Merge pull request #1 from eugenp/master

pull

algorithms-miscellaneous-3/README.md

@@ -4,3 +4,4 @@
 - [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)
 - [Converting Between Roman and Arabic Numerals in Java](http://www.baeldung.com/java-convert-roman-arabic)
 - [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
+- [Checking If a List Is Sorted in Java](https://www.baeldung.com/java-check-if-list-sorted)

algorithms-miscellaneous-3/pom.xml

@@ -18,6 +18,18 @@
             <version>${org.assertj.core.version}</version>
             <scope>test</scope>
         </dependency>
+        
+        <dependency>
+        	<groupId>org.apache.commons</groupId>
+        	<artifactId>commons-collections4</artifactId>
+        	<version>${commons-collections4.version}</version>
+        </dependency>
+        
+        <dependency>
+        	<groupId>com.google.guava</groupId>
+        	<artifactId>guava</artifactId>
+        	<version>${guava.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -34,6 +46,7 @@
 
     <properties>
         <org.assertj.core.version>3.9.0</org.assertj.core.version>
+        <commons-collections4.version>4.3</commons-collections4.version>
+        <guava.version>28.0-jre</guava.version>
     </properties>
-
 </project>

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/checksortedlist/Employee.java

@@ -0,0 +1,34 @@
+package com.baeldung.algorithms.checksortedlist;
+
+public class Employee {
+
+    long id;
+
+    String name;
+
+    public Employee() {
+    }
+
+    public Employee(long id, String name) {
+        super();
+        this.id = id;
+        this.name = name;
+    }
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/checksortedlist/SortedListChecker.java

@@ -0,0 +1,87 @@
+package com.baeldung.algorithms.checksortedlist;
+
+import static org.apache.commons.collections4.CollectionUtils.isEmpty;
+
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.List;
+
+import com.google.common.collect.Comparators;
+import com.google.common.collect.Ordering;;
+
+public class SortedListChecker {
+
+    private SortedListChecker() {
+        throw new AssertionError();
+    }
+
+    public static boolean checkIfSortedUsingIterativeApproach(List<String> listOfStrings) {
+        if (isEmpty(listOfStrings) || listOfStrings.size() == 1) {
+            return true;
+        }
+
+        Iterator<String> iter = listOfStrings.iterator();
+        String current, previous = iter.next();
+        while (iter.hasNext()) {
+            current = iter.next();
+            if (previous.compareTo(current) > 0) {
+                return false;
+            }
+            previous = current;
+        }
+        return true;
+    }
+
+    public static boolean checkIfSortedUsingIterativeApproach(List<Employee> employees, Comparator<Employee> employeeComparator) {
+        if (isEmpty(employees) || employees.size() == 1) {
+            return true;
+        }
+
+        Iterator<Employee> iter = employees.iterator();
+        Employee current, previous = iter.next();
+        while (iter.hasNext()) {
+            current = iter.next();
+            if (employeeComparator.compare(previous, current) > 0) {
+                return false;
+            }
+            previous = current;
+        }
+        return true;
+    }
+
+    public static boolean checkIfSortedUsingRecursion(List<String> listOfStrings) {
+        return isSortedRecursive(listOfStrings, listOfStrings.size());
+    }
+
+    public static boolean isSortedRecursive(List<String> listOfStrings, int index) {
+        if (index < 2) {
+            return true;
+        } else if (listOfStrings.get(index - 2)
+            .compareTo(listOfStrings.get(index - 1)) > 0) {
+            return false;
+        } else {
+            return isSortedRecursive(listOfStrings, index - 1);
+        }
+    }
+
+    public static boolean checkIfSortedUsingOrderingClass(List<String> listOfStrings) {
+        return Ordering.<String> natural()
+            .isOrdered(listOfStrings);
+    }
+
+    public static boolean checkIfSortedUsingOrderingClass(List<Employee> employees, Comparator<Employee> employeeComparator) {
+        return Ordering.from(employeeComparator)
+            .isOrdered(employees);
+    }
+
+    public static boolean checkIfSortedUsingOrderingClassHandlingNull(List<String> listOfStrings) {
+        return Ordering.<String> natural()
+            .nullsLast()
+            .isOrdered(listOfStrings);
+    }
+
+    public static boolean checkIfSortedUsingComparators(List<String> listOfStrings) {
+        return Comparators.isInOrder(listOfStrings, Comparator.<String> naturalOrder());
+    }
+
+}

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/checksortedlist/SortedListCheckerUnitTest.java

@@ -0,0 +1,106 @@
+package com.baeldung.algorithms.checksortedlist;
+
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingComparators;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingIterativeApproach;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingOrderingClass;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingRecursion;
+import static java.util.Arrays.asList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class SortedListCheckerUnitTest {
+
+    private List<String> sortedListOfString;
+    private List<String> unsortedListOfString;
+    private List<String> singletonList;
+
+    private List<Employee> employeesSortedByName;
+    private List<Employee> employeesNotSortedByName;
+
+    @Before
+    public void setUp() {
+        sortedListOfString = asList("Canada", "HK", "LA", "NJ", "NY");
+        unsortedListOfString = asList("LA", "HK", "NJ", "NY", "Canada");
+        singletonList = Collections.singletonList("NY");
+
+        employeesSortedByName = asList(new Employee(1L, "John"), new Employee(2L, "Kevin"), new Employee(3L, "Mike"));
+        employeesNotSortedByName = asList(new Employee(1L, "Kevin"), new Employee(2L, "John"), new Employee(3L, "Mike"));
+    }
+
+    @Test
+    public void givenSortedList_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenSingleElementList_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(singletonList)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingIterativeApproach_thenReturnFalse() {
+        assertThat(checkIfSortedUsingIterativeApproach(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedListOfEmployees_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(employeesSortedByName, Comparator.comparing(Employee::getName))).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedListOfEmployees_whenUsingIterativeApproach_thenReturnFalse() {
+        assertThat(checkIfSortedUsingIterativeApproach(employeesNotSortedByName, Comparator.comparing(Employee::getName))).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingRecursion_thenReturnTrue() {
+        assertThat(checkIfSortedUsingRecursion(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenSingleElementList_whenUsingRecursion_thenReturnTrue() {
+        assertThat(checkIfSortedUsingRecursion(singletonList)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingRecursion_thenReturnFalse() {
+        assertThat(checkIfSortedUsingRecursion(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingGuavaOrdering_thenReturnTrue() {
+        assertThat(checkIfSortedUsingOrderingClass(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingGuavaOrdering_thenReturnFalse() {
+        assertThat(checkIfSortedUsingOrderingClass(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedListOfEmployees_whenUsingGuavaOrdering_thenReturnTrue() {
+        assertThat(checkIfSortedUsingOrderingClass(employeesSortedByName, Comparator.comparing(Employee::getName))).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedListOfEmployees_whenUsingGuavaOrdering_thenReturnFalse() {
+        assertThat(checkIfSortedUsingOrderingClass(employeesNotSortedByName, Comparator.comparing(Employee::getName))).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingGuavaComparators_thenReturnTrue() {
+        assertThat(checkIfSortedUsingComparators(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingGuavaComparators_thenReturnFalse() {
+        assertThat(checkIfSortedUsingComparators(unsortedListOfString)).isFalse();
+    }
+
+}

autovalue/pom.xml

@@ -29,6 +29,12 @@
                 </exclusion>
             </exclusions>
         </dependency>
+        <dependency>
+            <groupId>com.google.auto.service</groupId>
+            <artifactId>auto-service</artifactId>
+            <version>${auto-service.version}</version>
+            <optional>true</optional>
+        </dependency>
 
         <dependency>
             <groupId>com.google.inject</groupId>
@@ -40,6 +46,7 @@
     <properties>
         <auto-value.version>1.3</auto-value.version>
         <auto-factory.version>1.0-beta5</auto-factory.version>
+        <auto-service.version>1.0-rc5</auto-service.version>
         <guice.version>4.2.0</guice.version>
     </properties>
 

autovalue/src/main/java/com/baeldung/autoservice/BingTranslationServiceProvider.java

@@ -0,0 +1,14 @@
+package com.baeldung.autoservice;
+
+import com.google.auto.service.AutoService;
+
+import java.util.Locale;
+
+@AutoService(TranslationService.class)
+public class BingTranslationServiceProvider implements TranslationService {
+    @Override
+    public String translate(String message, Locale from, Locale to) {
+        // implementation details
+        return message + " (translated by Bing)"; 
+    }
+}

autovalue/src/main/java/com/baeldung/autoservice/GoogleTranslationServiceProvider.java

@@ -0,0 +1,14 @@
+package com.baeldung.autoservice;
+
+import com.google.auto.service.AutoService;
+
+import java.util.Locale;
+
+@AutoService(TranslationService.class)
+public class GoogleTranslationServiceProvider implements TranslationService {
+    @Override
+    public String translate(String message, Locale from, Locale to) {
+        // implementation details
+        return message + " (translated by Google)"; 
+    }
+}

autovalue/src/main/java/com/baeldung/autoservice/TranslationService.java

@@ -0,0 +1,7 @@
+package com.baeldung.autoservice;
+
+import java.util.Locale;
+
+public interface TranslationService {
+    String translate(String message, Locale from, Locale to);
+}

autovalue/src/test/java/com/baeldung/autoservice/TranslationServiceUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.autoservice;
+
+import com.baeldung.autoservice.TranslationService;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ServiceLoader;
+import java.util.stream.StreamSupport;
+
+import static org.junit.Assert.assertEquals;
+
+public class TranslationServiceUnitTest {
+
+    private ServiceLoader<TranslationService> loader;
+
+    @Before
+    public void setUp() {
+        loader = ServiceLoader.load(TranslationService.class);
+    }
+
+    @Test
+    public void whenServiceLoaderLoads_thenLoadsAllProviders() {
+        long count = StreamSupport.stream(loader.spliterator(), false).count();
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void whenServiceLoaderLoadsGoogleService_thenGoogleIsLoaded() {
+        TranslationService googleService = StreamSupport.stream(loader.spliterator(), false)
+          .filter(p -> p.getClass().getSimpleName().equals("GoogleTranslationServiceProvider"))
+          .findFirst()
+          .get();
+		
+        String message = "message";
+        assertEquals(message + " (translated by Google)", googleService.translate(message, null, null));
+    }
+}

core-groovy-2/README.md

@@ -5,4 +5,5 @@
 - [String Matching in Groovy](http://www.baeldung.com/)
 - [Template Engines in Groovy](https://www.baeldung.com/groovy-template-engines)
 - [Groovy def Keyword](https://www.baeldung.com/groovy-def-keyword)
-- [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)
+- [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)
+- [Working with XML in Groovy](https://www.baeldung.com/groovy-xml)

core-java-modules/core-java-8-2/src/main/java/com/baeldung/forEach/ReverseList.java

