Merge branch 'master' into JAVA-6511-p2

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/astar/RouteFinder.java

@@ -8,6 +8,9 @@ import java.util.PriorityQueue;
 import java.util.Queue;
 import java.util.stream.Collectors;
 
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
 public class RouteFinder<T extends GraphNode> {
     private final Graph<T> graph;
     private final Scorer<T> nextNodeScorer;
@@ -28,11 +31,11 @@ public class RouteFinder<T extends GraphNode> {
         openSet.add(start);
 
         while (!openSet.isEmpty()) {
-            System.out.println("Open Set contains: " + openSet.stream().map(RouteNode::getCurrent).collect(Collectors.toSet()));
+            log.debug("Open Set contains: " + openSet.stream().map(RouteNode::getCurrent).collect(Collectors.toSet()));
             RouteNode<T> next = openSet.poll();
-            System.out.println("Looking at node: " + next);
+            log.debug("Looking at node: " + next);
             if (next.getCurrent().equals(to)) {
-                System.out.println("Found our destination!");
+                log.debug("Found our destination!");
 
                 List<T> route = new ArrayList<>();
                 RouteNode<T> current = next;
@@ -41,7 +44,7 @@ public class RouteFinder<T extends GraphNode> {
                     current = allNodes.get(current.getPrevious());
                 } while (current != null);
 
-                System.out.println("Route: " + route);
+                log.debug("Route: " + route);
                 return route;
             }
 
@@ -55,7 +58,7 @@ public class RouteFinder<T extends GraphNode> {
                     nextNode.setRouteScore(newScore);
                     nextNode.setEstimatedScore(newScore + targetScorer.computeCost(connection, to));
                     openSet.add(nextNode);
-                    System.out.println("Found a better route to node: " + nextNode);
+                    log.debug("Found a better route to node: " + nextNode);
                 }
             });
         }

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/astar/underground/RouteFinderIntegrationTest.java

@@ -1,5 +1,7 @@
 package com.baeldung.algorithms.astar.underground;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -10,9 +12,13 @@ import java.util.stream.Stream;
 
 import com.baeldung.algorithms.astar.Graph;
 import com.baeldung.algorithms.astar.RouteFinder;
+
+import lombok.extern.slf4j.Slf4j;
+
 import org.junit.Before;
 import org.junit.Test;
 
+@Slf4j
 public class RouteFinderIntegrationTest {
 
     private Graph<Station> underground;
@@ -637,7 +643,8 @@ public class RouteFinderIntegrationTest {
     @Test
     public void findRoute() {
         List<Station> route = routeFinder.findRoute(underground.getNode("74"), underground.getNode("7"));
+        assertThat(route).size().isPositive();
 
-        System.out.println(route.stream().map(Station::getName).collect(Collectors.toList()));
+        route.stream().map(Station::getName).collect(Collectors.toList()).forEach(station -> log.debug(station));
     }
 }

algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/prim/PrimUnitTest.java

@@ -1,10 +1,10 @@
 package com.baeldung.algorithms.prim;
 
+import org.junit.Test;
+
 import java.util.ArrayList;
 import java.util.List;
 
-import org.junit.Test;
-
 public class PrimUnitTest {
 
     @Test

algorithms-searching/src/main/java/com/baeldung/algorithms/dfs/Graph.java

@@ -29,6 +29,7 @@ public class Graph {
         stack.push(start);
         while (!stack.isEmpty()) {
             int current = stack.pop();
+            if(!isVisited[current]){
                 isVisited[current] = true;
                 visit(current);
                 for (int dest : adjVertices.get(current)) {
@@ -37,6 +38,7 @@ public class Graph {
                 }
             }
         }
+    }
 
     public void dfs(int start) {
         boolean[] isVisited = new boolean[adjVertices.size()];

algorithms-searching/src/main/java/com/baeldung/algorithms/suffixtree/SuffixTree.java

@@ -8,7 +8,9 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 public class SuffixTree {
+
     private static final Logger LOGGER = LoggerFactory.getLogger(SuffixTree.class);
+
     private static final String WORD_TERMINATION = "$";
     private static final int POSITION_UNDEFINED = -1;
     private Node root;
@@ -23,7 +25,7 @@ public class SuffixTree {
     }
 
     public List<String> searchText(String pattern) {
-        LOGGER.info("Searching for pattern \"{}\"", pattern);
+        LOGGER.debug("Searching for pattern \"{}\"", pattern);
         List<String> result = new ArrayList<>();
         List<Node> nodes = getAllNodesInTraversePath(pattern, root, false);
 
@@ -41,11 +43,11 @@ public class SuffixTree {
     }
 
     private void addSuffix(String suffix, int position) {
-        LOGGER.info(">>>>>>>>>>>> Adding new suffix {}", suffix);
+        LOGGER.debug(">>>>>>>>>>>> Adding new suffix {}", suffix);
         List<Node> nodes = getAllNodesInTraversePath(suffix, root, true);
         if (nodes.size() == 0) {
             addChildNode(root, suffix, position);
-            LOGGER.info("{}", printTree());
+            LOGGER.debug("{}", printTree());
         } else {
             Node lastNode = nodes.remove(nodes.size() - 1);
             String newText = suffix;
@@ -58,7 +60,7 @@ public class SuffixTree {
                 newText = newText.substring(existingSuffixUptoLastNode.length());
             }
             extendNode(lastNode, newText, position);
-            LOGGER.info("{}", printTree());
+            LOGGER.debug("{}", printTree());
         }
     }
 

algorithms-searching/src/test/java/com/baeldung/algorithms/dfs/GraphUnitTest.java

@@ -2,7 +2,6 @@ package com.baeldung.algorithms.dfs;
 
 import java.util.List;
 
-import com.baeldung.algorithms.dfs.Graph;
 import org.junit.Test;
 
 public class GraphUnitTest {

algorithms-searching/src/test/java/com/baeldung/algorithms/quadtree/QuadTreeSearchUnitTest.java

@@ -27,16 +27,16 @@ public class QuadTreeSearchUnitTest {
             Point point = new Point(points[i][0], points[i][1]);
             quadTree.addPoint(point);
         }
-        LOGGER.info("\n" + quadTree.printTree(""));
+        LOGGER.debug("\n" + quadTree.printTree(""));
-        LOGGER.info("==============================================");
+        LOGGER.debug("==============================================");
     }
 
     @Test
     public void givenQuadTree_whenSearchingForRange_thenReturn1MatchingItem() {
         Region searchArea = new Region(200, 200, 250, 250);
         List<Point> result = quadTree.search(searchArea, null, "");
-        LOGGER.info(result.toString());
+        LOGGER.debug(result.toString());
-        LOGGER.info(quadTree.printSearchTraversePath());
+        LOGGER.debug(quadTree.printSearchTraversePath());
 
         Assert.assertEquals(1, result.size());
         Assert.assertArrayEquals(new float[] { 245, 238 },
@@ -47,8 +47,8 @@ public class QuadTreeSearchUnitTest {
     public void givenQuadTree_whenSearchingForRange_thenReturn2MatchingItems() {
         Region searchArea = new Region(0, 0, 100, 100);
         List<Point> result = quadTree.search(searchArea, null, "");
-        LOGGER.info(result.toString());
+        LOGGER.debug(result.toString());
-        LOGGER.info(quadTree.printSearchTraversePath());
+        LOGGER.debug(quadTree.printSearchTraversePath());
 
         Assert.assertEquals(2, result.size());
         Assert.assertArrayEquals(new float[] { 21, 25 },

apache-kafka/README.md

@@ -3,7 +3,7 @@
 This module contains articles about Apache Kafka.
 
