmlUtil.serialize(xmlFile.text)
+}
+
+
+}

core-groovy-2/src/test/groovy/com/baeldung/xml/XmlParserUnitTest.groovy

@@ -0,0 +1,94 @@
+package com.baeldung.xml
+
+
+import spock.lang.Shared
+import spock.lang.Specification
+
+class XmlParserUnitTest extends Specification {
+
+    def xmlFile = getClass().getResourceAsStream("articles.xml")
+
+    @Shared
+    def parser = new XmlParser()
+
+    def "Should read XML file properly"() {
+        given: "XML file"
+
+        when: "Using XmlParser to read file"
+        def articles = parser.parse(xmlFile)
+
+        then: "Xml is loaded properly"
+        articles.'*'.size() == 4
+        articles.article[0].author.firstname.text() == "Siena"
+        articles.article[2].'release-date'.text() == "2018-06-12"
+        articles.article[3].title.text() == "Java 12 insights"
+        articles.article.find { it.author.'@id'.text() == "3" }.author.firstname.text() == "Daniele"
+    }
+
+
+    def "Should add node to existing com.baeldung.xml using NodeBuilder"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Adding node to com.baeldung.xml"
+        def articleNode = new NodeBuilder().article(id: '5') {
+            title('Traversing XML in the nutshell')
+            author {
+                firstname('Martin')
+                lastname('Schmidt')
+            }
+            'release-date'('2019-05-18')
+        }
+        articles.append(articleNode)
+
+        then: "Node is added to com.baeldung.xml properly"
+        articles.'*'.size() == 5
+        articles.article[4].title.text() == "Traversing XML in the nutshell"
+    }
+
+    def "Should replace node"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Adding node to com.baeldung.xml"
+        def articleNode = new NodeBuilder().article(id: '5') {
+            title('Traversing XML in the nutshell')
+            author {
+                firstname('Martin')
+                lastname('Schmidt')
+            }
+            'release-date'('2019-05-18')
+        }
+        articles.article[0].replaceNode(articleNode)
+
+        then: "Node is added to com.baeldung.xml properly"
+        articles.'*'.size() == 4
+        articles.article[0].title.text() == "Traversing XML in the nutshell"
+    }
+
+    def "Should modify node"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Changing value of one of the nodes"
+        articles.article.each { it.'release-date'[0].value = "2019-05-18" }
+
+        then: "XML is updated"
+        articles.article.findAll { it.'release-date'.text() != "2019-05-18" }.isEmpty()
+    }
+
+    def "Should remove article from com.baeldung.xml"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Removing all articles but with id==3"
+        articles.article
+          .findAll { it.author.'@id'.text() != "3" }
+          .each { articles.remove(it) }
+
+        then: "There is only one article left"
+        articles.children().size() == 1
+        articles.article[0].author.'@id'.text() == "3"
+    }
+
+}

core-groovy-2/src/test/groovy/com/baeldung/xml/XmlSlurperUnitTest.groovy

@@ -0,0 +1,102 @@
+package com.baeldung.xml
+
+
+import groovy.xml.XmlUtil
+import spock.lang.Shared
+import spock.lang.Specification
+
+class XmlSlurperUnitTest extends Specification {
+
+    def xmlFile = getClass().getResourceAsStream("articles.xml")
+
+    @Shared
+    def parser = new XmlSlurper()
+
+    def "Should read XML file properly"() {
+        given: "XML file"
+
+        when: "Using XmlSlurper to read file"
+        def articles = parser.parse(xmlFile)
+
+        then: "Xml is loaded properly"
+        articles.'*'.size() == 4
+        articles.article[0].author.firstname == "Siena"
+        articles.article[2].'release-date' == "2018-06-12"
+        articles.article[3].title == "Java 12 insights"
+        articles.article.find { it.author.'@id' == "3" }.author.firstname == "Daniele"
+    }
+
+    def "Should add node to existing com.baeldung.xml"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Adding node to com.baeldung.xml"
+        articles.appendNode {
+            article(id: '5') {
+                title('Traversing XML in the nutshell')
+                author {
+                    firstname('Martin')
+                    lastname('Schmidt')
+                }
+                'release-date'('2019-05-18')
+            }
+        }
+
+        articles = parser.parseText(XmlUtil.serialize(articles))
+
+        then: "Node is added to com.baeldung.xml properly"
+        articles.'*'.size() == 5
+        articles.article[4].title == "Traversing XML in the nutshell"
+    }
+
+    def "Should modify node"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Changing value of one of the nodes"
+        articles.article.each { it.'release-date' = "2019-05-18" }
+
+        then: "XML is updated"
+        articles.article.findAll { it.'release-date' != "2019-05-18" }.isEmpty()
+    }
+
+    def "Should replace node"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Replacing node"
+        articles.article[0].replaceNode {
+            article(id: '5') {
+                title('Traversing XML in the nutshell')
+                author {
+                    firstname('Martin')
+                    lastname('Schmidt')
+                }
+                'release-date'('2019-05-18')
+            }
+        }
+
+        articles = parser.parseText(XmlUtil.serialize(articles))
+
+        then: "Node is replaced properly"
+        articles.'*'.size() == 4
+        articles.article[0].title == "Traversing XML in the nutshell"
+    }
+
+    def "Should remove article from com.baeldung.xml"() {
+        given: "XML object"
+        def articles = parser.parse(xmlFile)
+
+        when: "Removing all articles but with id==3"
+        articles.article
+          .findAll { it.author.'@id' != "3" }
+          .replaceNode {}
+
+        articles = parser.parseText(XmlUtil.serialize(articles))
+
+        then: "There is only one article left"
+        articles.children().size() == 1
+        articles.article[0].author.'@id' == "3"
+    }
+
+}

core-groovy-2/src/test/resources/com/baeldung/xml/articles.xml

@@ -0,0 +1,34 @@
+<articles>
+    <article>
+        <title>First steps in Java</title>
+        <author id='1'>
+            <firstname>Siena</firstname>
+            <lastname>Kerr</lastname>
+        </author>
+        <release-date>2018-12-01</release-date>
+    </article>
+    <article>
+        <title>Dockerize your SpringBoot application</title>
+        <author id='2'>
+            <firstname>Jonas</firstname>
+            <lastname>Lugo</lastname>
+        </author>
+        <release-date>2018-12-01</release-date>
+    </article>
+    <article>
+        <title>SpringBoot tutorial</title>
+        <author id='3'>
+            <firstname>Daniele</firstname>
+            <lastname>Ferguson</lastname>
+        </author>
+        <release-date>2018-06-12</release-date>
+    </article>
+    <article>
+        <title>Java 12 insights</title>
+        <author id='1'>
+            <firstname>Siena</firstname>
+            <lastname>Kerr</lastname>
+        </author>
+        <release-date>2018-07-22</release-date>
+    </article>
+</articles>

core-groovy-2/src/test/resources/com/baeldung/xml/articles_short_formatted.xml

@@ -0,0 +1,18 @@
+<articles>
+  <article>
+    <title>First steps in Java</title>
+    <author id='1'>
+      <firstname>Siena</firstname>
+      <lastname>Kerr</lastname>
+    </author>
+    <release-date>2018-12-01</release-date>
+  </article>
+  <article>
+    <title>Dockerize your SpringBoot application</title>
+    <author id='2'>
+      <firstname>Jonas</firstname>
+      <lastname>Lugo</lastname>
+    </author>
+    <release-date>2018-12-01</release-date>
+  </article>
+</articles>

core-java-lang/src/main/java/com/baeldung/error/ErrorGenerator.java

@@ -1,15 +0,0 @@
-package com.baeldung.error;
-
-public class ErrorGenerator {
-    public void throwException() throws Exception {
-        throw new Exception("checked");
-    }
-
-    public void throwRuntimeException() {
-        throw new RuntimeException("unchecked");
-    }
-
-    public void throwError() {
-        throw new Error("unchecked");
-    }
-}

core-java-lang/src/test/java/com/baeldung/error/ErrorGeneratorUnitTest.java

@@ -1,51 +0,0 @@
-package com.baeldung.error;
-
-import org.junit.Assert;
-import org.junit.Before;
-import org.junit.Test;
-
-public class ErrorGeneratorUnitTest {
-
-    private ErrorGenerator errorGenerator;
-
-    @Before
-    public void setUp() {
-        errorGenerator = new ErrorGenerator();
-    }
-
-    @Test
-    public void whenCheckedException_thenIsCaughtByCatchException() {
-        try {
-            errorGenerator.throwException();
-        } catch (Exception e) {
-            // caught! -> test pass
-        }
-    }
-
-    @Test
-    public void whenUncheckedException_thenIsCaughtByCatchException() {
-        try {
-            errorGenerator.throwRuntimeException();
-        } catch (Exception e) {
-            // caught! -> test pass
-        }
-    }
-
-    @Test(expected = Error.class)
-    public void whenError_thenIsNotCaughtByCatchException() {
-        try {
-            errorGenerator.throwError();
-        } catch (Exception e) {
-            Assert.fail(); // errors are not caught by catch exception
-        }
-    }
-
-    @Test
-    public void whenError_thenIsCaughtByCatchError() {
-        try {
-            errorGenerator.throwError();
-        } catch (Error e) {
-            // caught! -> test pass
-        }
-    }
-}

core-java-modules/README.md

@@ -1,3 +1,5 @@
 ## Relevant articles:
 
