Resolved merge conflicts

.gitignore

@@ -31,3 +31,5 @@ spring-openid/src/main/resources/application.properties
 .recommenders/
 /spring-hibernate4/nbproject/
 spring-security-openid/src/main/resources/application.properties
+
+spring-all/*.log

.travis.yml

@@ -1,6 +1,6 @@
 language: java
 
-install: travis_wait 60 mvn -q test
+install: travis_wait 60 mvn -q test -fae
 
 before_script:
   - echo "MAVEN_OPTS='-Xmx2048M -Xss128M -XX:MaxPermSize=2048M -XX:+CMSClassUnloadingEnabled -XX:+UseConcMarkSweepGC -XX:+TieredCompilation -XX:TieredStopAtLevel=1 -XX:-UseGCOverheadLimit'" > ~/.mavenrc

JGit/pom.xml

@@ -6,6 +6,13 @@
     <version>1.0-SNAPSHOT</version>
     <packaging>jar</packaging>
     <url>http://maven.apache.org</url>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+         
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>1.8</maven.compiler.source>

Twitter4J/pom.xml

@@ -8,6 +8,12 @@
   <name>Twitter4J</name>
   <url>http://maven.apache.org</url>
     
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+         
 	<properties>
 	    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 	    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

algorithms/README.md

@@ -5,3 +5,4 @@
 - [Ant Colony Optimization](http://www.baeldung.com/java-ant-colony-optimization)
 - [Validating Input With Finite Automata in Java](http://www.baeldung.com/finite-automata-java)
 - [Introduction to Jenetics Library](http://www.baeldung.com/jenetics)
+- [Check If a Number Is Prime in Java](http://www.baeldung.com/java-prime-numbers)

algorithms/pom.xml

@@ -13,6 +13,12 @@
 		<commons-math3.version>3.6.1</commons-math3.version>
 	</properties>
 
+            <parent>
+                <groupId>com.baeldung</groupId>
+                <artifactId>parent-modules</artifactId>
+                <version>1.0.0-SNAPSHOT</version>
+             </parent>	
+
 	<dependencies>
 		<dependency>
             <groupId>org.apache.commons</groupId>
@@ -39,7 +45,6 @@
 	</dependencies>
 
 	<build>
-		<defaultGoal>install</defaultGoal>
 		<pluginManagement>
 			<plugins>
 				<plugin>
@@ -56,6 +61,17 @@
 					<artifactId>exec-maven-plugin</artifactId>
 					<version>${exec-maven-plugin.version}</version>
 				</plugin>
+
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-surefire-plugin</artifactId>
+					<configuration>
+						<excludes>
+							<exclude>**/*LongRunningUnitTest.java</exclude>
+							<exclude>**/*IntegrationTest.java</exclude>
+						</excludes>
+					</configuration>
+				</plugin>
 			</plugins>
 		</pluginManagement>
 	</build>

algorithms/src/test/java/algorithms/AntColonyOptimizationLongRunningUnitTest.java

@@ -0,0 +1,22 @@
+package algorithms;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.baeldung.algorithms.ga.ant_colony.AntColonyOptimization;
+
+public class AntColonyOptimizationLongRunningUnitTest {
+
+    @Test
+    public void testGenerateRandomMatrix() {
+        AntColonyOptimization antTSP = new AntColonyOptimization(5);
+        Assert.assertNotNull(antTSP.generateRandomMatrix(5));
+    }
+
+    @Test
+    public void testStartAntOptimization() {
+        AntColonyOptimization antTSP = new AntColonyOptimization(5);
+        Assert.assertNotNull(antTSP.solve());
+    }
+
+}

algorithms/src/test/java/algorithms/AntColonyOptimizationTest.java

@@ -1,22 +0,0 @@
-package algorithms;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-import com.baeldung.algorithms.ga.ant_colony.AntColonyOptimization;
-
-public class AntColonyOptimizationTest {
-
-	@Test
-	public void testGenerateRandomMatrix() {
-		AntColonyOptimization antTSP = new AntColonyOptimization(5);
-		Assert.assertNotNull(antTSP.generateRandomMatrix(5));
-	}
-
-	@Test
-	public void testStartAntOptimization() {
-		AntColonyOptimization antTSP = new AntColonyOptimization(5);
-		Assert.assertNotNull(antTSP.solve());
-	}
-
-}

algorithms/src/test/java/algorithms/BinaryGeneticAlgorithmLongRunningUnitTest.java

@@ -0,0 +1,16 @@
+package algorithms;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.baeldung.algorithms.ga.binary.SimpleGeneticAlgorithm;
+
+public class BinaryGeneticAlgorithmLongRunningUnitTest {
+
+    @Test
+    public void testGA() {
+        SimpleGeneticAlgorithm ga = new SimpleGeneticAlgorithm();
+        Assert.assertTrue(ga.runAlgorithm(50, "1011000100000100010000100000100111001000000100000100000000001111"));
+    }
+
+}

algorithms/src/test/java/algorithms/BinaryGeneticAlgorithmUnitTest.java

@@ -1,16 +0,0 @@
-package algorithms;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-import com.baeldung.algorithms.ga.binary.SimpleGeneticAlgorithm;
-
-public class BinaryGeneticAlgorithmUnitTest {
-
-	@Test
-	public void testGA() {
-		SimpleGeneticAlgorithm ga = new SimpleGeneticAlgorithm();
-		Assert.assertTrue(ga.runAlgorithm(50, "1011000100000100010000100000100111001000000100000100000000001111"));
-	}
-
-}

algorithms/src/test/java/algorithms/DijkstraAlgorithmLongRunningUnitTest.java

@@ -11,7 +11,7 @@ import java.util.List;
 
 import static org.junit.Assert.assertTrue;
 
-public class DijkstraAlgorithmTest {
+public class DijkstraAlgorithmLongRunningUnitTest {
 
     @Test
     public void whenSPPSolved_thenCorrect() {
@@ -56,19 +56,29 @@ public class DijkstraAlgorithmTest {
         for (Node node : graph.getNodes()) {
             switch (node.getName()) {
             case "B":
-                assertTrue(node.getShortestPath().equals(shortestPathForNodeB));
+                assertTrue(node
+                  .getShortestPath()
+                  .equals(shortestPathForNodeB));
                 break;
             case "C":
-                assertTrue(node.getShortestPath().equals(shortestPathForNodeC));
+                assertTrue(node
+                  .getShortestPath()
+                  .equals(shortestPathForNodeC));
                 break;
             case "D":
-                assertTrue(node.getShortestPath().equals(shortestPathForNodeD));
+                assertTrue(node
+                  .getShortestPath()
+                  .equals(shortestPathForNodeD));
                 break;
             case "E":
-                assertTrue(node.getShortestPath().equals(shortestPathForNodeE));
+                assertTrue(node
+                  .getShortestPath()
+                  .equals(shortestPathForNodeE));
                 break;
             case "F":
-                assertTrue(node.getShortestPath().equals(shortestPathForNodeF));
+                assertTrue(node
+                  .getShortestPath()
+                  .equals(shortestPathForNodeF));
                 break;
             }
         }

algorithms/src/test/java/algorithms/RtFiniteStateMachineLongRunningUnitTest.java

@@ -1,28 +1,27 @@
 package algorithms;
 
-import static org.junit.Assert.*;
-import org.junit.Test;
 import com.baeldung.automata.*;
+import org.junit.Test;
 
-/**
+import static org.junit.Assert.assertTrue;
- * Tests for {@link RtFiniteStateMachine}
+
- */
+public final class RtFiniteStateMachineLongRunningUnitTest {
-public final class RtFiniteStateMachineTest {
 
     @Test
     public void acceptsSimplePair() {
         String json = "{\"key\":\"value\"}";
         FiniteStateMachine machine = this.buildJsonStateMachine();
-        for (int i=0;i<json.length();i++) {
+        for (int i = 0; i < json.length(); i++) {
             machine = machine.switchState(String.valueOf(json.charAt(i)));
         }
         assertTrue(machine.canStop());
     }
+
     @Test
     public void acceptsMorePairs() {
         String json = "{\"key1\":\"value1\",\"key2\":\"value2\"}";
         FiniteStateMachine machine = this.buildJsonStateMachine();
-        for (int i=0;i<json.length();i++) {
+        for (int i = 0; i < json.length(); i++) {
             machine = machine.switchState(String.valueOf(json.charAt(i)));
         }
         assertTrue(machine.canStop());
@@ -32,7 +31,7 @@ public final class RtFiniteStateMachineTest {
     public void missingColon() {
         String json = "{\"key\"\"value\"}";
         FiniteStateMachine machine = this.buildJsonStateMachine();
-        for (int i=0;i<json.length();i++) {
+        for (int i = 0; i < json.length(); i++) {
             machine = machine.switchState(String.valueOf(json.charAt(i)));
         }
     }
@@ -56,20 +55,12 @@ public final class RtFiniteStateMachineTest {
         second.with(new RtTransition("\"", third));
         //Add transitions with chars 0-9 and a-z
         for (int i = 0; i < 26; i++) {
-            if(i<10) {
+            if (i < 10) {
-                third = third.with(
+                third = third.with(new RtTransition(String.valueOf(i), third));
-                    new RtTransition(String.valueOf(i), third)
+                sixth = sixth.with(new RtTransition(String.valueOf(i), sixth));
-                );
-                sixth = sixth.with(
-                    new RtTransition(String.valueOf(i), sixth)
-                );
             }
-            third = third.with(
+            third = third.with(new RtTransition(String.valueOf((char) ('a' + i)), third));
-                new RtTransition(String.valueOf((char) ('a' + i)), third)
+            sixth = sixth.with(new RtTransition(String.valueOf((char) ('a' + i)), sixth));
-            );
-            sixth = sixth.with(
-                new RtTransition(String.valueOf((char) ('a' + i)), sixth)
-            );
         }
         third.with(new RtTransition("\"", fourth));
         fourth.with(new RtTransition(":", fifth));

algorithms/src/test/java/algorithms/SimulatedAnnealingLongRunningUnitTest.java

@@ -5,7 +5,7 @@ import org.junit.Test;
 
 import com.baeldung.algorithms.ga.annealing.SimulatedAnnealing;
 
-public class SimulatedAnnealingTest {
+public class SimulatedAnnealingLongRunningUnitTest {
 
     @Test
     public void testSimulateAnnealing() {

algorithms/src/test/java/com/baeldung/algorithms/primechecker/BigIntegerPrimeCheckerTest.java

@@ -1,28 +0,0 @@
-package com.baeldung.algorithms.primechecker;
-
-import static org.junit.Assert.assertTrue;
-
-import org.junit.Test;
-
-import com.baeldung.algorithms.primechecker.BigIntegerPrimeChecker;
-import com.baeldung.algorithms.primechecker.PrimeChecker;
-
-public class BigIntegerPrimeCheckerTest {
-
-    BigIntegerPrimeChecker primeChecker = new BigIntegerPrimeChecker();
-    
-    @Test
-    public void givenPrimeNumber_whenCheckIsPrime_thenTrue(){
-        assertTrue(primeChecker.isPrime(13l));
-        assertTrue(primeChecker.isPrime(1009L));
-        assertTrue(primeChecker.isPrime(74207281L));
-    }
-    
-    @Test
-    public void givenNonPrimeNumber_whenCheckIsPrime_thenFalse(){
-        assertTrue(!primeChecker.isPrime(50L));
-        assertTrue(!primeChecker.isPrime(1001L));
-        assertTrue(!primeChecker.isPrime(74207282L));
-    }
-    
-}

algorithms/src/test/java/com/baeldung/algorithms/primechecker/BruteForcePrimeCheckerTest.java

@@ -1,27 +0,0 @@
-package com.baeldung.algorithms.primechecker;
-
-import org.junit.Test;
-
-import com.baeldung.algorithms.primechecker.BruteForcePrimeChecker;
-
-import static org.junit.Assert.*;
-
-public class BruteForcePrimeCheckerTest {
-
-    BruteForcePrimeChecker primeChecker = new BruteForcePrimeChecker();
-    
-    @Test
-    public void givenPrimeNumber_whenCheckIsPrime_thenTrue(){
-        assertTrue(primeChecker.isPrime(13));
-        assertTrue(primeChecker.isPrime(1009));
-    }
-    
-    @Test
-    public void givenNonPrimeNumber_whenCheckIsPrime_thenFalse(){
-        assertTrue(!primeChecker.isPrime(50));
-        assertTrue(!primeChecker.isPrime(1001));
-    }
-    
-    
-    
-}

algorithms/src/test/java/com/baeldung/algorithms/primechecker/OptimisedPrimeCheckerTest.java