 ### Relevant articles
-- [Kafka Streams vs Kafka Consumer](https://www.baeldung.com/java-kafka-streams-vs-kafka-consumer)
+- [Kafka Streams vs. Kafka Consumer](https://www.baeldung.com/java-kafka-streams-vs-kafka-consumer)
 - [Kafka Topic Creation Using Java](https://www.baeldung.com/kafka-topic-creation)
 - [Using Kafka MockConsumer](https://www.baeldung.com/kafka-mockconsumer)
 - [Using Kafka MockProducer](https://www.baeldung.com/kafka-mockproducer)
@@ -12,6 +12,7 @@ This module contains articles about Apache Kafka.
 - [Kafka Connect Example with MQTT and MongoDB](https://www.baeldung.com/kafka-connect-mqtt-mongodb)
 - [Building a Data Pipeline with Flink and Kafka](https://www.baeldung.com/kafka-flink-data-pipeline)
 - [Exactly Once Processing in Kafka with Java](https://www.baeldung.com/kafka-exactly-once)
+- [Custom Serializers in Apache Kafka](https://www.baeldung.com/kafka-custom-serializer)
 
 
 ##### Building the project

apache-kafka/pom.xml

@@ -161,6 +161,12 @@
             <artifactId>spark-cassandra-connector-java_2.11</artifactId>
             <version>${com.datastax.spark.spark-cassandra-connector-java.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
     </dependencies>
 
     <properties>
@@ -175,6 +181,7 @@
         <graphframes.version>0.8.1-spark3.0-s_2.12</graphframes.version>
         <com.datastax.spark.spark-cassandra-connector.version>2.5.2</com.datastax.spark.spark-cassandra-connector.version>
         <com.datastax.spark.spark-cassandra-connector-java.version>1.6.0-M1</com.datastax.spark.spark-cassandra-connector-java.version>
+        <lombok.version>1.18.20</lombok.version>
     </properties>
 
 </project>

apache-kafka/src/main/java/com/baeldung/kafka/dto/MessageDto.java

@@ -0,0 +1,15 @@
+package com.baeldung.kafka.dto;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@AllArgsConstructor
+@NoArgsConstructor
+@Builder
+public class MessageDto {
+    private String message;
+    private String version;
+}

apache-kafka/src/main/java/com/baeldung/kafka/serdes/CustomDeserializer.java

@@ -0,0 +1,35 @@
+package com.baeldung.kafka.serdes;
+
+import com.baeldung.kafka.dto.MessageDto;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.kafka.common.errors.SerializationException;
+import org.apache.kafka.common.serialization.Deserializer;
+
+import java.util.Map;
+
+public class CustomDeserializer implements Deserializer<MessageDto> {
+
+    private ObjectMapper objectMapper = new ObjectMapper();
+
+    @Override
+    public void configure(Map<String, ?> configs, boolean isKey) {
+    }
+
+    @Override
+    public MessageDto deserialize(String topic, byte[] data) {
+        try {
+            if (data == null){
+                System.out.println("Null received at deserializing");
+                return null;
+            }
+            System.out.println("Deserializing...");
+            return objectMapper.readValue(new String(data, "UTF-8"), MessageDto.class);
+        } catch (Exception e) {
+            throw new SerializationException("Error when deserializing byte[] to MessageDto");
+        }
+    }
+
+    @Override
+    public void close() {
+    }
+}

apache-kafka/src/main/java/com/baeldung/kafka/serdes/CustomSerializer.java

@@ -0,0 +1,34 @@
+package com.baeldung.kafka.serdes;
+
+import com.baeldung.kafka.dto.MessageDto;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.kafka.common.errors.SerializationException;
+import org.apache.kafka.common.serialization.Serializer;
+
+import java.util.Map;
+
+public class CustomSerializer implements Serializer<MessageDto> {
+    private final ObjectMapper objectMapper = new ObjectMapper();
+
+    @Override
+    public void configure(Map<String, ?> configs, boolean isKey) {
+    }
+
+    @Override
+    public byte[] serialize(String topic, MessageDto data) {
+        try {
+            if (data == null){
+                System.out.println("Null received at serializing");
+                return null;
+            }
+            System.out.println("Serializing...");
+            return objectMapper.writeValueAsBytes(data);
+        } catch (Exception e) {
+            throw new SerializationException("Error when serializing MessageDto to byte[]");
+        }
+    }
+
+    @Override
+    public void close() {
+    }
+}

apache-kafka/src/test/java/com/baeldung/kafka/serdes/KafkaSerDesLiveTest.java

@@ -0,0 +1,92 @@
+package com.baeldung.kafka.serdes;
+
+import com.baeldung.kafka.dto.MessageDto;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.clients.consumer.ConsumerRecords;
+import org.apache.kafka.clients.consumer.KafkaConsumer;
+import org.apache.kafka.clients.producer.KafkaProducer;
+import org.apache.kafka.clients.producer.ProducerConfig;
+import org.apache.kafka.clients.producer.ProducerRecord;
+import org.junit.Before;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.testcontainers.containers.KafkaContainer;
+import org.testcontainers.utility.DockerImageName;
+
+import java.time.Duration;
+import java.util.Arrays;
+import java.util.Properties;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.Assert.assertEquals;
+
+public class KafkaSerDesLiveTest {
+    private static final String CONSUMER_APP_ID = "consumer_id";
+    private static final String CONSUMER_GROUP_ID = "group_id";
+
+    @ClassRule
+    public static KafkaContainer kafka = new KafkaContainer(DockerImageName.parse("confluentinc/cp-kafka:5.4.3"));
+    private final String TOPIC = "mytopic";
+
+    private static KafkaConsumer<String, MessageDto> createKafkaConsumer() {
+
+        Properties props = new Properties();
+        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, kafka.getBootstrapServers());
+        props.put(ConsumerConfig.CLIENT_ID_CONFIG, CONSUMER_APP_ID);
+        props.put(ConsumerConfig.GROUP_ID_CONFIG, CONSUMER_GROUP_ID);
+        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
+        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");
+        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, "com.baeldung.kafka.serdes.CustomDeserializer");
+
+        return new KafkaConsumer<>(props);
+
+    }
+
+    private static KafkaProducer<String, MessageDto> createKafkaProducer() {
+
+        Properties props = new Properties();
+        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafka.getBootstrapServers());
+        props.put(ProducerConfig.CLIENT_ID_CONFIG, CONSUMER_APP_ID);
+        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
+        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, "com.baeldung.kafka.serdes.CustomSerializer");
+
+        return new KafkaProducer(props);
+
+    }
+
+    @Before
+    public void setUp() {
+    }
+
+    @Test
+    public void givenKafkaClientShouldSerializeAndDeserialize() throws InterruptedException {
+
+        MessageDto msgProd = MessageDto.builder().message("test").version("1.0").build();
+
+        KafkaProducer<String, MessageDto> producer = createKafkaProducer();
+        producer.send(new ProducerRecord<String, MessageDto>(TOPIC, "1", msgProd));
+        System.out.println("Message sent " + msgProd);
+        producer.close();
+
+        Thread.sleep(2000);
+
+        AtomicReference<MessageDto> msgCons = new AtomicReference<>();
+
+        KafkaConsumer<String, MessageDto> consumer = createKafkaConsumer();
+        consumer.subscribe(Arrays.asList(TOPIC));
+
+        ConsumerRecords<String, MessageDto> records = consumer.poll(Duration.ofSeconds(1));
+        records.forEach(record -> {
+            msgCons.set(record.value());
+            System.out.println("Message received " + record.value());
+        });
+
+        consumer.close();
+
+        assertEquals(msgProd, msgCons.get());
+
+    }
+
+}
+
+