 - [Multi-Module Maven Application with Java Modules](https://www.baeldung.com/maven-multi-module-project-java-jpms)
+- [Guide to Java FileChannel](https://www.baeldung.com/java-filechannel)
+- [Understanding the NumberFormatException in Java](https://www.baeldung.com/java-number-format-exception)

core-java-modules/core-java-10/src/main/java/com/baeldung/set/CopySets.java

@@ -0,0 +1,13 @@
+package com.baeldung.set;
+
+import java.util.Set;
+
+public class CopySets {
+
+    // Using Java 10
+    public static <T> Set<T> copyBySetCopyOf(Set<T> original) {
+        Set<T> copy = Set.copyOf(original);
+        return copy;
+    }
+
+}

core-java-modules/core-java-11/README.md

@@ -7,4 +7,5 @@
 - [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
 - [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
 - [Guide to jlink](https://www.baeldung.com/jlink)
+- [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)
 - [Transforming an Empty String into an Empty Optional](https://www.baeldung.com/java-empty-string-to-empty-optional)

core-java-modules/core-java-8-2/README.md

@@ -3,5 +3,6 @@
 ## Core Java 8 Cookbooks and Examples (part 2)
 
 ### Relevant Articles: 
-- [Anonymous Classes in Java](https://www.baeldung.com/java-anonymous-classes)
+- [Anonymous Classes in Java](http://www.baeldung.com/)
+- [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)
 - [Run JAR Application With Command Line Arguments](https://www.baeldung.com/java-run-jar-with-arguments)

core-java-modules/core-java-8-2/pom.xml

@@ -30,7 +30,6 @@
             <artifactId>icu4j</artifactId>
             <version>${icu.version}</version>
         </dependency>
-
     </dependencies>
 
     <build>

core-java-modules/core-java-8-2/src/main/resources/META-INF/persistence.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<persistence xmlns="http://java.sun.com/xml/ns/persistence"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
+	version="2.0">
+
+	<persistence-unit
+		name="com.baeldung.optionalReturnType"
+		transaction-type="RESOURCE_LOCAL">
+		<description>Persist Optional Return Type Demo</description>
+		<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+		<class>com.baeldung.optionalReturnType.User</class>
+		<class>com.baeldung.optionalReturnType.UserOptional</class>
+		<!-- 
+		<class>com.baeldung.optionalReturnType.UserOptionalField</class>
+		-->
+		<exclude-unlisted-classes>true</exclude-unlisted-classes>
+
+		<properties>
+			<property name="javax.persistence.jdbc.driver"
+				value="org.h2.Driver" />
+			<property name="javax.persistence.jdbc.url"
+				value="jdbc:h2:mem:test" />
+			<property name="javax.persistence.jdbc.user" value="sa" />
+			<property name="javax.persistence.jdbc.password" value="" />
+			<property name="hibernate.dialect"
+				value="org.hibernate.dialect.H2Dialect" />
+			<property name="hibernate.hbm2ddl.auto" value="create-drop" />
+			<property name="show_sql" value="true" />
+			<property name="hibernate.temp.use_jdbc_metadata_defaults"
+				value="false" />
+		</properties>
+	</persistence-unit>
+</persistence>

core-java-modules/core-java-9/README.md

@@ -28,6 +28,6 @@
 - [Java 9 Convenience Factory Methods for Collections](https://www.baeldung.com/java-9-collections-factory-methods)
 - [Java 9 Stream API Improvements](https://www.baeldung.com/java-9-stream-api)
 - [A Guide to Java 9 Modularity](https://www.baeldung.com/java-9-modularity)
-- [Java 9 Platform Module API](https://www.baeldung.com/java-9-module-api)
+- [Java 9 java.lang.Module API](https://www.baeldung.com/java-9-module-api)
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Filtering a Stream of Optionals in Java](https://www.baeldung.com/java-filter-stream-of-optional)

core-java-modules/core-java-9/src/modules/com.baeldung.logging.slf4j/com/baeldung/logging/slf4j/Slf4jLogger.java

@@ -75,7 +75,7 @@ public class Slf4jLogger implements System.Logger {
         if (!isLoggable(level)) {
             return;
         }
-        String message = MessageFormat.format (format, params);
+        String message = MessageFormat.format(format, params);
 
         switch (level) {
         case TRACE:

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

@@ -15,3 +15,4 @@
 - [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
 - [Sorting Arrays in Java](https://www.baeldung.com/java-sorting-arrays)
 - [Convert a Float to a Byte Array in Java](https://www.baeldung.com/java-convert-float-to-byte-array)
+- [Converting Between Stream and Array in Java](https://www.baeldung.com/java-stream-to-array)

core-java-modules/core-java-collections-set/pom.xml

@@ -24,10 +24,20 @@
         <artifactId>commons-collections4</artifactId>
         <version>${commons-collections4.version}</version>
     </dependency>
+    <dependency>
+        <groupId>com.google.code.gson</groupId>
+        <artifactId>gson</artifactId>
+        <version>2.8.5</version>
+    </dependency>
+    <dependency>
+        <groupId>commons-lang</groupId>
+        <artifactId>commons-lang</artifactId>
+        <version>2.6</version>
+    </dependency>
     </dependencies>
 
     <properties>
         <commons-collections4.version>4.3</commons-collections4.version>
         <guava.version>27.1-jre</guava.version>
     </properties>
-</project>
+</project>

core-java-modules/core-java-collections-set/src/main/java/com/baeldung/set/CopySets.java

@@ -0,0 +1,59 @@
+package com.baeldung.set;
+
+import java.io.Serializable;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang.SerializationUtils;
+
+import com.google.gson.Gson;
+
+public class CopySets {
+
+    // Copy Constructor
+    public static <T> Set<T> copyByConstructor(Set<T> original) {
+        Set<T> copy = new HashSet<>(original);
+        return copy;
+    }
+
+    // Set.addAll
+    public static <T> Set<T> copyBySetAddAll(Set<T> original) {
+        Set<T> copy = new HashSet<>();
+        copy.addAll(original);
+        return copy;
+    }
+
+    // Set.clone
+    public static <T> Set<T> copyBySetClone(HashSet<T> original) {
+        Set<T> copy = (Set<T>) original.clone();
+        return copy;
+    }
+
+    // JSON
+    public static <T> Set<T> copyByJson(Set<T> original) {
+        Gson gson = new Gson();
+        String jsonStr = gson.toJson(original);
+        Set<T> copy = gson.fromJson(jsonStr, Set.class);
+
+        return copy;
+    }
+
+    // Apache Commons Lang
+    public static <T extends Serializable> Set<T> copyByApacheCommonsLang(Set<T> original) {
+        Set<T> copy = new HashSet<>();
+        for (T item : original) {
+            copy.add((T) SerializationUtils.clone(item));
+        }
+        return copy;
+    }
+
+    // Collectors.toSet
+    public static <T extends Serializable> Set<T> copyByCollectorsToSet(Set<T> original) {
+        Set<T> copy = original.stream()
+            .collect(Collectors.toSet());
+
+        return copy;
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/delay/Delay.java

@@ -1,4 +1,4 @@
-package com.baeldung.delay;
+package com.baeldung.concurrent.delay;
 
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
@@ -61,6 +61,7 @@ public class Delay {
 
         executorService.schedule(Delay::someTask1, delayInSeconds, TimeUnit.SECONDS);
 
+        executorService.shutdown();
     }
 
     private static void fixedRateServiceTask(Integer delayInSeconds) {
@@ -78,6 +79,7 @@ public class Delay {
 
         sf.cancel(true);
 
+        executorService.shutdown();
     }
 
     private static void someTask1() {

core-java-modules/core-java-exceptions/src/test/java/com/baeldung/exception/error/ErrorGeneratorUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.error;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class ErrorGeneratorUnitTest {
+
+    @Test(expected = AssertionError.class)
+    public void whenError_thenIsNotCaughtByCatchException() {
+        try {
+            throw new AssertionError();
+        } catch (Exception e) {
+            Assert.fail(); // errors are not caught by catch exception
+        }
+    }
+
+    @Test
+    public void whenError_thenIsCaughtByCatchError() {
+        try {
+            throw new AssertionError();
+        } catch (Error e) {
+            // caught! -> test pass
+        }
+    }
+}

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

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

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

@@ -0,0 +1,3 @@
+## Relevant articles:
+
+- [Determine File Creating Date in Java](https://www.baeldung.com/file-creation-date-java)

core-java-modules/core-java-nio/src/main/java/com/baeldung/creationdate/CreationDateResolver.java

@@ -0,0 +1,35 @@
+package com.baeldung.creationdate;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileTime;
+import java.time.Instant;
+import java.util.Optional;
+
+public class CreationDateResolver {
+
+    public Instant resolveCreationTimeWithBasicAttributes(Path path) {
+        try {
+            final BasicFileAttributes attr = Files.readAttributes(path, BasicFileAttributes.class);
+            final FileTime fileTime = attr.creationTime();
+
+            return fileTime.toInstant();
+        } catch (IOException ex) {
+            throw new RuntimeException("An issue occured went wrong when resolving creation time", ex);
+        }
+    }
+
+    public Optional<Instant> resolveCreationTimeWithAttribute(Path path) {
+        try {
+            final FileTime creationTime = (FileTime) Files.getAttribute(path, "creationTime");
+
+            return Optional
+              .ofNullable(creationTime)
+              .map((FileTime::toInstant));
+        } catch (IOException ex) {
+            throw new RuntimeException("An issue occured went wrong when resolving creation time", ex);
+        }
+    }
+}

core-java-modules/core-java-nio/src/test/java/com/baeldung/creationdate/CreationDateResolverUnitTest.java