@@ -1,26 +0,0 @@
-package com.baeldung.algorithms.primechecker;
-
-import static org.junit.Assert.assertTrue;
-
-import org.junit.Test;
-
-import com.baeldung.algorithms.primechecker.OptimisedPrimeChecker;
-import com.baeldung.algorithms.primechecker.PrimeChecker;
-
-public class OptimisedPrimeCheckerTest {
-
-    OptimisedPrimeChecker primeChecker = new OptimisedPrimeChecker();
-    
-    @Test
-    public void givenPrimeNumber_whenCheckIsPrime_thenTrue(){
-        assertTrue(primeChecker.isPrime(13));
-        assertTrue(primeChecker.isPrime(1009));
-    }
-    
-    @Test
-    public void givenNonPrimeNumber_whenCheckIsPrime_thenFalse(){
-        assertTrue(!primeChecker.isPrime(50));
-        assertTrue(!primeChecker.isPrime(1001));
-    }
-    
-}

algorithms/src/test/java/com/baeldung/algorithms/primechecker/PrimeCheckerTest.java

@@ -0,0 +1,69 @@
+package com.baeldung.algorithms.primechecker;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class PrimeCheckerTest {
+
+    private final BigIntegerPrimeChecker primeChecker = new BigIntegerPrimeChecker();
+    
+    @Test
+    public void whenCheckIsPrime_thenTrue(){
+        assertTrue(primeChecker.isPrime(13l));
+        assertTrue(primeChecker.isPrime(1009L));
+        assertTrue(primeChecker.isPrime(74207281L));
+    }
+    
+    @Test
+    public void whenCheckIsPrime_thenFalse(){
+        assertTrue(!primeChecker.isPrime(50L));
+        assertTrue(!primeChecker.isPrime(1001L));
+        assertTrue(!primeChecker.isPrime(74207282L));
+    }
+
+    private final BruteForcePrimeChecker bfPrimeChecker = new BruteForcePrimeChecker();
+
+    @Test
+    public void whenBFCheckIsPrime_thenTrue(){
+        assertTrue(bfPrimeChecker.isPrime(13));
+        assertTrue(bfPrimeChecker.isPrime(1009));
+    }
+
+    @Test
+    public void whenBFCheckIsPrime_thenFalse(){
+        assertFalse(bfPrimeChecker.isPrime(50));
+        assertFalse(bfPrimeChecker.isPrime(1001));
+    }
+
+
+    private final OptimisedPrimeChecker optimisedPrimeChecker = new OptimisedPrimeChecker();
+
+    @Test
+    public void whenOptCheckIsPrime_thenTrue(){
+        assertTrue(optimisedPrimeChecker.isPrime(13));
+        assertTrue(optimisedPrimeChecker.isPrime(1009));
+    }
+
+    @Test
+    public void whenOptCheckIsPrime_thenFalse(){
+        assertFalse(optimisedPrimeChecker.isPrime(50));
+        assertFalse(optimisedPrimeChecker.isPrime(1001));
+    }
+
+    private final PrimesPrimeChecker primesPrimeChecker = new PrimesPrimeChecker();
+
+    @Test
+    public void whenPrimesCheckIsPrime_thenTrue() {
+        assertTrue(primesPrimeChecker.isPrime(13));
+        assertTrue(primesPrimeChecker.isPrime(1009));
+    }
+
+    @Test
+    public void whenPrimesCheckIsPrime_thenFalse() {
+        assertFalse(primesPrimeChecker.isPrime(50));
+        assertFalse(primesPrimeChecker.isPrime(1001));
+    }
+    
+}

algorithms/src/test/java/com/baeldung/algorithms/primechecker/PrimesPrimeCheckerTest.java

@@ -1,25 +0,0 @@
-package com.baeldung.algorithms.primechecker;
-
-import static org.junit.Assert.assertTrue;
-
-import org.junit.Test;
-
-import com.baeldung.algorithms.primechecker.PrimeChecker;
-import com.baeldung.algorithms.primechecker.PrimesPrimeChecker;
-
-public class PrimesPrimeCheckerTest {
-    PrimesPrimeChecker primeChecker = new PrimesPrimeChecker();
-
-    @Test
-    public void givenPrimeNumber_whenCheckIsPrime_thenTrue() {
-        assertTrue(primeChecker.isPrime(13));
-        assertTrue(primeChecker.isPrime(1009));
-    }
-
-    @Test
-    public void givenNonPrimeNumber_whenCheckIsPrime_thenFalse() {
-        assertTrue(!primeChecker.isPrime(50));
-        assertTrue(!primeChecker.isPrime(1001));
-    }
-
-}

apache-bval/pom.xml

@@ -5,6 +5,11 @@
 	<artifactId>apache-bval</artifactId>
 	<version>0.0.1-SNAPSHOT</version>
 
+            <parent>
+                <groupId>com.baeldung</groupId>
+                <artifactId>parent-modules</artifactId>
+                <version>1.0.0-SNAPSHOT</version>
+             </parent>
 	<dependencies>
 		<dependency>
 			<groupId>org.apache.bval</groupId>

apache-cxf/cxf-aegis/src/test/java/com/baeldung/cxf/aegis/BaeldungTest.java

@@ -3,8 +3,10 @@ package com.baeldung.cxf.aegis;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
 
+import org.junit.After;
 import org.junit.Test;
 
+import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.lang.reflect.Type;
@@ -90,4 +92,12 @@ public class BaeldungTest {
         xmlReader.close();
         return courseRepo;
     }
+
+    @After
+    public void cleanup(){
+        File testFile = new File(fileName);
+        if (testFile.exists()) {
+           testFile.delete();     
+        }
+    }
 }

apache-cxf/cxf-jaxrs-implementation/pom.xml

@@ -54,6 +54,12 @@
             <groupId>org.apache.httpcomponents</groupId>
             <artifactId>httpclient</artifactId>
             <version>${httpclient.version}</version>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>
         </dependency>
     </dependencies>
 </project>

apache-cxf/cxf-spring/pom.xml

@@ -24,6 +24,12 @@
             <groupId>org.springframework</groupId>
             <artifactId>spring-context</artifactId>
             <version>${spring.version}</version>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>
         </dependency>
         <dependency>
             <groupId>org.springframework</groupId>

apache-cxf/pom.xml

@@ -6,6 +6,12 @@
     <version>0.0.1-SNAPSHOT</version>
     <packaging>pom</packaging>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <modules>
         <module>cxf-introduction</module>
         <module>cxf-spring</module>

apache-fop/pom.xml

@@ -7,6 +7,12 @@
 
     <name>apache-fop</name>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <dependencies>
 
         <!-- logging -->
@@ -28,11 +34,6 @@
             <version>${org.slf4j.version}</version>
             <!-- <scope>runtime</scope> --> <!-- some spring dependencies need to compile against jcl -->
         </dependency>
-        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
-            <groupId>org.slf4j</groupId>
-            <artifactId>log4j-over-slf4j</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
 
         <!-- test scoped -->
 
@@ -78,6 +79,10 @@
                     <groupId>org.apache.avalon.framework</groupId>
                     <artifactId>avalon-framework-impl</artifactId>
                 </exclusion>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>                
             </exclusions>
         </dependency>
 
@@ -90,6 +95,12 @@
             <groupId>avalon-framework</groupId>
             <artifactId>avalon-framework-impl</artifactId>
             <version>${avalon-framework.version}</version>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>            
         </dependency>
 
         <dependency>

apache-poi/pom.xml

@@ -5,6 +5,12 @@
     <artifactId>apache-poi</artifactId>
     <version>0.0.1-SNAPSHOT</version>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <properties>
         <maven-compiler-plugin.version>3.6.0</maven-compiler-plugin.version>
         <junit.version>4.12</junit.version>
@@ -42,6 +48,12 @@
             <groupId>org.jxls</groupId>
             <artifactId>jxls-jexcel</artifactId>
             <version>${jexcel.version}</version>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>            
         </dependency>	
     </dependencies>
 </project>

apache-poi/src/test/java/com/baeldung/jexcel/JExcelTest.java

@@ -19,6 +19,7 @@ import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
 import org.junit.Before;
+import org.junit.After;
 
 public class JExcelTest {
 
@@ -53,4 +54,11 @@ public class JExcelTest {
             .get(1));
     }
 
+    @After
+    public void cleanup(){
+        File testFile = new File(fileLocation);
+        if (testFile.exists()) {
+           testFile.delete();     
+        }
+    }
 }

apache-poi/src/test/java/com/baeldung/poi/excel/ExcelTest.java

@@ -16,6 +16,7 @@ import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
 import org.junit.Before;
+import org.junit.After;
 
 public class ExcelTest {
 
@@ -50,4 +51,11 @@ public class ExcelTest {
             .get(1));
     }
 
+    @After
+    public void cleanup(){
+        File testFile = new File(fileLocation);
+        if (testFile.exists()) {
+           testFile.delete();     
+        }
+    }
 }

apache-solrj/pom.xml

@@ -7,6 +7,12 @@
     <packaging>jar</packaging>
     <name>apache-solrj</name>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
 	<properties>
 		<junit.version>4.12</junit.version>
 		<maven-surefire-plugin.version>2.19.1</maven-surefire-plugin.version>

apache-thrift/pom.xml

@@ -6,6 +6,12 @@
     <version>0.0.1-SNAPSHOT</version>
     <packaging>pom</packaging>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <properties>
         <java.versin>1.8</java.versin>
         <junit.version>4.12</junit.version>
@@ -19,6 +25,12 @@
             <groupId>org.apache.thrift</groupId>
             <artifactId>libthrift</artifactId>
             <version>${thrift.version}</version>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>            
         </dependency>
 
         <dependency>

apache-velocity/pom.xml

@@ -9,6 +9,12 @@
     <packaging>war</packaging>
     <name>apache-velocity</name>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <properties>
         <jdk.version>1.8</jdk.version>
         <jstl.version>1.2</jstl.version>
@@ -55,6 +61,12 @@
             <artifactId>httpclient</artifactId>
             <version>${org.apache.httpcomponents.version}</version>
             <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <artifactId>commons-logging</artifactId>
+                    <groupId>commons-logging</groupId>
+                </exclusion>
+            </exclusions>            
         </dependency>
     </dependencies>
     <build>

aspectj/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-- [Intro to AspectJ](http://www.baeldung.com/aspectj)
-- [Spring Performance Logging](http://www.baeldung.com/spring-performance-logging)

aspectj/pom.xml

@@ -1,138 +0,0 @@
-<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>aspectj</artifactId>
-    <version>0.0.1-SNAPSHOT</version>
-    <name>aspectj</name>
-
-    <dependencies>
-        <dependency>
-            <groupId>org.aspectj</groupId>
-            <artifactId>aspectjrt</artifactId>
-            <version>${aspectj.version}</version>
-        </dependency>
-
-        <dependency>
-            <groupId>org.aspectj</groupId>
-            <artifactId>aspectjweaver</artifactId>
-            <version>${aspectj.version}</version>
-        </dependency>
-
-        <!-- utils -->
-        <dependency>
-            <groupId>org.slf4j</groupId>
-            <artifactId>slf4j-api</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
-
-        <dependency>
-            <groupId>ch.qos.logback</groupId>
-            <artifactId>logback-classic</artifactId>
-            <version>${logback.version}</version>
-        </dependency>
-
-        <dependency>
-            <groupId>ch.qos.logback</groupId>
-            <artifactId>logback-core</artifactId>
-            <version>${logback.version}</version>
-        </dependency>
-
-        <!-- unit test -->
-        <dependency>
-            <groupId>junit</groupId>
-            <artifactId>junit</artifactId>
-            <version>${junit.version}</version>
-        </dependency>
-
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-context</artifactId>
-            <version>4.3.4.RELEASE</version>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-beans</artifactId>
-            <version>4.3.4.RELEASE</version>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-core</artifactId>
-            <version>4.3.4.RELEASE</version>
-        </dependency>
-        <dependency>
-            <groupId>cglib</groupId>
-            <artifactId>cglib</artifactId>
-            <version>3.2.4</version>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-aop</artifactId>
-            <version>4.3.4.RELEASE</version>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <finalName>aspectj</finalName>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-compiler-plugin</artifactId>
-                <version>${maven-compiler-plugin.version}</version>
-                <configuration>
-                    <source>${source.version}</source>
-                    <target>${source.version}</target>
-                </configuration>
-
-            </plugin>
-
-            <plugin>
-                <groupId>org.codehaus.mojo</groupId>
-                <artifactId>aspectj-maven-plugin</artifactId>
-                <version>1.7</version>
-                <configuration>
-                    <complianceLevel>${source.version}</complianceLevel>
-                    <source>${source.version}</source>
-                    <target>${source.version}</target>
-                    <showWeaveInfo>true</showWeaveInfo>
-                    <verbose>true</verbose>
-                    <Xlint>ignore</Xlint>
-                    <encoding>${project.build.sourceEncoding}</encoding>
-                    <!-- Post-compile weaving -->
-                    <!-- <weaveDependencies> <weaveDependency> <groupId>org.agroup</groupId> <artifactId>to-weave</artifactId> </weaveDependency> 
-                        <weaveDependency> <groupId>org.anothergroup</groupId> <artifactId>gen</artifactId> </weaveDependency> </weaveDependencies> -->
-                </configuration>
-                <executions>
-                    <execution>
-                        <goals>
-                            <goal>compile</goal>
-                            <goal>test-compile</goal>
-                        </goals>
-                    </execution>
-                </executions>
-            </plugin>
-
-            <!-- <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-surefire-plugin</artifactId> <version>2.10</version> 
-                <configuration> <argLine>-javaagent:"${settings.localRepository}"/org/aspectj/aspectjweaver/${aspectj.version}/aspectjweaver-${aspectj.version}.jar</argLine> 
-                <useSystemClassLoader>true</useSystemClassLoader> <forkMode>always</forkMode> </configuration> </plugin> -->
-        </plugins>
-    </build>
-
-    <properties>
-        <source.version>1.8</source.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <aspectj.version>1.8.9</aspectj.version>
-        <org.slf4j.version>1.7.21</org.slf4j.version>
-        <logback.version>1.1.7</logback.version>
-        <maven-compiler-plugin.version>3.6.0</maven-compiler-plugin.version>
-        <junit.version>4.12</junit.version>
-    </properties>
-
-</project>