apache-libraries/pom.xml

@@ -133,6 +133,11 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
         <dependency>
             <groupId>com.jayway.awaitility</groupId>
             <artifactId>awaitility</artifactId>
@@ -196,7 +201,6 @@
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
         <avro.version>1.8.2</avro.version>
-        <slf4j.version>1.7.25</slf4j.version>
         <beam.version>2.19.0</beam.version>
         <assertj.version>3.9.0</assertj.version>
         <bval.version>1.1.2</bval.version>

apache-libraries/src/main/resources/log4j2.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<Configuration status="WARN">
+    <Appenders>
+        <Console name="Console" target="SYSTEM_OUT">
+            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
+        </Console>
+    </Appenders>
+    <Loggers>
+        <Logger name="org.apache.meecrowave" level="warn">
+            <AppenderRef ref="Console"/>
+        </Logger>
+
+        <Root level="info">
+            <AppenderRef ref="Console"/>
+        </Root>
+    </Loggers>
+</Configuration>

apache-libraries/src/test/java/com/baeldung/apache/beam/intro/WordCountUnitTest.java

@@ -10,7 +10,6 @@ import com.baeldung.apache.beam.intro.WordCount;
 public class WordCountUnitTest {
     
     @Test
-    // @Ignore
     public void givenInputFile_whenWordCountRuns_thenJobFinishWithoutError() {
         boolean jobDone = WordCount.wordCount("src/test/resources/wordcount.txt", "target/output");
         assertTrue(jobDone);

apache-spark/src/main/resources/log4j.properties

@@ -0,0 +1,42 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# Set everything to be logged to the console
+log4j.rootCategory=WARN, console
+log4j.appender.console=org.apache.log4j.ConsoleAppender
+log4j.appender.console.target=System.err
+log4j.appender.console.layout=org.apache.log4j.PatternLayout
+log4j.appender.console.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss} %p %c{1}: %m%n
+
+# Set the default spark-shell log level to WARN. When running the spark-shell, the
+# log level for this class is used to overwrite the root logger's log level, so that
+# the user can have different defaults for the shell and regular Spark apps.
+log4j.logger.org.apache.spark.repl.Main=WARN
+
+# Settings to quiet third party logs that are too verbose
+log4j.logger.org.spark_project.jetty=WARN
+log4j.logger.org.spark_project.jetty.util.component.AbstractLifeCycle=ERROR
+log4j.logger.org.apache.spark.repl.SparkIMain$exprTyper=INFO
+log4j.logger.org.apache.spark.repl.SparkILoop$SparkILoopInterpreter=INFO
+
+# SPARK-9183: Settings to avoid annoying messages when looking up nonexistent UDFs in SparkSQL with Hive support
+log4j.logger.org.apache.hadoop.hive.metastore.RetryingHMSHandler=FATAL
+log4j.logger.org.apache.hadoop.hive.ql.exec.FunctionRegistry=ERROR
+
+# Parquet related logging
+log4j.logger.org.apache.parquet.CorruptStatistics=ERROR
+log4j.logger.parquet.CorruptStatistics=ERROR

apache-tapestry/pom.xml

@@ -32,7 +32,6 @@
         <!-- Uncomment this to add support for file uploads: -->
         <!-- <dependency> <groupId>org.apache.tapestry</groupId> <artifactId>tapestry-upload</artifactId> 
             <version>${tapestry-release-version}</version> </dependency> -->
-
         <!-- A dependency on either JUnit or TestNG is required, or the surefire plugin (which runs the 
             tests) will fail, preventing Maven from packaging the WAR. Tapestry includes a large number of testing 
             facilities designed for use with TestNG (http://testng.org/), so it's recommended. -->
@@ -110,8 +109,6 @@
         </plugins>
     </build>
 
-    <reporting />
-
     <repositories>
         <repository>
             <id>jboss</id>

apache-thrift/pom.xml

@@ -29,7 +29,7 @@
         <dependency>
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-simple</artifactId>
-            <version>${org.slf4j.slf4j-simple.version}</version>
+            <version>${org.slf4j.version}</version>
             <scope>test</scope>
         </dependency>
     </dependencies>
@@ -61,7 +61,6 @@
     <properties>
         <thrift.version>0.10.0</thrift.version>
         <maven-thrift.version>0.1.11</maven-thrift.version>
-        <org.slf4j.slf4j-simple.version>1.7.12</org.slf4j.slf4j-simple.version>
         <build-helper-maven-plugin.version>3.0.0</build-helper-maven-plugin.version>
     </properties>
 

aws/README.md

@@ -6,7 +6,7 @@ This module contains articles about Amazon Web Services (AWS)
 
 - [AWS Lambda Using DynamoDB With Java](https://www.baeldung.com/aws-lambda-dynamodb-java)
 - [AWS S3 with Java](https://www.baeldung.com/aws-s3-java)
-- [AWS Lambda With Java](https://www.baeldung.com/java-aws-lambda)
+- [A Basic AWS Lambda Example With Java](https://www.baeldung.com/java-aws-lambda)
 - [Managing EC2 Instances in Java](https://www.baeldung.com/ec2-java)
 - [Multipart Uploads in Amazon S3 with Java](https://www.baeldung.com/aws-s3-multipart-upload)
 - [Integration Testing with a Local DynamoDB Instance](https://www.baeldung.com/dynamodb-local-integration-tests)

axon/src/main/java/com/baeldung/axon/OrderApplicationConfiguration.java

@@ -0,0 +1,18 @@
+package com.baeldung.axon;
+
+import org.axonframework.eventsourcing.EventCountSnapshotTriggerDefinition;
+import org.axonframework.eventsourcing.SnapshotTriggerDefinition;
+import org.axonframework.eventsourcing.Snapshotter;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class OrderApplicationConfiguration {
+
+    @Bean
+    public SnapshotTriggerDefinition orderAggregateSnapshotTriggerDefinition(Snapshotter snapshotter,
+                                                                             @Value("${axon.aggregate.order.snapshot-threshold:250}") int threshold) {
+        return new EventCountSnapshotTriggerDefinition(snapshotter, threshold);
+    }
+}

axon/src/main/java/com/baeldung/axon/commandmodel/order/OrderAggregate.java

@@ -23,7 +23,7 @@ import java.util.Map;
 
 import static org.axonframework.modelling.command.AggregateLifecycle.apply;
 
-@Aggregate
+@Aggregate(snapshotTriggerDefinition = "orderAggregateSnapshotTriggerDefinition")
 public class OrderAggregate {
 
