Merge remote-tracking branch 'upstream/master'

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

@@ -54,3 +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/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-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/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/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/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/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>

core-java-persistence/src/main/java/com/baeldung/connectionpool/BasicConnectionPool.java

@@ -1,85 +1,92 @@
-package com.baeldung.connectionpool.connectionpools;
-
-import java.sql.Connection;
-import java.sql.DriverManager;
-import java.sql.SQLException;
-import java.util.ArrayList;
-import java.util.List;
-
-public class BasicConnectionPool implements ConnectionPool {
-
-    private final String url;
-    private final String user;
-    private final String password;
-    private final List<Connection> connectionPool;
-    private final List<Connection> usedConnections = new ArrayList<>();
-    private static final int INITIAL_POOL_SIZE = 10;
-    private final int MAX_POOL_SIZE = 20;
-    
-    public static BasicConnectionPool create(String url, String user, String password) throws SQLException {
-        List<Connection> pool = new ArrayList<>(INITIAL_POOL_SIZE);
-        for (int i = 0; i < INITIAL_POOL_SIZE; i++) {
-            pool.add(createConnection(url, user, password));
-        }
-        return new BasicConnectionPool(url, user, password, pool);
-    }
-    
-    private BasicConnectionPool(String url, String user, String password, List<Connection> connectionPool) {
-        this.url = url;
-        this.user = user;
-        this.password = password;
-        this.connectionPool = connectionPool;
-    }
-    
-    @Override
-    public Connection getConnection() throws SQLException {
-        if (connectionPool.isEmpty()) {
-            if (usedConnections.size() < MAX_POOL_SIZE) {
-                connectionPool.add(createConnection(url, user, password));
-            } else {
-                throw new RuntimeException("Maximum pool size reached, no available connections!");
-            }
-        }
-
-        Connection connection = connectionPool.remove(connectionPool.size() - 1);
-        usedConnections.add(connection);
-        return connection;
-    }
-    
-    @Override
-    public boolean releaseConnection(Connection connection) {
-        connectionPool.add(connection);
-        return usedConnections.remove(connection);
-    }
-    
-    private static Connection createConnection(String url, String user, String password) throws SQLException {
-        return DriverManager.getConnection(url, user, password);
-    }
-    
-    public int getSize() {
-        return connectionPool.size() + usedConnections.size();
-    }
-
-    @Override
-    public String getUrl() {
-        return url;
-    }
-
-    @Override
-    public String getUser() {
-        return user;
-    }
-
-    @Override
-    public String getPassword() {
-        return password;
-    }
-
-    public void shutdown() throws SQLException {
-        usedConnections.forEach(this::releaseConnection);
-        for (Connection c : connectionPool) {
-            c.close();
-        }
-        connectionPool.clear();
-    }
-}
+package com.baeldung.connectionpool;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class BasicConnectionPool implements ConnectionPool {
+
+    private final String url;
+    private final String user;
+    private final String password;
+    private final List<Connection> connectionPool;
+    private final List<Connection> usedConnections = new ArrayList<>();
+    private static final int INITIAL_POOL_SIZE = 10;
+    private final int MAX_POOL_SIZE = 20;
+
+    public static BasicConnectionPool create(String url, String user, String password) throws SQLException {
+        List<Connection> pool = new ArrayList<>(INITIAL_POOL_SIZE);
+        for (int i = 0; i < INITIAL_POOL_SIZE; i++) {
+            pool.add(createConnection(url, user, password));
+        }
+        return new BasicConnectionPool(url, user, password, pool);
+    }
+
+    private BasicConnectionPool(String url, String user, String password, List<Connection> connectionPool) {
+        this.url = url;
+        this.user = user;
+        this.password = password;
+        this.connectionPool = connectionPool;
+    }
+
+    @Override
+    public Connection getConnection() throws SQLException {
+        if (connectionPool.isEmpty()) {
+            if (usedConnections.size() < MAX_POOL_SIZE) {
+                connectionPool.add(createConnection(url, user, password));
+            } else {
+                throw new RuntimeException("Maximum pool size reached, no available connections!");
+            }
+        }
+
+        Connection connection = connectionPool.remove(connectionPool.size() - 1);
+        usedConnections.add(connection);
+        return connection;
+    }
+
+    @Override
+    public boolean releaseConnection(Connection connection) {
+        connectionPool.add(connection);
+        return usedConnections.remove(connection);
+    }
+
+    private static Connection createConnection(String url, String user, String password) throws SQLException {
+        return DriverManager.getConnection(url, user, password);
+    }
+
+    @Override
+    public int getSize() {
+        return connectionPool.size() + usedConnections.size();
+    }
+
+    @Override
+    public List<Connection> getConnectionPool() {
+        return connectionPool;
+    }
+    
+    @Override
+    public String getUrl() {
+        return url;
+    }
+
+    @Override
+    public String getUser() {
+        return user;
+    }
+
+    @Override
+    public String getPassword() {
+        return password;
+    }
+    
+    @Override
+    public void shutdown() throws SQLException {
+        usedConnections.forEach(this::releaseConnection);
+        for (Connection c : connectionPool) {
+            c.close();
+        }
+        connectionPool.clear();
+    }
+}

core-java-persistence/src/main/java/com/baeldung/connectionpool/C3poDataSource.java

