Merge pull request #4 from eugenp/master

updated master

.gitignore

@@ -48,3 +48,12 @@ dependency-reduced-pom.xml
 *.so
 *.dylib
 *.dll
+
+xml/src/test/resources/example_dom4j_new.xml
+xml/src/test/resources/example_dom4j_updated.xml
+xml/src/test/resources/example_jaxb_new.xml
+core-java-io/hard_link.txt
+core-java-io/target_link.txt
+core-java/src/main/java/com/baeldung/manifest/MANIFEST.MF
+ethereum/logs/
+jmeter/src/main/resources/*-JMeter.csv

README.md

@@ -19,7 +19,7 @@ In additional to Spring, the following technologies are in focus: `core Java`, `
 
 Building the project
 ====================
-To do the full build, do: `mvn install -Dgib.enabled=false`
+To do the full build, do: `mvn install -Pdefault -Dgib.enabled=false`
 
 
 Working with the code in Eclipse

apache-meecrowave/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles: 
+================================
+- [Building a Microservice with Apache Meecrowave](http://www.baeldung.com/apache-meecrowave)

core-java-8/README.md

@@ -46,7 +46,6 @@
 - [Overview of Java Built-in Annotations](http://www.baeldung.com/java-default-annotations)
 - [Finding Min/Max in an Array with Java](http://www.baeldung.com/java-array-min-max)
 - [Internationalization and Localization in Java 8](http://www.baeldung.com/java-8-localization)
-- [Filtering Kotlin Collections](http://www.baeldung.com/kotlin-filter-collection)
 - [How to Find an Element in a List with Java](http://www.baeldung.com/find-list-element-java)
 - [Measure Elapsed Time in Java](http://www.baeldung.com/java-measure-elapsed-time)
 - [Java Optional – orElse() vs orElseGet()](http://www.baeldung.com/java-optional-or-else-vs-or-else-get)
@@ -55,3 +54,5 @@
 - [Java 8 Unsigned Arithmetic Support](http://www.baeldung.com/java-unsigned-arithmetic)
 - [How to Get the Start and the End of a Day using Java](http://www.baeldung.com/java-day-start-end)
 - [Generalized Target-Type Inference in Java](http://www.baeldung.com/java-generalized-target-type-inference)
+- [Image to Base64 String Conversion](http://www.baeldung.com/java-base64-image-string)
+- [Calculate Age in Java](http://www.baeldung.com/java-get-age)

core-java-8/pom.xml

@@ -99,6 +99,16 @@
             <artifactId>joda-time</artifactId>
             <version>${joda.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.aspectj</groupId>
+            <artifactId>aspectjrt</artifactId>
+            <version>${asspectj.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.aspectj</groupId>
+            <artifactId>aspectjweaver</artifactId>
+            <version>${asspectj.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -170,6 +180,7 @@
         <joda.version>2.10</joda.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
+        <asspectj.version>1.8.9</asspectj.version>
         <avaitility.version>1.7.0</avaitility.version>
         <jmh-core.version>1.19</jmh-core.version>
         <jmh-generator.version>1.19</jmh-generator.version>

core-java-8/src/main/java/com/baeldung/aspect/ChangeCallsToCurrentTimeInMillisMethod.aj

@@ -0,0 +1,9 @@
+package com.baeldung.aspect;
+
+public aspect ChangeCallsToCurrentTimeInMillisMethod {
+    long around():
+            call(public static native long java.lang.System.currentTimeMillis())
+                    && within(user.code.base.pckg.*) {
+        return 0;
+    }
+}