     @AggregateIdentifier

core-groovy-2/pom.xml

@@ -166,7 +166,6 @@
         <hsqldb.version>2.4.0</hsqldb.version>
         <spock-core.version>1.1-groovy-2.4</spock-core.version>
         <groovy-wslite.version>1.1.3</groovy-wslite.version>
-        <logback.version>1.2.3</logback.version>
         <groovy.version>2.5.7</groovy.version>
         <assembly.plugin.version>3.1.0</assembly.plugin.version>
         <compiler.plugin.version>3.8.0</compiler.plugin.version>

core-java-modules/core-java-11-2/README.md

@@ -8,3 +8,4 @@ This module contains articles about Java 11 core features
 - [Guide to Java 8’s Collectors](https://www.baeldung.com/java-8-collectors)
 - [New Features in Java 11](https://www.baeldung.com/java-11-new-features)
 - [Getting the Java Version at Runtime](https://www.baeldung.com/get-java-version-runtime)
+- [Invoking a SOAP Web Service in Java](https://www.baeldung.com/java-soap-web-service)

core-java-modules/core-java-12/README.md

@@ -2,3 +2,4 @@
 
 - [String API Updates in Java 12](https://www.baeldung.com/java12-string-api)
 - [New Features in Java 12](https://www.baeldung.com/java-12-new-features)
+- [Compare the Content of Two Files in Java](https://www.baeldung.com/java-compare-files)

core-java-modules/core-java-16/README.md

@@ -1,3 +1,7 @@
 ### Relevant articles:
 
 - [Collect a Java Stream to an Immutable Collection](https://www.baeldung.com/java-stream-immutable-collection)
+- [Guide to mapMulti in Stream API](https://www.baeldung.com/java-mapmulti)
+- [Collecting Stream Elements into a List in Java](https://www.baeldung.com/java-stream-to-list-collecting)
+- [New Features in Java 16](https://www.baeldung.com/java-16-new-features)
+- [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)

core-java-modules/core-java-16/pom.xml

@@ -28,6 +28,18 @@
             <artifactId>commons-lang3</artifactId>
             <version>3.12.0</version>
         </dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-engine</artifactId>
+			<version>${junit-jupiter.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-api</artifactId>
+			<version>${junit-jupiter.version}</version>
+			<scope>test</scope>
+		</dependency>
     </dependencies>
 
     <build>
@@ -37,17 +49,38 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>${maven-compiler-plugin.version}</version>
                 <configuration>
+                    <release>${maven.compiler.release}</release>
+					<compilerArgs>--enable-preview</compilerArgs>
                     <source>${maven.compiler.source.version}</source>
                     <target>${maven.compiler.target.version}</target>
                 </configuration>
             </plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>${surefire.plugin.version}</version>
+				<configuration>
+					<argLine>--enable-preview</argLine>
+					<forkCount>1</forkCount>
+				</configuration>
+				<dependencies>
+					<dependency>
+						<groupId>org.apache.maven.surefire</groupId>
+						<artifactId>surefire-api</artifactId>
+						<version>${surefire.plugin.version}</version>
+					</dependency>
+				</dependencies>
+			</plugin>
         </plugins>
     </build>
 
     <properties>
         <maven.compiler.source.version>16</maven.compiler.source.version>
         <maven.compiler.target.version>16</maven.compiler.target.version>
-		<assertj.version>3.6.1</assertj.version>
+		<maven.compiler.release>16</maven.compiler.release>
+		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+		<surefire.plugin.version>3.0.0-M5</surefire.plugin.version>
+		<assertj.version>3.17.2</assertj.version>
     </properties>
 
 </project>

core-java-modules/core-java-16/src/main/java/com/baeldung/features/HelloWorld.java

@@ -0,0 +1,7 @@
+package com.baeldung.features;
+
+interface HelloWorld {
+    default String hello() {
+        return "world";
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/OuterClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.features;
+
+import com.baeldung.features.record.Book;
+
+public class OuterClass {
+    class InnerClass {
+        Book book = new Book("Title", "author", "isbn");
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/VectorExample.java

@@ -0,0 +1,23 @@
+package com.baeldung.features;
+
+import jdk.incubator.vector.IntVector;
+
+public class VectorExample {
+    public int[] scalarComputation(int[] a, int[] b) {
+        var c = new int[a.length];
+        for (int i = 0; i < a.length; i++) {
+            c[i] = a[i] * b[i];
+        }
+        return c;
+    }
+
+    public int[] vectorComputation(int[] a, int[] b) {
+        var c = new int[a.length];
+
+        var vectorA = IntVector.fromArray(IntVector.SPECIES_128, a, 0);
+        var vectorB = IntVector.fromArray(IntVector.SPECIES_128, b, 0);
+        var vectorC = vectorA.mul(vectorB);
+        vectorC.intoArray(c, 0);
+        return c;
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/model/Book.java

@@ -0,0 +1,44 @@
+package com.baeldung.features.model;
+
+import java.util.Objects;
+
+public final class Book {
+    private final String title;
+    private final String author;
+    private final String isbn;
+
+    public Book(String title, String author, String isbn) {
+        this.title = title;
+        this.author = author;
+        this.isbn = isbn;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Book book = (Book) o;
+        return Objects.equals(title, book.title) && Objects.equals(author, book.author) && Objects.equals(isbn, book.isbn);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(title, author, isbn);
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/record/Book.java

@@ -0,0 +1,4 @@
+package com.baeldung.features.record;
+
+public record Book(String title, String author, String isbn) {
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/sealed/JungleAnimal.java

@@ -0,0 +1,4 @@
+package com.baeldung.features.sealed;
+
+public sealed interface JungleAnimal permits Monkey, Snake  {
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/sealed/Monkey.java

@@ -0,0 +1,4 @@
+package com.baeldung.features.sealed;
+
+public final class Monkey implements JungleAnimal {
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/sealed/Sealed.java

@@ -0,0 +1,13 @@
+package com.baeldung.features.sealed;
+
+public class Sealed {
+    public static void main(String... args) {
+        JungleAnimal j = new Monkey();
+
+        if (j instanceof Monkey m) {
+            // do logic
+        } else if (j instanceof Snake s) {
+            // do logic
+        }
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/features/sealed/Snake.java

@@ -0,0 +1,4 @@
+package com.baeldung.features.sealed;
+
+public non-sealed class Snake implements JungleAnimal {
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPost.java

@@ -1,5 +1,8 @@
 package com.baeldung.java_16_features.groupingby;
 
+import java.util.IntSummaryStatistics;
+
+
 public class BlogPost {
     
     private String title;
@@ -7,6 +10,8 @@ public class BlogPost {
     private BlogPostType type;
     private int likes;
     record AuthPostTypesLikes(String author, BlogPostType type, int likes) {};
+    record PostcountTitlesLikesStats(long postCount, String titles, IntSummaryStatistics likesStats){};
+    record TitlesBoundedSumOfLikes(String titles, int boundedSumOfLikes) {};
     
     public BlogPost(String title, String author, BlogPostType type, int likes) {
         this.title = title;

core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/mapmulti/Album.java

@@ -0,0 +1,49 @@
+package com.baeldung.java_16_features.mapmulti;
+
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang3.tuple.ImmutablePair;
+import org.apache.commons.lang3.tuple.Pair;
+
+public class Album {
+
+    private String albumName;
+    private int albumCost;
+    private List<Artist> artists;
+
+    Album(String name, int albumCost, List<Artist> artists) {
+        this.albumName = name;
+        this.artists = artists;
+        this.albumCost = albumCost;
+    }
+
+    public void artistAlbumPairsToMajorLabels(Consumer<Pair<String, String>> consumer) {
+
+        for (Artist artist : artists) {
+            if (artist.isAssociatedMajorLabels()) {
+                String concatLabels = artist.getMajorLabels()
+                    .stream()
+                    .collect(Collectors.joining(","));
+                consumer.accept(new ImmutablePair<>(artist.getName() + ":" + albumName, concatLabels));
+            }
+        }
+    }
+
+    public String getAlbumName() {
+        return albumName;
+    }
+
+    public int getAlbumCost() {
+        return albumCost;
+    }
+
+    List<Artist> getArtists() {
+        return artists;
+    }
+
+    public String toString() {
+        return albumName;
+    }
+}