@@ -1,28 +1,28 @@
-package com.baeldung.connectionpool.connectionpools;
-
-import com.mchange.v2.c3p0.ComboPooledDataSource;
-import java.beans.PropertyVetoException;
-import java.sql.Connection;
-import java.sql.SQLException;
-
-public class C3poDataSource {
-
-    private static final ComboPooledDataSource cpds = new ComboPooledDataSource();
-
-    static {
-        try {
-            cpds.setDriverClass("org.h2.Driver");
-            cpds.setJdbcUrl("jdbc:h2:mem:test");
-            cpds.setUser("user");
-            cpds.setPassword("password");
-        } catch (PropertyVetoException e) {
-            e.printStackTrace();
-        }
-    }
-    
-    public static Connection getConnection() throws SQLException {
-        return cpds.getConnection();
-    }
-    
-    private C3poDataSource(){}
+package com.baeldung.connectionpool;
+
+import com.mchange.v2.c3p0.ComboPooledDataSource;
+import java.beans.PropertyVetoException;
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class C3poDataSource {
+
+    private static final ComboPooledDataSource cpds = new ComboPooledDataSource();
+
+    static {
+        try {
+            cpds.setDriverClass("org.h2.Driver");
+            cpds.setJdbcUrl("jdbc:h2:mem:test");
+            cpds.setUser("user");
+            cpds.setPassword("password");
+        } catch (PropertyVetoException e) {
+            e.printStackTrace();
+        }
+    }
+    
+    public static Connection getConnection() throws SQLException {
+        return cpds.getConnection();
+    }
+    
+    private C3poDataSource(){}
 }

core-java-persistence/src/main/java/com/baeldung/connectionpool/ConnectionPool.java

@@ -1,18 +1,24 @@
-package com.baeldung.connectionpool.connectionpools;
-
-import java.sql.Connection;
-import java.sql.SQLException;
-import java.util.List;
-
-public interface ConnectionPool {
-
-    Connection getConnection() throws SQLException;
-    
-    boolean releaseConnection(Connection connection);
-    
-    String getUrl();
-    
-    String getUser();
-
-    String getPassword();
+package com.baeldung.connectionpool;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.List;
+
+public interface ConnectionPool {
+
+    Connection getConnection() throws SQLException;
+    
+    boolean releaseConnection(Connection connection);
+    
+    List<Connection> getConnectionPool();
+    
+    int getSize();
+    
+    String getUrl();
+    
+    String getUser();
+
+    String getPassword();
+    
+    void shutdown() throws SQLException;;
 }   

core-java-persistence/src/main/java/com/baeldung/connectionpool/DBCPDataSource.java

@@ -1,25 +1,25 @@
-package com.baeldung.connectionpool.connectionpools;
-
-import java.sql.Connection;
-import java.sql.SQLException;
-import org.apache.commons.dbcp2.BasicDataSource;
-
-public class DBCPDataSource {
-    
-    private static final BasicDataSource ds = new BasicDataSource();
-    
-    static {
-        ds.setUrl("jdbc:h2:mem:test");
-        ds.setUsername("user");
-        ds.setPassword("password");
-        ds.setMinIdle(5);
-        ds.setMaxIdle(10);
-        ds.setMaxOpenPreparedStatements(100);
-    }
-    
-    public static Connection getConnection() throws SQLException {
-        return ds.getConnection();
-    }
-    
-    private DBCPDataSource(){}
-}
+package com.baeldung.connectionpool;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import org.apache.commons.dbcp2.BasicDataSource;
+
+public class DBCPDataSource {
+    
+    private static final BasicDataSource ds = new BasicDataSource();
+    
+    static {
+        ds.setUrl("jdbc:h2:mem:test");
+        ds.setUsername("user");
+        ds.setPassword("password");
+        ds.setMinIdle(5);
+        ds.setMaxIdle(10);
+        ds.setMaxOpenPreparedStatements(100);
+    }
+    
+    public static Connection getConnection() throws SQLException {
+        return ds.getConnection();
+    }
+    
+    private DBCPDataSource(){}
+}

core-java-persistence/src/main/java/com/baeldung/connectionpool/HikariCPDataSource.java