assertj/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-- [AssertJ’s Java 8 Features](http://www.baeldung.com/assertJ-java-8-features)
-- [AssertJ for Guava](http://www.baeldung.com/assertJ-for-guava)

assertj/pom.xml

@@ -1,61 +0,0 @@
-<?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>assertj</artifactId>
-    <version>1.0.0-SNAPSHOT</version>
-
-    <dependencies>
-
-        <dependency>
-            <groupId>com.google.guava</groupId>
-            <artifactId>guava</artifactId>
-            <version>${guava.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-guava</artifactId>
-            <version>3.0.0</version>
-        </dependency>
-
-        <dependency>
-            <groupId>junit</groupId>
-            <artifactId>junit</artifactId>
-            <version>${junit.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-core</artifactId>
-            <version>${assertj-core.version}</version>
-            <scope>test</scope>
-        </dependency>
-
-    </dependencies>
-
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-compiler-plugin</artifactId>
-                <version>${maven-compiler-plugin.version}</version>
-                <configuration>
-                    <source>1.8</source>
-                    <target>1.8</target>
-                </configuration>
-            </plugin>
-        </plugins>
-    </build>
-
-    <properties>
-        <guava.version>19.0</guava.version>
-        <assertj-guava.version>3.1.0</assertj-guava.version>
-        <junit.version>4.12</junit.version>
-        <assertj-core.version>3.6.1</assertj-core.version>
-
-        <maven-compiler-plugin.version>3.6.0</maven-compiler-plugin.version>
-    </properties>
-
-</project>

autovalue/pom.xml

@@ -6,6 +6,12 @@
     <version>1.0</version>
     <name>autovalue</name>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <build>
         <plugins>
             <plugin>

aws/pom.xml

@@ -7,6 +7,12 @@
 	<packaging>jar</packaging>
 	<name>aws</name>
 
+	<parent>
+	    <groupId>com.baeldung</groupId>
+	    <artifactId>parent-modules</artifactId>
+	    <version>1.0.0-SNAPSHOT</version>
+	 </parent>
+     
 	<properties>
 		<commons-io.version>2.5</commons-io.version>
 		<aws-lambda-java-events.version>1.3.0</aws-lambda-java-events.version>
@@ -19,12 +25,24 @@
 			<groupId>com.amazonaws</groupId>
 			<artifactId>aws-lambda-java-core</artifactId>
 			<version>${aws-lambda-java-core.version}</version>
+			<exclusions>
+				<exclusion>
+				    <artifactId>commons-logging</artifactId>
+				    <groupId>commons-logging</groupId>
+				</exclusion>
+			</exclusions>
 		</dependency>
 
 		<dependency>
 			<groupId>com.amazonaws</groupId>
 			<artifactId>aws-lambda-java-events</artifactId>
 			<version>${aws-lambda-java-events.version}</version>
+			<exclusions>
+				<exclusion>
+				    <artifactId>commons-logging</artifactId>
+				    <groupId>commons-logging</groupId>
+				</exclusion>
+			</exclusions>			
 		</dependency>
 
 		<dependency>

cdi/pom.xml

@@ -7,6 +7,12 @@
     <artifactId>cdi</artifactId>
     <version>1.0-SNAPSHOT</version>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <dependencies>
         <dependency>
             <groupId>org.springframework</groupId>

core-java-9/README.md

@@ -12,3 +12,4 @@
 - [Spring Security – Redirect to the Previous URL After Login](http://www.baeldung.com/spring-security-redirect-login)
 - [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
 - [Introduction to Java 9 StackWalking API](http://www.baeldung.com/java-9-stackwalking-api)
+- [Introduction to Project Jigsaw](http://www.baeldung.com/project-jigsaw-java-modularity)

core-java/README.md

@@ -92,3 +92,12 @@
 - [Removing all nulls from a List in Java](http://www.baeldung.com/java-remove-nulls-from-list)
 - [Removing all duplicates from a List in Java](http://www.baeldung.com/java-remove-duplicates-from-list)
 - [An Introduction to ThreadLocal in Java](http://www.baeldung.com/java-threadlocal)
+- [Using Math.pow in Java](http://www.baeldung.com/java-math-pow)
+- [Converting Strings to Enums in Java](http://www.baeldung.com/java-string-to-enum)
+- [Flattening Nested Collections in Java](http://www.baeldung.com/java-flatten-nested-collections)
+- [Quick Guide to the Java StringTokenizer](http://www.baeldung.com/java-stringtokenizer)
+- [JVM Log Forging](http://www.baeldung.com/jvm-log-forging)
+- [Guide to sun.misc.Unsafe](http://www.baeldung.com/java-unsafe)
+- [HashSet and TreeSet Comparison](http://www.baeldung.com/java-hashset-vs-treeset)
+- [How to Perform a Simple HTTP Request in Java](http://www.baeldung.com/java-http-request)
+- [Call Methods at Runtime Using Java Reflection](http://www.baeldung.com/java-method-reflection)

core-java/pom.xml

@@ -8,6 +8,12 @@
 
     <name>core-java</name>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+     </parent>
+     
     <dependencies>
         
         <!-- utils -->
@@ -92,11 +98,6 @@
             <version>${org.slf4j.version}</version>
             <!-- <scope>runtime</scope> --> <!-- some spring dependencies need to compile against jcl -->
         </dependency>
-        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
-            <groupId>org.slf4j</groupId>
-            <artifactId>log4j-over-slf4j</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
         <dependency>
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>
@@ -104,6 +105,13 @@
             <scope>provided</scope>
         </dependency>
         
+		<!-- mysql -->
+        <dependency>
+            <groupId>mysql</groupId>
+            <artifactId>mysql-connector-java</artifactId>
+            <version>${mysql.version}</version>
+        </dependency>
+
         <!-- test scoped -->
 
         <dependency>
@@ -140,13 +148,6 @@
             <scope>test</scope>
         </dependency>
 
-        <dependency>
-            <groupId>org.testng</groupId>
-            <artifactId>testng</artifactId>
-            <version>${testng.version}</version>
-            <scope>test</scope>
-        </dependency>
-
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
@@ -171,11 +172,28 @@
             <artifactId>moneta</artifactId>
             <version>1.1</version>
         </dependency>
+		<dependency>
+			<groupId>org.owasp.esapi</groupId>
+			<artifactId>esapi</artifactId>
+			<version>2.1.0.1</version>
+			<exclusions>
+				<exclusion>
+					<artifactId>commons-logging</artifactId>
+					<groupId>commons-logging</groupId>
+				</exclusion>
+			</exclusions>        
+		</dependency>               
 
 		<dependency>
 		    <groupId>org.owasp.esapi</groupId>
 		    <artifactId>esapi</artifactId>
 		    <version>2.1.0.1</version>
+	                <exclusions>
+	                    <exclusion>
+	                        <artifactId>commons-logging</artifactId>
+	                        <groupId>commons-logging</groupId>
+	                    </exclusion>
+	                </exclusions>        
 		</dependency>    
 
     </dependencies>
@@ -190,7 +208,6 @@
         </resources>
 
         <plugins>
-
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
@@ -200,7 +217,6 @@
                     <target>1.8</target>
                 </configuration>
             </plugin>
-
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
@@ -209,11 +225,11 @@
                         <exclude>**/*IntegrationTest.java</exclude>
                         <exclude>**/*LongRunningUnitTest.java</exclude>
                         <exclude>**/*ManualTest.java</exclude>
+                        <exclude>**/JdbcTest.java</exclude>
                     </excludes>
                     <testFailureIgnore>true</testFailureIgnore>
                 </configuration>
             </plugin>
-
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-dependency-plugin</artifactId>
@@ -244,7 +260,6 @@
                     </archive>
                 </configuration>
             </plugin>
-
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-assembly-plugin</artifactId>
@@ -268,7 +283,6 @@
                     </execution>
                 </executions>
             </plugin>
-
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-shade-plugin</artifactId>
@@ -289,7 +303,6 @@
                     </execution>
                 </executions>
             </plugin>
-
             <plugin>
                 <groupId>com.jolira</groupId>
                 <artifactId>onejar-maven-plugin</artifactId>
@@ -306,7 +319,6 @@
                     </execution>
                 </executions>
             </plugin>
-
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
@@ -322,7 +334,6 @@
                     </execution>
                 </executions>
             </plugin>
-
         </plugins>
 
     </build>
@@ -370,6 +381,9 @@
         <org.slf4j.version>1.7.21</org.slf4j.version>
         <logback.version>1.1.7</logback.version>
         
+        <!-- mysql -->
+        <mysql.version>6.0.6</mysql.version>
+
         <!-- util -->
         <guava.version>21.0</guava.version>
         <commons-lang3.version>3.5</commons-lang3.version>
@@ -387,7 +401,6 @@
         <org.hamcrest.version>1.3</org.hamcrest.version>
         <junit.version>4.12</junit.version>
         <mockito.version>1.10.19</mockito.version>
-        <testng.version>6.10</testng.version>
         <assertj.version>3.6.1</assertj.version>
         <avaitility.version>1.7.0</avaitility.version>
 

core-java/src/main/java/com/baeldung/concurrent/phaser/LongRunningAction.java

@@ -0,0 +1,27 @@
+package com.baeldung.concurrent.phaser;
+
+import java.util.concurrent.Phaser;
+
+class LongRunningAction implements Runnable {
+    private String threadName;
+    private Phaser ph;
+
+    LongRunningAction(String threadName, Phaser ph) {
+        this.threadName = threadName;
+        this.ph = ph;
+        ph.register();
+    }
+
+    @Override
+    public void run() {
+        System.out.println("This is phase " + ph.getPhase());
+        System.out.println("Thread " + threadName + " before long running action");
+        ph.arriveAndAwaitAdvance();
+        try {
+            Thread.sleep(20);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        ph.arriveAndDeregister();
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/skiplist/Event.java

@@ -0,0 +1,21 @@
+package com.baeldung.concurrent.skiplist;
+
+import java.time.ZonedDateTime;
+
+public class Event {
+    private final ZonedDateTime eventTime;
+    private final String content;
+
+    public Event(ZonedDateTime eventTime, String content) {
+        this.eventTime = eventTime;
+        this.content = content;
+    }
+
+    public ZonedDateTime getEventTime() {
+        return eventTime;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/skiplist/EventWindowSort.java

@@ -0,0 +1,29 @@
+package com.baeldung.concurrent.skiplist;
+
+import java.time.ZonedDateTime;
+import java.util.Comparator;
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ConcurrentSkipListMap;
+
+public class EventWindowSort {
+    private final ConcurrentSkipListMap<ZonedDateTime, String> events
+            = new ConcurrentSkipListMap<>(Comparator.comparingLong(value -> value.toInstant().toEpochMilli()));
+
+    public void acceptEvent(Event event) {
+        events.put(event.getEventTime(), event.getContent());
+    }
+
+    public ConcurrentNavigableMap<ZonedDateTime, String> getEventsFromLastMinute() {
+        return events.tailMap(ZonedDateTime
+                .now()
+                .minusMinutes(1));
+    }
+
+    public ConcurrentNavigableMap<ZonedDateTime, String> getEventsOlderThatOneMinute() {
+        return events.headMap(ZonedDateTime
+                .now()
+                .minusMinutes(1));
+    }
+
+}
+

core-java/src/main/java/com/baeldung/concurrent/sleepwait/ThreadA.java

@@ -0,0 +1,27 @@
+package com.baeldung.concurrent.sleepwait;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/***
+ * Example of waking up a waiting thread
+ */
+public class ThreadA {
+
+    private static final Logger LOG = LoggerFactory.getLogger(ThreadA.class);
+
+    private static final ThreadB b = new ThreadB();
+
+    public static void main(String... args) throws InterruptedException {
+        b.start();
+
+        synchronized (b) {
+            while (b.sum == 0) {
+                LOG.debug("Waiting for ThreadB to complete...");
+                b.wait();
+            }
+
+            LOG.debug("ThreadB has completed. Sum from that thread is: " + b.sum);
+        }
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/sleepwait/ThreadB.java