core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/mapmulti/Artist.java

@@ -0,0 +1,50 @@
+package com.baeldung.java_16_features.mapmulti;
+
+import java.util.List;
+import java.util.Objects;
+
+public class Artist {
+
+    private final String name;
+    private boolean associatedMajorLabels;
+    private List<String> majorLabels;
+
+    Artist(String name, boolean associatedMajorLabels, List<String> majorLabels) {
+        this.name = name;
+        this.associatedMajorLabels = associatedMajorLabels;
+        this.majorLabels = majorLabels;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public boolean isAssociatedMajorLabels() {
+        return associatedMajorLabels;
+    }
+
+    public List<String> getMajorLabels() {
+        return majorLabels;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(name);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Artist other = (Artist) obj;
+        return Objects.equals(name, other.name);
+    }
+
+    public String toString() {
+        return name;
+    }
+}

core-java-modules/core-java-16/src/main/java/module-info.java

@@ -0,0 +1,4 @@
+module core.java {
+    requires jdk.incubator.vector;
+    requires org.apache.commons.lang3;
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/features/DayPeriodSupportUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalTime;
+import java.time.format.DateTimeFormatter;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DayPeriodSupportUnitTest {
+
+    @Test
+    public void givenASpecificTime_whenFormattingUsingTheBSymbol_thenExpectVerbosePeriodOfDay() {
+        LocalTime date = LocalTime.parse("15:25:08.690791");
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("h B");
+        assertThat(date.format(formatter)).isEqualTo("3 in the afternoon");
+
+        formatter = DateTimeFormatter.ofPattern("h BBBB");
+        assertThat(date.format(formatter)).isEqualTo("3 in the afternoon");
+
+        formatter = DateTimeFormatter.ofPattern("h BBBBB");
+        assertThat(date.format(formatter)).isEqualTo("3 in the afternoon");
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/features/HelloWorldUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.features;
+
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+
+import static java.lang.ClassLoader.getSystemClassLoader;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class HelloWorldUnitTest {
+
+    @Test
+    public void givenAnInterfaceWithDefaulMethod_whenCreatingProxyInstance_thenCanInvokeDefaultMethod() throws Exception {
+        Object proxy = Proxy.newProxyInstance(getSystemClassLoader(), new Class<?>[] { HelloWorld.class },
+            (prox, method, args) -> {
+                if (method.isDefault()) {
+                    return InvocationHandler.invokeDefault(prox, method, args);
+                }
+                return method.invoke(prox, args);
+            }
+        );
+        Method method = proxy.getClass().getMethod("hello");
+        assertThat(method.invoke(proxy)).isEqualTo("world");
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/features/InstanceOfPatternMatchingUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class InstanceOfPatternMatchingUnitTest {
+
+    @Test
+    void givenTheNewPatternMatchingAbility_whenComparingAgainstTheTradiationalApproach_thenBothVariablesAreEqual() {
+        Object obj = "TEST";
+
+        if (obj instanceof String a) {
+            String b = (String) obj;
+            assertThat(a).isEqualTo(b);
+        }
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/features/StreamToListUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StreamToListUnitTest {
+
+    @Test
+    void givenAStream_whenCreatingANewListFromStream_thenCollectorsOrInbuiltFunctionAreEquivalent() {
+        List<String> integersAsString = Arrays.asList("1", "2", "3");
+        List<Integer> ints = integersAsString.stream().map(Integer::parseInt).collect(Collectors.toList());
+        List<Integer> intsEquivalent = integersAsString.stream().map(Integer::parseInt).toList();
+        assertThat(ints).isEqualTo(intsEquivalent);
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/features/VectorExampleUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+class VectorExampleUnitTest {
+
+    @Test
+    void givenAScalarComputation_whenCalculatingUsingVectorAPI_thenResultIsSameAsPreviousMethodOfComputation() {
+        VectorExample objectUnderTest = new VectorExample();
+
+        int[] a = {1, 2, 3, 4};
+        int[] b = {5, 6, 7, 8};
+
+        int[] result = objectUnderTest.scalarComputation(a, b);
+        int[] result2 = objectUnderTest.vectorComputation(a, b);
+
+        assertArrayEquals(result, result2);
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/java_16_features/groupingby/JavaGroupingByCollectorUnitTest.java

@@ -5,6 +5,8 @@ import static java.util.stream.Collectors.averagingInt;
 import static java.util.stream.Collectors.counting;
 import static java.util.stream.Collectors.groupingBy;
 import static java.util.stream.Collectors.groupingByConcurrent;
+import static java.util.stream.Collectors.collectingAndThen;
+import static java.util.stream.Collectors.toMap;
 import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.mapping;
 import static java.util.stream.Collectors.maxBy;
@@ -13,6 +15,7 @@ import static java.util.stream.Collectors.summingInt;
 import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toSet;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.offset;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -251,4 +254,49 @@ public class JavaGroupingByCollectorUnitTest {
         assertThat(blogPost.getLikes()).isEqualTo(20);
     }
 
+    @Test
+    public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingCollectingAndThen() {
+
+        Map<String, BlogPost.PostcountTitlesLikesStats> postsPerAuthor = posts.stream()
+            .collect(groupingBy(BlogPost::getAuthor, collectingAndThen(toList(), list -> {
+                long count = list.stream()
+                    .map(BlogPost::getTitle)
+                    .collect(counting());
+                String titles = list.stream()
+                    .map(BlogPost::getTitle)
+                    .collect(joining(" : "));
+                IntSummaryStatistics summary = list.stream()
+                    .collect(summarizingInt(BlogPost::getLikes));
+                return new BlogPost.PostcountTitlesLikesStats(count, titles, summary);
+            })));
+
+        BlogPost.PostcountTitlesLikesStats result = postsPerAuthor.get("Author 1");
+        assertThat(result.postCount()).isEqualTo(3L);
+        assertThat(result.titles()).isEqualTo("News item 1 : Programming guide : Tech review 2");
+        assertThat(result.likesStats().getMax()).isEqualTo(20);
+        assertThat(result.likesStats().getMin()).isEqualTo(15);
+        assertThat(result.likesStats().getAverage()).isEqualTo(16.666d, offset(0.001d));
+    }
+
+    @Test
+    public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingToMap() {
+
+        int maxValLikes = 17;
+        Map<String, BlogPost.TitlesBoundedSumOfLikes> postsPerAuthor = posts.stream()
+            .collect(toMap(BlogPost::getAuthor, post -> {
+                int likes = (post.getLikes() > maxValLikes) ? maxValLikes : post.getLikes();
+                return new BlogPost.TitlesBoundedSumOfLikes(post.getTitle(), likes);
+            }, (u1, u2) -> {
+                int likes = (u2.boundedSumOfLikes() > maxValLikes) ? maxValLikes : u2.boundedSumOfLikes();
+                return new BlogPost.TitlesBoundedSumOfLikes(u1.titles()
+                    .toUpperCase() + " : "
+                    + u2.titles()
+                        .toUpperCase(),
+                    u1.boundedSumOfLikes() + likes);
+            }));
+        
+        BlogPost.TitlesBoundedSumOfLikes result = postsPerAuthor.get("Author 1");
+        assertThat(result.titles()).isEqualTo("NEWS ITEM 1 : PROGRAMMING GUIDE : TECH REVIEW 2");
+        assertThat(result.boundedSumOfLikes()).isEqualTo(47);
+    }
 }

core-java-modules/core-java-16/src/test/java/com/baeldung/java_16_features/mapmulti/JavaStreamMapMultiUnitTest.java