@@ -0,0 +1,45 @@
+package com.baeldung.creationdate;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.time.Instant;
+import java.util.Optional;
+
+import static org.junit.Assert.assertTrue;
+
+public class CreationDateResolverUnitTest {
+
+    private final CreationDateResolver creationDateResolver = new CreationDateResolver();
+
+    @Test
+    public void givenFile_whenGettingCreationDateTimeFromBasicAttributes_thenReturnDate() throws Exception {
+
+        final File file = File.createTempFile("createdFile", ".txt");
+        final Path path = file.toPath();
+
+        final Instant response = creationDateResolver.resolveCreationTimeWithBasicAttributes(path);
+
+        assertTrue(Instant
+          .now()
+          .isAfter(response));
+
+    }
+
+    @Test
+    public void givenFile_whenGettingCreationDateTimeFromAttribute_thenReturnDate() throws Exception {
+
+        final File file = File.createTempFile("createdFile", ".txt");
+        final Path path = file.toPath();
+
+        final Optional<Instant> response = creationDateResolver.resolveCreationTimeWithAttribute(path);
+
+        response.ifPresent((value) -> {
+            assertTrue(Instant
+              .now()
+              .isAfter(value));
+        });
+
+    }
+}

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

@@ -0,0 +1,5 @@
+=========
+
+## Core Java Optional
+
+### Relevant Articles: 

core-java-modules/core-java-optional/pom.xml

@@ -0,0 +1,53 @@
+<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>
+  <parent>
+    <groupId>com.baeldung.core-java-modules</groupId>
+    <artifactId>core-java-modules</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>core-java-optional</artifactId>
+  <version>0.1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        <hibernate.core.version>5.4.0.Final</hibernate.core.version>
+        <h2database.version>1.4.197</h2database.version>
+        <jackson.databind.version>2.9.8</jackson.databind.version>
+    </properties>
+  
+    <dependencies>
+        <dependency>
+            <groupId>org.hibernate</groupId>
+            <artifactId>hibernate-core</artifactId>
+            <version>${hibernate.core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>${h2database.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.databind.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+
+    </build>
+</project>

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/HandleOptionalTypeExample.java

@@ -0,0 +1,41 @@
+package com.baeldung.optionalReturnType;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+public class HandleOptionalTypeExample {
+    static Map<String, User> usersByName = new HashMap();
+    static {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("baeldung");
+        usersByName.put("baeldung", user1);
+    }
+
+    public static void main(String[] args) {
+        changeUserName("baeldung", "baeldung-new");
+        changeUserName("user", "user-new");
+    }
+
+    public static void changeUserName(String oldFirstName, String newFirstName) {
+        Optional<User> userOpt = findUserByName(oldFirstName);
+        if (userOpt.isPresent()) {
+            User user = userOpt.get();
+            user.setFirstName(newFirstName);
+
+            System.out.println("user with name " + oldFirstName + " is changed to " + user.getFirstName());
+        } else {
+            // user is missing
+            System.out.println("user with name " + oldFirstName + " is not found.");
+        }
+    }
+
+    public static Optional<User> findUserByName(String name) {
+        // look up the user in the database, the user object below could be null
+        User user = usersByName.get(name);
+        Optional<User> opt = Optional.ofNullable(user);
+
+        return opt;
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/OptionalToJsonExample.java

@@ -0,0 +1,19 @@
+package com.baeldung.optionalReturnType;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class OptionalToJsonExample {
+    public static void main(String[] args) {
+        UserOptional user = new UserOptional();
+        user.setUserId(1l);
+        user.setFirstName("Bael Dung");
+
+        ObjectMapper om = new ObjectMapper();
+        try {
+            System.out.print("user in json is:" + om.writeValueAsString(user));
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample.java

@@ -0,0 +1,26 @@
+package com.baeldung.optionalReturnType;
+
+import java.util.Optional;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistOptionalTypeExample {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager entityManager = emf.createEntityManager();
+
+    // to run this app, uncomment the follow line in META-INF/persistence.xml
+    // <class>com.baeldung.optionalReturnType.UserOptionalField</class>
+    public static void main(String[] args) {
+        UserOptionalField user1 = new UserOptionalField();
+        user1.setUserId(1l);
+        user1.setFirstName(Optional.of("Bael Dung"));
+        entityManager.persist(user1);
+
+        UserOptional user2 = entityManager.find(UserOptional.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/PersistOptionalTypeExample2.java

@@ -0,0 +1,22 @@
+package com.baeldung.optionalReturnType;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistOptionalTypeExample2 {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager em = emf.createEntityManager();
+
+    public static void main(String[] args) {
+        UserOptional user1 = new UserOptional();
+        user1.setUserId(1l);
+        user1.setFirstName("Bael Dung");
+        em.persist(user1);
+
+        UserOptional user2 = em.find(UserOptional.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/PersistUserExample.java

@@ -0,0 +1,22 @@
+package com.baeldung.optionalReturnType;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+
+public class PersistUserExample {
+    static String persistenceUnit = "com.baeldung.optionalReturnType";
+    static EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
+
+    static EntityManager em = emf.createEntityManager();
+
+    public static void main(String[] args) {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("Bael Dung");
+        em.persist(user1);
+
+        User user2 = em.find(User.class, 1l);
+        System.out.print("User2.firstName:" + user2.getFirstName());
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/SerializeOptionalTypeExample.java

@@ -0,0 +1,41 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+import java.util.Optional;
+
+public class SerializeOptionalTypeExample {
+    public static void main(String[] args) {
+        User user1 = new User();
+        user1.setUserId(1l);
+        user1.setFirstName("baeldung");
+
+        serializeObject(user1, "user1.ser");
+
+        UserOptionalField user2 = new UserOptionalField();
+        user2.setUserId(1l);
+        user2.setFirstName(Optional.of("baeldung"));
+
+        serializeObject(user2, "user2.ser");
+
+    }
+
+    public static void serializeObject(Object object, String fileName) {
+        // Serialization
+        try {
+            FileOutputStream file = new FileOutputStream(fileName);
+            ObjectOutputStream out = new ObjectOutputStream(file);
+
+            out.writeObject(object);
+
+            out.close();
+            file.close();
+
+            System.out.println("Object " + object.toString() + " has been serialized to file " + fileName);
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/User.java

@@ -0,0 +1,31 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class User implements Serializable {
+    @Id
+    private long userId;
+
+    private String firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/UserOptional.java

@@ -0,0 +1,35 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+import javax.persistence.Column;
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class UserOptional implements Serializable {
+    @Id
+    private long userId;
+
+    @Column(nullable = true)
+    private String firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public Optional<String> getFirstName() {
+        return Optional.ofNullable(firstName);
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+        Optional.ofNullable(firstName);
+    }
+
+}

core-java-modules/core-java-optional/src/main/java/com/baeldung/optionalReturnType/UserOptionalField.java

@@ -0,0 +1,31 @@
+package com.baeldung.optionalReturnType;
+
+import java.io.Serializable;
+import java.util.Optional;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class UserOptionalField implements Serializable {
+    @Id
+    private long userId;
+
+    private Optional<String> firstName;
+
+    public long getUserId() {
+        return userId;
+    }
+
+    public void setUserId(long userId) {
+        this.userId = userId;
+    }
+
+    public Optional<String> getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(Optional<String> firstName) {
+        this.firstName = firstName;
+    }
+}

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

@@ -51,4 +51,5 @@
 - [Java Bitwise Operators](https://www.baeldung.com/java-bitwise-operators)
 - [Guide to Creating and Running a Jar File in Java](https://www.baeldung.com/java-create-jar)
 - [Making a JSON POST Request With HttpURLConnection](https://www.baeldung.com/httpurlconnection-post)
+- [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
 - [Convert Hex to ASCII in Java](https://www.baeldung.com/java-convert-hex-to-ascii)

core-java-modules/core-java/src/main/java/com/baeldung/README.md

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

core-java-modules/core-java/src/main/java/com/baeldung/graph/Graph.java

@@ -19,7 +19,7 @@ public class Graph {
 
     void removeVertex(String label) {
         Vertex v = new Vertex(label);
-        adjVertices.values().stream().map(e -> e.remove(v)).collect(Collectors.toList());
+        adjVertices.values().stream().forEach(e -> e.remove(v));
         adjVertices.remove(new Vertex(label));
     }
 

core-java-modules/core-java/src/test/java/com/baeldung/graph/GraphUnitTest.java

@@ -1,20 +1,31 @@
 package com.baeldung.graph;
 
-import org.junit.Assert;
+import static org.junit.Assert.assertEquals;
 import org.junit.Test;
 
-public class GraphTraversalUnitTest {
+public class GraphUnitTest {
     @Test
     public void givenAGraph_whenTraversingDepthFirst_thenExpectedResult() {
         Graph graph = createGraph();
-        Assert.assertEquals("[Bob, Rob, Maria, Alice, Mark]", 
+        assertEquals("[Bob, Rob, Maria, Alice, Mark]", 
             GraphTraversal.depthFirstTraversal(graph, "Bob").toString());
     }
     
     @Test
     public void givenAGraph_whenTraversingBreadthFirst_thenExpectedResult() {
         Graph graph = createGraph();
-        Assert.assertEquals("[Bob, Alice, Rob, Mark, Maria]", 
+       assertEquals("[Bob, Alice, Rob, Mark, Maria]", 
+            GraphTraversal.breadthFirstTraversal(graph, "Bob").toString());
+    }
+    
+    @Test
+    public void givenAGraph_whenRemoveVertex_thenVertedNotFound() {
+        Graph graph = createGraph();
+        assertEquals("[Bob, Alice, Rob, Mark, Maria]", 
+            GraphTraversal.breadthFirstTraversal(graph, "Bob").toString());
+        
+        graph.removeVertex("Maria");
+        assertEquals("[Bob, Alice, Rob, Mark]", 
             GraphTraversal.breadthFirstTraversal(graph, "Bob").toString());
     }
     

core-java-modules/pom.xml

@@ -16,6 +16,7 @@
     <modules>
         <module>pre-jpms</module>
         <module>core-java-exceptions</module>
+        <module>core-java-optional</module>
     </modules>
     