core-java-8/src/test/java/com/baeldung/list/AddElementsUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.list;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.*;
+
+import static org.junit.Assert.*;
+
+public class AddElementsUnitTest {
+
+    List<Flower> flowers;
+
+    @Before
+    public void init() {
+        this.flowers = new ArrayList<>(Arrays.asList(
+                new Flower("Poppy", 12),
+                new Flower("Anemone", 8),
+                new Flower("Catmint", 12)));
+    }
+
+    @Test
+    public void givenAList_whenTargetListIsEmpty_thenReturnTargetListWithNewItems() {
+        List<Flower> anotherList = new ArrayList<>();
+        anotherList.addAll(flowers);
+
+        assertEquals(anotherList.size(), flowers.size());
+        Assert.assertTrue(anotherList.containsAll(flowers));
+    }
+
+    @Test
+    public void givenAList_whenTargetListIsEmpty_thenReturnTargetListWithOneModifiedElementByConstructor() {
+        List<Flower> anotherList = new ArrayList<>();
+        anotherList.addAll(flowers);
+
+        Flower flower = anotherList.get(0);
+        flower.setPetals(flowers.get(0).getPetals() * 3);
+
+        assertEquals(anotherList.size(), flowers.size());
+        Assert.assertTrue(anotherList.containsAll(flowers));
+    }
+
+    @Test
+    public void givenAListAndElements_whenUseCollectionsAddAll_thenAddElementsToTargetList() {
+        List<Flower> target = new ArrayList<>();
+
+        Collections.addAll(target, flowers.get(0), flowers.get(1), flowers.get(2), flowers.get(0));
+
+        assertEquals(target.size(), 4);
+    }
+
+    @Test
+    public void givenTwoList_whenSourceListDoesNotHaveNullElements_thenAddElementsToTargetListSkipFirstElementByStreamProcess() {
+        List<Flower> flowerVase = new ArrayList<>();
+
+        flowers.stream()
+                .skip(1)
+                .forEachOrdered(flowerVase::add);
+
+        assertEquals(flowerVase.size() + 1, flowers.size());
+        assertFalse(flowerVase.containsAll(flowers));
+    }
+
+    @Test
+    public void givenTwoList_whenSourceListDoesNotHaveNullElements_thenAddElementsToTargetListFilteringElementsByStreamProcess() {
+        List<Flower> flowerVase = new ArrayList<>();
+
+        flowers.stream()
+                .filter(f -> f.getPetals() > 10)
+                .forEachOrdered(flowerVase::add);
+
+        assertEquals(flowerVase.size() + 1, flowers.size());
+        assertFalse(flowerVase.containsAll(flowers));
+    }
+
+    @Test
+    public void givenAList_whenListIsNotNull_thenAddElementsToListByStreamProcessWihtOptional() {
+        List<Flower> target = new ArrayList<>();
+
+        Optional.ofNullable(flowers)
+                .ifPresent(target::addAll);
+
+        assertNotNull(target);
+        assertEquals(target.size(), 3);
+    }
+}

core-java-8/src/test/java/com/baeldung/util/CurrentDateTimeUnitTest.java

@@ -1,6 +1,7 @@
 package com.baeldung.util;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import java.time.Clock;
 import java.time.Instant;
@@ -9,6 +10,8 @@ import java.time.LocalTime;
 import java.time.ZoneId;
 import java.time.temporal.ChronoField;
 
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeUtils;
 import org.junit.Test;
 
 public class CurrentDateTimeUnitTest {
@@ -39,5 +42,4 @@ public class CurrentDateTimeUnitTest {
 
         assertEquals(clock.instant().getEpochSecond(), now.getEpochSecond());
     }
-
 }

core-java-9/pom.xml

@@ -19,11 +19,23 @@
             <version>${awaitility.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
             <version>${guava.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -50,6 +62,8 @@
 
     <properties>
         <!-- testing -->
+        <assertj.version>3.10.0</assertj.version>
+        <junit.platform.version>1.2.0</junit.platform.version>
         <awaitility.version>1.7.0</awaitility.version>
         <maven.compiler.source>1.9</maven.compiler.source>
         <maven.compiler.target>1.9</maven.compiler.target>

core-java-9/src/main/java/com/baeldung/java9/language/stream/StreamsGroupingCollectionFilter.java