@@ -0,0 +1,20 @@
+package com.baeldung.concurrent.sleepwait;
+
+/***
+ * Example of waking up a waiting thread
+ */
+class ThreadB extends Thread {
+    int sum;
+
+    @Override
+    public void run() {
+        synchronized (this) {
+            int i = 0;
+            while (i < 100000) {
+                sum += i;
+                i++;
+            }
+            notify();
+        }
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/sleepwait/WaitSleepExample.java

@@ -0,0 +1,29 @@
+package com.baeldung.concurrent.sleepwait;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/***
+ * Example of wait() and sleep() methods
+ */
+public class WaitSleepExample {
+
+    private static final Logger LOG = LoggerFactory.getLogger(WaitSleepExample.class);
+
+    private static final Object LOCK = new Object();
+
+    public static void main(String... args) throws InterruptedException {
+        sleepWaitInSyncronizedBlocks();
+    }
+
+    private static void sleepWaitInSyncronizedBlocks() throws InterruptedException {
+        Thread.sleep(1000); // called on the thread
+        LOG.debug("Thread '" + Thread.currentThread().getName() + "' is woken after sleeping for 1 second");
+
+        synchronized (LOCK) {
+            LOCK.wait(1000); // called on the object, synchronization required
+            LOG.debug("Object '" + LOCK + "' is woken after waiting for 1 second");
+        }
+    }
+    
+}

core-java/src/main/java/com/baeldung/dirmonitoring/DirectoryMonitoringExample.java

@@ -1,14 +1,19 @@
 package com.baeldung.dirmonitoring;
 
-import java.io.File;
-
 import org.apache.commons.io.monitor.FileAlterationListener;
 import org.apache.commons.io.monitor.FileAlterationListenerAdaptor;
 import org.apache.commons.io.monitor.FileAlterationMonitor;
 import org.apache.commons.io.monitor.FileAlterationObserver;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
 
 public class DirectoryMonitoringExample {
 
+    private static final Logger LOG = LoggerFactory.getLogger(DirectoryMonitoringExample.class);
+
+
     public static final int POLL_INTERVAL = 500;
 
     public static void main(String[] args) throws Exception {
@@ -17,17 +22,17 @@ public class DirectoryMonitoringExample {
         FileAlterationListener listener = new FileAlterationListenerAdaptor() {
             @Override
             public void onFileCreate(File file) {
-                System.out.println("File: " + file.getName() + " created");
+                LOG.debug("File: " + file.getName() + " created");
             }
 
             @Override
             public void onFileDelete(File file) {
-                System.out.println("File: " + file.getName() + " deleted");
+                LOG.debug("File: " + file.getName() + " deleted");
             }
 
             @Override
             public void onFileChange(File file) {
-                System.out.println("File: " + file.getName() + " changed");
+                LOG.debug("File: " + file.getName() + " changed");
             }
         };
         observer.addListener(listener);

core-java/src/main/java/com/baeldung/doublecolon/MacbookPro.java

@@ -1,9 +1,14 @@
 package com.baeldung.doublecolon;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.util.function.Function;
 
 public class MacbookPro extends Computer {
 
+    private static final Logger LOG = LoggerFactory.getLogger(MacbookPro.class);
+
     public MacbookPro(int age, String color) {
         super(age, color);
     }
@@ -14,12 +19,12 @@ public class MacbookPro extends Computer {
 
     @Override
     public void turnOnPc() {
-        System.out.println("MacbookPro turned on");
+        LOG.debug("MacbookPro turned on");
     }
 
     @Override
     public void turnOffPc() {
-        System.out.println("MacbookPro turned off");
+        LOG.debug("MacbookPro turned off");
     }
 
     @Override
@@ -27,7 +32,7 @@ public class MacbookPro extends Computer {
 
         Function<Double, Double> function = super::calculateValue;
         final Double pcValue = function.apply(initialValue);
-        System.out.println("First value is:" + pcValue);
+        LOG.debug("First value is:" + pcValue);
         return pcValue + (initialValue / 10);
 
     }

core-java/src/main/java/com/baeldung/dynamicproxy/DynamicInvocationHandler.java

@@ -0,0 +1,19 @@
+package com.baeldung.dynamicproxy;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+
+public class DynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(DynamicInvocationHandler.class);
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        LOGGER.info("Invoked method: {}", method.getName());
+
+        return 42;
+    }
+}

core-java/src/main/java/com/baeldung/dynamicproxy/TimingDynamicInvocationHandler.java

@@ -0,0 +1,36 @@
+package com.baeldung.dynamicproxy;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class TimingDynamicInvocationHandler implements InvocationHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(TimingDynamicInvocationHandler.class);
+    private final Map<String, Method> methods = new HashMap<>();
+
+    private Object target;
+
+    public TimingDynamicInvocationHandler(Object target) {
+        this.target = target;
+
+        for(Method method: target.getClass().getDeclaredMethods()) {
+            this.methods.put(method.getName(), method);
+        }
+    }
+
+    @Override
+    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+        long start = System.nanoTime();
+        Object result = methods.get(method.getName()).invoke(target, args);
+        long elapsed = System.nanoTime() - start;
+
+        LOGGER.info("Executing {} finished in {} ns", method.getName(), elapsed);
+
+        return result;
+    }
+}

core-java/src/main/java/com/baeldung/exceptions/StackTraceToString.java

@@ -0,0 +1,30 @@
+package com.baeldung.exceptions;
+
+import org.apache.commons.lang3.exception.ExceptionUtils;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+public class StackTraceToString {
+
+    public static void main(String[] args) {
+        // Convert a StackTrace to String using core java
+        try {
+            throw new NullPointerException();
+        } catch (Exception e) {
+            StringWriter sw = new StringWriter();
+            PrintWriter pw = new PrintWriter(sw);
+            e.printStackTrace(pw);
+
+            System.out.println(sw.toString());
+        }
+
+        // Convert a StackTrace to String using Apache Commons
+        try {
+            throw new IndexOutOfBoundsException();
+        } catch (Exception e) {
+            System.out.println(ExceptionUtils.getStackTrace(e));
+        }
+    }
+
+}

core-java/src/main/java/com/baeldung/http/ParameterStringBuilder.java

@@ -0,0 +1,21 @@
+package com.baeldung.http;
+
+import java.io.UnsupportedEncodingException;
+import java.net.URLEncoder;
+import java.util.Map;
+
+public class ParameterStringBuilder {
+    public static String getParamsString(Map<String, String> params) throws UnsupportedEncodingException {
+        StringBuilder result = new StringBuilder();
+
+        for (Map.Entry<String, String> entry : params.entrySet()) {
+            result.append(URLEncoder.encode(entry.getKey(), "UTF-8"));
+            result.append("=");
+            result.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
+            result.append("&");
+        }
+
+        String resultString = result.toString();
+        return resultString.length() > 0 ? resultString.substring(0, resultString.length() - 1) : resultString;
+    }
+}

core-java/src/main/java/com/baeldung/java/map/MyKey.java

@@ -1,6 +1,11 @@
 package com.baeldung.java.map;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public class MyKey {
+    private static final Logger LOG = LoggerFactory.getLogger(MyKey.class);
+    
     private String name;
     private int id;
 
@@ -27,7 +32,7 @@ public class MyKey {
 
     @Override
     public int hashCode() {
-        System.out.println("Calling hashCode()");
+        LOG.debug("Calling hashCode()");
         return id;
     }
 
@@ -38,7 +43,7 @@ public class MyKey {
 
     @Override
     public boolean equals(Object obj) {
-        System.out.println("Calling equals() for key: " + obj);
+        LOG.debug("Calling equals() for key: " + obj);
         if (this == obj)
             return true;
         if (obj == null)

core-java/src/main/java/com/baeldung/java/reflection/Operations.java

@@ -0,0 +1,21 @@
+package com.baeldung.java.reflection;
+
+public class Operations {
+
+    public double publicSum(int a, double b) {
+        return a + b;
+    }
+
+    public static double publicStaticMultiply(float a, long b) {
+        return a * b;
+    }
+
+    private boolean privateAnd(boolean a, boolean b) {
+        return a && b;
+    }
+
+    protected int protectedMax(int a, int b) {
+        return a > b ? a : b;
+    }
+
+}

core-java/src/main/java/com/baeldung/jdbc/Employee.java

@@ -0,0 +1,51 @@
+package com.baeldung.jdbc;
+
+public class Employee {
+    private int id;
+    private String name;
+    private String position;
+    private double salary;
+
+    public Employee() {
+    }
+
+    public Employee(int id, String name, double salary, String position) {
+        this.id = id;
+        this.name = name;
+        this.salary = salary;
+        this.position = position;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public double getSalary() {
+        return salary;
+    }
+
+    public void setSalary(double salary) {
+        this.salary = salary;
+    }
+
+    public String getPosition() {
+        return position;
+    }
+
+    public void setPosition(String position) {
+        this.position = position;
+    }
+
+}

core-java/src/main/java/com/baeldung/jmx/Game.java

@@ -1,23 +1,28 @@
 package com.baeldung.jmx;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 public class Game implements GameMBean {
 
+    private static final Logger LOG = LoggerFactory.getLogger(Game.class);
+
     private String playerName;
 
     @Override
     public void playFootball(String clubName) {
-        System.out.println(this.playerName + " playing football for " + clubName);
+        LOG.debug(this.playerName + " playing football for " + clubName);
     }
 
     @Override
     public String getPlayerName() {
-        System.out.println("Return playerName " + this.playerName);
+        LOG.debug("Return playerName " + this.playerName);
         return playerName;
     }
 
     @Override
     public void setPlayerName(String playerName) {
-        System.out.println("Set playerName to value " + playerName);
+        LOG.debug("Set playerName to value " + playerName);
         this.playerName = playerName;
     }
 

core-java/src/main/java/com/baeldung/jmx/JMXTutorialMainlauncher.java

@@ -1,19 +1,20 @@
 package com.baeldung.jmx;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.management.*;
 import java.lang.management.ManagementFactory;
-import javax.management.InstanceAlreadyExistsException;
-import javax.management.MBeanRegistrationException;
-import javax.management.MBeanServer;
-import javax.management.MalformedObjectNameException;
-import javax.management.NotCompliantMBeanException;
-import javax.management.ObjectName;
 
 public class JMXTutorialMainlauncher {
 
+    private static final Logger LOG = LoggerFactory.getLogger(JMXTutorialMainlauncher.class);
+
+
     public static void main(String[] args) {
         // TODO Auto-generated method stub
 
-        System.out.println("This is basic JMX tutorial");
+        LOG.debug("This is basic JMX tutorial");
         ObjectName objectName = null;
         try {
             objectName = new ObjectName("com.baeldung.tutorial:type=basic,name=game");
@@ -27,8 +28,8 @@ public class JMXTutorialMainlauncher {
         } catch (InstanceAlreadyExistsException | MBeanRegistrationException | NotCompliantMBeanException e) {
             e.printStackTrace();
         }
-        System.out.println("Registration for Game mbean with the platform server is successfull");
+        LOG.debug("Registration for Game mbean with the platform server is successfull");
-        System.out.println("Please open jconsole to access Game mbean");
+        LOG.debug("Please open jconsole to access Game mbean");
         while (true) {
             // to ensure application does not terminate
         }

core-java/src/main/java/com/baeldung/socket/EchoClient.java

@@ -1,9 +1,16 @@
 package com.baeldung.socket;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.io.*;
 import java.net.*;
 
 public class EchoClient {
+
+
+    private static final Logger LOG = LoggerFactory.getLogger(EchoClient.class);
+    
     private Socket clientSocket;
     private PrintWriter out;
     private BufferedReader in;
@@ -14,7 +21,7 @@ public class EchoClient {
             out = new PrintWriter(clientSocket.getOutputStream(), true);
             in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
         } catch (IOException e) {
-            System.out.print(e);
+            LOG.debug("Error when initializing connection", e);
         }
 
     }
@@ -34,7 +41,7 @@ public class EchoClient {
             out.close();
             clientSocket.close();
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug("error when closing", e);
         }
 
     }

core-java/src/main/java/com/baeldung/socket/EchoMultiServer.java

@@ -1,9 +1,15 @@
 package com.baeldung.socket;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.net.*;
 import java.io.*;
 
 public class EchoMultiServer {
+
+    private static final Logger LOG = LoggerFactory.getLogger(EchoMultiServer.class);
+
     private ServerSocket serverSocket;
 
     public void start(int port) {
@@ -57,7 +63,7 @@ public class EchoMultiServer {
                 clientSocket.close();
 