 </project>

core-kotlin-2/src/main/kotlin/com/baeldung/jvmannotations/Document.kt

@@ -9,19 +9,3 @@ interface Document {
 
     fun getType() = "document"
 }
-
-class TextDocument : Document {
-    override fun getType() = "text"
-
-    fun transformList(list : List<Number>) : List<Number> {
-        return list.filter { n -> n.toInt() > 1 }
-    }
-
-    fun transformListInverseWildcards(list : List<@JvmSuppressWildcards Number>) : List<@JvmWildcard Number> {
-        return list.filter { n -> n.toInt() > 1 }
-    }
-
-    var list : List<@JvmWildcard Any> = ArrayList()
-}
-
-class XmlDocument(d : Document) : Document by d

core-kotlin-2/src/main/kotlin/com/baeldung/jvmannotations/TextDocument.kt

@@ -0,0 +1,16 @@
+package com.baeldung.jvmannotations
+
+import java.util.*
+class TextDocument : Document {
+    override fun getType() = "text"
+
+    fun transformList(list : List<Number>) : List<Number> {
+        return list.filter { n -> n.toInt() > 1 }
+    }
+
+    fun transformListInverseWildcards(list : List<@JvmSuppressWildcards Number>) : List<@JvmWildcard Number> {
+        return list.filter { n -> n.toInt() > 1 }
+    }
+
+    var list : List<@JvmWildcard Any> = ArrayList()
+}

core-kotlin-2/src/main/kotlin/com/baeldung/jvmannotations/XmlDocument.kt

@@ -0,0 +1,5 @@
+package com.baeldung.jvmannotations
+
+import java.util.*
+
+class XmlDocument(d : Document) : Document by d

core-kotlin-2/src/test/kotlin/com/baeldung/range/DocumentTest.kt

@@ -3,6 +3,8 @@ package com.baeldung.range
 import org.junit.Test
 import kotlin.test.assertEquals
 
+import com.baeldung.jvmannotations.*;
+
 class DocumentTest {
 
     @Test

ddd/README.md

@@ -1,3 +1,5 @@
 ### Relevant articles
 
 - [Persisting DDD Aggregates](https://www.baeldung.com/spring-persisting-ddd-aggregates)
+- [Double Dispatch in DDD](https://www.baeldung.com/ddd-double-dispatch)
+- [DDD Aggregates and @DomainEvents](https://www.baeldung.com/spring-data-ddd)

docker/docker-compose.yml

@@ -0,0 +1,61 @@
+version: '3'
+
+services:
+
+## VOLUME CONTAINER-TO-CONTAINER AND HOST-TO-CONTAINER TEST ##
+
+  volumes-example-service:
+    image: alpine:latest
+    container_name: volumes-example-service
+    volumes: 
+      - /tmp:/my-volumes/host-volume
+      - /home:/my-volumes/readonly-host-volume:ro
+      - my-named-global-volume:/my-volumes/named-global-volume    
+    tty: true # Needed to keep the container running
+
+  another-volumes-example-service:
+    image: alpine:latest
+    container_name: another-volumes-example-service
+    volumes: 
+      - my-named-global-volume:/another-path/the-same-named-global-volume
+    tty: true # Needed to keep the container running
+
+## NETWORK CONTAINER-TO-CONTAINER TEST ##
+
+  network-example-service:
+    image: karthequian/helloworld:latest
+    container_name: network-example-service
+    networks:
+      - my-shared-network
+
+  another-service-in-the-same-network:
+    image: alpine:latest
+    container_name: another-service-in-the-same-network
+    networks: 
+      - my-shared-network
+
+    tty: true # Needed to keep the container running
+
+  another-service-in-its-own-network:
+    image: alpine:latest
+    container_name: another-service-in-its-own-network
+    networks: 
+      - my-private-network
+    tty: true # Needed to keep the container running
+
+## NETWORK HOST-TO-CONTAINER TEST ##
+
+  network-example-service-available-to-host-on-port-1337:
+    image: karthequian/helloworld:latest
+    container_name: network-example-service-available-to-host-on-port-1337
+    networks: 
+      - my-shared-network
+    ports:
+      - "1337:80"
+
+volumes:
+  my-named-global-volume:
+
+networks:
+  my-shared-network: {}
+  my-private-network: {}

jackson-2/pom.xml

@@ -28,6 +28,13 @@
             <artifactId>jackson-dataformat-yaml</artifactId>
             <version>2.9.8</version>
         </dependency>
+        
+        <!-- CSV -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.dataformat</groupId>
+            <artifactId>jackson-dataformat-csv</artifactId>
+            <version>2.9.8</version>
+        </dependency>        
 
         <!-- Allow use of LocalDate -->
         <dependency>

jackson-2/src/main/java/com/baeldung/jackson/csv/JsonCsvConverter.java

@@ -0,0 +1,59 @@
+package com.baeldung.jackson.csv;
+
+import java.io.File;
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.OrderLine;
+import com.baeldung.jackson.mixin.OrderLineForCsv;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.MappingIterator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.dataformat.csv.CsvMapper;
+import com.fasterxml.jackson.dataformat.csv.CsvSchema;
+import com.fasterxml.jackson.dataformat.csv.CsvSchema.Builder;
+
+public class JsonCsvConverter {
+    
+    public static void JsonToCsv(File jsonFile, File csvFile) throws IOException {
+        JsonNode jsonTree = new ObjectMapper().readTree(jsonFile);
+        
+        Builder csvSchemaBuilder = CsvSchema.builder();
+        JsonNode firstObject = jsonTree.elements().next();
+        firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
+        CsvSchema csvSchema = csvSchemaBuilder
+            .build()
+            .withHeader();
+        
+        CsvMapper csvMapper = new CsvMapper();
+        csvMapper.writerFor(JsonNode.class)
+            .with(csvSchema)
+            .writeValue(csvFile, jsonTree);
+    }
+    
+    public static void csvToJson(File csvFile, File jsonFile) throws IOException {
+        CsvSchema orderLineSchema = CsvSchema.emptySchema().withHeader();
+        CsvMapper csvMapper = new CsvMapper();
+        MappingIterator<OrderLine> orderLines = csvMapper.readerFor(OrderLine.class)
+            .with(orderLineSchema)
+            .readValues(csvFile);
+        
+        new ObjectMapper()
+            .configure(SerializationFeature.INDENT_OUTPUT, true)
+            .writeValue(jsonFile, orderLines.readAll());
+    }
+
+    public static void JsonToFormattedCsv(File jsonFile, File csvFile) throws IOException {
+        CsvMapper csvMapper = new CsvMapper();
+        CsvSchema csvSchema = csvMapper
+            .schemaFor(OrderLineForCsv.class)
+            .withHeader();
+        csvMapper.addMixIn(OrderLine.class, OrderLineForCsv.class);
+        
+        OrderLine[] orderLines = new ObjectMapper()
+            .readValue(jsonFile, OrderLine[].class);
+        csvMapper.writerFor(OrderLine[].class)
+            .with(csvSchema)
+            .writeValue(csvFile, orderLines);
+    }
+}

jackson-2/src/main/java/com/baeldung/jackson/mixin/OrderLineForCsv.java

@@ -0,0 +1,25 @@
+package com.baeldung.jackson.mixin;
+
+import java.math.BigDecimal;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+
+@JsonPropertyOrder({
+    "count",
+    "name"
+})
+public abstract class OrderLineForCsv {
+    
+    @JsonProperty("name")
+    private String item; 
+    
+    @JsonProperty("count")
+    private int quantity; 
+    
+    @JsonIgnore
+    private BigDecimal unitPrice;
+    
+
+}

jackson-2/src/main/resources/orderLines.csv

@@ -0,0 +1,3 @@
+item,quantity,unitPrice
+"No. 9 Sprockets",12,1.23
+"Widget (10mm)",4,3.45

jackson-2/src/main/resources/orderLines.json

@@ -0,0 +1,9 @@
+[ {
+  "item" : "No. 9 Sprockets",
+  "quantity" : 12,
+  "unitPrice" : 1.23
+}, {
+  "item" : "Widget (10mm)",
+  "quantity" : 4,
+  "unitPrice" : 3.45
+} ]

jackson-2/src/test/java/com/baeldung/jackson/csv/CsvUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.jackson.csv;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.util.List;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.core.JsonParseException;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.google.common.io.Files;
+
+
+public class CsvUnitTest {
+
+    @Test
+    public void givenJsonInput_thenWriteCsv() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.JsonToCsv(new File("src/main/resources/orderLines.json"), 
+            new File("src/main/resources/csvFromJson.csv"));
+        
+        assertEquals(readFile("src/main/resources/csvFromJson.csv"),
+            readFile("src/test/resources/expectedCsvFromJson.csv"));
+    }
+    
+    @Test
+    public void givenCsvInput_thenWritesJson() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.csvToJson(new File("src/main/resources/orderLines.csv"), 
+            new File("src/main/resources/jsonFromCsv.json"));
+        
+        assertEquals(readFile("src/main/resources/jsonFromCsv.json"),
+            readFile("src/test/resources/expectedJsonFromCsv.json"));
+        
+    }
+    
+    @Test
+    public void givenJsonInput_thenWriteFormattedCsvOutput() throws JsonParseException, JsonMappingException, IOException {
+        JsonCsvConverter.JsonToFormattedCsv(new File("src/main/resources/orderLines.json"), 
+            new File("src/main/resources/formattedCsvFromJson.csv"));
+
+        assertEquals(readFile("src/main/resources/formattedCsvFromJson.csv"),
+            readFile("src/test/resources/expectedFormattedCsvFromJson.csv"));
+        
+    }
+    
+    private List<String> readFile(String filename) throws IOException {
+        return Files.readLines(new File(filename), Charset.forName("utf-8"));
+    }
+    
+    
+}
+;