@@ -0,0 +1,84 @@
+package com.baeldung.forEach;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Consumer;
+
+class ReverseList extends ArrayList<String> {
+
+    List<String> list = Arrays.asList("A", "B", "C", "D");
+
+    Consumer<String> removeElement = s -> {
+        System.out.println(s + " " + list.size());
+        if (s != null && s.equals("A")) {
+            list.remove("D");
+        }
+    };
+
+    @Override
+    public Iterator<String> iterator() {
+
+        final int startIndex = this.size() - 1;
+        final List<String> list = this;
+        return new Iterator<String>() {
+
+            int currentIndex = startIndex;
+
+            @Override
+            public boolean hasNext() {
+                return currentIndex >= 0;
+            }
+
+            @Override
+            public String next() {
+                String next = list.get(currentIndex);
+                currentIndex--;
+                return next;
+            }
+
+            @Override
+            public void remove() {
+                throw new UnsupportedOperationException();
+            }
+        };
+    }
+
+    public void forEach(Consumer<? super String> action) {
+        for (String s : this) {
+            action.accept(s);
+        }
+    }
+
+    public void iterateParallel() {
+        list.forEach(System.out::print);
+        System.out.print(" ");
+        list.parallelStream().forEach(System.out::print);
+    }
+
+    public void iterateReverse() {
+        List<String> myList = new ReverseList();
+        myList.addAll(list);
+        myList.forEach(System.out::print);
+        System.out.print(" ");
+        myList.stream().forEach(System.out::print);
+    }
+
+    public void removeInCollectionForEach() {
+        list.forEach(removeElement);
+    }
+
+    public void removeInStreamForEach() {
+        list.stream().forEach(removeElement);
+    }
+
+    public static void main(String[] argv) {
+
+        ReverseList collectionForEach = new ReverseList();
+        collectionForEach.iterateParallel();
+        collectionForEach.iterateReverse();
+        collectionForEach.removeInCollectionForEach();
+        collectionForEach.removeInStreamForEach();
+    }
+}

core-java-modules/core-java-8-2/src/main/java/com/baeldung/stream/SkipLimitComparison.java

@@ -0,0 +1,46 @@
+package com.baeldung.stream;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class SkipLimitComparison {
+
+    public static void main(String[] args) {
+        skipExample();
+        limitExample();
+        limitInfiniteStreamExample();
+        getEvenNumbers(10, 10).stream()
+            .forEach(System.out::println);
+    }
+
+    public static void skipExample() {
+        Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+            .filter(i -> i % 2 == 0)
+            .skip(2)
+            .forEach(i -> System.out.print(i + " "));
+    }
+
+    public static void limitExample() {
+        Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+            .filter(i -> i % 2 == 0)
+            .limit(2)
+            .forEach(i -> System.out.print(i + " "));
+    }
+
+    public static void limitInfiniteStreamExample() {
+        Stream.iterate(0, i -> i + 1)
+            .filter(i -> i % 2 == 0)
+            .limit(10)
+            .forEach(System.out::println);
+    }
+
+    private static List<Integer> getEvenNumbers(int offset, int limit) {
+        return Stream.iterate(0, i -> i + 1)
+            .filter(i -> i % 2 == 0)
+            .skip(offset)
+            .limit(limit)
+            .collect(Collectors.toList());
+    }
+
+}

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

@@ -1,26 +1,35 @@
 <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.exception.numberformat</groupId>
-    <artifactId>core-java-exceptions</artifactId>
-    <version>0.0.1-SNAPSHOT</version>
-    <name>core-java-exceptions</name>
+	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.exception.numberformat</groupId>
+	<artifactId>core-java-exceptions</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>core-java-exceptions</name>
 
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>parent-java</artifactId>
-        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../../parent-java</relativePath>
-    </parent>
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-java</artifactId>
+		<version>0.0.1-SNAPSHOT</version>
+		<relativePath>../../parent-java</relativePath>
+	</parent>
 
-    <dependencies>
-        <dependency>
-            <groupId>junit</groupId>
-            <artifactId>junit</artifactId>
-            <version>4.12</version>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
+	<properties>
+		<commons-lang3.version>3.9</commons-lang3.version>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>4.12</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.commons</groupId>
+			<artifactId>commons-lang3</artifactId>
+			<version>${commons-lang3.version}</version>
+		</dependency>
+	</dependencies>
 
 </project>

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

@@ -1,7 +1,6 @@
-package com.baeldung.error;
+package com.baeldung.exception.error;
 
 import org.junit.Assert;
-import org.junit.Before;
 import org.junit.Test;
 
 public class ErrorGeneratorUnitTest {

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

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

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/rawtype/RawTypeDemo.java

@@ -0,0 +1,25 @@
+package com.baeldung.rawtype;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RawTypeDemo {
+
+	public static void main(String[] args) {
+		RawTypeDemo rawTypeDemo = new RawTypeDemo();
+		rawTypeDemo.methodA();
+	}
+
+	public void methodA() {
+		// parameterized type
+		List<String> listStr = new ArrayList<>();
+		listStr.add("Hello Folks!");
+		methodB(listStr);
+		String s = listStr.get(1); // ClassCastException at run time
+	}
+
+	public void methodB(List rawList) { // Inexpressive raw type
+		rawList.add(1); // Unsafe operation
+	}
+
+}

core-java-modules/core-java-lang-syntax/src/main/java/com/baeldung/breakloop/LoopBreaking.java

@@ -0,0 +1,47 @@
+package com.baeldung.breakloop;
+
+public class LoopBreaking {
+
+    public String simpleBreak() {
+        String result = "";
+        for (int outerCounter = 0; outerCounter < 2; outerCounter++) {
+            result += "outer" + outerCounter;
+            for (int innerCounter = 0; innerCounter < 2; innerCounter++) {
+                result += "inner" + innerCounter;
+                if (innerCounter == 0) {
+                    break;
+                }
+            }
+        }
+        return result;
+    }
+
+    public String labelBreak() {
+        String result = "";
+        myBreakLabel:
+        for (int outerCounter = 0; outerCounter < 2; outerCounter++) {
+            result += "outer" + outerCounter;
+            for (int innerCounter = 0; innerCounter < 2; innerCounter++) {
+                result += "inner" + innerCounter;
+                if (innerCounter == 0) {
+                    break myBreakLabel;
+                }
+            }
+        }
+        return result;
+    }
+
+    public String usingReturn() {
+        String result = "";
+        for (int outerCounter = 0; outerCounter < 2; outerCounter++) {
+            result += "outer" + outerCounter;
+            for (int innerCounter = 0; innerCounter < 2; innerCounter++) {
+                result += "inner" + innerCounter;
+                if (innerCounter == 0) {
+                    return result;
+                }
+            }
+        }
+        return "failed";
+    }
+}

core-java-modules/core-java-lang-syntax/src/test/java/com/baeldung/breakloop/LoopBreakingUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.breakloop;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class LoopBreakingUnitTest {
+
+    private LoopBreaking loopBreaking = new LoopBreaking();
+
+    @Test
+    void whenUsingBreak_shouldBreakInnerLoop() {
+        assertEquals("outer0inner0outer1inner0", loopBreaking.simpleBreak());
+    }
+
+    @Test
+    void whenUsingLabeledBreak_shouldBreakInnerLoopAndOuterLoop() {
+        assertEquals("outer0inner0", loopBreaking.labelBreak());
+    }
+
+    @Test
+    void whenUsingReturn_shouldBreakInnerLoopAndOuterLoop() {
+        assertEquals("outer0inner0", loopBreaking.usingReturn());
+    }
+}

easy-random/pom.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>easy-random</artifactId>
+    <name>easy-random</name>
+
+    <parent>
+        <artifactId>parent-modules</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jeasy</groupId>
+            <artifactId>easy-random-core</artifactId>
+            <version>4.0.0</version>
+        </dependency>
+    </dependencies>
+
+</project>

easy-random/src/main/java/org/baeldung/easy/random/model/Department.java

@@ -0,0 +1,17 @@
+package org.baeldung.easy.random.model;
+
+import java.util.StringJoiner;
+
+public class Department {
+    private String depName;
+
+    public Department(String depName) {
+        this.depName = depName;
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", Department.class.getSimpleName() + "[", "]").add("depName='" + depName + "'")
+            .toString();
+    }
+}

easy-random/src/main/java/org/baeldung/easy/random/model/Employee.java

@@ -0,0 +1,70 @@
+package org.baeldung.easy.random.model;
+
+import java.util.*;
+
+public class Employee {
+
+    private long id;
+    private String firstName;
+    private String lastName;
+    private Department department;
+    private Collection<Employee> coworkers;
+    private Map<YearQuarter, Grade> quarterGrades;
+
+    public Employee(long id, String firstName, String lastName, Department department) {
+        this.id = id;
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.department = department;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        Employee employee = (Employee) o;
+        return id == employee.id;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id);
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public long getId() {
+        return id;
+    }
+
+    public Department getDepartment() {
+        return department;
+    }
+
+    public Collection<Employee> getCoworkers() {
+        return Collections.unmodifiableCollection(coworkers);
+    }
+
+    public Map<YearQuarter, Grade> getQuarterGrades() {
+        return Collections.unmodifiableMap(quarterGrades);
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", Employee.class.getSimpleName() + "[", "]").add("id=" + id)
+            .add("firstName='" + firstName + "'")
+            .add("lastName='" + lastName + "'")
+            .add("department=" + department)
+            .add("coworkers size=" + ((coworkers == null) ? 0 : coworkers.size()))
+            .add("quarterGrades=" + quarterGrades)
+            .toString();
+    }
+}

easy-random/src/main/java/org/baeldung/easy/random/model/Grade.java

@@ -0,0 +1,22 @@
+package org.baeldung.easy.random.model;
+
+import java.util.StringJoiner;
+
+public class Grade {
+
+    private int grade;
+
+    public Grade(int grade) {
+        this.grade = grade;
+    }
+
+    public int getGrade() {
+        return grade;
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", Grade.class.getSimpleName() + "[", "]").add("grade=" + grade)
+            .toString();
+    }
+}

easy-random/src/main/java/org/baeldung/easy/random/model/Person.java

@@ -0,0 +1,30 @@
+package org.baeldung.easy.random.model;
+
+import java.util.StringJoiner;
+
+public class Person {
+
+    private String firstName;
+    private String lastName;
+    private Integer age;
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public Integer getAge() {
+        return age;
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", Person.class.getSimpleName() + "[", "]").add("firstName='" + firstName + "'")
+            .add("lastName='" + lastName + "'")
+            .add("age=" + age)
+            .toString();
+    }
+}

easy-random/src/main/java/org/baeldung/easy/random/model/YearQuarter.java

@@ -0,0 +1,50 @@
+package org.baeldung.easy.random.model;
+
+import java.time.LocalDate;
+import java.util.Objects;
+import java.util.StringJoiner;
+
+public class YearQuarter {
+
+    private LocalDate startDate;
+    private LocalDate endDate;
+
+    public YearQuarter(LocalDate startDate) {
+        this.startDate = startDate;
+        autoAdjustEndDate();
+    }
+
+    private void autoAdjustEndDate() {
+        endDate = startDate.plusMonths(3L);
+    }
+
+    public LocalDate getStartDate() {
+        return startDate;
+    }
+
+    public LocalDate getEndDate() {
+        return endDate;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        YearQuarter quarter = (YearQuarter) o;
+        return Objects.equals(startDate, quarter.startDate) && Objects.equals(endDate, quarter.endDate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(startDate, endDate);
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", YearQuarter.class.getSimpleName() + "[", "]").add("startDate=" + startDate)
+            .add("endDate=" + endDate)
+            .toString();
+    }
+}

easy-random/src/main/java/org/baeldung/easy/random/randomizer/YearQuarterRandomizer.java