@@ -0,0 +1,27 @@
+package com.baeldung.java9.language.stream;
+
+import static java.util.stream.Collectors.filtering;
+import static java.util.stream.Collectors.groupingBy;
+import static java.util.stream.Collectors.toList;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+
+public class StreamsGroupingCollectionFilter {
+
+    static public Map<Integer, List<Integer>> findEvenNumbersAfterGroupingByQuantityOfDigits(Collection<Integer> baseCollection) {
+        Function<Integer, Integer> getQuantityOfDigits = item -> (int) Math.log10(item) + 1;
+
+        return baseCollection.stream()
+            .collect(groupingBy(getQuantityOfDigits, filtering(item -> item % 2 == 0, toList())));
+    }
+
+    static public Map<Integer, List<Integer>> findEvenNumbersBeforeGroupingByQuantityOfDigits(Collection<Integer> baseCollection) {
+
+        return baseCollection.stream()
+            .filter(item -> item % 2 == 0)
+            .collect(groupingBy(item -> (int) Math.log10(item) + 1, toList()));
+    }
+}

core-java-9/src/main/java/com/baeldung/java9/maps/initialize/MapsInitializer.java

@@ -0,0 +1,33 @@
+package com.baeldung.java9.maps.initialize;
+
+import java.util.AbstractMap;
+import java.util.HashMap;
+import java.util.Map;
+
+public class MapsInitializer {
+
+    @SuppressWarnings("unused")
+    public void createMapWithMapOf() {
+        Map<String, String> emptyMap = Map.of();
+        Map<String, String> singletonMap = Map.of("key1", "value");
+        Map<String, String> map = Map.of("key1","value1", "key2", "value2");
+    }
+    
+    public void createMapWithMapEntries() {
+        Map<String, String> map = Map.ofEntries(
+            new AbstractMap.SimpleEntry<String, String>("name", "John"),
+            new AbstractMap.SimpleEntry<String, String>("city", "budapest"),
+            new AbstractMap.SimpleEntry<String, String>("zip", "000000"),
+            new AbstractMap.SimpleEntry<String, String>("home", "1231231231")
+            );
+    }
+    
+    @SuppressWarnings("unused")
+    public void createMutableMaps() {
+        Map<String, String> map = new HashMap<String, String> (Map.of("key1","value1", "key2", "value2"));
+        Map<String, String> map2 = new HashMap<String, String> ( Map.ofEntries(
+            new AbstractMap.SimpleEntry<String, String>("name", "John"),
+            new AbstractMap.SimpleEntry<String, String>("city", "budapest")));
+        
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/language/stream/CollectionFilterUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.java9.language.stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.junit.platform.runner.JUnitPlatform;
+import org.junit.runner.RunWith;
+
+@RunWith(JUnitPlatform.class)
+public class CollectionFilterUnitTest {
+
+    private static final Collection<Integer> BASE_INTEGER_COLLECTION = Arrays.asList(9, 12, 55, 56, 101, 115, 8002, 223, 2668, 19, 8);
+    private static final Map<Integer, List<Integer>> EXPECTED_EVEN_FILTERED_AFTER_GROUPING_MAP = createExpectedFilterAfterGroupingMap();
+    private static Map<Integer, List<Integer>> createExpectedFilterAfterGroupingMap() {
+        Map<Integer, List<Integer>> map = new HashMap<>();
+        map.put(1, Arrays.asList(8));
+        map.put(2, Arrays.asList(12, 56));
+        map.put(3, Collections.emptyList());
+        map.put(4, Arrays.asList(8002, 2668));
+        return map;
+
+    }
+
+    private static final Map<Integer, List<Integer>> EXPECTED_EVEN_FILTERED_BEFORE_GROUPING_MAP = createExpectedFilterBeforeGroupingMap();
+    private static Map<Integer, List<Integer>> createExpectedFilterBeforeGroupingMap() {
+        Map<Integer, List<Integer>> map = new HashMap<>();
+        map.put(1, Arrays.asList(8));
+        map.put(2, Arrays.asList(12, 56));
+        map.put(4, Arrays.asList(8002, 2668));
+        return map;
+
+    }
+
+    @Test
+    public void givenAStringCollection_whenFilteringFourLetterWords_thenObtainTheFilteredCollection() {
+        Map<Integer, List<Integer>> filteredAfterGroupingMap = StreamsGroupingCollectionFilter.findEvenNumbersAfterGroupingByQuantityOfDigits(BASE_INTEGER_COLLECTION);
+        Map<Integer, List<Integer>> filteredBeforeGroupingMap = StreamsGroupingCollectionFilter.findEvenNumbersBeforeGroupingByQuantityOfDigits(BASE_INTEGER_COLLECTION);
+
+        assertThat(filteredAfterGroupingMap).containsAllEntriesOf(EXPECTED_EVEN_FILTERED_AFTER_GROUPING_MAP);
+        assertThat(filteredBeforeGroupingMap).doesNotContainKey(3)
+            .containsAllEntriesOf(EXPECTED_EVEN_FILTERED_BEFORE_GROUPING_MAP);
+    }
+
+}