jackson-2/src/test/resources/expectedCsvFromJson.csv

@@ -0,0 +1,3 @@
+item,quantity,unitPrice
+"No. 9 Sprockets",12,1.23
+"Widget (10mm)",4,3.45

jackson-2/src/test/resources/expectedFormattedCsvFromJson.csv

@@ -0,0 +1,3 @@
+count,name
+12,"No. 9 Sprockets"
+4,"Widget (10mm)"

jackson-2/src/test/resources/expectedJsonFromCsv.json

@@ -0,0 +1,9 @@
+[ {
+  "item" : "No. 9 Sprockets",
+  "quantity" : 12,
+  "unitPrice" : 1.23
+}, {
+  "item" : "Widget (10mm)",
+  "quantity" : 4,
+  "unitPrice" : 3.45
+} ]

java-collections-conversions/src/main/java/com/baeldung/convertToMap/Book.java

@@ -0,0 +1,48 @@
+package com.baeldung.convertToMap;
+
+public class Book {
+    private String name;
+    private int releaseYear;
+    private String isbn;
+
+
+    @Override
+    public String toString() {
+        return "Book{" +
+                "name='" + name + '\'' +
+                ", releaseYear=" + releaseYear +
+                ", isbn='" + isbn + '\'' +
+                '}';
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getReleaseYear() {
+        return releaseYear;
+    }
+
+    public void setReleaseYear(int releaseYear) {
+        this.releaseYear = releaseYear;
+    }
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public Book(String name, int releaseYear, String isbn) {
+        this.name = name;
+        this.releaseYear = releaseYear;
+        this.isbn = isbn;
+    }
+}
+

java-collections-conversions/src/main/java/com/baeldung/convertToMap/ConvertToMap.java

@@ -0,0 +1,33 @@
+package com.baeldung.convertToMap;
+
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class ConvertToMap {
+    public Map<String, String> listToMap(List<Book> books) {
+        return books.stream().collect(Collectors.toMap(Book::getIsbn, Book::getName));
+    }
+
+    public Map<Integer, Book> listToMapWithDupKeyError(List<Book> books) {
+        return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity()));
+    }
+
+    public Map<Integer, Book> listToMapWithDupKey(List<Book> books) {
+        return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity(), (existing, replacement) -> existing));
+    }
+
+    public Map<Integer, Book> listToConcurrentMap(List<Book> books) {
+        return books.stream().collect(Collectors.toMap(Book::getReleaseYear, Function.identity(), (o1, o2) -> o1, ConcurrentHashMap::new));
+    }
+
+    public TreeMap<String, Book> listToSortedMap(List<Book> books) {
+        return books.stream()
+                .sorted(Comparator.comparing(Book::getName))
+                .collect(Collectors.toMap(Book::getName, Function.identity(), (o1, o2) -> o1, TreeMap::new));
+    }
+
+
+}
+

java-collections-conversions/src/test/java/com/baeldung/convertToMap/ConvertToMapUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.convertToMap;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import static org.junit.Assert.*;
+
+import org.junit.Before;
+import org.junit.Test;
+
+
+public class ConvertToMapUnitTest {
+
+    private List<Book> bookList;
+    private ConvertToMap convertToMap = new ConvertToMap();
+
+    @Before
+    public void init() {
+        bookList = new ArrayList<>();
+        bookList.add(new Book("The Fellowship of the Ring", 1954, "0395489318"));
+        bookList.add(new Book("The Two Towers", 1954, "0345339711"));
+        bookList.add(new Book("The Return of the King", 1955, "0618129111"));
+    }
+
+    @Test
+    public void whenConvertFromListToMap() {
+        assertTrue(convertToMap.listToMap(bookList).size() == 3);
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void whenMapHasDuplicateKey_without_merge_function_then_runtime_exception() {
+        convertToMap.listToMapWithDupKeyError(bookList);
+    }
+
+    @Test
+    public void whenMapHasDuplicateKeyThenMergeFunctionHandlesCollision() {
+        Map<Integer, Book> booksByYear = convertToMap.listToMapWithDupKey(bookList);
+        assertEquals(2, booksByYear.size());
+        assertEquals("0395489318", booksByYear.get(1954).getIsbn());
+    }
+
+    @Test
+    public void whenCreateConcurrentHashMap() {
+        assertTrue(convertToMap.listToConcurrentMap(bookList) instanceof ConcurrentHashMap);
+    }
+
+    @Test
+    public void whenMapisSorted() {
+        assertTrue(convertToMap.listToSortedMap(bookList).firstKey().equals("The Fellowship of the Ring"));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/search/SubstringSearchUnitTest.java

@@ -10,7 +10,7 @@ import org.junit.Test;
 /**
  * BAEL-2832: Different ways to check if a Substring could be found in a String.
  */
-public class SubstringSearch {
+public class SubstringSearchUnitTest {
 
     @Test
     public void searchSubstringWithIndexOf() {

jee-7/README.md

@@ -6,3 +6,4 @@
 - [A Guide to Java EE Web-Related Annotations](http://www.baeldung.com/javaee-web-annotations)
 - [Introduction to Testing with Arquillian](http://www.baeldung.com/arquillian)
 - [Java EE 7 Batch Processing](https://www.baeldung.com/java-ee-7-batch-processing)
+- [The Difference Between CDI and EJB Singleton](https://www.baeldung.com/jee-cdi-vs-ejb-singleton)

jersey/README.md

@@ -3,3 +3,4 @@
 - [Bean Validation in Jersey](https://www.baeldung.com/jersey-bean-validation)
 - [Set a Response Body in JAX-RS](https://www.baeldung.com/jax-rs-response)
 - [Exploring the Jersey Test Framework](https://www.baeldung.com/jersey-test)
+- [Explore Jersey Request Parameters](https://www.baeldung.com/jersey-request-parameters)

jersey/src/test/java/com/baeldung/jersey/server/rest/FruitResourceIntegrationTest.java

@@ -26,6 +26,7 @@ public class FruitResourceIntegrationTest extends JerseyTest {
     protected Application configure() {
         enable(TestProperties.LOG_TRAFFIC);
         enable(TestProperties.DUMP_ENTITY);
+        forceSet(TestProperties.CONTAINER_PORT, "0");
 
         ViewApplicationConfig config = new ViewApplicationConfig();
         config.register(FruitExceptionMapper.class);

kotlin-libraries-2/README.md

@@ -1,3 +1,4 @@
 ## Relevant articles:
 
 - [Jackson Support for Kotlin](https://www.baeldung.com/jackson-kotlin)
+- [Introduction to RxKotlin](https://www.baeldung.com/rxkotlin)

kotlin-quasar/pom.xml

@@ -0,0 +1,120 @@
+<?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</groupId>
+    <artifactId>kotlin-quasar</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+    <name>kotlin-quasar</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-stdlib-jdk8</artifactId>
+            <version>${kotlin.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-test</artifactId>
+            <version>${kotlin.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>co.paralleluniverse</groupId>
+            <artifactId>quasar-core</artifactId>
+            <version>${quasar.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>co.paralleluniverse</groupId>
+            <artifactId>quasar-actors</artifactId>
+            <version>${quasar.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>co.paralleluniverse</groupId>
+            <artifactId>quasar-reactive-streams</artifactId>
+            <version>${quasar.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>co.paralleluniverse</groupId>
+            <artifactId>quasar-kotlin</artifactId>
+            <version>${quasar.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <sourceDirectory>src/main/kotlin</sourceDirectory>
+        <testSourceDirectory>src/test/kotlin</testSourceDirectory>
+        <plugins>
+            <plugin>
+                <groupId>org.jetbrains.kotlin</groupId>
+                <artifactId>kotlin-maven-plugin</artifactId>
+                <version>${kotlin.version}</version>
+                <executions>
+                    <execution>
+                        <id>compile</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>compile</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>test-compile</id>
+                        <phase>test-compile</phase>
+                        <goals>
+                            <goal>test-compile</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <jvmTarget>1.8</jvmTarget>
+                </configuration>
+            </plugin>
+            <plugin>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <version>3.1.1</version>
+                <executions>
+                    <execution>
+                        <id>getClasspathFilenames</id>
+                        <goals>
+                            <goal>properties</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.22.1</version>
+                <configuration>
+                    <argLine>-Dco.paralleluniverse.fibers.verifyInstrumentation=true</argLine>
+                    <argLine>-javaagent:${co.paralleluniverse:quasar-core:jar}</argLine>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>exec-maven-plugin</artifactId>
+                <version>1.3.2</version>
+                <configuration>
+                    <workingDirectory>target/classes</workingDirectory>
+                    <executable>echo</executable>
+                    <arguments>
+                        <argument>-javaagent:${co.paralleluniverse:quasar-core:jar}</argument>
+                        <argument>-classpath</argument> <classpath/>
+                        <argument>com.baeldung.quasar.QuasarHelloWorldKt</argument>
+                    </arguments>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <quasar.version>0.8.0</quasar.version>
+        <kotlin.version>1.3.31</kotlin.version>
+    </properties>
+</project>

kotlin-quasar/src/main/kotlin/com/baeldung/quasar/QuasarHelloWorld.kt

@@ -0,0 +1,19 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.fibers.Fiber
+import co.paralleluniverse.strands.SuspendableRunnable
+
+
+/**
+ * Entrypoint into the application
+ */
+fun main(args: Array<String>) {
+    class Runnable : SuspendableRunnable {
+        override fun run() {
+            println("Hello")
+        }
+    }
+    val result = Fiber<Void>(Runnable()).start()
+    result.join()
+    println("World")
+}