@@ -0,0 +1,18 @@
+package org.baeldung.easy.random.randomizer;
+
+import org.baeldung.easy.random.model.YearQuarter;
+import org.jeasy.random.api.Randomizer;
+
+import java.time.LocalDate;
+import java.time.Month;
+
+public class YearQuarterRandomizer implements Randomizer<YearQuarter> {
+
+    private LocalDate date = LocalDate.of(1990, Month.SEPTEMBER, 25);
+
+    @Override
+    public YearQuarter getRandomValue() {
+        date = date.plusMonths(3);
+        return new YearQuarter(date);
+    }
+}

easy-random/src/test/java/org/baeldung/easy/random/EasyRandomUnitTest.java

@@ -0,0 +1,63 @@
+package org.baeldung.easy.random;
+
+import org.baeldung.easy.random.model.Employee;
+import org.baeldung.easy.random.model.Person;
+import org.baeldung.easy.random.model.YearQuarter;
+import org.baeldung.easy.random.randomizer.YearQuarterRandomizer;
+import org.jeasy.random.EasyRandom;
+import org.jeasy.random.EasyRandomParameters;
+import org.jeasy.random.FieldPredicates;
+import org.jeasy.random.TypePredicates;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class EasyRandomUnitTest {
+
+    @Test
+    void givenDefaultConfiguration_thenGenerateSingleObject() {
+        EasyRandom generator = new EasyRandom();
+        Person person = generator.nextObject(Person.class);
+
+        assertNotNull(person.getAge());
+        assertNotNull(person.getFirstName());
+        assertNotNull(person.getLastName());
+    }
+
+    @Test
+    void givenDefaultConfiguration_thenGenerateObjectsList() {
+        EasyRandom generator = new EasyRandom();
+        List<Person> persons = generator.objects(Person.class, 5)
+            .collect(Collectors.toList());
+
+        assertEquals(5, persons.size());
+    }
+
+    @Test
+    void givenCustomConfiguration_thenGenerateSingleEmployee() {
+        EasyRandomParameters parameters = new EasyRandomParameters();
+        parameters.stringLengthRange(3, 3);
+        parameters.collectionSizeRange(5, 5);
+        parameters.excludeField(FieldPredicates.named("lastName").and(FieldPredicates.inClass(Employee.class)));
+        parameters.excludeType(TypePredicates.inPackage("not.existing.pkg"));
+        parameters.randomize(YearQuarter.class, new YearQuarterRandomizer());
+
+        EasyRandom generator = new EasyRandom(parameters);
+        Employee employee = generator.nextObject(Employee.class);
+
+        assertEquals(3, employee.getFirstName().length());
+        assertEquals(5, employee.getCoworkers().size());
+        assertEquals(5, employee.getQuarterGrades().size());
+        assertNotNull(employee.getDepartment());
+
+        assertNull(employee.getLastName());
+
+        for (YearQuarter key : employee.getQuarterGrades().keySet()) {
+            assertEquals(key.getStartDate(), key.getEndDate().minusMonths(3L));
+        }
+    }
+
+}

java-collections-conversions/src/test/java/com/baeldung/convert/iteratortolist/ConvertIteratorToListServiceUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.convertiteratortolist;
+package com.baeldung.convert.iteratortolist;
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.collection.IsCollectionWithSize.hasSize;

java-dates-2/pom.xml

@@ -20,6 +20,13 @@
             <artifactId>joda-time</artifactId>
             <version>${joda-time.version}</version>
         </dependency>
+        
+        <!-- https://mvnrepository.com/artifact/commons-validator/commons-validator -->
+        <dependency>
+            <groupId>commons-validator</groupId>
+            <artifactId>commons-validator</artifactId>
+            <version>1.6</version>
+        </dependency>
 
         <!-- test scoped -->
         <dependency>

java-dates-2/src/main/java/com/baeldung/date/validation/DateValidator.java

@@ -0,0 +1,5 @@
+package com.baeldung.date.validation;
+
+public interface DateValidator {
+   boolean isValid(String dateStr);
+}

java-dates-2/src/main/java/com/baeldung/date/validation/DateValidatorUsingApacheValidator.java

@@ -0,0 +1,11 @@
+package com.baeldung.date.validation;
+
+import org.apache.commons.validator.GenericValidator;
+
+public class DateValidatorUsingApacheValidator implements DateValidator {
+
+    @Override
+    public boolean isValid(String dateStr) {
+        return GenericValidator.isDate(dateStr, "yyyy-MM-dd", true); 
+    }
+}

java-dates-2/src/main/java/com/baeldung/date/validation/DateValidatorUsingDateFormat.java

@@ -0,0 +1,25 @@
+package com.baeldung.date.validation;
+
+import java.text.DateFormat;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+
+public class DateValidatorUsingDateFormat implements DateValidator {
+    private String dateFormat;
+
+    public DateValidatorUsingDateFormat(String dateFormat) {
+        this.dateFormat = dateFormat;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        DateFormat sdf = new SimpleDateFormat(this.dateFormat);
+        sdf.setLenient(false);
+        try {
+            sdf.parse(dateStr);
+        } catch (ParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

java-dates-2/src/main/java/com/baeldung/date/validation/DateValidatorUsingDateTimeFormatter.java

@@ -0,0 +1,22 @@
+package com.baeldung.date.validation;
+
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
+public class DateValidatorUsingDateTimeFormatter implements DateValidator {
+    private DateTimeFormatter dateFormatter;
+    
+    public DateValidatorUsingDateTimeFormatter(DateTimeFormatter dateFormatter) {
+        this.dateFormatter = dateFormatter;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        try {
+            this.dateFormatter.parse(dateStr);
+        } catch (DateTimeParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

java-dates-2/src/main/java/com/baeldung/date/validation/DateValidatorUsingLocalDate.java

@@ -0,0 +1,23 @@
+package com.baeldung.date.validation;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
+public class DateValidatorUsingLocalDate implements DateValidator {
+    private DateTimeFormatter dateFormatter;
+    
+    public DateValidatorUsingLocalDate(DateTimeFormatter dateFormatter) {
+        this.dateFormatter = dateFormatter;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        try {
+            LocalDate.parse(dateStr, this.dateFormatter);
+        } catch (DateTimeParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

java-dates-2/src/test/java/com/baeldung/date/validation/DateValidatorUsingApacheValidatorUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.commons.validator.GenericValidator;
+import org.junit.Test;
+
+public class DateValidatorUsingApacheValidatorUnitTest {
+
+    @Test
+    public void whenValidDatePassed_ThenTrue() {
+        assertTrue(GenericValidator.isDate("2019-02-28", "yyyy-MM-dd", true));
+    }
+
+    @Test
+    public void whenInvalidDatePassed_ThenFalse() {
+        assertFalse(GenericValidator.isDate("2019-02-29", "yyyy-MM-dd", true));
+    }
+}

java-dates-2/src/test/java/com/baeldung/date/validation/DateValidatorUsingDateFormatUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class DateValidatorUsingDateFormatUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateValidator validator = new DateValidatorUsingDateFormat("MM/dd/yyyy");
+        
+        assertTrue(validator.isValid("02/28/2019"));
+    }
+    
+    @Test
+    public void givenValidator_whenInvalidDatePassed_ThenFalse() {
+        DateValidator validator = new DateValidatorUsingDateFormat("MM/dd/yyyy");
+        
+        assertFalse(validator.isValid("02/30/2019"));
+    }
+}

java-dates-2/src/test/java/com/baeldung/date/validation/DateValidatorUsingDateTimeFormatterUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.time.format.DateTimeFormatter;
+import java.time.format.ResolverStyle;
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class DateValidatorUsingDateTimeFormatterUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd", Locale.US)
+            .withResolverStyle(ResolverStyle.STRICT);
+        DateValidator validator = new DateValidatorUsingDateTimeFormatter(dateFormatter);
+        
+        assertTrue(validator.isValid("2019-02-28"));
+    }
+    
+    @Test
+    public void givenValidator_whenInValidDatePassed_ThenFalse() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd", Locale.US)
+            .withResolverStyle(ResolverStyle.STRICT);
+        DateValidator validator = new DateValidatorUsingDateTimeFormatter(dateFormatter);
+        
+        assertFalse(validator.isValid("2019-02-30"));
+    }
+
+}

java-dates-2/src/test/java/com/baeldung/date/validation/DateValidatorUsingLocalDateUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.time.format.DateTimeFormatter;
+
+import org.junit.Test;
+
+public class DateValidatorUsingLocalDateUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.BASIC_ISO_DATE;
+        DateValidator validator = new DateValidatorUsingLocalDate(dateFormatter);
+        
+        assertTrue(validator.isValid("20190228"));
+    }
+    
+    @Test
+    public void givenValidator_whenInValidDatePassed_ThenFalse() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.BASIC_ISO_DATE;
+        DateValidator validator = new DateValidatorUsingLocalDate(dateFormatter);
+        
+        assertFalse(validator.isValid("20190230"));
+    }
+}

java-numbers/src/main/java/com/baeldung/random/SecureRandomDemo.java

@@ -0,0 +1,36 @@
+package com.baeldung.random;
+
+import java.security.SecureRandom;
+import java.security.NoSuchAlgorithmException;
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+import java.util.stream.DoubleStream;
+
+public interface SecureRandomDemo {
+
+    public static void generateSecureRandomValues() {
+        SecureRandom sr = new SecureRandom();
+
+        int randomInt = sr.nextInt();
+        long randomLong = sr.nextLong();
+        float randomFloat = sr.nextFloat();
+        double randomDouble = sr.nextDouble();
+        boolean randomBoolean = sr.nextBoolean();
+
+        IntStream randomIntStream = sr.ints();
+        LongStream randomLongStream = sr.longs();
+        DoubleStream randomDoubleStream = sr.doubles();
+
+        byte[] values = new byte[124];
+        sr.nextBytes(values);
+    }
+
+    public static SecureRandom getSecureRandomForAlgorithm(String algorithm) throws NoSuchAlgorithmException {
+        if (algorithm == null || algorithm.isEmpty()) {
+            return new SecureRandom();
+        }
+
+        return SecureRandom.getInstance(algorithm);
+    }
+
+}

java-streams-2/pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.baeldung.javastreams2</groupId>
     <artifactId>javastreams2</artifactId>
     <version>1.0</version>
-    <name>Stream Reduce</name>
+    <name>javastreams2</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -42,8 +42,8 @@
 	
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>1.9</maven.compiler.source>
+        <maven.compiler.target>1.9</maven.compiler.target>
         <assertj.version>3.11.1</assertj.version>
     </properties>
 </project>

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomForEach.java

@@ -0,0 +1,32 @@
+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.function.BiConsumer;
+import java.util.stream.Stream;
+
+public class CustomForEach {
+
+    public static class Breaker {
+        private boolean shouldBreak = false;
+
+        public void stop() {
+            shouldBreak = true;
+        }
+
+        boolean get() {
+            return shouldBreak;
+        }
+    }
+
+    public static <T> void forEach(Stream<T> stream, BiConsumer<T, Breaker> consumer) {
+        Spliterator<T> spliterator = stream.spliterator();
+        boolean hadNext = true;
+        Breaker breaker = new Breaker();
+
+        while (hadNext && !breaker.get()) {
+            hadNext = spliterator.tryAdvance(elem -> {
+                consumer.accept(elem, breaker);
+            });
+        }
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomSpliterator.java

@@ -0,0 +1,31 @@
+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.Spliterators;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+public class CustomSpliterator<T> extends Spliterators.AbstractSpliterator<T> {
+
+    private Spliterator<T> splitr;
+    private Predicate<T> predicate;
+    private boolean isMatched = true;
+
+    public CustomSpliterator(Spliterator<T> splitr, Predicate<T> predicate) {
+        super(splitr.estimateSize(), 0);
+        this.splitr = splitr;
+        this.predicate = predicate;
+    }
+
+    @Override
+    public boolean tryAdvance(Consumer<? super T> consumer) {
+        boolean hadNext = splitr.tryAdvance(elem -> {
+            if (predicate.test(elem) && isMatched) {
+                consumer.accept(elem);
+            } else {
+                isMatched = false;
+            }
+        });
+        return hadNext && isMatched;
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomTakeWhile.java