core-java-collections/README.md

@@ -30,3 +30,4 @@
 - [How to TDD a List Implementation in Java](http://www.baeldung.com/java-test-driven-list)
 - [How to Store Duplicate Keys in a Map in Java?](http://www.baeldung.com/java-map-duplicate-keys)
 - [Getting the Size of an Iterable in Java](http://www.baeldung.com/java-iterable-size)
+- [Iterating Backward Through a List](http://www.baeldung.com/java-list-iterate-backwards)

core-java-collections/pom.xml

@@ -36,19 +36,37 @@
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections-api</artifactId>
+            <version>${eclipse.collections.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections</artifactId>
+            <version>${eclipse.collections.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <properties>
+        <junit.platform.version>1.2.0</junit.platform.version>
         <commons-lang3.version>3.5</commons-lang3.version>
         <commons-collections4.version>4.1</commons-collections4.version>
         <collections-generic.version>4.01</collections-generic.version>
         <avaitility.version>1.7.0</avaitility.version>
         <assertj.version>3.6.1</assertj.version>
+        <eclipse.collections.version>9.2.0</eclipse.collections.version>
     </properties>
 </project>

core-java-collections/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java

@@ -1,18 +1,19 @@
 package com.baeldung.convertlisttomap;
 
+import com.google.common.collect.Maps;
+import org.apache.commons.collections4.MapUtils;
+
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
 
-import org.apache.commons.collections4.IterableUtils;
-import org.apache.commons.collections4.MapUtils;
-import com.google.common.collect.Maps;
-
 public class ConvertListToMapService {
 
     public Map<Integer, Animal> convertListBeforeJava8(List<Animal> list) {
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+
+        Map<Integer, Animal> map = new HashMap<>();
+
         for (Animal animal : list) {
             map.put(animal.getId(), animal);
         }
@@ -30,20 +31,9 @@ public class ConvertListToMapService {
         return map;
     }
 
-    public Map<Integer, Animal> convertListWithApacheCommons1(List<Animal> list) {
+    public Map<Integer, Animal> convertListWithApacheCommons(List<Animal> list) {
 
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
-
-        IterableUtils.forEach(list, animal -> {
-            map.put(animal.getId(), animal);
-        });
-
-        return map;
-    }
-
-    public Map<Integer, Animal> convertListWithApacheCommons2(List<Animal> list) {
-
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+        Map<Integer, Animal> map = new HashMap<>();
 
         MapUtils.populateMap(map, list, Animal::getId);
 

core-java-collections/src/main/java/com/baeldung/java/filtering/CollectionUtilsCollectionFilter.java

@@ -0,0 +1,16 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.collections4.Predicate;
+
+public class CollectionUtilsCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> apacheEventNumberPredicate = item -> item % 2 == 0;
+
+        CollectionUtils.filter(baseCollection, apacheEventNumberPredicate);
+        return baseCollection;
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/EclipseCollectionsCollectionFilter.java

@@ -0,0 +1,32 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import org.eclipse.collections.api.block.predicate.Predicate;
+import org.eclipse.collections.impl.factory.Lists;
+import org.eclipse.collections.impl.utility.Iterate;
+
+public class EclipseCollectionsCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> eclipsePredicate = item -> item % 2 == 0;
+        Collection<Integer> filteredList = Lists.mutable.ofAll(baseCollection)
+            .select(eclipsePredicate);
+
+        return filteredList;
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingIterate(Collection<Integer> baseCollection) {
+        Predicate<Integer> eclipsePredicate = new Predicate<Integer>() {
+            private static final long serialVersionUID = 1L;
+
+            @Override
+            public boolean accept(Integer arg0) {
+                return arg0 % 2 == 0;
+            }
+        };
+        Collection<Integer> filteredList = Iterate.select(baseCollection, eclipsePredicate);
+
+        return filteredList;
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/GuavaCollectionFilter.java