kotlin-quasar/src/test/kotlin/com/baeldung/quasar/ChannelsTest.kt

@@ -0,0 +1,155 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.fibers.Suspendable
+import co.paralleluniverse.kotlin.fiber
+import co.paralleluniverse.strands.channels.Channels
+import co.paralleluniverse.strands.channels.Selector
+import com.google.common.base.Function
+import org.junit.Test
+
+class ChannelsTest {
+    @Test
+    fun createChannel() {
+        Channels.newChannel<String>(0, // The size of the channel buffer
+                Channels.OverflowPolicy.BLOCK,  // The policy for when the buffer is full
+                true,  // Whether we should optimize for a single message producer
+                true) // Whether we should optimize for a single message consumer
+    }
+
+    @Test
+    fun blockOnMessage() {
+        val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+
+        fiber @Suspendable {
+            while (!channel.isClosed) {
+                val message = channel.receive()
+                println("Received: $message")
+            }
+            println("Stopped receiving messages")
+        }
+
+        channel.send("Hello")
+        channel.send("World")
+
+        channel.close()
+    }
+
+    @Test
+    fun selectReceiveChannels() {
+        val channel1 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+        val channel2 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+
+        fiber @Suspendable {
+            while (!channel1.isClosed && !channel2.isClosed) {
+                val received = Selector.select(Selector.receive(channel1), Selector.receive(channel2))
+
+                println("Received: $received")
+            }
+        }
+
+        fiber @Suspendable {
+            for (i in 0..10) {
+                channel1.send("Channel 1: $i")
+            }
+        }
+
+        fiber @Suspendable {
+            for (i in 0..10) {
+                channel2.send("Channel 2: $i")
+            }
+        }
+    }
+
+    @Test
+    fun selectSendChannels() {
+        val channel1 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+        val channel2 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+
+        fiber @Suspendable {
+            for (i in 0..10) {
+                Selector.select(
+                        Selector.send(channel1, "Channel 1: $i"),
+                        Selector.send(channel2, "Channel 2: $i")
+                )
+            }
+        }
+
+        fiber @Suspendable {
+            while (!channel1.isClosed) {
+                val msg = channel1.receive()
+                println("Read: $msg")
+            }
+        }
+
+        fiber @Suspendable {
+            while (!channel2.isClosed) {
+                val msg = channel2.receive()
+                println("Read: $msg")
+            }
+        }
+    }
+
+    @Test
+    fun tickerChannel() {
+        val channel = Channels.newChannel<String>(3, Channels.OverflowPolicy.DISPLACE)
+
+        for (i in 0..10) {
+            val tickerConsumer = Channels.newTickerConsumerFor(channel)
+            fiber @Suspendable {
+                while (!tickerConsumer.isClosed) {
+                    val message = tickerConsumer.receive()
+                    println("Received on $i: $message")
+                }
+                println("Stopped receiving messages on $i")
+            }
+        }
+
+        for (i in 0..50) {
+            channel.send("Message $i")
+        }
+
+        channel.close()
+    }
+
+
+    @Test
+    fun transformOnSend() {
+        val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+
+        fiber @Suspendable {
+            while (!channel.isClosed) {
+                val message = channel.receive()
+                println("Received: $message")
+            }
+            println("Stopped receiving messages")
+        }
+
+        val transformOnSend = Channels.mapSend(channel, Function<String, String> { msg: String? -> msg?.toUpperCase() })
+
+        transformOnSend.send("Hello")
+        transformOnSend.send("World")
+
+        channel.close()
+    }
+
+    @Test
+    fun transformOnReceive() {
+        val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
+
+        val transformOnReceive = Channels.map(channel, Function<String, String> { msg: String? -> msg?.reversed() })
+
+        fiber @Suspendable {
+            while (!transformOnReceive.isClosed) {
+                val message = transformOnReceive.receive()
+                println("Received: $message")
+            }
+            println("Stopped receiving messages")
+        }
+
+
+        channel.send("Hello")
+        channel.send("World")
+
+        channel.close()
+    }
+}

kotlin-quasar/src/test/kotlin/com/baeldung/quasar/DataflowTest.kt

@@ -0,0 +1,35 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.strands.dataflow.Val
+import co.paralleluniverse.strands.dataflow.Var
+import org.junit.Assert
+import org.junit.Test
+import java.util.concurrent.TimeUnit
+
+class DataflowTest {
+    @Test
+    fun testValVar() {
+        val a = Var<Int>()
+        val b = Val<Int>()
+
+        val c = Var<Int> { a.get() + b.get() }
+        val d = Var<Int> { a.get() * b.get() }
+
+        // (a*b) - (a+b)
+        val initialResult = Val<Int> { d.get() - c.get() }
+        val currentResult = Var<Int> { d.get() - c.get() }
+
+        a.set(2)
+        b.set(4)
+
+        Assert.assertEquals(2, initialResult.get())
+        Assert.assertEquals(2, currentResult.get())
+
+        a.set(3)
+
+        TimeUnit.SECONDS.sleep(1)
+
+        Assert.assertEquals(2, initialResult.get())
+        Assert.assertEquals(5, currentResult.get())
+    }
+}

kotlin-quasar/src/test/kotlin/com/baeldung/quasar/PiAsyncTest.kt

@@ -0,0 +1,53 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.fibers.Fiber
+import co.paralleluniverse.fibers.FiberAsync
+import co.paralleluniverse.fibers.Suspendable
+import co.paralleluniverse.kotlin.fiber
+import co.paralleluniverse.strands.Strand
+import org.junit.Assert
+import org.junit.Test
+import java.math.BigDecimal
+import java.util.concurrent.TimeUnit
+
+interface PiCallback {
+    fun success(result: BigDecimal)
+    fun failure(error: Exception)
+}
+
+fun computePi(callback: PiCallback) {
+    println("Starting calculations")
+    TimeUnit.SECONDS.sleep(2)
+    println("Finished calculations")
+    callback.success(BigDecimal("3.14"))
+}
+
+class PiAsync : PiCallback, FiberAsync<BigDecimal, Exception>() {
+    override fun success(result: BigDecimal) {
+        asyncCompleted(result)
+    }
+
+    override fun failure(error: Exception) {
+        asyncFailed(error)
+    }
+
+    override fun requestAsync() {
+        computePi(this)
+    }
+}
+
+class PiAsyncTest {
+    @Test
+    fun testPi() {
+        val result = fiber @Suspendable {
+            val pi = PiAsync()
+            println("Waiting to get PI on: " + Fiber.currentFiber().name)
+            val result = pi.run()
+            println("Got PI")
+
+            result
+        }.get()
+
+        Assert.assertEquals(BigDecimal("3.14"), result)
+    }
+}

kotlin-quasar/src/test/kotlin/com/baeldung/quasar/SuspendableCallableTest.kt

@@ -0,0 +1,48 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.fibers.Fiber
+import co.paralleluniverse.fibers.Suspendable
+import co.paralleluniverse.kotlin.fiber
+import co.paralleluniverse.strands.SuspendableCallable
+import org.junit.Assert
+import org.junit.Test
+import java.util.concurrent.TimeUnit
+
+
+class SuspendableCallableTest {
+    @Test
+    fun createFiber() {
+        class Callable : SuspendableCallable<String> {
+            override fun run(): String {
+                println("Inside Fiber")
+                return "Hello"
+            }
+        }
+        val result = Fiber<String>(Callable()).start()
+
+        Assert.assertEquals("Hello", result.get())
+    }
+
+    @Test
+    fun createFiberLambda() {
+        val lambda: (() -> String) = {
+            println("Inside Fiber Lambda")
+            "Hello"
+        }
+        val result = Fiber<String>(lambda)
+        result.start()
+
+        Assert.assertEquals("Hello", result.get())
+    }
+
+    @Test
+    fun createFiberDsl() {
+        val result = fiber @Suspendable {
+            TimeUnit.SECONDS.sleep(5)
+            println("Inside Fiber DSL")
+            "Hello"
+        }
+
+        Assert.assertEquals("Hello", result.get())
+    }
+}

kotlin-quasar/src/test/kotlin/com/baeldung/quasar/SuspensableRunnableTest.kt

@@ -0,0 +1,47 @@
+package com.baeldung.quasar
+
+import co.paralleluniverse.fibers.Fiber
+import co.paralleluniverse.fibers.Suspendable
+import co.paralleluniverse.kotlin.fiber
+import co.paralleluniverse.strands.SuspendableRunnable
+import org.junit.Test
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.TimeoutException
+
+
+class SuspensableRunnableTest {
+    @Test
+    fun createFiber() {
+        class Runnable : SuspendableRunnable {
+            override fun run() {
+                println("Inside Fiber")
+            }
+        }
+        val result = Fiber<Void>(Runnable()).start()
+        result.join()
+    }
+
+    @Test
+    fun createFiberLambda() {
+        val result = Fiber<Void> {
+            println("Inside Fiber Lambda")
+        }
+        result.start()
+        result.join()
+    }
+
+    @Test
+    fun createFiberDsl() {
+        fiber @Suspendable {
+            println("Inside Fiber DSL")
+        }.join()
+    }
+
+    @Test(expected = TimeoutException::class)
+    fun fiberTimeout() {
+        fiber @Suspendable {
+            TimeUnit.SECONDS.sleep(5)
+            println("Inside Fiber DSL")
+        }.join(2, TimeUnit.SECONDS)
+    }
+}

libraries-2/pom.xml

@@ -55,6 +55,39 @@
 			<artifactId>spring-boot-starter</artifactId>
 			<version>${spring-boot-starter.version}</version>
 		</dependency>
+
+		<!-- Dependencies for response decoder with okhttp -->
+		<dependency>
+			<groupId>com.squareup.okhttp3</groupId>
+			<artifactId>okhttp</artifactId>
+			<version>3.14.2</version>
+		</dependency>
+
+		<dependency>
+			<groupId>com.fasterxml.jackson.core</groupId>
+			<artifactId>jackson-databind</artifactId>
+			<version>2.9.9</version>
+		</dependency>
+
+		<dependency>
+			<groupId>com.google.code.gson</groupId>
+			<artifactId>gson</artifactId>
+			<version>2.8.5</version>
+		</dependency>
+
+		<dependency>
+			<groupId>com.squareup.okhttp3</groupId>
+			<artifactId>mockwebserver</artifactId>
+			<version>3.14.2</version>
+			<scope>test</scope>
+		</dependency>
+
+                <dependency>
+                    <groupId>edu.uci.ics</groupId>
+                    <artifactId>crawler4j</artifactId>
+                    <version>${crawler4j.version}</version>
+		</dependency>
+          
 	</dependencies>
 