@@ -0,0 +1,14 @@
+package com.baeldung.breakforeach;
+
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+public class CustomTakeWhile {
+
+    public static <T> Stream<T> takeWhile(Stream<T> stream, Predicate<T> predicate) {
+        CustomSpliterator<T> customSpliterator = new CustomSpliterator<>(stream.spliterator(), predicate);
+        return StreamSupport.stream(customSpliterator, false);
+    }
+
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/TakeWhileExample.java

@@ -0,0 +1,26 @@
+package com.baeldung.breakforeach;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+
+public class TakeWhileExample {
+
+    public static void takeWhileJava9() {
+        Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck")
+            .takeWhile(n -> n.length() % 2 != 0)
+            .forEach(System.out::println); // cat, dog
+    }
+
+    public static void plainForLoopWithBreak() {
+        List<String> list = asList("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        for (int i = 0; i < list.size(); i++) {
+            String item = list.get(i);
+            if (item.length() % 2 == 0) {
+                break;
+            }
+            System.out.println(item);
+        }
+    }
+}

java-streams-2/src/test/java/com/baeldung/breakforeach/BreakFromStreamForEachUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.breakforeach;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class BreakFromStreamForEachUnitTest {
+
+    @Test
+    public void whenCustomTakeWhileIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+
+        List<String> result = CustomTakeWhile.takeWhile(initialStream, x -> x.length() % 2 != 0)
+                .collect(Collectors.toList());
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+    @Test
+    public void whenCustomForEachIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        List<String> result = new ArrayList<>();
+
+        CustomForEach.forEach(initialStream, (elem, breaker) -> {
+            if (elem.length() % 2 == 0) {
+                breaker.stop();
+            } else {
+                result.add(elem);
+            }
+        });
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+}

java-streams-2/src/test/java/com/baeldung/convert/intstreams/IntStreamsConversionsUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.intstreams.conversion;
+package com.baeldung.convert.intstreams;
 
 import org.junit.Test;
 

java-strings-2/pom.xml

@@ -57,6 +57,26 @@
             <artifactId>commons-text</artifactId>
             <version>${commons-text.version}</version>
         </dependency>
+        <dependency>
+            <groupId>javax.validation</groupId>
+            <artifactId>validation-api</artifactId>
+            <version>2.0.0.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hibernate.validator</groupId>
+            <artifactId>hibernate-validator</artifactId>
+            <version>6.0.2.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.el</groupId>
+            <artifactId>javax.el-api</artifactId>
+            <version>3.0.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.glassfish.web</groupId>
+            <artifactId>javax.el</artifactId>
+            <version>2.2.6</version>
+        </dependency>
 
     </dependencies>
 
@@ -86,7 +106,7 @@
     <properties>
         <commons-lang3.version>3.8.1</commons-lang3.version>
         <icu4j.version>61.1</icu4j.version>
-        <guava.version>27.0.1-jre</guava.version>
+        <guava.version>28.0-jre</guava.version>
         <commons-text.version>1.4</commons-text.version>
     </properties>
 

java-strings-2/src/main/java/com/baeldung/string/emptystrings/EmptyStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.isEmpty();
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/Java5EmptyStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class Java5EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.length() == 0;
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/PlainJavaBlankStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class PlainJavaBlankStringCheck {
+
+    boolean isBlankString(String string) {
+        return string == null || string.trim().isEmpty();
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/SomeClassWithValidations.java

@@ -0,0 +1,14 @@
+package com.baeldung.string.emptystrings;
+
+import javax.validation.constraints.Pattern;
+
+class SomeClassWithValidations {
+
+    @Pattern(regexp = "\\A(?!\\s*\\Z).+")
+    private String someString;
+
+    SomeClassWithValidations setSomeString(String someString) {
+        this.someString = someString;
+        return this;
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/multiline/MultiLineString.java

@@ -0,0 +1,67 @@
+package com.baeldung.string.multiline;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
+
+public class MultiLineString {
+    
+    String newLine = System.getProperty("line.separator");
+    
+    public String stringConcatenation() {
+        return "Get busy living"
+                .concat(newLine)
+                .concat("or")
+                .concat(newLine)
+                .concat("get busy dying.")
+                .concat(newLine)
+                .concat("--Stephen King");
+    }
+    
+    public String stringJoin() {
+        return String.join(newLine,
+                           "Get busy living",
+                           "or",
+                           "get busy dying.",
+                           "--Stephen King");
+    }
+    
+    public String stringBuilder() {
+        return new StringBuilder()
+                .append("Get busy living")
+                .append(newLine)
+                .append("or")
+                .append(newLine)
+                .append("get busy dying.")
+                .append(newLine)
+                .append("--Stephen King")
+                .toString();
+    }
+    
+    public String stringWriter() {
+        StringWriter stringWriter = new StringWriter();
+        PrintWriter printWriter = new PrintWriter(stringWriter);
+        printWriter.println("Get busy living");
+        printWriter.println("or");
+        printWriter.println("get busy dying.");
+        printWriter.println("--Stephen King");
+        return stringWriter.toString();
+    }
+    
+    public String guavaJoiner() {
+        return Joiner.on(newLine).join(ImmutableList.of("Get busy living",
+            "or",
+            "get busy dying.",
+            "--Stephen King"));
+    }
+    
+    public String loadFromFile() throws IOException {
+        return new String(Files.readAllBytes(Paths.get("src/main/resources/stephenking.txt")));
+    }
+
+}

java-strings-2/src/main/java/com/baeldung/string/repetition/SubstringRepetition.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.repetition;
+
+public class SubstringRepetition {
+
+    public static boolean containsOnlySubstrings(String string) {
+
+        if (string.length() < 2) {
+            return false;
+        }
+
+        StringBuilder substr = new StringBuilder();
+        for (int i = 0; i < string.length() / 2; i++) {
+            substr.append(string.charAt(i));
+
+            String clearedFromSubstrings = string.replaceAll(substr.toString(), "");
+
+            if (clearedFromSubstrings.length() == 0) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public static boolean containsOnlySubstringsEfficient(String string) {
+
+        return ((string + string).indexOf(string, 1) != string.length());
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/reverse/ReverseStringExamples.java

@@ -0,0 +1,56 @@
+package com.baeldung.string.reverse;
+
+import org.apache.commons.lang3.StringUtils;
+
+public class ReverseStringExamples {
+
+    public static String reverse(String input) {
+        if (input == null) {
+            return null;
+        }
+
+        String output = "";
+
+        for (int i = input.length() - 1; i >= 0; i--) {
+            output = output + input.charAt(i);
+        }
+
+        return output;
+    }
+
+    public static String reverseUsingStringBuilder(String input) {
+        if (input == null) {
+            return null;
+        }
+
+        StringBuilder output = new StringBuilder(input).reverse();
+
+        return output.toString();
+    }
+
+    public static String reverseUsingApacheCommons(String input) {
+        return StringUtils.reverse(input);
+    }
+
+    public static String reverseTheOrderOfWords(String sentence) {
+        if (sentence == null) {
+            return null;
+        }
+
+        StringBuilder output = new StringBuilder();
+        String[] words = sentence.split(" ");
+
+        for (int i = words.length - 1; i >= 0; i--) {
+            output.append(words[i]);
+            output.append(" ");
+        }
+
+        return output.toString()
+            .trim();
+    }
+
+    public static String reverseTheOrderOfWordsUsingApacheCommons(String sentence) {
+        return StringUtils.reverseDelimited(sentence, ' ');
+    }
+
+}

java-strings-2/src/main/resources/stephenking.txt

@@ -0,0 +1,4 @@
+Get busy living
+or
+get busy dying.
+--Stephen King

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

@@ -0,0 +1,22 @@
+package com.baeldung.string;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+
+import com.baeldung.string.multiline.MultiLineString;
+
+public class MultiLineStringUnitTest {
+
+    
+    @Test
+    public void whenCompareMultiLineStrings_thenTheyAreAllTheSame() throws IOException {
+        MultiLineString ms = new MultiLineString();
+        assertEquals(ms.stringConcatenation(), ms.stringJoin());
+        assertEquals(ms.stringJoin(), ms.stringBuilder());
+        assertEquals(ms.stringBuilder(), ms.guavaJoiner());
+        assertEquals(ms.guavaJoiner(), ms.loadFromFile());
+    }
+    
+}

java-strings-2/src/test/java/com/baeldung/string/emptystrings/EmptyStringsUnitTest.java

@@ -0,0 +1,142 @@
+package com.baeldung.string.emptystrings;
+
+import static org.hamcrest.Matchers.iterableWithSize;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Set;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import com.google.common.base.Strings;
+
+public class EmptyStringsUnitTest {
+
+    private String emptyString = "";
+    private String blankString = "  \n\t  ";
+    private String nonEmptyString = "   someString   ";
+
+    /*
+     * EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenEmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * Java5EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new Java5EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * PlainJavaBlankStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsFalse() {
+        assertFalse(new PlainJavaBlankStringCheck().isBlankString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(blankString));
+    }
+
+    /*
+     * Apache Commons Lang StringUtils
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringUtilsIsBlankReturnsFalse() {
+        assertFalse(StringUtils.isBlank(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(blankString));
+    }
+
+    /*
+     * Google Guava Strings
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringsIsNullOrEmptyStringReturnsTrue() {
+        assertTrue(Strings.isNullOrEmpty(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(blankString));
+    }
+
+    /*
+     * Bean Validation
+     */
+    private ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    private Validator validator = factory.getValidator();
+
+    @Test
+    public void givenSomeEmptyString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(emptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenBeanValidationValidatesWithoutViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(nonEmptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(0));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(blankString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/repetition/SubstringRepetitionUnitTest.java