@@ -0,0 +1,17 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+
+import com.google.common.base.Predicate;
+import com.google.common.collect.Collections2;
+
+public class GuavaCollectionFilter {
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> guavaPredicate = item -> item % 2 == 0;
+
+        Collection<Integer> filteredCollection = Collections2.filter(baseCollection, guavaPredicate);
+        return filteredCollection;
+    }
+
+}

core-java-collections/src/main/java/com/baeldung/java/filtering/StreamsCollectionFilter.java

@@ -0,0 +1,26 @@
+package com.baeldung.java.filtering;
+
+import java.util.Collection;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class StreamsCollectionFilter {
+
+    public static <T> Collection<T> filterCollectionHelperMethod(Collection<T> baseCollection, Predicate<T> predicate) {
+        return baseCollection.stream()
+            .filter(predicate)
+            .collect(Collectors.toList());
+    }
+
+    static public Collection<Integer> findEvenNumbersUsingHelperMethod(Collection<Integer> baseCollection) {
+        return filterCollectionHelperMethod(baseCollection, item -> item % 2 == 0);
+    }
+
+    static public Collection<Integer> findEvenNumbers(Collection<Integer> baseCollection) {
+        Predicate<Integer> streamsPredicate = item -> item % 2 == 0;
+
+        return baseCollection.stream()
+            .filter(streamsPredicate)
+            .collect(Collectors.toList());
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/list/Flower.java

@@ -0,0 +1,28 @@
+package com.baeldung.java.list;
+
+public class Flower {
+
+    private String name;
+    private int petals;
+
+    public Flower(String name, int petals) {
+        this.name = name;
+        this.petals = petals;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getPetals() {
+        return petals;
+    }
+
+    public void setPetals(int petals) {
+        this.petals = petals;
+    }
+}

core-java-collections/src/main/java/com/baeldung/java/map/initialize/MapInitializer.java

@@ -0,0 +1,80 @@
+package com.baeldung.java.map.initialize;
+
+import java.util.AbstractMap;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class MapInitializer {
+
+    public static Map<String, String> articleMapOne;
+    static {
+        articleMapOne = new HashMap<>();
+        articleMapOne.put("ar01", "Intro to Map");
+        articleMapOne.put("ar02", "Some article");
+    }
+
+    public static Map<String, String> createSingletonMap() {
+        Map<String, String> passwordMap = Collections.singletonMap("username1", "password1");
+        return passwordMap;
+
+    }
+
+    public Map<String, String> createEmptyMap() {
+        Map<String, String> emptyMap = Collections.emptyMap();
+        return emptyMap;
+    }
+
+    public Map<String, String> createUsingDoubleBrace() {
+        Map<String, String> doubleBraceMap = new HashMap<String, String>() {
+
+            /**
+             * 
+             */
+            private static final long serialVersionUID = 1L;
+
+            {
+                put("key1", "value1");
+                put("key2", "value2");
+            }
+        };
+        return doubleBraceMap;
+    }
+
+    public Map<String, String> createMapUsingStreamStringArray() {
+        Map<String, String> map = Stream.of(new String[][] { { "Hello", "World" }, { "John", "Doe" }, })
+            .collect(Collectors.toMap(data -> data[0], data -> data[1]));
+
+        return map;
+    }
+
+    public Map<String, Integer> createMapUsingStreamObjectArray() {
+        Map<String, Integer> map = Stream.of(new Object[][] { { "data1", 1 }, { "data2", 2 }, })
+            .collect(Collectors.toMap(data -> (String) data[0], data -> (Integer) data[1]));
+
+        return map;
+    }
+
+    public Map<String, Integer> createMapUsingStreamSimpleEntry() {
+        Map<String, Integer> map = Stream.of(new AbstractMap.SimpleEntry<>("idea", 1), new AbstractMap.SimpleEntry<>("mobile", 2))
+            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+
+        return map;
+    }
+
+    public Map<String, Integer> createMapUsingStreamSimpleImmutableEntry() {
+        Map<String, Integer> map = Stream.of(new AbstractMap.SimpleImmutableEntry<>("idea", 1), new AbstractMap.SimpleImmutableEntry<>("mobile", 2))
+            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+
+        return map;
+    }
+
+    public Map<String, String> createImmutableMapWithStreams() {
+        Map<String, String> map = Stream.of(new String[][] { { "Hello", "World" }, { "John", "Doe" }, })
+            .collect(Collectors.collectingAndThen(Collectors.toMap(data -> data[0], data -> data[1]), Collections::<String, String> unmodifiableMap));
+        return map;
+
+    }
+}