             } catch (IOException e) {
-                e.printStackTrace();
+                LOG.debug(e.getMessage());
             }
         }
     }

core-java/src/main/java/com/baeldung/socket/EchoServer.java

@@ -1,9 +1,15 @@
 package com.baeldung.socket;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.net.*;
 import java.io.*;
 
 public class EchoServer {
+
+    private static final Logger LOG = LoggerFactory.getLogger(EchoServer.class);
+
     private ServerSocket serverSocket;
     private Socket clientSocket;
     private PrintWriter out;
@@ -24,7 +30,7 @@ public class EchoServer {
                 out.println(inputLine);
             }
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug(e.getMessage());
         }
 
     }
@@ -36,7 +42,7 @@ public class EchoServer {
             clientSocket.close();
             serverSocket.close();
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug(e.getMessage());
         }
 
     }

core-java/src/main/java/com/baeldung/socket/GreetClient.java

@@ -1,5 +1,8 @@
 package com.baeldung.socket;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -7,6 +10,9 @@ import java.io.PrintWriter;
 import java.net.Socket;
 
 public class GreetClient {
+
+    private static final Logger LOG = LoggerFactory.getLogger(EchoMultiServer.class);
+
     private Socket clientSocket;
     private PrintWriter out;
     private BufferedReader in;
@@ -17,7 +23,7 @@ public class GreetClient {
             out = new PrintWriter(clientSocket.getOutputStream(), true);
             in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
         } catch (IOException e) {
-
+            LOG.debug(e.getMessage());
         }
 
     }
@@ -37,7 +43,7 @@ public class GreetClient {
             out.close();
             clientSocket.close();
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug(e.getMessage());
         }
     }
 

core-java/src/main/java/com/baeldung/socket/GreetServer.java

@@ -1,9 +1,15 @@
 package com.baeldung.socket;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.net.*;
 import java.io.*;
 
 public class GreetServer {
+
+    private static final Logger LOG = LoggerFactory.getLogger(GreetServer.class);
+
     private ServerSocket serverSocket;
     private Socket clientSocket;
     private PrintWriter out;
@@ -21,7 +27,7 @@ public class GreetServer {
             else
                 out.println("unrecognised greeting");
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug(e.getMessage());
         }
 
     }
@@ -33,7 +39,7 @@ public class GreetServer {
             clientSocket.close();
             serverSocket.close();
         } catch (IOException e) {
-            e.printStackTrace();
+            LOG.debug(e.getMessage());
         }
 
     }

core-java/src/main/java/com/baeldung/stackoverflowerror/AccountHolder.java

@@ -0,0 +1,8 @@
+package com.baeldung.stackoverflowerror;
+
+public class AccountHolder {
+    private String firstName;
+    private String lastName;
+
+    AccountHolder jointAccountHolder = new AccountHolder();
+}

core-java/src/main/java/com/baeldung/stackoverflowerror/ClassOne.java

@@ -0,0 +1,16 @@
+package com.baeldung.stackoverflowerror;
+
+public class ClassOne {
+    private int oneValue;
+    private ClassTwo clsTwoInstance = null;
+
+    public ClassOne() {
+        oneValue = 0;
+        clsTwoInstance = new ClassTwo();
+    }
+
+    public ClassOne(int oneValue, ClassTwo clsTwoInstance) {
+        this.oneValue = oneValue;
+        this.clsTwoInstance = clsTwoInstance;
+    }
+}

core-java/src/main/java/com/baeldung/stackoverflowerror/ClassTwo.java

@@ -0,0 +1,16 @@
+package com.baeldung.stackoverflowerror;
+
+public class ClassTwo {
+    private int twoValue;
+    private ClassOne clsOneInstance = null;
+
+    public ClassTwo() {
+        twoValue = 10;
+        clsOneInstance = new ClassOne();
+    }
+
+    public ClassTwo(int twoValue, ClassOne clsOneInstance) {
+        this.twoValue = twoValue;
+        this.clsOneInstance = clsOneInstance;
+    }
+}

core-java/src/main/java/com/baeldung/stackoverflowerror/InfiniteRecursionWithTerminationCondition.java

@@ -0,0 +1,7 @@
+package com.baeldung.stackoverflowerror;
+
+public class InfiniteRecursionWithTerminationCondition {
+    public int calculateFactorial(final int number) {
+        return number == 1 ? 1 : number * calculateFactorial(number - 1);
+    }
+}

core-java/src/main/java/com/baeldung/stackoverflowerror/RecursionWithCorrectTerminationCondition.java

@@ -0,0 +1,7 @@
+package com.baeldung.stackoverflowerror;
+
+public class RecursionWithCorrectTerminationCondition {
+    public static int calculateFactorial(final int number) {
+        return number <= 1 ? 1 : number * calculateFactorial(number - 1);
+    }
+}

core-java/src/main/java/com/baeldung/stackoverflowerror/UnintendedInfiniteRecursion.java

@@ -0,0 +1,7 @@
+package com.baeldung.stackoverflowerror;
+
+public class UnintendedInfiniteRecursion {
+    public int calculateFactorial(int number) {
+        return number * calculateFactorial(number - 1);
+    }
+}

core-java/src/main/java/com/baeldung/stream/InfiniteStreams.java

@@ -1,9 +1,15 @@
 package com.baeldung.stream;
 
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.util.stream.Stream;
 
 public class InfiniteStreams {
+
+    private static final Logger LOG = LoggerFactory.getLogger(InfiniteStreams.class);
+
     public static void main(String[] args) {
         doWhileOldWay();
 
@@ -15,7 +21,7 @@ public class InfiniteStreams {
 
         int i = 0;
         while (i < 10) {
-            System.out.println(i);
+            LOG.debug("{}", i);
             i++;
         }
     }

core-java/src/main/java/com/baeldung/threadlocal/ThreadLocalWithUserContext.java

@@ -1,7 +1,11 @@
 package com.baeldung.threadlocal;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class ThreadLocalWithUserContext implements Runnable {
+    private static final Logger LOG = LoggerFactory.getLogger(ThreadLocalWithUserContext.class);
+    
     private static final ThreadLocal<Context> userContext = new ThreadLocal<>();
     private final Integer userId;
     private UserRepository userRepository = new UserRepository();
@@ -15,6 +19,6 @@ public class ThreadLocalWithUserContext implements Runnable {
     public void run() {
         String userName = userRepository.getUserNameForUserId(userId);
         userContext.set(new Context(userName));
-        System.out.println("thread context for given userId: " + userId + " is: " + userContext.get());
+        LOG.debug("thread context for given userId: " + userId + " is: " + userContext.get());
     }
 }

core-java/src/main/java/com/baeldung/transferqueue/Consumer.java

@@ -0,0 +1,42 @@
+package com.baeldung.transferqueue;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.TransferQueue;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class Consumer implements Runnable {
+    private static final Logger LOG = LoggerFactory.getLogger(Consumer.class);
+
+    
+    private final TransferQueue<String> transferQueue;
+    private final String name;
+    private final int numberOfMessagesToConsume;
+    public final AtomicInteger numberOfConsumedMessages = new AtomicInteger();
+
+    public Consumer(TransferQueue<String> transferQueue, String name, int numberOfMessagesToConsume) {
+        this.transferQueue = transferQueue;
+        this.name = name;
+        this.numberOfMessagesToConsume = numberOfMessagesToConsume;
+    }
+
+    @Override
+    public void run() {
+        for (int i = 0; i < numberOfMessagesToConsume; i++) {
+            try {
+                LOG.debug("Consumer: " + name + " is waiting to take element...");
+                String element = transferQueue.take();
+                longProcessing(element);
+                LOG.debug("Consumer: " + name + " received element: " + element);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    private void longProcessing(String element) throws InterruptedException {
+        numberOfConsumedMessages.incrementAndGet();
+        Thread.sleep(500);
+    }
+}

core-java/src/main/java/com/baeldung/transferqueue/Producer.java

@@ -0,0 +1,41 @@
+package com.baeldung.transferqueue;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TransferQueue;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class Producer implements Runnable {
+    private static final Logger LOG = LoggerFactory.getLogger(Producer.class);
+
+    private final TransferQueue<String> transferQueue;
+    private final String name;
+    private final Integer numberOfMessagesToProduce;
+    public final AtomicInteger numberOfProducedMessages = new AtomicInteger();
+
+    public Producer(TransferQueue<String> transferQueue, String name, Integer numberOfMessagesToProduce) {
+        this.transferQueue = transferQueue;
+        this.name = name;
+        this.numberOfMessagesToProduce = numberOfMessagesToProduce;
+    }
+
+    @Override
+    public void run() {
+        for (int i = 0; i < numberOfMessagesToProduce; i++) {
+            try {
+                LOG.debug("Producer: " + name + " is waiting to transfer...");
+                boolean added = transferQueue.tryTransfer("A" + i, 4000, TimeUnit.MILLISECONDS);
+                if (added) {
+                    numberOfProducedMessages.incrementAndGet();
+                    LOG.debug("Producer: " + name + " transferred element: A" + i);
+                } else {
+                    LOG.debug("can not add an element due to the timeout");
+                }
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+}

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

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
+        http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd" version="2.1">
+
+    <!-- JDO tutorial "unit" -->
+    <persistence-unit name="Tutorial">
+        <exclude-unlisted-classes/>
+		<properties>
+			<property name="javax.jdo.PersistenceManagerFactoryClass" value="org.datanucleus.api.jdo.JDOPersistenceManagerFactory"/>		
+		    <property name="javax.jdo.option.ConnectionURL" value="jdbc:h2:mem:mypersistence"/>
+		    <property name="javax.jdo.option.ConnectionDriverName" value="org.h2.Driver"/>
+		    <property name="javax.jdo.option.ConnectionUserName" value="sa"/>
+		    <property name="javax.jdo.option.ConnectionPassword" value=""/>
+		    <property name="datanucleus.schema.autoCreateAll" value="true"/>
+		</properties>
+    </persistence-unit>
+</persistence>
+

core-java/src/main/resources/log4j.properties

@@ -0,0 +1,6 @@
+log4j.rootLogger=DEBUG, A1
+
+log4j.appender.A1=org.apache.log4j.ConsoleAppender
+
+log4j.appender.A1.layout=org.apache.log4j.PatternLayout
+log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

core-java/src/test/java/com/baeldung/PrimitiveConversionsJUnitTest.java

@@ -1,14 +1,15 @@
 package com.baeldung;
 
 import org.junit.Test;
-import static org.junit.Assert.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static org.junit.Assert.assertEquals;
 
-/**
- *
- * @author paulo.motta
- */
 public class PrimitiveConversionsJUnitTest {
 
+    private static final Logger LOG = LoggerFactory.getLogger(PrimitiveConversionsJUnitTest.class);
+    
     @Test
     public void givenDataWithLessBits_whenAttributingToLargerSizeVariable_thenNoSpecialNotation() {
         int myInt = 127;
@@ -60,36 +61,36 @@ public class PrimitiveConversionsJUnitTest {
     @Test
     public void givenByteValue_whenConvertingToChar_thenWidenAndNarrowTakesPlace(){
         byte myLargeValueByte = (byte) 130;   //0b10000010
-        System.out.println(myLargeValueByte); //0b10000010 -126
+        LOG.debug("{}", myLargeValueByte); //0b10000010 -126
         assertEquals( -126, myLargeValueByte);
         
         int myLargeValueInt = myLargeValueByte;
-        System.out.println(myLargeValueInt); //0b11111111 11111111 11111111 10000010 -126
+        LOG.debug("{}", myLargeValueInt); //0b11111111 11111111 11111111 10000010 -126
         assertEquals( -126, myLargeValueInt);
         
         char myLargeValueChar = (char) myLargeValueByte;
-        System.out.println(myLargeValueChar);//0b11111111 10000010 unsigned 0xFF82
+        LOG.debug("{}", myLargeValueChar);//0b11111111 10000010 unsigned 0xFF82
         assertEquals(0xFF82, myLargeValueChar);
         
         myLargeValueInt = myLargeValueChar;
-        System.out.println(myLargeValueInt); //0b11111111 10000010  65410
+        LOG.debug("{}", myLargeValueInt); //0b11111111 10000010  65410
         assertEquals(65410, myLargeValueInt);
         
         byte myOtherByte = (byte) myLargeValueInt;
-        System.out.println(myOtherByte); //0b10000010 -126
+        LOG.debug("{}", myOtherByte); //0b10000010 -126
         assertEquals( -126, myOtherByte);
         
         
         char myLargeValueChar2 = 130; //This is an int not a byte!
-        System.out.println(myLargeValueChar2);//0b00000000 10000010 unsigned 0x0082
+        LOG.debug("{}", myLargeValueChar2);//0b00000000 10000010 unsigned 0x0082
         assertEquals(0x0082, myLargeValueChar2);
         
         int myLargeValueInt2 = myLargeValueChar2;
-        System.out.println(myLargeValueInt2); //0b00000000 10000010  130
+        LOG.debug("{}", myLargeValueInt2); //0b00000000 10000010  130
         assertEquals(130, myLargeValueInt2);
         
         byte myOtherByte2 = (byte) myLargeValueInt2;
-        System.out.println(myOtherByte2); //0b10000010 -126
+        LOG.debug("{}", myOtherByte2); //0b10000010 -126
         assertEquals( -126, myOtherByte2);
     }
     

core-java/src/test/java/com/baeldung/completablefuture/CompletableFutureUnitTest.java