@@ -0,0 +1,45 @@
+package com.baeldung.string.repetition;
+
+import static com.baeldung.string.repetition.SubstringRepetition.*;
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class SubstringRepetitionUnitTest {
+
+    private String validString = "aa";
+    private String validStringTwo = "ababab";
+    private String validStringThree = "baeldungbaeldung";
+
+    private String invalidString = "aca";
+    private String invalidStringTwo = "ababa";
+    private String invalidStringThree = "baeldungnonrepeatedbaeldung";
+
+    @Test
+    public void givenValidStrings_whenCheckIfContainsOnlySubstrings_thenReturnsTrue() {
+        assertTrue(containsOnlySubstrings(validString));
+        assertTrue(containsOnlySubstrings(validStringTwo));
+        assertTrue(containsOnlySubstrings(validStringThree));
+    }
+
+    @Test
+    public void givenInvalidStrings_whenCheckIfContainsOnlySubstrings_thenReturnsFalse() {
+        assertFalse(containsOnlySubstrings(invalidString));
+        assertFalse(containsOnlySubstrings(invalidStringTwo));
+        assertFalse(containsOnlySubstrings(invalidStringThree));
+    }
+
+    @Test
+    public void givenValidStrings_whenCheckEfficientlyIfContainsOnlySubstrings_thenReturnsTrue() {
+        assertTrue(containsOnlySubstringsEfficient(validString));
+        assertTrue(containsOnlySubstringsEfficient(validStringTwo));
+        assertTrue(containsOnlySubstringsEfficient(validStringThree));
+    }
+
+    @Test
+    public void givenInvalidStrings_whenCheckEfficientlyIfContainsOnlySubstrings_thenReturnsFalse() {
+        assertFalse(containsOnlySubstringsEfficient(invalidString));
+        assertFalse(containsOnlySubstringsEfficient(invalidStringTwo));
+        assertFalse(containsOnlySubstringsEfficient(invalidStringThree));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/reverse/ReverseStringExamplesUnitTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.string.reverse;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ReverseStringExamplesUnitTest {
+
+    private static final String STRING_INPUT = "cat";
+    private static final String STRING_INPUT_REVERSED = "tac";
+    private static final String SENTENCE = "The quick brown fox jumps over the lazy dog";
+    private static final String REVERSED_WORDS_SENTENCE = "dog lazy the over jumps fox brown quick The";
+
+    @Test
+    public void whenReverseIsCalled_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverse(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverse(null);
+        String reversedEmpty = ReverseStringExamples.reverse(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertEquals(null, reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseUsingStringBuilderIsCalled_ThenCorrectStringIsReturned() throws Exception {
+        String reversed = ReverseStringExamples.reverseUsingStringBuilder(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverseUsingStringBuilder(null);
+        String reversedEmpty = ReverseStringExamples.reverseUsingStringBuilder(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertEquals(null, reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseUsingApacheCommonsIsCalled_ThenCorrectStringIsReturned() throws Exception {
+        String reversed = ReverseStringExamples.reverseUsingApacheCommons(STRING_INPUT);
+        String reversedNull = ReverseStringExamples.reverseUsingApacheCommons(null);
+        String reversedEmpty = ReverseStringExamples.reverseUsingApacheCommons(StringUtils.EMPTY);
+
+        assertEquals(STRING_INPUT_REVERSED, reversed);
+        assertEquals(null, reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseTheOrderOfWordsIsCalled_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverseTheOrderOfWords(SENTENCE);
+        String reversedNull = ReverseStringExamples.reverseTheOrderOfWords(null);
+        String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWords(StringUtils.EMPTY);
+
+        assertEquals(REVERSED_WORDS_SENTENCE, reversed);
+        assertEquals(null, reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+    @Test
+    public void whenReverseTheOrderOfWordsUsingApacheCommonsIsCalled_ThenCorrectStringIsReturned() {
+        String reversed = ReverseStringExamples.reverseTheOrderOfWordsUsingApacheCommons(SENTENCE);
+        String reversedNull = ReverseStringExamples.reverseTheOrderOfWordsUsingApacheCommons(null);
+        String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWordsUsingApacheCommons(StringUtils.EMPTY);
+
+        assertEquals(REVERSED_WORDS_SENTENCE, reversed);
+        assertEquals(null, reversedNull);
+        assertEquals(StringUtils.EMPTY, reversedEmpty);
+    }
+
+}

libraries-2/README.md

@@ -4,4 +4,4 @@
 - [A Guide to jBPM with Java](https://www.baeldung.com/jbpm-java)
 - [Guide to Classgraph Library](https://www.baeldung.com/classgraph)
 - [Create a Java Command Line Program with Picocli](https://www.baeldung.com/java-picocli-create-command-line-program)
-
+- [Guide to Java Parallel Collectors Library](https://www.baeldung.com/java-parallel-collectors)

libraries-2/pom.xml

@@ -1,113 +1,154 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-
-	<modelVersion>4.0.0</modelVersion>
-	<artifactId>libraries2</artifactId>
-	<name>libraries2</name>
-
-	<parent>
-		<groupId>com.baeldung</groupId>
-		<artifactId>parent-modules</artifactId>
-		<version>1.0.0-SNAPSHOT</version>
-	</parent>
-
-	<repositories>
-		<repository>
-			<id>jboss-public-repository-group</id>
-			<name>JBoss Public Repository Group</name>
-			<url>http://repository.jboss.org/nexus/content/groups/public/</url>
-			<releases>
-				<enabled>true</enabled>
-				<updatePolicy>never</updatePolicy>
-			</releases>
-			<snapshots>
-				<enabled>true</enabled>
-				<updatePolicy>daily</updatePolicy>
-			</snapshots>
-		</repository>
-	</repositories>
-
-	<dependencies>
-		<dependency>
-			<groupId>org.assertj</groupId>
-			<artifactId>assertj-core</artifactId>
-			<version>${assertj.version}</version>
-		</dependency>
-		<dependency>
-			<groupId>io.github.classgraph</groupId>
-			<artifactId>classgraph</artifactId>
-			<version>${classgraph.version}</version>
-		</dependency>
-		<dependency>
-			<groupId>org.jbpm</groupId>
-			<artifactId>jbpm-test</artifactId>
-			<version>${jbpm.version}</version>
-		</dependency>
-		<dependency>
-			<groupId>info.picocli</groupId>
-			<artifactId>picocli</artifactId>
-			<version>${picocli.version}</version>
-		</dependency>
-		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter</artifactId>
-			<version>${spring-boot-starter.version}</version>
-		</dependency>
-		<dependency>
-			<groupId>net.openhft</groupId>
-			<artifactId>chronicle-map</artifactId>
-			<version>${chronicle.map.version}</version>
-			<exclusions>
-				<exclusion>
-					<groupId>com.sun.java</groupId>
-					<artifactId>tools</artifactId>
-				</exclusion>
-			</exclusions>
-		</dependency>
-
-		<!-- Dependencies for response decoder with okhttp -->
-		<dependency>
-			<groupId>com.squareup.okhttp3</groupId>
-			<artifactId>okhttp</artifactId>
-			<version>3.14.2</version>
-		</dependency>
-
-		<dependency>
-			<groupId>com.fasterxml.jackson.core</groupId>
-			<artifactId>jackson-databind</artifactId>
-			<version>2.9.9</version>
-		</dependency>
-
-		<dependency>
-			<groupId>com.google.code.gson</groupId>
-			<artifactId>gson</artifactId>
-			<version>2.8.5</version>
-		</dependency>
-
-		<dependency>
-			<groupId>com.squareup.okhttp3</groupId>
-			<artifactId>mockwebserver</artifactId>
-			<version>3.14.2</version>
-			<scope>test</scope>
-		</dependency>
-
-                <dependency>
-                    <groupId>edu.uci.ics</groupId>
-                    <artifactId>crawler4j</artifactId>
-                    <version>${crawler4j.version}</version>
-		</dependency>
-          
-	</dependencies>
-
-	<properties>
-		<assertj.version>3.6.2</assertj.version>
-		<classgraph.version>4.8.28</classgraph.version>
-		<jbpm.version>6.0.0.Final</jbpm.version>
-		<picocli.version>3.9.6</picocli.version>
-		<chronicle.map.version>3.17.2</chronicle.map.version>
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>libraries2</artifactId>
+    <name>libraries2</name>
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <repositories>
+        <repository>
+            <id>jboss-public-repository-group</id>
+            <name>JBoss Public Repository Group</name>
+            <url>http://repository.jboss.org/nexus/content/groups/public/</url>
+            <releases>
+                <enabled>true</enabled>
+                <updatePolicy>never</updatePolicy>
+            </releases>
+            <snapshots>
+                <enabled>true</enabled>
+                <updatePolicy>daily</updatePolicy>
+            </snapshots>
+        </repository>
+    </repositories>
+    <dependencies>
+        <dependency>
+            <groupId>org.mapdb</groupId>
+            <artifactId>mapdb</artifactId>
+            <version>${mapdb.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.pivovarit</groupId>
+            <artifactId>parallel-collectors</artifactId>
+            <version>1.1.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.github.classgraph</groupId>
+            <artifactId>classgraph</artifactId>
+            <version>${classgraph.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.jbpm</groupId>
+            <artifactId>jbpm-test</artifactId>
+            <version>${jbpm.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>info.picocli</groupId>
+            <artifactId>picocli</artifactId>
+            <version>${picocli.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.ejml</groupId>
+            <artifactId>ejml-all</artifactId>
+            <version>${ejml.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.nd4j</groupId>
+            <artifactId>nd4j-native</artifactId>
+            <version>${nd4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.la4j</groupId>
+            <artifactId>la4j</artifactId>
+            <version>${la4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>colt</groupId>
+            <artifactId>colt</artifactId>
+            <version>${colt.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+            <version>${spring-boot-starter.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>net.openhft</groupId>
+            <artifactId>chronicle-map</artifactId>
+            <version>${chronicle.map.version}</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>com.sun.java</groupId>
+                    <artifactId>tools</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        <!-- Dependencies for response decoder with okhttp -->
+        <dependency>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>okhttp</artifactId>
+            <version>3.14.2</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>2.9.9</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.8.5</version>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>mockwebserver</artifactId>
+            <version>3.14.2</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>edu.uci.ics</groupId>
+            <artifactId>crawler4j</artifactId>
+            <version>${crawler4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.github.jknack</groupId>
+            <artifactId>handlebars</artifactId>
+            <version>4.1.2</version>
+        </dependency>
+        <!-- Benchmarking -->
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
+    </dependencies>
+    <properties>
+	    <mapdb.version>3.0.7</mapdb.version>
+        <assertj.version>3.6.2</assertj.version>
+        <classgraph.version>4.8.28</classgraph.version>
+        <jbpm.version>6.0.0.Final</jbpm.version>
+        <picocli.version>3.9.6</picocli.version>
+        <chronicle.map.version>3.17.2</chronicle.map.version>
         <crawler4j.version>4.4.0</crawler4j.version>
-		<spring-boot-starter.version>2.1.4.RELEASE</spring-boot-starter.version>
-	</properties>
+        <spring-boot-starter.version>2.1.4.RELEASE</spring-boot-starter.version>
+        <ejml.version>0.38</ejml.version>
+        <nd4j.version>1.0.0-beta4</nd4j.version>
+        <colt.version>1.2.0</colt.version>
+        <la4j.version>0.6.0</la4j.version>
+        <jmh.version>1.19</jmh.version>
+    </properties>
 </project>

libraries-2/src/test/java/com/baeldung/handlebars/BasicUsageUnitTest.java

@@ -0,0 +1,109 @@
+package com.baeldung.handlebars;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.jknack.handlebars.Handlebars;
+import com.github.jknack.handlebars.Template;
+import com.github.jknack.handlebars.io.ClassPathTemplateLoader;
+import com.github.jknack.handlebars.io.TemplateLoader;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.Test;
+
+/**
+ * Showcases the tag usage and different template loading mechanisms.
+ *
+ * @author isaolmez
+ */
+public class BasicUsageUnitTest {
+
+    @Test
+    public void whenThereIsNoTemplateFile_ThenCompilesInline() throws IOException {
+        Handlebars handlebars = new Handlebars();
+        Template template = handlebars.compileInline("Hi {{this}}!");
+
+        String templateString = template.apply("Baeldung");
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    @Test
+    public void whenParameterMapIsSupplied_thenDisplays() throws IOException {
+        Handlebars handlebars = new Handlebars();
+        Template template = handlebars.compileInline("Hi {{name}}!");
+        Map<String, String> parameterMap = new HashMap<>();
+        parameterMap.put("name", "Baeldung");
+
+        String templateString = template.apply(parameterMap);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    @Test
+    public void whenParameterObjectIsSupplied_ThenDisplays() throws IOException {
+        Handlebars handlebars = new Handlebars();
+        Template template = handlebars.compileInline("Hi {{name}}!");
+        Person person = new Person();
+        person.setName("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    @Test
+    public void whenMultipleParametersAreSupplied_ThenDisplays() throws IOException {
+        Handlebars handlebars = new Handlebars();
+        Template template = handlebars.compileInline("Hi {{name}}! This is {{topic}}.");
+        Map<String, String> parameterMap = new HashMap<>();
+        parameterMap.put("name", "Baeldung");
+        parameterMap.put("topic", "Handlebars");
+
+        String templateString = template.apply(parameterMap);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung! This is Handlebars.");
+    }
+
+    @Test
+    public void whenNoLoaderIsGiven_ThenSearchesClasspath() throws IOException {
+        Handlebars handlebars = new Handlebars();
+        Template template = handlebars.compile("greeting");
+        Person person = getPerson("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    @Test
+    public void whenClasspathTemplateLoaderIsGiven_ThenSearchesClasspathWithPrefixSuffix() throws IOException {
+        TemplateLoader loader = new ClassPathTemplateLoader("/handlebars", ".html");
+        Handlebars handlebars = new Handlebars(loader);
+        Template template = handlebars.compile("greeting");
+        Person person = getPerson("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    @Test
+    public void whenMultipleLoadersAreGiven_ThenSearchesSequentially() throws IOException {
+        TemplateLoader firstLoader = new ClassPathTemplateLoader("/handlebars", ".html");
+        TemplateLoader secondLoader = new ClassPathTemplateLoader("/templates", ".html");
+        Handlebars handlebars = new Handlebars().with(firstLoader, secondLoader);
+        Template template = handlebars.compile("greeting");
+        Person person = getPerson("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Hi Baeldung!");
+    }
+
+    private Person getPerson(String name) {
+        Person person = new Person();
+        person.setName(name);
+        return person;
+    }
+}