@@ -0,0 +1,134 @@
+package com.baeldung.java_16_features.mapmulti;
+
+import static java.util.stream.Collectors.toList;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.offset;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.commons.lang3.tuple.ImmutablePair;
+import org.apache.commons.lang3.tuple.Pair;
+import org.junit.jupiter.api.Test;
+
+public class JavaStreamMapMultiUnitTest {
+
+    private static final List<Album> albums = Arrays.asList(new Album("album1", 10, Arrays.asList(new Artist("bob", true, Arrays.asList("label1", "label3")), new Artist("tom", true, Arrays.asList("label2", "label3")))),
+        new Album("album2", 20, Arrays.asList(new Artist("bill", true, Arrays.asList("label2", "label3")), new Artist("tom", true, Arrays.asList("label2", "label4")))));
+
+    @Test
+    public void givenAListOfintegers_whenMapMulti_thenGetListOfOfEvenDoublesPlusPercentage() {
+
+        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
+        double percentage = .01;
+        List<Double> evenDoubles = integers.stream()
+            .<Double> mapMulti((integer, consumer) -> {
+                if (integer % 2 == 0) {
+                    consumer.accept((double) integer * (1 + percentage));
+                }
+            })
+            .collect(toList());
+
+        assertThat(evenDoubles).containsAll(Arrays.asList(2.02D, 4.04D));
+    }
+
+    @Test
+    public void givenAListOfintegers_whenFilterMap_thenGetListOfOfEvenDoublesPlusPercentage() {
+
+        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
+        double percentage = .01;
+        List<Double> evenDoubles = integers.stream()
+            .filter(integer -> integer % 2 == 0)
+            .<Double> map(integer -> ((double) integer * (1 + percentage)))
+            .collect(toList());
+
+        assertThat(evenDoubles).containsAll(Arrays.asList(2.02D, 4.04D));
+    }
+
+    @Test
+    public void givenAListOfintegers_whenMapMultiToDouble_thenGetSumOfEvenNumbersAfterApplyPercentage() {
+
+        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5, 6, 7);
+        double percentage = .01;
+        double sum = integers.stream()
+            .mapMultiToDouble((integer, consumer) -> {
+                if (integer % 2 == 0) {
+                    consumer.accept(integer * (1 + percentage));
+                }
+            })
+            .sum();
+
+        assertThat(sum).isEqualTo(12.12, offset(0.001d));
+    }
+
+    @Test
+    public void givenAListOfAlbums_whenFlatMap_thenGetListOfArtistAlbumPairs() {
+
+        List<Pair<String, String>> artistAlbum = albums.stream()
+            .flatMap(album -> album.getArtists()
+                .stream()
+                .map(artist -> new ImmutablePair<String, String>(artist.getName(), album.getAlbumName())))
+            .collect(toList());
+
+        assertThat(artistAlbum).contains(new ImmutablePair<String, String>("bob", "album1"), new ImmutablePair<String, 
+            String>("tom", "album1"), new ImmutablePair<String, String>("bill", "album2"), new ImmutablePair<String, String>("tom", "album2"));
+    }
+
+    @Test
+    public void givenAListOfAlbums_whenMapMulti_thenGetListOfPairsOfArtistAlbum() {
+
+        List<Pair<String, String>> artistAlbum = albums.stream()
+            .<Pair<String, String>> mapMulti((album, consumer) -> {
+                for (Artist artist : album.getArtists()) {
+                    consumer.accept(new ImmutablePair<String, String>(artist.getName(), album.getAlbumName()));
+                }
+            })
+            .collect(toList());
+
+        assertThat(artistAlbum).contains(new ImmutablePair<String, String>("bob", "album1"), new ImmutablePair<String, String>("tom", "album1"), 
+            new ImmutablePair<String, String>("bill", "album2"), new ImmutablePair<String, String>("tom", "album2"));
+    }
+
+    @Test
+    public void givenAListOfAlbums_whenFlatMap_thenGetListOfArtistAlbumjPairsBelowGivenCost() {
+
+        int upperCost = 9;
+        List<Pair<String, String>> artistAlbum = albums.stream()
+            .flatMap(album -> album.getArtists()
+                .stream()
+                .filter(artist -> upperCost > album.getAlbumCost())
+                .map(artist -> new ImmutablePair<String, String>(artist.getName(), album.getAlbumName())))
+            .collect(toList());
+
+        assertTrue(artistAlbum.isEmpty());
+    }
+
+    @Test
+    public void givenAListOfAlbums_whenMapMulti_thenGetListOfArtistAlbumPairsBelowGivenCost() {
+
+        int upperCost = 9;
+        List<Pair<String, String>> artistAlbum = albums.stream()
+            .<Pair<String, String>> mapMulti((album, consumer) -> {
+                if (album.getAlbumCost() < upperCost) {
+                    for (Artist artist : album.getArtists()) {
+                        consumer.accept(new ImmutablePair<String, String>(artist.getName(), album.getAlbumName()));
+                    }
+                }
+            })
+            .collect(toList());
+
+        assertTrue(artistAlbum.isEmpty());
+    }
+
+    @Test
+    public void givenAListOfAlbums_whenMapMulti_thenGetPairsOfArtistMajorLabelsUsingMethodReference() {
+
+        List<Pair<String, String>> artistLabels = albums.stream()
+            .mapMulti(Album::artistAlbumPairsToMajorLabels)
+            .collect(toList());
+
+        assertThat(artistLabels).contains(new ImmutablePair<String, String>("bob:album1", "label1,label3"), new ImmutablePair<String, String>("tom:album1", "label2,label3"), 
+            new ImmutablePair<String, String>("bill:album2", "label2,label3"), new ImmutablePair<String, String>("tom:album2", "label2,label4"));
+    }
+}

core-java-modules/core-java-16/src/test/java/com/baeldung/streams/StreamToListComparisonWithCollectorsToListUnitTest.java