core-java-collections/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java

@@ -1,13 +1,14 @@
 package com.baeldung.convertlisttomap;
 
-import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.*;
+import org.junit.Before;
+import org.junit.Test;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
-import org.junit.Before;
-import org.junit.Test;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsInAnyOrder;
 
 public class ConvertListToMapServiceUnitTest {
     List<Animal> list;
@@ -29,6 +30,7 @@ public class ConvertListToMapServiceUnitTest {
         list.add(cow);
         Animal goat = new Animal(5, "Goat");
         list.add(goat);
+
     }
 
     @Test
@@ -56,18 +58,11 @@ public class ConvertListToMapServiceUnitTest {
     }
 
     @Test
-    public void givenAList_whenConvertWithApacheCommons1_thenReturnMapWithTheSameElements() {
+    public void givenAList_whenConvertWithApacheCommons_thenReturnMapWithTheSameElements() {
 
-        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons1(list);
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(list);
 
         assertThat(map.values(), containsInAnyOrder(list.toArray()));
     }
 
-    @Test
-    public void givenAList_whenConvertWithApacheCommons2_thenReturnMapWithTheSameElements() {
-
-        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons2(list);
-
-        assertThat(map.values(), containsInAnyOrder(list.toArray()));
-    }
 }

core-java-collections/src/test/java/com/baeldung/convertlisttomap/ConvertListWithDiplicatedIdToMapServiceUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.convertlisttomap;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.hasSize;
+
+public class ConvertListWithDiplicatedIdToMapServiceUnitTest {
+    List<Animal> duplicatedIdList;
+
+    private ConvertListToMapService convertListService = new ConvertListToMapService();
+
+    @Before
+    public void init() {
+
+        this.duplicatedIdList = new ArrayList<>();
+
+        Animal cat = new Animal(1, "Cat");
+        duplicatedIdList.add(cat);
+        Animal dog = new Animal(2, "Dog");
+        duplicatedIdList.add(dog);
+        Animal pig = new Animal(3, "Pig");
+        duplicatedIdList.add(pig);
+        Animal cow = new Animal(4, "Cow");
+        duplicatedIdList.add(cow);
+        Animal goat = new Animal(4, "Goat");
+        duplicatedIdList.add(goat);
+
+    }
+
+    @Test
+    public void givenADupIdList_whenConvertBeforeJava8_thenReturnMapWithRewrittenElement() {
+
+        Map<Integer, Animal> map = convertListService.convertListBeforeJava8(duplicatedIdList);
+
+        assertThat(map.values(), hasSize(4));
+        assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
+    }
+
+    @Test
+    public void givenADupIdList_whenConvertWithApacheCommons_thenReturnMapWithRewrittenElement() {
+
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(duplicatedIdList);
+
+        assertThat(map.values(), hasSize(4));
+        assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void givenADupIdList_whenConvertAfterJava8_thenException() {
+
+        convertListService.convertListAfterJava8(duplicatedIdList);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void givenADupIdList_whenConvertWithGuava_thenException() {
+
+        convertListService.convertListWithGuava(duplicatedIdList);
+
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/java/filtering/CollectionFiltersUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.java.filtering;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+
+import org.junit.jupiter.api.Test;
+import org.junit.platform.runner.JUnitPlatform;
+import org.junit.runner.RunWith;
+
+@RunWith(JUnitPlatform.class)
+public class CollectionFiltersUnitTest {
+
+    private static final Collection<Integer> BASE_INTEGER_COLLECTION = Arrays.asList(9, 14, 2, 7, 1, 5, 8);
+    private static final Collection<Integer> EXPECTED_EVEN_FILTERED_COLLECTION = Arrays.asList(14, 2, 8);
+
+    @Test
+    public void givenAStringCollection_whenFilteringFourLetterWords_thenObtainTheFilteredCollection() {
+        final Collection<String> baseStrings = Arrays.asList("java", "baeldung", "type", "example", "other");
+
+        Collection<String> filtered = StreamsCollectionFilter.filterCollectionHelperMethod(baseStrings, item -> item.length() == 4);
+
+        assertThat(filtered).containsExactlyInAnyOrder("java", "type");
+    }
+
+    @Test
+    public void givenAnIntegerCollection_whenFilteringEvenValues_thenObtainTheFilteredCollectionForAllCases() {
+        Collection<Integer> filteredWithStreams1 = StreamsCollectionFilter.findEvenNumbers(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithCollectionUtils = CollectionUtilsCollectionFilter.findEvenNumbers(new ArrayList<>(BASE_INTEGER_COLLECTION));