libraries-2/src/test/java/com/baeldung/handlebars/BuiltinHelperUnitTest.java

@@ -0,0 +1,106 @@
+package com.baeldung.handlebars;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.jknack.handlebars.Handlebars;
+import com.github.jknack.handlebars.Template;
+import com.github.jknack.handlebars.io.ClassPathTemplateLoader;
+import com.github.jknack.handlebars.io.TemplateLoader;
+import java.io.IOException;
+import org.junit.Test;
+
+/**
+ * Showcases the built-in template helpers.
+ *
+ * @author isaolmez
+ */
+public class BuiltinHelperUnitTest {
+
+    private TemplateLoader templateLoader = new ClassPathTemplateLoader("/handlebars", ".html");
+
+    @Test
+    public void whenUsedWith_ThenContextChanges() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("with");
+        Person person = getPerson("Baeldung");
+        person.getAddress().setStreet("World");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<h4>I live in World</h4>\n");
+    }
+
+    @Test
+    public void whenUsedWithMustacheStyle_ThenContextChanges() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("with_mustache");
+        Person person = getPerson("Baeldung");
+        person.getAddress().setStreet("World");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<h4>I live in World</h4>\n");
+    }
+
+    @Test
+    public void whenUsedEach_ThenIterates() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("each");
+        Person person = getPerson("Baeldung");
+        Person friend1 = getPerson("Java");
+        Person friend2 = getPerson("Spring");
+        person.getFriends().add(friend1);
+        person.getFriends().add(friend2);
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<span>Java is my friend.</span>\n"
+                                               + "\n<span>Spring is my friend.</span>\n");
+    }
+
+    @Test
+    public void whenUsedEachMustacheStyle_ThenIterates() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("each_mustache");
+        Person person = getPerson("Baeldung");
+        Person friend1 = getPerson("Java");
+        Person friend2 = getPerson("Spring");
+        person.getFriends().add(friend1);
+        person.getFriends().add(friend2);
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<span>Java is my friend.</span>\n"
+                                               + "\n<span>Spring is my friend.</span>\n");
+    }
+
+    @Test
+    public void whenUsedIf_ThenPutsCondition() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("if");
+        Person person = getPerson("Baeldung");
+        person.setBusy(true);
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<h4>Baeldung is busy.</h4>\n");
+    }
+
+    @Test
+    public void whenUsedIfMustacheStyle_ThenPutsCondition() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("if_mustache");
+        Person person = getPerson("Baeldung");
+        person.setBusy(true);
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<h4>Baeldung is busy.</h4>\n");
+    }
+
+    private Person getPerson(String name) {
+        Person person = new Person();
+        person.setName(name);
+        return person;
+    }
+}

libraries-2/src/test/java/com/baeldung/handlebars/CustomHelperUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.handlebars;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.jknack.handlebars.Handlebars;
+import com.github.jknack.handlebars.Helper;
+import com.github.jknack.handlebars.Options;
+import com.github.jknack.handlebars.Template;
+import com.github.jknack.handlebars.io.ClassPathTemplateLoader;
+import com.github.jknack.handlebars.io.TemplateLoader;
+import java.io.IOException;
+import org.junit.Test;
+
+/**
+ * Showcases implementing a custom template helper.
+ *
+ * @author isaolmez
+ */
+public class CustomHelperUnitTest {
+
+    private TemplateLoader templateLoader = new ClassPathTemplateLoader("/handlebars", ".html");
+
+    @Test
+    public void whenHelperIsCreated_ThenCanRegister() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        handlebars.registerHelper("isBusy", new Helper<Person>() {
+            @Override
+            public Object apply(Person context, Options options) throws IOException {
+                String busyString = context.isBusy() ? "busy" : "available";
+                return context.getName() + " - " + busyString;
+            }
+        });
+        Template template = handlebars.compile("person");
+        Person person = getPerson("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Baeldung - busy");
+    }
+
+    @Test
+    public void whenHelperSourceIsCreated_ThenCanRegister() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        handlebars.registerHelpers(new HelperSource());
+        Template template = handlebars.compile("person");
+        Person person = getPerson("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("Baeldung - busy");
+    }
+
+    private Person getPerson(String name) {
+        Person person = new Person();
+        person.setName(name);
+        person.setBusy(true);
+        return person;
+    }
+}

libraries-2/src/test/java/com/baeldung/handlebars/HelperSource.java

@@ -0,0 +1,9 @@
+package com.baeldung.handlebars;
+
+public class HelperSource {
+
+    public String isBusy(Person context) {
+        String busyString = context.isBusy() ? "busy" : "available";
+        return context.getName() + " - " + busyString;
+    }
+}

libraries-2/src/test/java/com/baeldung/handlebars/Person.java

@@ -0,0 +1,58 @@
+package com.baeldung.handlebars;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Person {
+
+    private String name;
+    private boolean busy;
+    private Address address = new Address();
+    private List<Person> friends = new ArrayList<>();
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public boolean isBusy() {
+        return busy;
+    }
+
+    public void setBusy(boolean busy) {
+        this.busy = busy;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public List<Person> getFriends() {
+        return friends;
+    }
+
+    public void setFriends(List<Person> friends) {
+        this.friends = friends;
+    }
+
+    public static class Address {
+
+        private String street;
+
+        public String getStreet() {
+            return street;
+        }
+
+        public void setStreet(String street) {
+            this.street = street;
+        }
+    }
+
+}

libraries-2/src/test/java/com/baeldung/handlebars/ReusingTemplatesUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.handlebars;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.jknack.handlebars.Handlebars;
+import com.github.jknack.handlebars.Template;
+import com.github.jknack.handlebars.io.ClassPathTemplateLoader;
+import com.github.jknack.handlebars.io.TemplateLoader;
+import java.io.IOException;
+import org.junit.Test;
+
+/**
+ * Showcases reusing the existing templates.
+ *
+ * @author isaolmez
+ */
+public class ReusingTemplatesUnitTest {
+
+    private TemplateLoader templateLoader = new ClassPathTemplateLoader("/handlebars", ".html");
+
+    @Test
+    public void whenOtherTemplateIsReferenced_ThenCanReuse() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("page");
+        Person person = new Person();
+        person.setName("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("<h4>Hi Baeldung!</h4>\n<p>This is the page Baeldung</p>");
+    }
+
+    @Test
+    public void whenBlockIsDefined_ThenCanOverrideWithPartial() throws IOException {
+        Handlebars handlebars = new Handlebars(templateLoader);
+        Template template = handlebars.compile("simplemessage");
+        Person person = new Person();
+        person.setName("Baeldung");
+
+        String templateString = template.apply(person);
+
+        assertThat(templateString).isEqualTo("\n<html>\n"
+                                               + "<body>\n"
+                                               + "\n  This is the intro\n\n"
+                                               + "\n  Hi there!\n\n"
+                                               + "</body>\n"
+                                               + "</html>");
+    }
+}

libraries-2/src/test/java/com/baeldung/mapdb/CollectionsUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.mapdb;
+
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.mapdb.Serializer;
+
+import java.util.NavigableSet;
+
+import static junit.framework.Assert.assertEquals;
+
+public class CollectionsUnitTest {
+
+    @Test
+    public void givenSetCreatedInDB_whenMultipleElementsAdded_checkOnlyOneExists() {
+
+        DB db = DBMaker.memoryDB().make();
+
+        NavigableSet<String> set = db.
+          treeSet("mySet")
+          .serializer(Serializer.STRING)
+          .createOrOpen();
+
+        String myString = "Baeldung!";
+
+        set.add(myString);
+        set.add(myString);
+
+        assertEquals(1, set.size());
+
+        db.close();
+    }
+}

libraries-2/src/test/java/com/baeldung/mapdb/HTreeMapUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.mapdb;
+
+import org.jetbrains.annotations.NotNull;
+import org.junit.Test;
+import org.mapdb.*;
+
+import java.io.IOException;
+
+import static junit.framework.Assert.assertEquals;
+
+public class HTreeMapUnitTest {
+
+    @Test
+    public void givenValidDB_whenHTreeMapAddedToAndRetrieved_CheckedRetrievalCorrect() {
+
+        DB db = DBMaker.memoryDB().make();
+
+        HTreeMap<String, String> hTreeMap = db
+          .hashMap("myTreMap")
+          .keySerializer(Serializer.STRING)
+          .valueSerializer(Serializer.STRING)
+          .create();
+
+        hTreeMap.put("key1", "value1");
+        hTreeMap.put("key2", "value2");
+
+        assertEquals(2, hTreeMap.size());
+
+        //add another value with the same key
+
+        hTreeMap.put("key1", "value3");
+
+        assertEquals(2, hTreeMap.size());
+        assertEquals("value3", hTreeMap.get("key1"));
+
+    }
+
+}

libraries-2/src/test/java/com/baeldung/mapdb/HelloBaeldungUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.mapdb;
+
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.mapdb.HTreeMap;
+
+import java.util.concurrent.ConcurrentMap;
+
+import static junit.framework.Assert.assertEquals;
+
+public class HelloBaeldungUnitTest {
+
+    @Test
+    public void givenInMemoryDBInstantiateCorrectly_whenDataSavedAndRetrieved_checkRetrievalCorrect() {
+
+        DB db = DBMaker.memoryDB().make();
+
+        String welcomeMessageKey = "Welcome Message";
+        String welcomeMessageString = "Hello Baeldung!";
+
+        HTreeMap myMap = db.hashMap("myMap").createOrOpen();
+        myMap.put(welcomeMessageKey, welcomeMessageString);
+
+        String welcomeMessageFromDB = (String) myMap.get(welcomeMessageKey);
+
+        db.close();
+
+        assertEquals(welcomeMessageString, welcomeMessageFromDB);
+    }
+
+    @Test
+    public void givenInFileDBInstantiateCorrectly_whenDataSavedAndRetrieved_checkRetrievalCorrect() {
+
+        DB db = DBMaker.fileDB("file.db").make();
+
+        String welcomeMessageKey = "Welcome Message";
+        String welcomeMessageString = "Hello Baeldung!";
+
+        HTreeMap myMap = db.hashMap("myMap").createOrOpen();
+        myMap.put(welcomeMessageKey, welcomeMessageString);
+
+        String welcomeMessageFromDB = (String) myMap.get(welcomeMessageKey);
+
+        db.close();
+
+        assertEquals(welcomeMessageString, welcomeMessageFromDB);
+    }
+}