@@ -0,0 +1,128 @@
+package com.baeldung.streams;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class StreamToListComparisonWithCollectorsToListUnitTest {
+
+    @Test
+    public void whenAddingtoCollectToList_thenSuccess() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toList());
+
+        Assertions.assertDoesNotThrow(() -> {
+            result.add("test");
+        });
+    }
+
+    @Test
+    public void whenSortingtoCollectToList_thenSuccess() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toList());
+
+        Assertions.assertDoesNotThrow(() -> {
+            result.sort(String::compareToIgnoreCase);
+        });
+    }
+
+    @Test
+    public void whenAddingCollectUnmodifiableToList_thenException() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toUnmodifiableList());
+
+        Assertions.assertThrows(UnsupportedOperationException.class, () -> {
+            result.add("test");
+        });
+    }
+
+    @Test
+    public void whenSortingCollectUnmodifiableToList_thenSortException() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toUnmodifiableList());
+
+        Assertions.assertThrows(UnsupportedOperationException.class, () -> {
+            result.sort(String::compareToIgnoreCase);
+        });
+    }
+
+    @Test
+    public void whenAddingStreamToList_thenException() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .toList();
+
+        Assertions.assertThrows(UnsupportedOperationException.class, () -> {
+            result.add("test");
+        });
+    }
+
+    @Test
+    public void whenSortingStreamToList_thenException() {
+
+        List<String> result = Stream.of(Locale.getISOCountries())
+          .toList();
+
+        Assertions.assertThrows(UnsupportedOperationException.class, () -> {
+            result.sort(String::compareToIgnoreCase);
+        });
+    }
+
+    @Test
+    public void whenComparingStreamToList_withCollectToList_thenEqual() {
+
+        List<String> streamToList = Stream.of(Locale.getISOCountries())
+          .toList();
+        List<String> collectToList = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toList());
+
+        Assertions.assertEquals(streamToList, collectToList);
+    }
+
+    @Test
+    public void whenComparingStreamToList_withUnmodifiedCollectToList_thenEqual() {
+
+        List<String> streamToList = Stream.of(Locale.getISOCountries())
+          .toList();
+        List<String> collectToUnmodifiableList = Stream.of(Locale.getISOCountries())
+          .collect(Collectors.toUnmodifiableList());
+
+        Assertions.assertEquals(streamToList, collectToUnmodifiableList);
+    }
+
+    @Test
+    public void whenNullCollectorsToList_thenSuccess() {
+
+        Assertions.assertDoesNotThrow(() -> {
+            Stream.of(null, null)
+              .collect(Collectors.toList());
+        });
+    }
+
+    @Test
+    public void whenNullCollectorsUnmodifiableToList_thenException() {
+
+        Assertions.assertThrows(NullPointerException.class, () -> {
+            Stream.of(null, null)
+              .collect(Collectors.toUnmodifiableList());
+        });
+    }
+
+    @Test
+    public void whenNullStreamToList_thenSuccess() {
+
+        Assertions.assertDoesNotThrow(() -> {
+            Stream.of(null, null)
+              .toList();
+        });
+    }
+
+}

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

@@ -4,7 +4,6 @@ This module contains articles about Java 8 core features
 
 ### Relevant Articles: 
 - [New Features in Java 8](https://www.baeldung.com/java-8-new-features)
-- [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)
 - [Strategy Design Pattern in Java 8](https://www.baeldung.com/java-strategy-pattern)
 - [Guide to Java 8 Comparator.comparing()](https://www.baeldung.com/java-8-comparator-comparing)
 - [Guide to the Java 8 forEach](https://www.baeldung.com/foreach-java)

core-java-modules/core-java-8/src/main/java/com/baeldung/java_8_features/groupingby/BlogPost.java

@@ -1,36 +0,0 @@
-package com.baeldung.java_8_features.groupingby;
-
-public class BlogPost {
-    private String title;
-    private String author;
-    private BlogPostType type;
-    private int likes;
-
-    public BlogPost(String title, String author, BlogPostType type, int likes) {
-        this.title = title;
-        this.author = author;
-        this.type = type;
-        this.likes = likes;
-    }
-
-    public String getTitle() {
-        return title;
-    }
-
-    public String getAuthor() {
-        return author;
-    }
-
-    public BlogPostType getType() {
-        return type;
-    }
-
-    public int getLikes() {
-        return likes;
-    }
-
-    @Override
-    public String toString() {
-        return "BlogPost{" + "title='" + title + '\'' + ", type=" + type + ", likes=" + likes + '}';
-    }
-}

core-java-modules/core-java-8/src/main/java/com/baeldung/java_8_features/groupingby/BlogPostType.java

@@ -1,5 +0,0 @@
-package com.baeldung.java_8_features.groupingby;
-
-public enum BlogPostType {
-    NEWS, REVIEW, GUIDE
-}

core-java-modules/core-java-8/src/main/java/com/baeldung/java_8_features/groupingby/Tuple.java

@@ -1,41 +0,0 @@
-package com.baeldung.java_8_features.groupingby;
-
-import java.util.Objects;
-
-public class Tuple {
-    private final BlogPostType type;
-    private final String author;
-
-    public Tuple(BlogPostType type, String author) {
-        this.type = type;
-        this.author = author;
-    }
-
-    public BlogPostType getType() {
-        return type;
-    }
-
-    public String getAuthor() {
-        return author;
-    }
-
-    @Override
-    public boolean equals(Object o) {
-        if (this == o)
-            return true;
-        if (o == null || getClass() != o.getClass())
-            return false;
-        Tuple tuple = (Tuple) o;
-        return type == tuple.type && author.equals(tuple.author);
-    }
-
-    @Override
-    public int hashCode() {
-        return Objects.hash(type, author);
-    }
-
-    @Override
-    public String toString() {
-        return "Tuple{" + "type=" + type + ", author='" + author + '\'' + '}';
-    }
-}

core-java-modules/core-java-8/src/test/java/com/baeldung/java_8_features/groupingby/Java8GroupingByCollectorUnitTest.java