+        Collection<Integer> filteredWithEclipseCollections = EclipseCollectionsCollectionFilter.findEvenNumbers(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithEclipseCollectionsUsingIterate = EclipseCollectionsCollectionFilter.findEvenNumbersUsingIterate(BASE_INTEGER_COLLECTION);
+        Collection<Integer> filteredWithGuava = GuavaCollectionFilter.findEvenNumbers(BASE_INTEGER_COLLECTION);
+
+        assertThat(filteredWithStreams1).hasSameElementsAs(filteredWithCollectionUtils)
+            .hasSameElementsAs(filteredWithEclipseCollections)
+            .hasSameElementsAs(filteredWithEclipseCollectionsUsingIterate)
+            .hasSameElementsAs(filteredWithEclipseCollectionsUsingIterate)
+            .hasSameElementsAs(filteredWithGuava)
+            .hasSameElementsAs(EXPECTED_EVEN_FILTERED_COLLECTION);
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/java/map/initialize/MapInitializerUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.java.map.initialize;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Map;
+
+import org.junit.Test;
+
+public class MapInitializerUnitTest {
+    
+    @Test
+    public void givenStaticMap_whenUpdated_thenCorrect() {
+        
+        MapInitializer.articleMapOne.put("NewArticle1", "Convert array to List");
+        
+        assertEquals(MapInitializer.articleMapOne.get("NewArticle1"), "Convert array to List");
+        
+    }
+    
+    @Test(expected=UnsupportedOperationException.class)
+    public void givenSingleTonMap_whenEntriesAdded_throwsException() {
+        
+        Map<String, String> map = MapInitializer.createSingletonMap();
+        map.put("username2", "password2");
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/list/listoflist/AddElementsToListUnitTest.java

@@ -0,0 +1,69 @@
+package com.baeldung.list.listoflist;
+
+import com.baeldung.java.list.Flower;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import java.util.*;
+import static org.junit.Assert.*;
+
+public class AddElementsToListUnitTest {
+
+    List<Flower> flowers;
+
+    @Before
+    public void init() {
+        this.flowers = new ArrayList<>(Arrays.asList(
+                new Flower("Poppy", 12),
+                new Flower("Anemone", 8),
+                new Flower("Catmint", 12)));
+    }
+    @Test
+    public void givenAList_whenTargetListIsEmpty_thenReturnTargetListWithNewItems() {
+        List<Flower> anotherList = new ArrayList<>();
+        anotherList.addAll(flowers);
+        assertEquals(anotherList.size(), flowers.size());
+        Assert.assertTrue(anotherList.containsAll(flowers));
+    }
+    @Test
+    public void givenAList_whenTargetListIsEmpty_thenReturnTargetListWithOneModifiedElementByConstructor() {
+        List<Flower> anotherList = new ArrayList<>();
+        anotherList.addAll(flowers);
+        Flower flower = anotherList.get(0);
+        flower.setPetals(flowers.get(0).getPetals() * 3);
+        assertEquals(anotherList.size(), flowers.size());
+        Assert.assertTrue(anotherList.containsAll(flowers));
+    }
+    @Test
+    public void givenAListAndElements_whenUseCollectionsAddAll_thenAddElementsToTargetList() {
+        List<Flower> target = new ArrayList<>();
+        Collections.addAll(target, flowers.get(0), flowers.get(1), flowers.get(2), flowers.get(0));
+        assertEquals(target.size(), 4);
+    }
+    @Test
+    public void givenTwoList_whenSourceListDoesNotHaveNullElements_thenAddElementsToTargetListSkipFirstElementByStreamProcess() {
+        List<Flower> flowerVase = new ArrayList<>();
+        flowers.stream()
+                .skip(1)
+                .forEachOrdered(flowerVase::add);
+        assertEquals(flowerVase.size() + 1, flowers.size());
+        assertFalse(flowerVase.containsAll(flowers));
+    }
+    @Test
+    public void givenTwoList_whenSourceListDoesNotHaveNullElements_thenAddElementsToTargetListFilteringElementsByStreamProcess() {
+        List<Flower> flowerVase = new ArrayList<>();
+        flowers.stream()
+                .filter(f -> f.getPetals() > 10)
+                .forEachOrdered(flowerVase::add);
+        assertEquals(flowerVase.size() + 1, flowers.size());
+        assertFalse(flowerVase.containsAll(flowers));
+    }
+    @Test
+    public void givenAList_whenListIsNotNull_thenAddElementsToListByStreamProcessWihtOptional() {
+        List<Flower> target = new ArrayList<>();
+        Optional.ofNullable(flowers)
+                .ifPresent(target::addAll);
+        assertNotNull(target);
+        assertEquals(target.size(), 3);
+    }
+}