libraries-2/src/test/java/com/baeldung/mapdb/InMemoryModesUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.mapdb;
+
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.mapdb.HTreeMap;
+import org.mapdb.Serializer;
+
+import static junit.framework.Assert.assertEquals;
+
+public class InMemoryModesUnitTest {
+
+    @Test
+    public void givenDBCreatedOnHeap_whenUsed_checkUsageCorrect() {
+
+        DB heapDB = DBMaker.heapDB().make();
+
+        HTreeMap<Integer, String> map = heapDB
+          .hashMap("myMap")
+          .keySerializer(Serializer.INTEGER)
+          .valueSerializer(Serializer.STRING)
+          .createOrOpen();
+
+        map.put(1, "ONE");
+
+        assertEquals("ONE", map.get(1));
+
+    }
+
+    @Test
+    public void givenDBCreatedBaseOnByteArray_whenUsed_checkUsageCorrect() {
+
+        DB heapDB = DBMaker.memoryDB().make();
+
+        HTreeMap<Integer, String> map = heapDB
+          .hashMap("myMap")
+          .keySerializer(Serializer.INTEGER)
+          .valueSerializer(Serializer.STRING)
+          .createOrOpen();
+
+        map.put(1, "ONE");
+
+        assertEquals("ONE", map.get(1));
+    }
+
+    @Test
+    public void givenDBCreatedBaseOnDirectByteBuffer_whenUsed_checkUsageCorrect() {
+
+        DB heapDB = DBMaker.memoryDirectDB().make();
+
+        HTreeMap<Integer, String> map = heapDB
+          .hashMap("myMap")
+          .keySerializer(Serializer.INTEGER)
+          .valueSerializer(Serializer.STRING)
+          .createOrOpen();
+
+        map.put(1, "ONE");
+
+        assertEquals("ONE", map.get(1));
+    }
+
+}

libraries-2/src/test/java/com/baeldung/mapdb/SortedTableMapUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.mapdb;
+
+import org.junit.Test;
+import org.mapdb.Serializer;
+import org.mapdb.SortedTableMap;
+import org.mapdb.volume.MappedFileVol;
+import org.mapdb.volume.Volume;
+
+import static junit.framework.Assert.assertEquals;
+
+public class SortedTableMapUnitTest {
+
+    private static final String VOLUME_LOCATION = "sortedTableMapVol.db";
+
+    @Test
+    public void givenValidSortedTableMapSetup_whenQueried_checkValuesCorrect() {
+
+        //create memory mapped volume, readonly false
+        Volume vol = MappedFileVol.FACTORY.makeVolume(VOLUME_LOCATION, false);
+
+        //create sink to feed the map with data
+        SortedTableMap.Sink<Integer, String> sink =
+          SortedTableMap.create(
+            vol,
+            Serializer.INTEGER,
+            Serializer.STRING
+          ).createFromSink();
+
+        //add content
+        for(int i = 0; i < 100; i++){
+          sink.put(i, "Value " + Integer.toString(i));
+        }
+
+        sink.create();
+
+        //now open in read-only mode
+        Volume openVol = MappedFileVol.FACTORY.makeVolume(VOLUME_LOCATION, true);
+
+        SortedTableMap<Integer, String> sortedTableMap = SortedTableMap.open(
+          openVol,
+          Serializer.INTEGER,
+          Serializer.STRING
+        );
+
+        assertEquals(100, sortedTableMap.size());
+    }
+}

libraries-2/src/test/java/com/baeldung/mapdb/TransactionsUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.mapdb;
+
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.mapdb.Serializer;
+
+import java.util.NavigableSet;
+
+import static junit.framework.Assert.assertEquals;
+
+public class TransactionsUnitTest {
+
+    @Test
+    public void givenValidDBSetup_whenTransactionCommittedAndRolledBack_checkPreviousStateAchieved() {
+
+        DB db = DBMaker.memoryDB().transactionEnable().make();
+
+        NavigableSet<String> set = db
+          .treeSet("mySet")
+          .serializer(Serializer.STRING)
+          .createOrOpen();
+
+        set.add("One");
+        set.add("Two");
+
+        db.commit();
+
+        assertEquals(2, set.size());
+
+        set.add("Three");
+
+        assertEquals(3, set.size());
+
+        db.rollback();
+
+        assertEquals(2, set.size());
+
+        db.close();
+    }
+}

libraries-2/src/test/java/com/baeldung/matrices/MatrixMultiplicationBenchmarking.java

@@ -0,0 +1,9 @@
+package com.baeldung.matrices;
+
+public class MatrixMultiplicationBenchmarking {
+
+    public static void main(String[] args) throws Exception {
+        org.openjdk.jmh.Main.main(args);
+    }
+
+}

libraries-2/src/test/java/com/baeldung/matrices/apache/RealMatrixUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.matrices.apache;
+
+import org.apache.commons.math3.linear.Array2DRowRealMatrix;
+import org.apache.commons.math3.linear.RealMatrix;
+import org.junit.jupiter.api.Test;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class RealMatrixUnitTest {
+
+    @Test
+    @Benchmark
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        RealMatrix firstMatrix = new Array2DRowRealMatrix(
+          new double[][] {
+            new double[] {1d, 5d},
+            new double[] {2d, 3d},
+            new double[] {1d ,7d}
+          }
+        );
+
+        RealMatrix secondMatrix = new Array2DRowRealMatrix(
+          new double[][] {
+            new double[] {1d, 2d, 3d, 7d},
+            new double[] {5d, 2d, 8d, 1d}
+          }
+        );
+
+        RealMatrix expected = new Array2DRowRealMatrix(
+          new double[][] {
+            new double[] {26d, 12d, 43d, 12d},
+            new double[] {17d, 10d, 30d, 17d},
+            new double[] {36d, 16d, 59d, 14d}
+          }
+        );
+
+        RealMatrix actual = firstMatrix.multiply(secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+}

libraries-2/src/test/java/com/baeldung/matrices/colt/DoubleMatrix2DUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.matrices.colt;
+
+import cern.colt.matrix.DoubleFactory2D;
+import cern.colt.matrix.DoubleMatrix2D;
+import cern.colt.matrix.linalg.Algebra;
+import org.junit.jupiter.api.Test;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class DoubleMatrix2DUnitTest {
+
+    @Test
+    @Benchmark
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        DoubleFactory2D doubleFactory2D = DoubleFactory2D.dense;
+
+        DoubleMatrix2D firstMatrix = doubleFactory2D.make(
+          new double[][] {
+            new double[] {1d, 5d},
+            new double[] {2d, 3d},
+            new double[] {1d ,7d}
+          }
+        );
+
+        DoubleMatrix2D secondMatrix = doubleFactory2D.make(
+          new double[][] {
+            new double[] {1d, 2d, 3d, 7d},
+            new double[] {5d, 2d, 8d, 1d}
+          }
+        );
+
+        DoubleMatrix2D expected = doubleFactory2D.make(
+          new double[][] {
+            new double[] {26d, 12d, 43d, 12d},
+            new double[] {17d, 10d, 30d, 17d},
+            new double[] {36d, 16d, 59d, 14d}
+          }
+        );
+
+        Algebra algebra = new Algebra();
+        DoubleMatrix2D actual = algebra.mult(firstMatrix, secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+}

libraries-2/src/test/java/com/baeldung/matrices/ejml/SimpleMatrixUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.matrices.ejml;
+
+import org.ejml.simple.SimpleMatrix;
+import org.junit.jupiter.api.Test;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class SimpleMatrixUnitTest {
+
+    @Test
+    @Benchmark
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        SimpleMatrix firstMatrix = new SimpleMatrix(
+          new double[][] {
+            new double[] {1d, 5d},
+            new double[] {2d, 3d},
+            new double[] {1d ,7d}
+          }
+        );
+
+        SimpleMatrix secondMatrix = new SimpleMatrix(
+          new double[][] {
+            new double[] {1d, 2d, 3d, 7d},
+            new double[] {5d, 2d, 8d, 1d}
+          }
+        );
+
+        SimpleMatrix expected = new SimpleMatrix(
+          new double[][] {
+            new double[] {26d, 12d, 43d, 12d},
+            new double[] {17d, 10d, 30d, 17d},
+            new double[] {36d, 16d, 59d, 14d}
+          }
+        );
+
+        SimpleMatrix actual = firstMatrix.mult(secondMatrix);
+
+        assertThat(actual).matches(m -> m.isIdentical(expected, 0d));
+    }
+
+}

libraries-2/src/test/java/com/baeldung/matrices/homemade/HomemadeMatrixUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.matrices.homemade;
+
+import org.junit.jupiter.api.Test;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class HomemadeMatrixUnitTest {
+
+    @Test
+    @Benchmark
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        double[][] firstMatrix = {
+          new double[]{1d, 5d},
+          new double[]{2d, 3d},
+          new double[]{1d, 7d}
+        };
+
+        double[][] secondMatrix = {
+          new double[]{1d, 2d, 3d, 7d},
+          new double[]{5d, 2d, 8d, 1d}
+        };
+
+        double[][] expected = {
+          new double[]{26d, 12d, 43d, 12d},
+          new double[]{17d, 10d, 30d, 17d},
+          new double[]{36d, 16d, 59d, 14d}
+        };
+
+        double[][] actual = multiplyMatrices(firstMatrix, secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+    private double[][] multiplyMatrices(double[][] firstMatrix, double[][] secondMatrix) {
+        double[][] result = new double[firstMatrix.length][secondMatrix[0].length];
+
+        for (int row = 0; row < result.length; row++) {
+            for (int col = 0; col < result[row].length; col++) {
+                result[row][col] = multiplyMatricesCell(firstMatrix, secondMatrix, row, col);
+            }
+        }
+
+        return result;
+    }
+
+    private double multiplyMatricesCell(double[][] firstMatrix, double[][] secondMatrix, int row, int col) {
+        double cell = 0;
+        for (int i = 0; i < secondMatrix.length; i++) {
+            cell += firstMatrix[row][i] * secondMatrix[i][col];
+        }
+        return cell;
+    }
+}

libraries-2/src/test/java/com/baeldung/matrices/la4j/Basic2DMatrixUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.matrices.la4j;
+
+import org.junit.jupiter.api.Test;
+import org.la4j.Matrix;
+import org.la4j.matrix.dense.Basic2DMatrix;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class Basic2DMatrixUnitTest {
+
+    @Test
+    @Benchmark
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        Matrix firstMatrix = new Basic2DMatrix(
+          new double[][]{
+            new double[]{1d, 5d},
+            new double[]{2d, 3d},
+            new double[]{1d, 7d}
+          }
+        );
+
+        Matrix secondMatrix = new Basic2DMatrix(
+          new double[][]{
+            new double[]{1d, 2d, 3d, 7d},
+            new double[]{5d, 2d, 8d, 1d}
+          }
+        );
+
+        Matrix expected = new Basic2DMatrix(
+          new double[][]{
+            new double[]{26d, 12d, 43d, 12d},
+            new double[]{17d, 10d, 30d, 17d},
+            new double[]{36d, 16d, 59d, 14d}
+          }
+        );
+
+        Matrix actual = firstMatrix.multiply(secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+}

libraries-2/src/test/java/com/baeldung/matrices/nd4j/INDArrayUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.matrices.nd4j;
+
+import org.junit.jupiter.api.Test;
+import org.nd4j.linalg.api.ndarray.INDArray;
+import org.nd4j.linalg.factory.Nd4j;
+import org.openjdk.jmh.annotations.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(value = 2)
+@Warmup(iterations = 5)
+@Measurement(iterations = 10)
+public class INDArrayUnitTest {
+
+    @Test
+    public void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        INDArray firstMatrix = Nd4j.create(
+          new double[][]{
+            new double[]{1d, 5d},
+            new double[]{2d, 3d},
+            new double[]{1d, 7d}
+          }
+        );
+
+        INDArray secondMatrix = Nd4j.create(
+          new double[][] {
+            new double[] {1d, 2d, 3d, 7d},
+            new double[] {5d, 2d, 8d, 1d}
+          }
+        );
+
+        INDArray expected = Nd4j.create(
+          new double[][] {
+            new double[] {26d, 12d, 43d, 12d},
+            new double[] {17d, 10d, 30d, 17d},
+            new double[] {36d, 16d, 59d, 14d}
+          }
+        );
+
+        INDArray actual = firstMatrix.mmul(secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+}

libraries-2/src/test/java/com/baeldung/parallel_collectors/ParallelCollectorsUnitTest.java