@@ -1,28 +1,28 @@
-package com.baeldung.connectionpool.connectionpools;
-
-import com.zaxxer.hikari.HikariConfig;
-import com.zaxxer.hikari.HikariDataSource;
-import java.sql.Connection;
-import java.sql.SQLException;
-
-public class HikariCPDataSource {
-    
-    private static final HikariConfig config = new HikariConfig();
-    private static final HikariDataSource ds;
-    
-    static {
-        config.setJdbcUrl("jdbc:h2:mem:test");
-        config.setUsername("user");
-        config.setPassword("password");
-        config.addDataSourceProperty("cachePrepStmts", "true");
-        config.addDataSourceProperty("prepStmtCacheSize", "250");
-        config.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
-        ds = new HikariDataSource(config);
-    }
-    
-    public static Connection getConnection() throws SQLException {
-        return ds.getConnection();
-    }
-    
-    private HikariCPDataSource(){}
-}
+package com.baeldung.connectionpool;
+
+import com.zaxxer.hikari.HikariConfig;
+import com.zaxxer.hikari.HikariDataSource;
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class HikariCPDataSource {
+    
+    private static final HikariConfig config = new HikariConfig();
+    private static final HikariDataSource ds;
+    
+    static {
+        config.setJdbcUrl("jdbc:h2:mem:test");
+        config.setUsername("user");
+        config.setPassword("password");
+        config.addDataSourceProperty("cachePrepStmts", "true");
+        config.addDataSourceProperty("prepStmtCacheSize", "250");
+        config.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
+        ds = new HikariDataSource(config);
+    }
+    
+    public static Connection getConnection() throws SQLException {
+        return ds.getConnection();
+    }
+    
+    private HikariCPDataSource(){}
+}

core-java-persistence/src/test/java/com/baeldung/connectionpool/BasicConnectionPoolUnitTest.java

@@ -1,10 +1,8 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.BasicConnectionPool;
-import com.baeldung.connectionpool.connectionpools.ConnectionPool;
 import java.sql.Connection;
 import java.sql.SQLException;
-import java.util.List;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;

core-java-persistence/src/test/java/com/baeldung/connectionpool/C3poDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.C3poDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java-persistence/src/test/java/com/baeldung/connectionpool/DBCPDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.DBCPDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java-persistence/src/test/java/com/baeldung/connectionpool/HikariCPDataSourceUnitTest.java

@@ -1,6 +1,5 @@
 package com.baeldung.connectionpool;
 
-import com.baeldung.connectionpool.connectionpools.HikariCPDataSource;
 import java.sql.SQLException;
 import static org.junit.Assert.assertTrue;
 import org.junit.Test;

core-java/README.md

@@ -163,3 +163,8 @@
 - [Console I/O in Java](http://www.baeldung.com/java-console-input-output)
 - [Guide to the java.util.Arrays Class](http://www.baeldung.com/java-util-arrays)
 - [Create a Custom Exception in Java](http://www.baeldung.com/java-new-custom-exception)
+- [Guide to java.util.GregorianCalendar](http://www.baeldung.com/java-gregorian-calendar)
+- [Java Global Exception Handler](http://www.baeldung.com/java-global-exception-handler)
+- [Encrypting and Decrypting Files in Java](http://www.baeldung.com/java-cipher-input-output-stream)
+- [How to Get the Size of an Object in Java](http://www.baeldung.com/java-size-of-object)
+- [Exception Handling in Java](http://www.baeldung.com/java-exceptions)

core-java/pom.xml

@@ -158,21 +158,6 @@
             <artifactId>jmimemagic</artifactId>
             <version>${jmime-magic.version}</version>
         </dependency>
-        <dependency>
-            <groupId>org.apache.commons</groupId>
-            <artifactId>commons-dbcp2</artifactId>
-            <version>${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>
         <!-- instrumentation -->
         <dependency>
             <groupId>org.javassist</groupId>
@@ -544,11 +529,6 @@
         <!-- testing -->
         <assertj-core.version>3.10.0</assertj-core.version>
 
-        <!-- JDBC pooling frameworks -->
-        <commons-dbcp2.version>2.4.0</commons-dbcp2.version>
-        <HikariCP.version>3.2.0</HikariCP.version>
-        <c3p0.version>0.9.5.2</c3p0.version>
-        
         <!-- maven plugins -->
         <maven-surefire-plugin.version>2.19.1</maven-surefire-plugin.version>
         <springframework.spring-web.version>4.3.4.RELEASE</springframework.spring-web.version>

core-kotlin/README.md

@@ -34,3 +34,5 @@
 - [Java EE 8 Security API](http://www.baeldung.com/java-ee-8-security)
 - [Kotlin with Ktor](http://www.baeldung.com/kotlin-ktor)
 - [Working with Enums in Kotlin](http://www.baeldung.com/kotlin-enum)
+- [Create a Java and Kotlin Project with Maven](http://www.baeldung.com/kotlin-maven-java-project)
+- [Reflection with Kotlin](http://www.baeldung.com/kotlin-reflection)

google-web-toolkit/README.md

@@ -0,0 +1,2 @@
+### Relevant Articles: 
+- [Introduction to GWT](http://www.baeldung.com/gwt)

google-web-toolkit/pom.xml

@@ -6,10 +6,16 @@
 	<!-- POM file generated with GWT webAppCreator -->
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>com.baeldung</groupId>
-	<artifactId>google-web-toolkit</artifactId>
+	<artifactId>google_web_toolkit</artifactId>
 	<packaging>war</packaging>
 	<version>1.0-SNAPSHOT</version>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
 	<dependencyManagement>
 		<dependencies>
 			<!-- ensure all GWT deps use the same version (unless overridden) -->