core-java-collections/src/test/java/com/baeldung/list/removefirst/RemoveFirstElementUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.list.removefirst;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class RemoveFirstElementUnitTest {
+
+    private List<String> list = new ArrayList<>();
+    private LinkedList<String> linkedList = new LinkedList<>();
+
+    @Before
+    public void init() {
+
+        list.add("cat");
+        list.add("dog");
+        list.add("pig");
+        list.add("cow");
+        list.add("goat");
+
+        linkedList.add("cat");
+        linkedList.add("dog");
+        linkedList.add("pig");
+        linkedList.add("cow");
+        linkedList.add("goat");
+    }
+
+    @Test
+    public void givenList_whenRemoveFirst_thenRemoved() {
+        list.remove(0);
+
+        assertThat(list, hasSize(4));
+        assertThat(list, not(contains("cat")));
+    }
+
+    @Test
+    public void givenLinkedList_whenRemoveFirst_thenRemoved() {
+
+        linkedList.removeFirst();
+
+        assertThat(linkedList, hasSize(4));
+        assertThat(linkedList, not(contains("cat")));
+    }
+
+}

core-java-io/README.md

@@ -28,3 +28,5 @@
 - [Guide to Java NIO2 Asynchronous Channel APIs](http://www.baeldung.com/java-nio-2-async-channels)
 - [A Guide to NIO2 Asynchronous Socket Channel](http://www.baeldung.com/java-nio2-async-socket-channel)
 - [Download a File From an URL in Java](http://www.baeldung.com/java-download-file)
+- [Create a Symbolic Link with Java](http://www.baeldung.com/java-symlink)
+- [Quick Use of FilenameFilter](http://www.baeldung.com/java-filename-filter)

core-java-persistence/pom.xml

@@ -0,0 +1,59 @@
+<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.core-java-persistence</groupId>
+    <artifactId>core-java-persistence</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-persistence</name>
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>${h2database.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-dbcp2</artifactId>
+            <version>${commons-dbcp2.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.zaxxer</groupId>
+            <artifactId>HikariCP</artifactId>
+            <version>${HikariCP.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.mchange</groupId>
+            <artifactId>c3p0</artifactId>
+            <version>${c3p0.version}</version>
+        </dependency>
+    </dependencies>
+    <build>
+        <finalName>core-java-persistence</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>    
+    <properties>
+        <assertj-core.version>3.10.0</assertj-core.version>
+        <h2database.version>1.4.197</h2database.version>
+        <commons-dbcp2.version>2.4.0</commons-dbcp2.version>
+        <HikariCP.version>3.2.0</HikariCP.version>
+        <c3p0.version>0.9.5.2</c3p0.version>
+    </properties>
+</project>