@@ -0,0 +1,168 @@
+package com.baeldung.parallel_collectors;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.stream.Collectors;
+
+import static com.pivovarit.collectors.ParallelCollectors.parallel;
+import static com.pivovarit.collectors.ParallelCollectors.parallelOrdered;
+import static com.pivovarit.collectors.ParallelCollectors.parallelToCollection;
+import static com.pivovarit.collectors.ParallelCollectors.parallelToList;
+import static com.pivovarit.collectors.ParallelCollectors.parallelToMap;
+import static com.pivovarit.collectors.ParallelCollectors.parallelToStream;
+
+public class ParallelCollectorsUnitTest {
+
+    @Test
+    public void shouldProcessInParallelWithStreams() {
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        List<String> results = ids.parallelStream()
+          .map(i -> fetchById(i))
+          .collect(Collectors.toList());
+
+        System.out.println(results);
+    }
+
+    @Test
+    public void shouldProcessInParallelWithParallelCollectors() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        CompletableFuture<List<String>> results = ids.stream()
+          .collect(parallelToList(i -> fetchById(i), executor, 4));
+
+        System.out.println(results.join());
+    }
+
+    @Test
+    public void shouldCollectToList() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        List<String> results = ids.stream()
+          .collect(parallelToList(i -> fetchById(i), executor, 4))
+          .join();
+
+        System.out.println(results); // [user-1, user-2, user-3]
+    }
+
+    @Test
+    public void shouldCollectToCollection() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        List<String> results = ids.stream()
+          .collect(parallelToCollection(i -> fetchById(i), LinkedList::new, executor, 4))
+          .join();
+
+        System.out.println(results); // [user-1, user-2, user-3]
+    }
+
+    @Test
+    public void shouldCollectToStream() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        Map<Integer, List<String>> results = ids.stream()
+          .collect(parallelToStream(i -> fetchById(i), executor, 4))
+          .thenApply(stream -> stream.collect(Collectors.groupingBy(i -> i.length())))
+          .join();
+
+        System.out.println(results); // [user-1, user-2, user-3]
+    }
+
+    @Test
+    public void shouldStreamInCompletionOrder() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        ids.stream()
+          .collect(parallel(i -> fetchByIdWithRandomDelay(i), executor, 4))
+          .forEach(System.out::println);
+    }
+
+    @Test
+    public void shouldStreamInOriginalOrder() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        ids.stream()
+          .collect(parallelOrdered(i -> fetchByIdWithRandomDelay(i), executor, 4))
+          .forEach(System.out::println);
+    }
+
+    @Test
+    public void shouldCollectToMap() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        Map<Integer, String> results = ids.stream()
+          .collect(parallelToMap(i -> i, i -> fetchById(i), executor, 4))
+          .join();
+
+        System.out.println(results); // {1=user-1, 2=user-2, 3=user-3}
+    }
+
+    @Test
+    public void shouldCollectToTreeMap() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        Map<Integer, String> results = ids.stream()
+          .collect(parallelToMap(i -> i, i -> fetchById(i), TreeMap::new,  executor, 4))
+          .join();
+
+        System.out.println(results); // {1=user-1, 2=user-2, 3=user-3}
+    }
+
+    @Test
+    public void shouldCollectToTreeMapAndResolveClashes() {
+        ExecutorService executor = Executors.newFixedThreadPool(10);
+
+        List<Integer> ids = Arrays.asList(1, 2, 3);
+
+        Map<Integer, String> results = ids.stream()
+          .collect(parallelToMap(i -> i, i -> fetchById(i), TreeMap::new, (s1, s2) -> s1,   executor, 4))
+          .join();
+
+        System.out.println(results); // {1=user-1, 2=user-2, 3=user-3}
+    }
+
+    private static String fetchById(int id) {
+        try {
+            Thread.sleep(100);
+        } catch (InterruptedException e) {
+            // ignore shamelessly
+        }
+
+        return "user-" + id;
+    }
+
+    private static String fetchByIdWithRandomDelay(int id) {
+        try {
+            Thread.sleep(ThreadLocalRandom.current().nextInt(1000));
+        } catch (InterruptedException e) {
+            // ignore shamelessly
+        }
+
+        return "user-" + id;
+    }
+}

libraries-2/src/test/resources/greeting.hbs

@@ -0,0 +1 @@
+Hi {{name}}!

libraries-2/src/test/resources/handlebars/each.html

@@ -0,0 +1,3 @@
+{{#each friends}}
+<span>{{name}} is my friend.</span>
+{{/each}}

libraries-2/src/test/resources/handlebars/each_mustache.html

@@ -0,0 +1,3 @@
+{{#each friends}}
+<span>{{name}} is my friend.</span>
+{{/each}}

libraries-2/src/test/resources/handlebars/greeting.html

@@ -0,0 +1 @@
+Hi {{name}}!

libraries-2/src/test/resources/handlebars/header.html

@@ -0,0 +1 @@
+<h4>Hi {{name}}!</h4>

libraries-2/src/test/resources/handlebars/if.html

@@ -0,0 +1,5 @@
+{{#if busy}}
+<h4>{{name}} is busy.</h4>
+{{else}}
+<h4>{{name}} is not busy.</h4>
+{{/if}}

libraries-2/src/test/resources/handlebars/if_mustache.html

@@ -0,0 +1,5 @@
+{{#if busy}}
+<h4>{{name}} is busy.</h4>
+{{^}}
+<h4>{{name}} is not busy.</h4>
+{{/if}}

libraries-2/src/test/resources/handlebars/messagebase.html

@@ -0,0 +1,9 @@
+<html>
+<body>
+{{#block "intro"}}
+  This is the intro
+{{/block}}
+{{#block "message"}}
+{{/block}}
+</body>
+</html>

libraries-2/src/test/resources/handlebars/page.html

@@ -0,0 +1,2 @@
+{{>header}}
+<p>This is the page {{name}}</p>

libraries-2/src/test/resources/handlebars/person.html

@@ -0,0 +1 @@
+{{#isBusy this}}{{/isBusy}}

libraries-2/src/test/resources/handlebars/simplemessage.html

@@ -0,0 +1,4 @@
+{{#partial "message" }}
+  Hi there!
+{{/partial}}
+{{> messagebase}}

libraries-2/src/test/resources/handlebars/with.html

@@ -0,0 +1,3 @@
+{{#with address}}
+<h4>I live in {{street}}</h4>
+{{/with}}

libraries-2/src/test/resources/handlebars/with_mustache.html

@@ -0,0 +1,3 @@
+{{#address}}
+<h4>I live in {{street}}</h4>
+{{/address}}

libraries-server/pom.xml

@@ -65,7 +65,7 @@
             <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
-		
+
         <!-- tomcat -->
         <dependency>
             <groupId>org.apache.tomcat</groupId>
@@ -96,6 +96,19 @@
              <artifactId>smack-java7</artifactId>
              <version>${smack.version}</version>
          </dependency>
+
+        <!-- NanoHTTPD -->
+        <dependency>
+            <groupId>org.nanohttpd</groupId>
+            <artifactId>nanohttpd</artifactId>
+            <version>${nanohttpd.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.nanohttpd</groupId>
+            <artifactId>nanohttpd-nanolets</artifactId>
+            <version>${nanohttpd.version}</version>
+        </dependency>
+
     </dependencies>
 
     <properties>
@@ -107,7 +120,8 @@
         <commons.collections.version>4.1</commons.collections.version>
         <tomcat.version>8.5.24</tomcat.version>
         <smack.version>4.3.1</smack.version>
-		<eclipse.paho.client.mqttv3.version>1.2.0</eclipse.paho.client.mqttv3.version>
+        <eclipse.paho.client.mqttv3.version>1.2.0</eclipse.paho.client.mqttv3.version>
+        <nanohttpd.version>2.3.1</nanohttpd.version>
     </properties>
 
 </project>

libraries-server/src/main/java/com/baeldung/nanohttpd/ApplicationController.java

@@ -0,0 +1,38 @@
+package com.baeldung.nanohttpd;
+
+import fi.iki.elonen.NanoHTTPD;
+import fi.iki.elonen.router.RouterNanoHTTPD;
+
+import java.io.IOException;
+
+public class ApplicationController extends RouterNanoHTTPD {
+
+    ApplicationController() throws IOException {
+        super(8072);
+        addMappings();
+        start(NanoHTTPD.SOCKET_READ_TIMEOUT, false);
+    }
+
+    @Override
+    public void addMappings() {
+        addRoute("/", IndexHandler.class);
+        addRoute("/users", UserHandler.class);
+    }
+
+    public static class UserHandler extends DefaultHandler {
+        @Override
+        public String getText() {
+            return "UserA, UserB, UserC";
+        }
+
+        @Override
+        public String getMimeType() {
+            return MIME_PLAINTEXT;
+        }
+
+        @Override
+        public Response.IStatus getStatus() {
+            return Response.Status.OK;
+        }
+    }
+}

libraries-server/src/main/java/com/baeldung/nanohttpd/ItemGetController.java

@@ -0,0 +1,22 @@
+package com.baeldung.nanohttpd;
+
+import fi.iki.elonen.NanoHTTPD;
+
+import java.io.IOException;
+
+public class ItemGetController extends NanoHTTPD {
+
+    ItemGetController() throws IOException {
+        super(8071);
+        start(NanoHTTPD.SOCKET_READ_TIMEOUT, false);
+    }
+
+    @Override
+    public Response serve(IHTTPSession session) {
+        if (session.getMethod() == Method.GET) {
+            String itemIdRequestParam = session.getParameters().get("itemId").get(0);
+            return newFixedLengthResponse("Requested itemId = " + itemIdRequestParam);
+        }
+        return newFixedLengthResponse(Response.Status.NOT_FOUND, MIME_PLAINTEXT, "The requested resource does not exist");
+    }
+}

libraries-server/src/test/java/com/baeldung/nanohttpd/ApplicationControllerUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.nanohttpd;
+
+import org.apache.commons.io.IOUtils;
+import org.apache.http.HttpResponse;
+import org.apache.http.client.HttpClient;
+import org.apache.http.client.methods.HttpGet;
+import org.apache.http.impl.client.HttpClientBuilder;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.*;
+
+public class ApplicationControllerUnitTest {
+
+    private static final String BASE_URL = "http://localhost:8072/";
+    private static final HttpClient CLIENT = HttpClientBuilder.create().build();
+
+    @BeforeClass
+    public static void setUp() throws IOException {
+        new ApplicationController();
+    }
+
+    @Test
+    public void givenServer_whenRootRouteRequested_thenHelloWorldReturned() throws IOException {
+        HttpResponse response = CLIENT.execute(new HttpGet(BASE_URL));
+        assertTrue(IOUtils.toString(response.getEntity().getContent()).contains("Hello world!"));
+        assertEquals(200, response.getStatusLine().getStatusCode());
+    }
+
+    @Test
+    public void givenServer_whenUsersRequested_thenThenAllUsersReturned() throws IOException {
+        HttpResponse response = CLIENT.execute(new HttpGet(BASE_URL + "users"));
+        assertEquals("UserA, UserB, UserC", IOUtils.toString(response.getEntity().getContent()));
+    }
+}