 	<properties>
@@ -62,6 +95,7 @@
 		<classgraph.version>4.8.28</classgraph.version>
 		<jbpm.version>6.0.0.Final</jbpm.version>
 		<picocli.version>3.9.6</picocli.version>
+        <crawler4j.version>4.4.0</crawler4j.version>
 		<spring-boot-starter.version>2.1.4.RELEASE</spring-boot-starter.version>
 	</properties>
 </project>

libraries-2/src/main/java/com/baeldung/crawler4j/CrawlerStatistics.java

@@ -0,0 +1,22 @@
+package com.baeldung.crawler4j;
+
+public class CrawlerStatistics {
+    private int processedPageCount = 0;
+    private int totalLinksCount = 0;
+    
+    public void incrementProcessedPageCount() {
+        processedPageCount++;
+    }
+    
+    public void incrementTotalLinksCount(int linksCount) {
+        totalLinksCount += linksCount;
+    }
+    
+    public int getProcessedPageCount() {
+        return processedPageCount;
+    }
+    
+    public int getTotalLinksCount() {
+        return totalLinksCount;
+    }
+}

libraries-2/src/main/java/com/baeldung/crawler4j/HtmlCrawler.java

@@ -0,0 +1,48 @@
+package com.baeldung.crawler4j;
+
+import java.util.Set;
+import java.util.regex.Pattern;
+
+import edu.uci.ics.crawler4j.crawler.Page;
+import edu.uci.ics.crawler4j.crawler.WebCrawler;
+import edu.uci.ics.crawler4j.parser.HtmlParseData;
+import edu.uci.ics.crawler4j.url.WebURL;
+
+public class HtmlCrawler extends WebCrawler {
+
+    private final static Pattern EXCLUSIONS = Pattern.compile(".*(\\.(css|js|xml|gif|jpg|png|mp3|mp4|zip|gz|pdf))$");
+    
+    private CrawlerStatistics stats;
+    
+    public HtmlCrawler(CrawlerStatistics stats) {
+        this.stats = stats;
+    }
+
+    @Override
+    public boolean shouldVisit(Page referringPage, WebURL url) {
+        String urlString = url.getURL().toLowerCase();
+        return !EXCLUSIONS.matcher(urlString).matches() 
+            && urlString.startsWith("https://www.baeldung.com/");
+    }
+
+    @Override
+    public void visit(Page page) {
+        String url = page.getWebURL().getURL();
+        stats.incrementProcessedPageCount();
+
+        if (page.getParseData() instanceof HtmlParseData) {
+            HtmlParseData htmlParseData = (HtmlParseData) page.getParseData();
+            String title = htmlParseData.getTitle();
+            String text = htmlParseData.getText();
+            String html = htmlParseData.getHtml();
+            Set<WebURL> links = htmlParseData.getOutgoingUrls();
+            stats.incrementTotalLinksCount(links.size());
+
+            System.out.printf("Page with title '%s' %n", title);
+            System.out.printf("    Text length: %d %n", text.length());
+            System.out.printf("    HTML length: %d %n", html.length());
+            System.out.printf("    %d outbound links %n", links.size());
+        }
+    }
+
+}

libraries-2/src/main/java/com/baeldung/crawler4j/HtmlCrawlerController.java

@@ -0,0 +1,36 @@
+package com.baeldung.crawler4j;
+
+import java.io.File;
+
+import edu.uci.ics.crawler4j.crawler.CrawlConfig;
+import edu.uci.ics.crawler4j.crawler.CrawlController;
+import edu.uci.ics.crawler4j.fetcher.PageFetcher;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtConfig;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtServer;
+
+public class HtmlCrawlerController {
+
+    public static void main(String[] args) throws Exception {
+        File crawlStorage = new File("src/test/resources/crawler4j");
+        CrawlConfig config = new CrawlConfig();
+        config.setCrawlStorageFolder(crawlStorage.getAbsolutePath());
+        config.setMaxDepthOfCrawling(2);
+
+        int numCrawlers = 12;
+
+        PageFetcher pageFetcher = new PageFetcher(config);
+        RobotstxtConfig robotstxtConfig = new RobotstxtConfig();
+        RobotstxtServer robotstxtServer = new RobotstxtServer(robotstxtConfig, pageFetcher);
+        CrawlController controller = new CrawlController(config, pageFetcher, robotstxtServer);
+
+        controller.addSeed("https://www.baeldung.com/");
+
+        CrawlerStatistics stats = new CrawlerStatistics();
+        CrawlController.WebCrawlerFactory<HtmlCrawler> factory = () -> new HtmlCrawler(stats);
+
+        controller.start(factory, numCrawlers);
+        System.out.printf("Crawled %d pages %n", stats.getProcessedPageCount());
+        System.out.printf("Total Number of outbound links = %d %n", stats.getTotalLinksCount());
+    }
+
+}

libraries-2/src/main/java/com/baeldung/crawler4j/ImageCrawler.java

@@ -0,0 +1,49 @@
+package com.baeldung.crawler4j;
+
+import java.io.File;
+import java.util.regex.Pattern;
+
+import edu.uci.ics.crawler4j.crawler.Page;
+import edu.uci.ics.crawler4j.crawler.WebCrawler;
+import edu.uci.ics.crawler4j.parser.BinaryParseData;
+import edu.uci.ics.crawler4j.url.WebURL;
+
+public class ImageCrawler extends WebCrawler {
+    private final static Pattern EXCLUSIONS = Pattern.compile(".*(\\.(css|js|xml|gif|png|mp3|mp4|zip|gz|pdf))$");
+
+    private static final Pattern IMG_PATTERNS = Pattern.compile(".*(\\.(jpg|jpeg))$");
+
+    private File saveDir;
+
+    public ImageCrawler(File saveDir) {
+        this.saveDir = saveDir;
+    }
+
+    @Override
+    public boolean shouldVisit(Page referringPage, WebURL url) {
+        String urlString = url.getURL().toLowerCase();
+        if (EXCLUSIONS.matcher(urlString).matches()) {
+            return false;
+        }
+
+        if (IMG_PATTERNS.matcher(urlString).matches() 
+            || urlString.startsWith("https://www.baeldung.com/")) {
+            return true;
+        }
+
+        return false;
+    }
+
+    @Override
+    public void visit(Page page) {
+        String url = page.getWebURL().getURL();
+        if (IMG_PATTERNS.matcher(url).matches() 
+            && page.getParseData() instanceof BinaryParseData) {
+            String extension = url.substring(url.lastIndexOf("."));
+            int contentLength = page.getContentData().length;
+
+            System.out.printf("Extension is '%s' with content length %d %n", extension, contentLength);
+        }
+    }
+
+}

libraries-2/src/main/java/com/baeldung/crawler4j/ImageCrawlerController.java

@@ -0,0 +1,36 @@
+package com.baeldung.crawler4j;
+
+import java.io.File;
+
+import edu.uci.ics.crawler4j.crawler.CrawlConfig;
+import edu.uci.ics.crawler4j.crawler.CrawlController;
+import edu.uci.ics.crawler4j.fetcher.PageFetcher;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtConfig;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtServer;
+
+public class ImageCrawlerController {
+
+    public static void main(String[] args) throws Exception {
+        File crawlStorage = new File("src/test/resources/crawler4j");
+        CrawlConfig config = new CrawlConfig();
+        config.setCrawlStorageFolder(crawlStorage.getAbsolutePath());
+        config.setIncludeBinaryContentInCrawling(true);
+        config.setMaxPagesToFetch(500);
+        
+        File saveDir = new File("src/test/resources/crawler4j");
+        
+        int numCrawlers = 12;
+        
+        PageFetcher pageFetcher = new PageFetcher(config);
+        RobotstxtConfig robotstxtConfig = new RobotstxtConfig();
+        RobotstxtServer robotstxtServer = new RobotstxtServer(robotstxtConfig, pageFetcher);
+        CrawlController controller = new CrawlController(config, pageFetcher, robotstxtServer);
+        
+        controller.addSeed("https://www.baeldung.com/");
+        
+        CrawlController.WebCrawlerFactory<ImageCrawler> factory = () -> new ImageCrawler(saveDir);
+        
+        controller.start(factory, numCrawlers);
+    }
+
+}