@@ -1,20 +1,21 @@
 package com.baeldung.completablefuture;
 
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
-import java.util.concurrent.CancellationException;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
-
-import org.junit.Test;
-
 public class CompletableFutureUnitTest {
 
+    private static final Logger LOG = LoggerFactory.getLogger(CompletableFutureUnitTest.class);
+
+
     @Test
     public void whenRunningCompletableFutureAsynchronously_thenGetMethodWaitsForResult() throws InterruptedException, ExecutionException {
         Future<String> completableFuture = calculateAsync();
@@ -72,7 +73,7 @@ public class CompletableFutureUnitTest {
     public void whenAddingThenAcceptToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
         CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
 
-        CompletableFuture<Void> future = completableFuture.thenAccept(s -> System.out.println("Computation returned: " + s));
+        CompletableFuture<Void> future = completableFuture.thenAccept(s -> LOG.debug("Computation returned: " + s));
 
         future.get();
     }
@@ -81,7 +82,7 @@ public class CompletableFutureUnitTest {
     public void whenAddingThenRunToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
         CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
 
-        CompletableFuture<Void> future = completableFuture.thenRun(() -> System.out.println("Computation finished."));
+        CompletableFuture<Void> future = completableFuture.thenRun(() -> LOG.debug("Computation finished."));
 
         future.get();
     }
@@ -111,7 +112,7 @@ public class CompletableFutureUnitTest {
 
     @Test
     public void whenUsingThenAcceptBoth_thenWaitForExecutionOfBothFutures() throws ExecutionException, InterruptedException {
-        CompletableFuture.supplyAsync(() -> "Hello").thenAcceptBoth(CompletableFuture.supplyAsync(() -> " World"), (s1, s2) -> System.out.println(s1 + s2));
+        CompletableFuture.supplyAsync(() -> "Hello").thenAcceptBoth(CompletableFuture.supplyAsync(() -> " World"), (s1, s2) -> LOG.debug(s1 + s2));
     }
 
     @Test

core-java/src/test/java/com/baeldung/concurrent/accumulator/LongAccumulatorTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.concurrent.accumulator;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAccumulator;
+import java.util.function.LongBinaryOperator;
+import java.util.stream.IntStream;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class LongAccumulatorTest {
+
+    @Test
+    public void givenLongAccumulator_whenApplyActionOnItFromMultipleThrads_thenShouldProduceProperResult() throws InterruptedException {
+        //given
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+        LongBinaryOperator sum = Long::sum;
+        LongAccumulator accumulator = new LongAccumulator(sum, 0L);
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable accumulateAction = () -> IntStream
+                .rangeClosed(0, numberOfIncrements)
+                .forEach(accumulator::accumulate);
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(accumulateAction);
+        }
+
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+        assertEquals(accumulator.get(), 20200);
+
+
+    }
+}

core-java/src/test/java/com/baeldung/concurrent/adder/LongAdderTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.concurrent.adder;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAdder;
+import java.util.stream.IntStream;
+
+import static com.jayway.awaitility.Awaitility.await;
+import static junit.framework.TestCase.assertEquals;
+
+public class LongAdderTest {
+    @Test
+    public void givenMultipleThread_whenTheyWriteToSharedLongAdder_thenShouldCalculateSumForThem() throws InterruptedException {
+        //given
+        LongAdder counter = new LongAdder();
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable incrementAction = () -> IntStream
+          .range(0, numberOfIncrements)
+          .forEach((i) -> counter.increment());
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(incrementAction);
+        }
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+
+        assertEquals(counter.sum(), numberOfIncrements * numberOfThreads);
+        assertEquals(counter.sum(), numberOfIncrements * numberOfThreads);
+    }
+
+    @Test
+    public void givenMultipleThread_whenTheyWriteToSharedLongAdder_thenShouldCalculateSumForThemAndResetAdderAfterward() throws InterruptedException {
+        //given
+        LongAdder counter = new LongAdder();
+        ExecutorService executorService = Executors.newFixedThreadPool(8);
+
+        int numberOfThreads = 4;
+        int numberOfIncrements = 100;
+
+        //when
+        Runnable incrementAction = () -> IntStream
+          .range(0, numberOfIncrements)
+          .forEach((i) -> counter.increment());
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(incrementAction);
+        }
+
+        //then
+        executorService.awaitTermination(500, TimeUnit.MILLISECONDS);
+        executorService.shutdown();
+
+        assertEquals(counter.sumThenReset(), numberOfIncrements * numberOfThreads);
+
+        await().until(() -> assertEquals(counter.sum(), 0));
+    }
+}

core-java/src/test/java/com/baeldung/concurrent/copyonwrite/CopyOnWriteArrayListTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.concurrent.copyonwrite;
+
+
+import org.junit.Test;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+public class CopyOnWriteArrayListTest {
+
+    @Test
+    public void givenCopyOnWriteList_whenIterateAndAddElementToUnderneathList_thenShouldNotChangeIterator() {
+        //given
+        final CopyOnWriteArrayList<Integer> numbers =
+                new CopyOnWriteArrayList<>(new Integer[]{1, 3, 5, 8});
+
+        //when
+        Iterator<Integer> iterator = numbers.iterator();
+        numbers.add(10);
+
+        //then
+        List<Integer> result = new LinkedList<>();
+        iterator.forEachRemaining(result::add);
+        assertThat(result).containsOnly(1, 3, 5, 8);
+
+        //and
+        Iterator<Integer> iterator2 = numbers.iterator();
+        List<Integer> result2 = new LinkedList<>();
+        iterator2.forEachRemaining(result2::add);
+
+        //then
+        assertThat(result2).containsOnly(1, 3, 5, 8, 10);
+
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void givenCopyOnWriteList_whenIterateOverItAndTryToRemoveElement_thenShouldThrowException() {
+        //given
+        final CopyOnWriteArrayList<Integer> numbers =
+                new CopyOnWriteArrayList<>(new Integer[]{1, 3, 5, 8});
+
+        //when
+        Iterator<Integer> iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            iterator.remove();
+        }
+    }
+}

core-java/src/test/java/com/baeldung/concurrent/future/SquareCalculatorIntegrationTest.java

@@ -1,22 +1,22 @@
 package com.baeldung.concurrent.future;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
-
-import java.util.concurrent.CancellationException;
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
-
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TestName;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.*;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class SquareCalculatorIntegrationTest {
+
+    private static final Logger LOG = LoggerFactory.getLogger(SquareCalculatorIntegrationTest.class);
 
-public class SquareCalculatorUnitTest {
 
     @Rule
     public TestName name = new TestName();
@@ -33,7 +33,7 @@ public class SquareCalculatorUnitTest {
         Future<Integer> result2 = squareCalculator.calculate(1000);
 
         while (!result1.isDone() || !result2.isDone()) {
-            System.out.println(String.format("Task 1 is %s and Task 2 is %s.", result1.isDone() ? "done" : "not done", result2.isDone() ? "done" : "not done"));
+            LOG.debug(String.format("Task 1 is %s and Task 2 is %s.", result1.isDone() ? "done" : "not done", result2.isDone() ? "done" : "not done"));
 
             Thread.sleep(300);
         }
@@ -59,7 +59,7 @@ public class SquareCalculatorUnitTest {
         Future<Integer> result2 = squareCalculator.calculate(1000);
 
         while (!result1.isDone() || !result2.isDone()) {
-            System.out.println(String.format("Task 1 is %s and Task 2 is %s.", result1.isDone() ? "done" : "not done", result2.isDone() ? "done" : "not done"));
+            LOG.debug(String.format("Task 1 is %s and Task 2 is %s.", result1.isDone() ? "done" : "not done", result2.isDone() ? "done" : "not done"));
 
             Thread.sleep(300);
         }
@@ -89,6 +89,6 @@ public class SquareCalculatorUnitTest {
 
     @After
     public void end() {
-        System.out.println(String.format("Test %s took %s ms \n", name.getMethodName(), System.currentTimeMillis() - start));
+        LOG.debug(String.format("Test %s took %s ms \n", name.getMethodName(), System.currentTimeMillis() - start));
     }
 }

core-java/src/test/java/com/baeldung/concurrent/phaser/PhaserTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.concurrent.phaser;
+
+import org.junit.FixMethodOrder;
+import org.junit.Test;
+import org.junit.runners.MethodSorters;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Phaser;
+
+import static junit.framework.TestCase.assertEquals;
+
+@FixMethodOrder(MethodSorters.NAME_ASCENDING)
+public class PhaserTest {
+
+    @Test
+    public void givenPhaser_whenCoordinateWorksBetweenThreads_thenShouldCoordinateBetweenMultiplePhases() {
+        //given
+        ExecutorService executorService = Executors.newCachedThreadPool();
+        Phaser ph = new Phaser(1);
+        assertEquals(0, ph.getPhase());
+
+        //when
+        executorService.submit(new LongRunningAction("thread-1", ph));
+        executorService.submit(new LongRunningAction("thread-2", ph));
+        executorService.submit(new LongRunningAction("thread-3", ph));
+
+        //then
+        ph.arriveAndAwaitAdvance();
+        assertEquals(1, ph.getPhase());
+
+        //and
+        executorService.submit(new LongRunningAction("thread-4", ph));
+        executorService.submit(new LongRunningAction("thread-5", ph));
+        ph.arriveAndAwaitAdvance();
+        assertEquals(2, ph.getPhase());
+
+
+        ph.arriveAndDeregister();
+    }
+}

core-java/src/test/java/com/baeldung/concurrent/priorityblockingqueue/PriorityBlockingQueueIntegrationTest.java

@@ -1,6 +1,8 @@
 package com.baeldung.concurrent.priorityblockingqueue;
 
 import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
 import java.util.concurrent.PriorityBlockingQueue;
@@ -9,7 +11,10 @@ import java.util.concurrent.TimeUnit;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.util.Lists.newArrayList;
 
-public class PriorityBlockingQueueUnitTest {
+public class PriorityBlockingQueueIntegrationTest {
+
+    private static final Logger LOG = LoggerFactory.getLogger(PriorityBlockingQueueIntegrationTest.class);
+
 
     @Test
     public void givenUnorderedValues_whenPolling_thenShouldOrderQueue() throws InterruptedException {
@@ -32,11 +37,11 @@ public class PriorityBlockingQueueUnitTest {
         PriorityBlockingQueue<Integer> queue = new PriorityBlockingQueue<>();
 
         final Thread thread = new Thread(() -> {
-            System.out.println("Polling...");
+            LOG.debug("Polling...");
             while (true) {
                 try {
                     Integer poll = queue.take();
-                    System.out.println("Polled: " + poll);
+                    LOG.debug("Polled: " + poll);
                 } catch (InterruptedException e) {
                 }
             }
@@ -44,7 +49,7 @@ public class PriorityBlockingQueueUnitTest {
         thread.start();
 
         Thread.sleep(TimeUnit.SECONDS.toMillis(5));
-        System.out.println("Adding to queue");
+        LOG.debug("Adding to queue");
 
         queue.addAll(newArrayList(1, 5, 6, 1, 2, 6, 7));
         Thread.sleep(TimeUnit.SECONDS.toMillis(1));

core-java/src/test/java/com/baeldung/concurrent/skiplist/ConcurrentSkipListSetIntegrationTest.java

@@ -0,0 +1,120 @@
+package com.baeldung.concurrent.skiplist;
+
+import org.junit.Test;
+
+import java.time.ZonedDateTime;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.IntStream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class ConcurrentSkipListSetIntegrationTest {
+
+    @Test
+    public void givenThreadsProducingEvents_whenGetForEventsFromLastMinute_thenReturnThoseEventsInTheLockFreeWay() throws InterruptedException {
+        //given
+        ExecutorService executorService = Executors.newFixedThreadPool(3);
+        EventWindowSort eventWindowSort = new EventWindowSort();
+        int numberOfThreads = 2;
+        //when
+        Runnable producer = () -> IntStream
+          .rangeClosed(0, 100)
+          .forEach(index -> eventWindowSort.acceptEvent(new Event(ZonedDateTime
+            .now()
+            .minusSeconds(index), UUID
+            .randomUUID()
+            .toString())));
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(producer);
+        }
+
+        Thread.sleep(500);
+
+        ConcurrentNavigableMap<ZonedDateTime, String> eventsFromLastMinute = eventWindowSort.getEventsFromLastMinute();
+
+        long eventsOlderThanOneMinute = eventsFromLastMinute
+          .entrySet()
+          .stream()
+          .filter(e -> e
+            .getKey()
+            .isBefore(ZonedDateTime
+              .now()
+              .minusMinutes(1)))
+          .count();
+        assertEquals(eventsOlderThanOneMinute, 0);
+
+        long eventYoungerThanOneMinute = eventsFromLastMinute
+          .entrySet()
+          .stream()
+          .filter(e -> e
+            .getKey()
+            .isAfter(ZonedDateTime
+              .now()
+              .minusMinutes(1)))
+          .count();
+
+        //then
+        assertTrue(eventYoungerThanOneMinute > 0);
+
+        executorService.awaitTermination(1, TimeUnit.SECONDS);
+        executorService.shutdown();
+    }
+
+    @Test
+    public void givenThreadsProducingEvents_whenGetForEventsOlderThanOneMinute_thenReturnThoseEventsInTheLockFreeWay() throws InterruptedException {
+        //given
+        ExecutorService executorService = Executors.newFixedThreadPool(3);
+        EventWindowSort eventWindowSort = new EventWindowSort();
+        int numberOfThreads = 2;
+        //when
+        Runnable producer = () -> IntStream
+          .rangeClosed(0, 100)
+          .forEach(index -> eventWindowSort.acceptEvent(new Event(ZonedDateTime
+            .now()
+            .minusSeconds(index), UUID
+            .randomUUID()
+            .toString())));
+
+        for (int i = 0; i < numberOfThreads; i++) {
+            executorService.execute(producer);
+        }
+
+        Thread.sleep(500);
+
+        ConcurrentNavigableMap<ZonedDateTime, String> eventsFromLastMinute = eventWindowSort.getEventsOlderThatOneMinute();
+
+        long eventsOlderThanOneMinute = eventsFromLastMinute
+          .entrySet()
+          .stream()
+          .filter(e -> e
+            .getKey()
+            .isBefore(ZonedDateTime
+              .now()
+              .minusMinutes(1)))
+          .count();
+        assertTrue(eventsOlderThanOneMinute > 0);
+
+        long eventYoungerThanOneMinute = eventsFromLastMinute
+          .entrySet()
+          .stream()
+          .filter(e -> e
+            .getKey()
+            .isAfter(ZonedDateTime
+              .now()
+              .minusMinutes(1)))
+          .count();
+
+        //then
+        assertEquals(eventYoungerThanOneMinute, 0);
+
+        executorService.awaitTermination(1, TimeUnit.SECONDS);
+        executorService.shutdown();
+    }
+
+}

core-java/src/test/java/com/baeldung/dateapi/JavaDurationTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.dateapi;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
+
+import org.junit.Test;
+
+public class JavaDurationTest {
+
+    @Test
+    public void test2() {
+        Instant start = Instant.parse("2017-10-03T10:15:30.00Z");
+        Instant end = Instant.parse("2017-10-03T10:16:30.00Z");
+
+        Duration duration = Duration.between(start, end);
+
+        assertFalse(duration.isNegative());
+
+        assertEquals(60, duration.getSeconds());
+        assertEquals(1, duration.toMinutes());
+
+        Duration fromDays = Duration.ofDays(1);
+        assertEquals(86400, fromDays.getSeconds());
+
+        Duration fromMinutes = Duration.ofMinutes(60);
+        assertEquals(1, fromMinutes.toHours());
+
+        assertEquals(120, duration.plusSeconds(60).getSeconds());
+        assertEquals(30, duration.minusSeconds(30).getSeconds());
+
+        assertEquals(120, duration.plus(60, ChronoUnit.SECONDS).getSeconds());
+        assertEquals(30, duration.minus(30, ChronoUnit.SECONDS).getSeconds());
+
+        Duration fromChar1 = Duration.parse("P1DT1H10M10.5S");
+        Duration fromChar2 = Duration.parse("PT10M");
+    }
+
+}

core-java/src/test/java/com/baeldung/dateapi/JavaPeriodTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.dateapi;
+
+import org.apache.log4j.Logger;
+import org.junit.Test;
+
+import java.time.LocalDate;
+import java.time.Period;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+public class JavaPeriodTest {
+
+    private static final Logger LOG = Logger.getLogger(JavaPeriodTest.class);
+
+    @Test
+    public void whenTestPeriod_thenOk() {
+
+        LocalDate startDate = LocalDate.of(2015, 2, 15);
+        LocalDate endDate = LocalDate.of(2017, 1, 21);
+
+        Period period = Period.between(startDate, endDate);
+
+        LOG.info(String.format("Years:%d months:%d days:%d", period.getYears(), period.getMonths(), period.getDays()));
+
+        assertFalse(period.isNegative());
+        assertEquals(56, period.plusDays(50).getDays());
+        assertEquals(9, period.minusMonths(2).getMonths());
+
+        Period fromUnits = Period.of(3, 10, 10);
+        Period fromDays = Period.ofDays(50);
+        Period fromMonths = Period.ofMonths(5);
+        Period fromYears = Period.ofYears(10);
+        Period fromWeeks = Period.ofWeeks(40);
+
+        assertEquals(280, fromWeeks.getDays());
+
+        Period fromCharYears = Period.parse("P2Y");
+        assertEquals(2, fromCharYears.getYears());
+        Period fromCharUnits = Period.parse("P2Y3M5D");
+        assertEquals(5, fromCharUnits.getDays());
+    }
+
+}

core-java/src/test/java/com/baeldung/dynamicproxy/DynamicProxyTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.dynamicproxy;
+
+import org.junit.Test;
+
+import java.lang.reflect.Proxy;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class DynamicProxyTest {
+
+    @Test
+    public void givenDynamicProxy_thenPutWorks() {
+        Map proxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, new DynamicInvocationHandler());
+
+        proxyInstance.put("hello", "world");
+    }
+
+    @Test
+    public void givenInlineDynamicProxy_thenGetWorksOtherMethodsDoNot() {
+        Map proxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, (proxy, method, methodArgs) -> {
+
+            if (method.getName().equals("get")) {
+                return 42;
+            } else {
+                throw new UnsupportedOperationException("Unsupported method: " + method.getName());
+            }
+        });
+
+        int result = (int) proxyInstance.get("hello");
+
+        assertEquals(42, result);
+
+        try {
+            proxyInstance.put("hello", "world");
+            fail();
+        } catch(UnsupportedOperationException e) {
+            // expected
+        }
+    }
+
+    @Test
+    public void givenTimingDynamicProxy_thenMethodInvokationsProduceTiming() {
+        Map mapProxyInstance = (Map) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { Map.class }, new TimingDynamicInvocationHandler(new HashMap<>()));
+
+        mapProxyInstance.put("hello", "world");
+        assertEquals("world", mapProxyInstance.get("hello"));
+
+        CharSequence csProxyInstance = (CharSequence) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(), new Class[] { CharSequence.class }, new TimingDynamicInvocationHandler("Hello World"));
+
+        assertEquals('l', csProxyInstance.charAt(2));
+        assertEquals(11, csProxyInstance.length());
+    }
+
+}

core-java/src/test/java/com/baeldung/functionalinterface/FunctionalInterfaceUnitTest.java

@@ -1,8 +1,9 @@
 package com.baeldung.functionalinterface;
 
-import static org.junit.Assert.assertArrayEquals;
+import com.google.common.util.concurrent.Uninterruptibles;
-import static org.junit.Assert.assertEquals;
+import org.junit.Test;
-import static org.junit.Assert.assertTrue;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.Arrays;
 import java.util.HashMap;
@@ -14,12 +15,13 @@ import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-import org.junit.Test;
+import static org.junit.Assert.*;
-
-import com.google.common.util.concurrent.Uninterruptibles;
 
 public class FunctionalInterfaceUnitTest {
 
+    private static final Logger LOG = LoggerFactory.getLogger(FunctionalInterfaceUnitTest.class);
+
+
     @Test
     public void whenPassingLambdaToComputeIfAbsent_thenTheValueGetsComputedAndPutIntoMap() {
         Map<String, Integer> nameMap = new HashMap<>();
@@ -65,7 +67,7 @@ public class FunctionalInterfaceUnitTest {
 
     @Test
     public void whenPassingLambdaToThreadConstructor_thenLambdaInferredToRunnable() {
-        Thread thread = new Thread(() -> System.out.println("Hello From Another Thread"));
+        Thread thread = new Thread(() -> LOG.debug("Hello From Another Thread"));
         thread.start();
     }
 
@@ -93,7 +95,7 @@ public class FunctionalInterfaceUnitTest {
     @Test
     public void whenUsingConsumerInForEach_thenConsumerExecutesForEachListElement() {
         List<String> names = Arrays.asList("John", "Freddy", "Samuel");
-        names.forEach(name -> System.out.println("Hello, " + name));
+        names.forEach(name -> LOG.debug("Hello, " + name));
     }
 
     @Test
@@ -103,7 +105,7 @@ public class FunctionalInterfaceUnitTest {
         ages.put("Freddy", 24);
         ages.put("Samuel", 30);
 
-        ages.forEach((name, age) -> System.out.println(name + " is " + age + " years old"));
+        ages.forEach((name, age) -> LOG.debug(name + " is " + age + " years old"));
     }
 
     @Test

core-java/src/test/java/com/baeldung/http/HttpRequestTest.java

@@ -0,0 +1,126 @@
+package com.baeldung.http;
+
+import org.apache.commons.lang.StringUtils;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+import java.io.BufferedReader;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.net.CookieManager;
+import java.net.HttpCookie;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+public class HttpRequestTest {
+
+    @Test
+    public void whenGetRequest_thenOk() throws IOException {
+        URL url = new URL("http://example.com");
+        HttpURLConnection con = (HttpURLConnection) url.openConnection();
+        con.setRequestMethod("GET");
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("param1", "val");
+        con.setDoOutput(true);
+        DataOutputStream out = new DataOutputStream(con.getOutputStream());
+        out.writeBytes(ParameterStringBuilder.getParamsString(parameters));
+        out.flush();
+        out.close();
+
+        con.setConnectTimeout(5000);
+        con.setReadTimeout(5000);
+
+        int status = con.getResponseCode();
+        BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
+        String inputLine;
+        StringBuffer content = new StringBuffer();
+        while ((inputLine = in.readLine()) != null) {
+            content.append(inputLine);
+        }
+        in.close();
+
+        assertEquals("status code incorrect", status, 200);
+        assertTrue("content incorrect", content.toString().contains("Example Domain"));
+    }
+
+    @Test
+    public void whenPostRequest_thenOk() throws IOException {
+        URL url = new URL("http://example.com");
+        HttpURLConnection con = (HttpURLConnection) url.openConnection();
+        con.setRequestMethod("POST");
+        con.setRequestProperty("Content-Type", "application/json");
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("param1", "val");
+        con.setDoOutput(true);
+        DataOutputStream out = new DataOutputStream(con.getOutputStream());
+        out.writeBytes(ParameterStringBuilder.getParamsString(parameters));
+        out.flush();
+        out.close();
+
+        int status = con.getResponseCode();
+        BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
+        String inputLine;
+        StringBuffer content = new StringBuffer();
+        while ((inputLine = in.readLine()) != null) {
+            content.append(inputLine);
+        }
+        in.close();
+
+        assertEquals("status code incorrect", status, 200);
+    }
+
+    @Test
+    public void whenGetCookies_thenOk() throws IOException {
+        URL url = new URL("http://example.com");
+        HttpURLConnection con = (HttpURLConnection) url.openConnection();
+        con.setRequestMethod("GET");
+
+        CookieManager cookieManager = new CookieManager();
+        String cookiesHeader = con.getHeaderField("Set-Cookie");
+        Optional<HttpCookie> usernameCookie = null;
+        if (cookiesHeader != null) {
+            List<HttpCookie> cookies = HttpCookie.parse(cookiesHeader);
+            cookies.forEach(cookie -> cookieManager.getCookieStore().add(null, cookie));
+            usernameCookie = cookies.stream().findAny().filter(cookie -> cookie.getName().equals("username"));
+        }
+
+        if (usernameCookie == null) {
+            cookieManager.getCookieStore().add(null, new HttpCookie("username", "john"));
+        }
+
+        con.disconnect();
+
+        con = (HttpURLConnection) url.openConnection();
+        con.setRequestProperty("Cookie", StringUtils.join(cookieManager.getCookieStore().getCookies(), ";"));
+
+        int status = con.getResponseCode();
+
+        assertEquals("status code incorrect", status, 200);
+    }
+
+    @Test
+    public void whenRedirect_thenOk() throws IOException {
+        URL url = new URL("http://example.com");
+        HttpURLConnection con = (HttpURLConnection) url.openConnection();
+        con.setRequestMethod("GET");
+
+        con.setInstanceFollowRedirects(true);
+        int status = con.getResponseCode();
+
+        if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM) {
+            String location = con.getHeaderField("Location");
+            URL newUrl = new URL(location);
+            con = (HttpURLConnection) newUrl.openConnection();
+        }
+
+        assertEquals("status code incorrect", con.getResponseCode(), 200);
+    }
+
+}

core-java/src/test/java/com/baeldung/java/collections/ConcurrentModificationExceptionTest.java