libraries-2/src/main/java/com/baeldung/crawler4j/MultipleCrawlerController.java

@@ -0,0 +1,54 @@
+package com.baeldung.crawler4j;
+
+import java.io.File;
+
+import edu.uci.ics.crawler4j.crawler.CrawlConfig;
+import edu.uci.ics.crawler4j.crawler.CrawlController;
+import edu.uci.ics.crawler4j.fetcher.PageFetcher;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtConfig;
+import edu.uci.ics.crawler4j.robotstxt.RobotstxtServer;
+
+public class MultipleCrawlerController {
+    public static void main(String[] args) throws Exception {
+        File crawlStorageBase = new File("src/test/resources/crawler4j");
+        CrawlConfig htmlConfig = new CrawlConfig();
+        CrawlConfig imageConfig = new CrawlConfig();
+        
+        htmlConfig.setCrawlStorageFolder(new File(crawlStorageBase, "html").getAbsolutePath());
+        imageConfig.setCrawlStorageFolder(new File(crawlStorageBase, "image").getAbsolutePath());
+        imageConfig.setIncludeBinaryContentInCrawling(true);
+        
+        htmlConfig.setMaxPagesToFetch(500);
+        imageConfig.setMaxPagesToFetch(1000);
+        
+        PageFetcher pageFetcherHtml = new PageFetcher(htmlConfig);
+        PageFetcher pageFetcherImage = new PageFetcher(imageConfig);
+        
+        RobotstxtConfig robotstxtConfig = new RobotstxtConfig();
+        RobotstxtServer robotstxtServer = new RobotstxtServer(robotstxtConfig, pageFetcherHtml);
+
+        CrawlController htmlController = new CrawlController(htmlConfig, pageFetcherHtml, robotstxtServer);
+        CrawlController imageController = new CrawlController(imageConfig, pageFetcherImage, robotstxtServer);
+        
+        htmlController.addSeed("https://www.baeldung.com/");
+        imageController.addSeed("https://www.baeldung.com/");
+        
+        CrawlerStatistics stats = new CrawlerStatistics();
+        CrawlController.WebCrawlerFactory<HtmlCrawler> htmlFactory = () -> new HtmlCrawler(stats);
+        
+        File saveDir = new File("src/test/resources/crawler4j");
+        CrawlController.WebCrawlerFactory<ImageCrawler> imageFactory = () -> new ImageCrawler(saveDir);
+        
+        imageController.startNonBlocking(imageFactory, 7);
+        htmlController.startNonBlocking(htmlFactory, 10);
+        
+
+        htmlController.waitUntilFinish();
+        System.out.printf("Crawled %d pages %n", stats.getProcessedPageCount());
+        System.out.printf("Total Number of outbound links = %d %n", stats.getTotalLinksCount());
+
+        imageController.waitUntilFinish();
+        System.out.printf("Image Crawler is finished.");
+        
+    }
+}

libraries-2/src/test/java/com/baeldung/okhttp/ResponseDecoderUnitTest.java

@@ -0,0 +1,102 @@
+package com.baeldung.okhttp;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.gson.Gson;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.ResponseBody;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import java.io.InputStreamReader;
+
+public class ResponseDecoderUnitTest {
+
+    @Rule public ExpectedException exceptionRule = ExpectedException.none();
+
+    @Rule public MockWebServer server = new MockWebServer();
+
+    SimpleEntity sampleResponse;
+
+    MockResponse mockResponse;
+
+    OkHttpClient client;
+
+    @Before
+    public void setUp() {
+        sampleResponse = new SimpleEntity("Baeldung");
+        client = new OkHttpClient.Builder().build();
+        mockResponse = new MockResponse()
+          .setResponseCode(200)
+          .setHeader("Content-Type", "application/json")
+          .setBody(new Gson().toJson(sampleResponse));
+    }
+
+    @Test
+    public void givenJacksonDecoder_whenGetStringOfResponse_thenExpectSimpleEntity() throws Exception {
+        server.enqueue(mockResponse);
+        Request request = new Request.Builder()
+          .url(server.url(""))
+          .build();
+        ResponseBody responseBody = client
+          .newCall(request)
+          .execute()
+          .body();
+
+        Assert.assertNotNull(responseBody);
+        Assert.assertNotEquals(0, responseBody.contentLength());
+
+        ObjectMapper objectMapper = new ObjectMapper();
+        SimpleEntity entity = objectMapper.readValue(responseBody.string(), SimpleEntity.class);
+
+        Assert.assertNotNull(entity);
+        Assert.assertEquals(sampleResponse.getName(), entity.getName());
+    }
+
+    @Test
+    public void givenGsonDecoder_whenGetByteStreamOfResponse_thenExpectSimpleEntity() throws Exception {
+        server.enqueue(mockResponse);
+        Request request = new Request.Builder()
+          .url(server.url(""))
+          .build();
+        ResponseBody responseBody = client
+          .newCall(request)
+          .execute()
+          .body();
+
+        Assert.assertNotNull(responseBody);
+        Assert.assertNotEquals(0, responseBody.contentLength());
+
+        Gson gson = new Gson();
+        SimpleEntity entity = gson.fromJson(new InputStreamReader(responseBody.byteStream()), SimpleEntity.class);
+
+        Assert.assertNotNull(entity);
+        Assert.assertEquals(sampleResponse.getName(), entity.getName());
+    }
+
+    @Test
+    public void givenGsonDecoder_whenGetStringOfResponse_thenExpectSimpleEntity() throws Exception {
+        server.enqueue(mockResponse);
+        Request request = new Request.Builder()
+          .url(server.url(""))
+          .build();
+        ResponseBody responseBody = client
+          .newCall(request)
+          .execute()
+          .body();
+
+        Assert.assertNotNull(responseBody);
+
+        Gson gson = new Gson();
+        SimpleEntity entity = gson.fromJson(responseBody.string(), SimpleEntity.class);
+
+        Assert.assertNotNull(entity);
+        Assert.assertEquals(sampleResponse.getName(), entity.getName());
+    }
+
+}

libraries-2/src/test/java/com/baeldung/okhttp/SimpleEntity.java

@@ -0,0 +1,22 @@
+package com.baeldung.okhttp;
+
+public class SimpleEntity {
+    protected String name;
+
+    public SimpleEntity(String name) {
+        this.name = name;
+    }
+
+    //no-arg constructor, getters and setters here
+    
+    public SimpleEntity() {
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

libraries-data/pom.xml

@@ -263,6 +263,16 @@
             <groupId>org.apache.storm</groupId>
             <artifactId>storm-core</artifactId>
             <version>${storm.version}</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.slf4j</groupId>
+                    <artifactId>slf4j-log4j12</artifactId>
+                </exclusion>
+                <exclusion>
+                    <groupId>org.slf4j</groupId>
+                    <artifactId>log4j-over-slf4j</artifactId>
+                </exclusion>
+            </exclusions>
         </dependency>
 
         <dependency>

libraries-data/src/test/java/com/baeldung/flink/BackupCreatorIntegrationTest.java

@@ -26,6 +26,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 
 public class BackupCreatorIntegrationTest {
@@ -88,7 +89,7 @@ public class BackupCreatorIntegrationTest {
         SerializationSchema<Backup> serializationSchema = new BackupSerializationSchema();
         byte[] backupProcessed = serializationSchema.serialize(backup);
         
-        assertEquals(backupSerialized, backupProcessed);
+        assertArrayEquals(backupSerialized, backupProcessed);
     }
 
     private static class CollectingSink implements SinkFunction<Backup> {

libraries/src/main/java/com/baeldung/ftp/FtpClient.java

@@ -59,5 +59,6 @@ class FtpClient {
     void downloadFile(String source, String destination) throws IOException {
         FileOutputStream out = new FileOutputStream(destination);
         ftp.retrieveFile(source, out);
+        out.close();
     }
 }

libraries/src/test/java/com/baeldung/serenity/spring/AdderMethodDirtiesContextIntegrationTest.java

@@ -28,7 +28,7 @@ public class AdderMethodDirtiesContextIntegrationTest {
     @Test
     public void _1_givenNumber_whenAdd_thenSumWrong() {
         adderServiceSteps.whenAdd();
-        adderServiceSteps.sumWrong();
+        adderServiceSteps.summedUp();
     }
 
     @Rule

logging-modules/log4j2/pom.xml

@@ -78,7 +78,7 @@
 
     <profiles>
         <profile>
-            <id>integration</id>
+            <id>integration-lite-first</id>
             <build>
                 <plugins>
                     <plugin>

logging-modules/log4j2/src/test/java/com/baeldung/logging/log4j2/appender/MapAppenderIntegrationTest.java

@@ -23,7 +23,7 @@ public class MapAppenderIntegrationTest {
 
     @Test
     public void whenLoggerEmitsLoggingEvent_thenAppenderReceivesEvent() throws Exception {
-        logger.info("Test from {}", this.getClass()
+        logger.error("Error log message from {}", this.getClass()
             .getSimpleName());
         LoggerContext context = LoggerContext.getContext(false);
         Configuration config = context.getConfiguration();

maven/README.md

@@ -16,3 +16,4 @@
 - [Multi-Module Project with Maven](https://www.baeldung.com/maven-multi-module)
 - [Maven Enforcer Plugin](https://www.baeldung.com/maven-enforcer-plugin)
 - [Eclipse Error: web.xml is missing and failOnMissingWebXml is set to true](https://www.baeldung.com/eclipse-error-web-xml-missing)
+- [Guide to Maven Profiles](https://www.baeldung.com/maven-profiles)

patterns/README.md

@@ -1,6 +0,0 @@
-### Relevant Articles:
-- [A Guide to the Front Controller Pattern in Java](http://www.baeldung.com/java-front-controller-pattern)
-- [Introduction to Intercepting Filter Pattern in Java](http://www.baeldung.com/intercepting-filter-pattern-in-java)
-- [Introduction to the Null Object Pattern](https://www.baeldung.com/java-null-object-pattern)
-- [The Dependency Inversion Principle in Java](https://www.baeldung.com/java-dependency-inversion-principle)
-- [Avoid Check for Null Statement in Java](https://www.baeldung.com/java-avoid-null-check)

patterns/design-patterns-2/README.md

@@ -1,3 +1,5 @@
 ### Relevant Articles
 
 - [The Mediator Pattern in Java](https://www.baeldung.com/java-mediator-pattern)
+- [Introduction to the Null Object Pattern](https://www.baeldung.com/java-null-object-pattern)
+- [Avoid Check for Null Statement in Java](https://www.baeldung.com/java-avoid-null-check)