@@ -6,9 +6,10 @@ import java.util.*;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import static java.util.Arrays.asList;
-import static org.testng.Assert.assertEquals;
+import static org.junit.Assert.assertEquals;
 
 public class ConcurrentModificationExceptionTest {
+
     @Test
     public void changingContentWithSetDoesNotThrowConcurrentModificationException() throws Exception {
         ArrayList<Object> array = new ArrayList<>(asList(0, "one", 2, "three"));

core-java/src/test/java/com/baeldung/java/concurrentmap/ConcurrentNavigableMapManualTests.java

@@ -8,7 +8,9 @@ import java.util.TreeMap;
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import static org.testng.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
 
 public class ConcurrentNavigableMapManualTests {
 

core-java/src/test/java/com/baeldung/java/doublebrace/DoubleBraceTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.java.doublebrace;
+
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collectors.collectingAndThen;
+import static java.util.stream.Collectors.toSet;
+import static org.junit.Assert.assertTrue;
+
+public class DoubleBraceTest {
+
+    @Test
+    public void whenInitializeSetWithoutDoubleBraces_containsElements() {
+        final Set<String> countries = new HashSet<>();
+        countries.add("India");
+        countries.add("USSR");
+        countries.add("USA");
+        assertTrue(countries.contains("India"));
+    }
+
+    @Test
+    public void whenInitializeSetWithDoubleBraces_containsElements() {
+        final Set<String> countries = new HashSet<String>() {
+
+            {
+                add("India");
+                add("USSR");
+                add("USA");
+            }
+        };
+        assertTrue(countries.contains("India"));
+    }
+
+    @Test
+    public void whenInitializeUnmodifiableSetWithDoubleBrace_containsElements() {
+         Set<String> countries = Stream.of("India", "USSR", "USA")
+           .collect(collectingAndThen(toSet(), Collections::unmodifiableSet));
+
+        assertTrue(countries.contains("India"));
+    }
+
+}

core-java/src/test/java/com/baeldung/java/map/MapTest.java

@@ -1,24 +1,18 @@
 package com.baeldung.java.map;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
-
-import java.util.Collection;
-import java.util.Comparator;
-import java.util.ConcurrentModificationException;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.LinkedHashMap;
-import java.util.Map;
-import java.util.Map.Entry;
-import java.util.Set;
-import java.util.TreeMap;
-
 import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.*;
+import java.util.Map.Entry;
+
+import static org.junit.Assert.*;
 
 public class MapTest {
+    private static final Logger LOG = LoggerFactory.getLogger(MapTest.class);
+
+    
     @Test
     public void givenHashMap_whenRetrievesKeyset_thenCorrect() {
         Map<String, String> map = new HashMap<>();
@@ -208,22 +202,22 @@ public class MapTest {
         MyKey k2 = new MyKey(2, "secondKey");
         MyKey k3 = new MyKey(2, "thirdKey");
 
-        System.out.println("storing value for k1");
+        LOG.debug("storing value for k1");
         map.put(k1, "firstValue");
 
-        System.out.println("storing value for k2");
+        LOG.debug("storing value for k2");
         map.put(k2, "secondValue");
 
-        System.out.println("storing value for k3");
+        LOG.debug("storing value for k3");
         map.put(k3, "thirdValue");
 
-        System.out.println("retrieving value for k1");
+        LOG.debug("retrieving value for k1");
         String v1 = map.get(k1);
 
-        System.out.println("retrieving value for k2");
+        LOG.debug("retrieving value for k2");
         String v2 = map.get(k2);
 
-        System.out.println("retrieving value for k3");
+        LOG.debug("retrieving value for k3");
         String v3 = map.get(k3);
 
         assertEquals("firstValue", v1);

core-java/src/test/java/com/baeldung/java/nio2/async/AsyncEchoClient.java

@@ -1,5 +1,8 @@
 package com.baeldung.java.nio2.async;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -10,6 +13,8 @@ import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 
 public class AsyncEchoClient {
+    private static final Logger LOG = LoggerFactory.getLogger(AsyncEchoClient.class);
+
     private AsynchronousSocketChannel client;
     private Future<Void> future;
     private static AsyncEchoClient instance;
@@ -75,11 +80,11 @@ public class AsyncEchoClient {
         client.start();
         BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
         String line;
-        System.out.println("Message to server:");
+        LOG.debug("Message to server:");
         while ((line = br.readLine()) != null) {
             String response = client.sendMessage(line);
-            System.out.println("response from server: " + response);
+            LOG.debug("response from server: " + response);
-            System.out.println("Message to server:");
+            LOG.debug("Message to server:");
         }
     }
 

core-java/src/test/java/com/baeldung/java/nio2/attributes/BasicAttribsTest.java

@@ -2,6 +2,8 @@ package com.baeldung.java.nio2.attributes;
 
 import org.junit.BeforeClass;
 import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.nio.file.Files;
@@ -15,6 +17,10 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 public class BasicAttribsTest {
+
+    private static final Logger LOG = LoggerFactory.getLogger(BasicAttribsTest.class);
+
+
     private static final String HOME = System.getProperty("user.home");
     private static BasicFileAttributes basicAttribs;
 
@@ -31,9 +37,9 @@ public class BasicAttribsTest {
         FileTime modified = basicAttribs.lastModifiedTime();
         FileTime accessed = basicAttribs.lastAccessTime();
 
-        System.out.println("Created: " + created);
+        LOG.debug("Created: " + created);
-        System.out.println("Modified: " + modified);
+        LOG.debug("Modified: " + modified);
-        System.out.println("Accessed: " + accessed);
+        LOG.debug("Accessed: " + accessed);
 
     }
 

core-java/src/test/java/com/baeldung/java/reflection/OperationsUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.java.reflection;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThat;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+import org.junit.Test;
+
+public class OperationsUnitTest {
+
+    public OperationsUnitTest() {
+    }
+
+    @Test(expected = IllegalAccessException.class)
+    public void givenObject_whenInvokePrivateMethod_thenFail() throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
+        Method andPrivateMethod = Operations.class.getDeclaredMethod("privateAnd", boolean.class, boolean.class);
+
+        Operations operationsInstance = new Operations();
+        Boolean result = (Boolean) andPrivateMethod.invoke(operationsInstance, true, false);
+
+        assertFalse(result);
+    }
+
+    @Test
+    public void givenObject_whenInvokePrivateMethod_thenCorrect() throws Exception {
+        Method andPrivatedMethod = Operations.class.getDeclaredMethod("privateAnd", boolean.class, boolean.class);
+        andPrivatedMethod.setAccessible(true);
+
+        Operations operationsInstance = new Operations();
+        Boolean result = (Boolean) andPrivatedMethod.invoke(operationsInstance, true, false);
+
+        assertFalse(result);
+    }
+
+    @Test
+    public void givenObject_whenInvokePublicMethod_thenCorrect() throws Exception {
+        Method sumInstanceMethod = Operations.class.getMethod("publicSum", int.class, double.class);
+
+        Operations operationsInstance = new Operations();
+        Double result = (Double) sumInstanceMethod.invoke(operationsInstance, 1, 3);
+
+        assertThat(result, equalTo(4.0));
+    }
+
+    @Test
+    public void givenObject_whenInvokeStaticMethod_thenCorrect() throws Exception {
+        Method multiplyStaticMethod = Operations.class.getDeclaredMethod("publicStaticMultiply", float.class, long.class);
+
+        Double result = (Double) multiplyStaticMethod.invoke(null, 3.5f, 2);
+
+        assertThat(result, equalTo(7.0));
+    }
+
+}

core-java/src/test/java/com/baeldung/java/reflection/operations/MoreOperationsUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.java.reflection.operations;
+
+import com.baeldung.java.reflection.*;
+import static org.hamcrest.CoreMatchers.equalTo;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+import org.junit.Test;
+import static org.junit.Assert.assertThat;
+
+public class MoreOperationsUnitTest {
+
+    public MoreOperationsUnitTest() {
+    }
+
+    @Test(expected = IllegalAccessException.class)
+    public void givenObject_whenInvokeProtectedMethod_thenFail() throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
+        Method maxProtectedMethod = Operations.class.getDeclaredMethod("protectedMax", int.class, int.class);
+
+        Operations operationsInstance = new Operations();
+        Integer result = (Integer) maxProtectedMethod.invoke(operationsInstance, 2, 4);
+        
+        assertThat(result, equalTo(4));
+    }
+
+    @Test
+    public void givenObject_whenInvokeProtectedMethod_thenCorrect() throws Exception {
+        Method maxProtectedMethod = Operations.class.getDeclaredMethod("protectedMax", int.class, int.class);
+        maxProtectedMethod.setAccessible(true);
+
+        Operations operationsInstance = new Operations();
+        Integer result = (Integer) maxProtectedMethod.invoke(operationsInstance, 2, 4);
+
+        assertThat(result, equalTo(4));
+    }
+
+}

core-java/src/test/java/com/baeldung/java/set/SetTest.java

@@ -0,0 +1,99 @@
+package com.baeldung.java.set;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.*;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class SetTest {
+
+    private static final Logger LOG = LoggerFactory.getLogger(SetTest.class);
+
+    @Test
+    public void givenTreeSet_whenRetrievesObjects_thenNaturalOrder() {
+        Set<String> set = new TreeSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add("Awesome");
+        assertEquals(3, set.size());
+        assertTrue(set.iterator()
+            .next()
+            .equals("Awesome"));
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void givenTreeSet_whenAddNullObject_thenNullPointer() {
+        Set<String> set = new TreeSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add(null);
+    }
+
+    @Test
+    public void givenHashSet_whenAddNullObject_thenOK() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add(null);
+        assertEquals(3, set.size());
+    }
+
+    @Test
+    public void givenHashSetAndTreeSet_whenAddObjects_thenHashSetIsFaster() {
+
+        long hashSetInsertionTime = measureExecution(() -> {
+            Set<String> set = new HashSet<>();
+            set.add("Baeldung");
+            set.add("is");
+            set.add("Awesome");
+        });
+
+        long treeSetInsertionTime = measureExecution(() -> {
+            Set<String> set = new TreeSet<>();
+            set.add("Baeldung");
+            set.add("is");
+            set.add("Awesome");
+        });
+
+        LOG.debug("HashSet insertion time: {}", hashSetInsertionTime);
+        LOG.debug("TreeSet insertion time: {}", treeSetInsertionTime);
+    }
+
+    @Test
+    public void givenHashSetAndTreeSet_whenAddDuplicates_thenOnlyUnique() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        set.add("Baeldung");
+        assertTrue(set.size() == 1);
+
+        Set<String> set2 = new TreeSet<>();
+        set2.add("Baeldung");
+        set2.add("Baeldung");
+        assertTrue(set2.size() == 1);
+    }
+
+    @Test(expected = ConcurrentModificationException.class)
+    public void givenHashSet_whenModifyWhenIterator_thenFailFast() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        Iterator<String> it = set.iterator();
+
+        while (it.hasNext()) {
+            set.add("Awesome");
+            it.next();
+        }
+    }
+
+    private static long measureExecution(Runnable task) {
+        long startTime = System.nanoTime();
+        task.run();
+        long endTime = System.nanoTime();
+        long executionTime = endTime - startTime;
+        LOG.debug(String.valueOf(executionTime));
+        return executionTime;
+    }
+}

core-java/src/test/java/com/baeldung/java8/Java8ForEachTest.java

@@ -1,13 +1,17 @@
 package com.baeldung.java8;
 
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
 
-import org.junit.Test;
-
 public class Java8ForEachTest {
 
+    private static final Logger LOG = LoggerFactory.getLogger(Java8ForEachTest.class);
+
     @Test
     public void compareForEachMethods_thenPrintResults() {
 
@@ -19,33 +23,33 @@ public class Java8ForEachTest {
         names.add("Ellen");
 
         // Java 5 - for-loop
-        System.out.println("--- Enhanced for-loop ---");
+        LOG.debug("--- Enhanced for-loop ---");
         for (String name : names) {
-            System.out.println(name);
+            LOG.debug(name);
         }
 
         // Java 8 - forEach
-        System.out.println("--- forEach method ---");
+        LOG.debug("--- forEach method ---");
-        names.forEach(name -> System.out.println(name));
+        names.forEach(name -> LOG.debug(name));
 
         // Anonymous inner class that implements Consumer interface
-        System.out.println("--- Anonymous inner class ---");
+        LOG.debug("--- Anonymous inner class ---");
         names.forEach(new Consumer<String>() {
             public void accept(String name) {
-                System.out.println(name);
+                LOG.debug(name);
             }
         });
 
         // Create a Consumer implementation to then use in a forEach method
         Consumer<String> consumerNames = name -> {
-            System.out.println(name);
+            LOG.debug(name);
         };
-        System.out.println("--- Implementation of Consumer interface ---");
+        LOG.debug("--- Implementation of Consumer interface ---");
         names.forEach(consumerNames);
 
         // Print elements using a Method Reference
-        System.out.println("--- Method Reference ---");
+        LOG.debug("--- Method Reference ---");
-        names.forEach(System.out::println);
+        names.forEach(LOG::debug);
 
     }