@@ -1,215 +0,0 @@
-package com.baeldung.java_8_features.groupingby;
-
-import static java.util.Comparator.comparingInt;
-import static java.util.stream.Collectors.averagingInt;
-import static java.util.stream.Collectors.counting;
-import static java.util.stream.Collectors.groupingBy;
-import static java.util.stream.Collectors.groupingByConcurrent;
-import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.mapping;
-import static java.util.stream.Collectors.maxBy;
-import static java.util.stream.Collectors.summarizingInt;
-import static java.util.stream.Collectors.summingInt;
-import static java.util.stream.Collectors.toList;
-import static java.util.stream.Collectors.toSet;
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
-
-import java.util.Arrays;
-import java.util.EnumMap;
-import java.util.IntSummaryStatistics;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
-import java.util.Set;
-import java.util.concurrent.ConcurrentMap;
-
-import org.junit.Test;
-
-public class Java8GroupingByCollectorUnitTest {
-
-    private static final List<BlogPost> posts = Arrays.asList(new BlogPost("News item 1", "Author 1", BlogPostType.NEWS, 15), new BlogPost("Tech review 1", "Author 2", BlogPostType.REVIEW, 5),
-        new BlogPost("Programming guide", "Author 1", BlogPostType.GUIDE, 20), new BlogPost("News item 2", "Author 2", BlogPostType.NEWS, 35), new BlogPost("Tech review 2", "Author 1", BlogPostType.REVIEW, 15));
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByType_thenGetAMapBetweenTypeAndPosts() {
-        Map<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType));
-
-        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
-            .size());
-        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
-            .size());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndTheirTitlesAreJoinedInAString_thenGetAMapBetweenTypeAndCsvTitles() {
-        Map<BlogPostType, String> postsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
-
-        assertEquals("Post titles: [News item 1, News item 2]", postsPerType.get(BlogPostType.NEWS));
-        assertEquals("Post titles: [Programming guide]", postsPerType.get(BlogPostType.GUIDE));
-        assertEquals("Post titles: [Tech review 1, Tech review 2]", postsPerType.get(BlogPostType.REVIEW));
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndSumTheLikes_thenGetAMapBetweenTypeAndPostLikes() {
-        Map<BlogPostType, Integer> likesPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
-
-        assertEquals(50, likesPerType.get(BlogPostType.NEWS)
-            .intValue());
-        assertEquals(20, likesPerType.get(BlogPostType.REVIEW)
-            .intValue());
-        assertEquals(20, likesPerType.get(BlogPostType.GUIDE)
-            .intValue());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeInAnEnumMap_thenGetAnEnumMapBetweenTypeAndPosts() {
-        EnumMap<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
-
-        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
-            .size());
-        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
-            .size());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeInSets_thenGetAMapBetweenTypesAndSetsOfPosts() {
-        Map<BlogPostType, Set<BlogPost>> postsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, toSet()));
-
-        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
-            .size());
-        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
-            .size());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeConcurrently_thenGetAMapBetweenTypeAndPosts() {
-        ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = posts.parallelStream()
-            .collect(groupingByConcurrent(BlogPost::getType));
-
-        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
-            .size());
-        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
-            .size());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndAveragingLikes_thenGetAMapBetweenTypeAndAverageNumberOfLikes() {
-        Map<BlogPostType, Double> averageLikesPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
-
-        assertEquals(25, averageLikesPerType.get(BlogPostType.NEWS)
-            .intValue());
-        assertEquals(20, averageLikesPerType.get(BlogPostType.GUIDE)
-            .intValue());
-        assertEquals(10, averageLikesPerType.get(BlogPostType.REVIEW)
-            .intValue());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndCounted_thenGetAMapBetweenTypeAndNumberOfPosts() {
-        Map<BlogPostType, Long> numberOfPostsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, counting()));
-
-        assertEquals(2, numberOfPostsPerType.get(BlogPostType.NEWS)
-            .intValue());
-        assertEquals(1, numberOfPostsPerType.get(BlogPostType.GUIDE)
-            .intValue());
-        assertEquals(2, numberOfPostsPerType.get(BlogPostType.REVIEW)
-            .intValue());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndMaxingLikes_thenGetAMapBetweenTypeAndMaximumNumberOfLikes() {
-        Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
-
-        assertTrue(maxLikesPerPostType.get(BlogPostType.NEWS)
-            .isPresent());
-        assertEquals(35, maxLikesPerPostType.get(BlogPostType.NEWS)
-            .get()
-            .getLikes());
-
-        assertTrue(maxLikesPerPostType.get(BlogPostType.GUIDE)
-            .isPresent());
-        assertEquals(20, maxLikesPerPostType.get(BlogPostType.GUIDE)
-            .get()
-            .getLikes());
-
-        assertTrue(maxLikesPerPostType.get(BlogPostType.REVIEW)
-            .isPresent());
-        assertEquals(15, maxLikesPerPostType.get(BlogPostType.REVIEW)
-            .get()
-            .getLikes());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByAuthorAndThenByType_thenGetAMapBetweenAuthorAndMapsBetweenTypeAndBlogPosts() {
-        Map<String, Map<BlogPostType, List<BlogPost>>> map = posts.stream()
-            .collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
-
-        assertEquals(1, map.get("Author 1")
-            .get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, map.get("Author 1")
-            .get(BlogPostType.GUIDE)
-            .size());
-        assertEquals(1, map.get("Author 1")
-            .get(BlogPostType.REVIEW)
-            .size());
-
-        assertEquals(1, map.get("Author 2")
-            .get(BlogPostType.NEWS)
-            .size());
-        assertEquals(1, map.get("Author 2")
-            .get(BlogPostType.REVIEW)
-            .size());
-        assertNull(map.get("Author 2")
-            .get(BlogPostType.GUIDE));
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByTypeAndSummarizingLikes_thenGetAMapBetweenTypeAndSummary() {
-        Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = posts.stream()
-            .collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
-
-        IntSummaryStatistics newsLikeStatistics = likeStatisticsPerType.get(BlogPostType.NEWS);
-
-        assertEquals(2, newsLikeStatistics.getCount());
-        assertEquals(50, newsLikeStatistics.getSum());
-        assertEquals(25.0, newsLikeStatistics.getAverage(), 0.001);
-        assertEquals(35, newsLikeStatistics.getMax());
-        assertEquals(15, newsLikeStatistics.getMin());
-    }
-
-    @Test
-    public void givenAListOfPosts_whenGroupedByComplexMapKeyType_thenGetAMapBetweenTupleAndList() {
-        Map<Tuple, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
-            .collect(groupingBy(post -> new Tuple(post.getType(), post.getAuthor())));
-
-        List<BlogPost> result = postsPerTypeAndAuthor.get(new Tuple(BlogPostType.GUIDE, "Author 1"));
-
-        assertThat(result.size()).isEqualTo(1);
-
-        BlogPost blogPost = result.get(0);
-
-        assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
-        assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
-        assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
-    }
-}

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

@@ -10,3 +10,4 @@ This module contains articles about advanced operations on arrays in Java. They
 - [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
 - [Comparing Arrays in Java](https://www.baeldung.com/java-comparing-arrays)
 - [Concatenate Two Arrays in Java](https://www.baeldung.com/java-concatenate-arrays)
+- [Performance of System.arraycopy() vs. Arrays.copyOf()](https://www.baeldung.com/java-system-arraycopy-arrays-copyof-performance)

core-java-modules/core-java-arrays-operations-advanced/pom.xml

@@ -26,10 +26,50 @@
             <version>${assertj-core.version}</version>
             <scope>test</scope>
         </dependency>
+
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>
         <assertj-core.version>3.10.0</assertj-core.version>
+        <jmh.version>1.33</jmh.version>
     </properties>
 
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <configuration>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <archive>
+                        <manifest>
+                            <mainClass>com.baeldung.copyarraymethodsperformance.BenchmarkRunner</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
 </project>

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/copyarraymethodsperformance/BenchmarkRunner.java

@@ -0,0 +1,11 @@
+package com.baeldung.copyarraymethodsperformance;
+
+public class BenchmarkRunner {
+
+    public static void main(String[] args) throws Exception {
+
+        org.openjdk.jmh.Main.main(args);
+
+    }
+
+}

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/copyarraymethodsperformance/ObjectsCopyBenchmark.java

@@ -0,0 +1,42 @@
+package com.baeldung.copyarraymethodsperformance;
+
+import org.openjdk.jmh.annotations.*;
+
+import java.util.Arrays;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@State(Scope.Thread)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 10)
+@Fork(1)
+@Measurement(iterations = 100)
+public class ObjectsCopyBenchmark {
+
+    @Param({ "10", "1000000" })
+    public int SIZE;
+    Integer[] src;
+
+    @Setup
+    public void setup() {
+        Random r = new Random();
+        src = new Integer[SIZE];
+
+        for (int i = 0; i < SIZE; i++) {
+            src[i] = r.nextInt();
+        }
+    }
+
+    @Benchmark
+    public Integer[] systemArrayCopyBenchmark() {
+        Integer[] target = new Integer[SIZE];
+        System.arraycopy(src, 0, target, 0, SIZE);
+        return target;
+    }
+
+    @Benchmark
+    public Integer[] arraysCopyOfBenchmark() {
+        return Arrays.copyOf(src, SIZE);
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/copyarraymethodsperformance/PrimitivesCopyBenchmark.java

@@ -0,0 +1,43 @@
+package com.baeldung.copyarraymethodsperformance;
+
+import org.openjdk.jmh.annotations.*;
+
+import java.util.Arrays;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@State(Scope.Thread)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 10)
+@Fork(1)
+@Measurement(iterations = 100)
+public class PrimitivesCopyBenchmark {
+
+    @Param({ "10", "1000000" })
+    public int SIZE;
+
+    int[] src;
+
+    @Setup
+    public void setup() {
+        Random r = new Random();
+        src = new int[SIZE];
+
+        for (int i = 0; i < SIZE; i++) {
+            src[i] = r.nextInt();
+        }
+    }
+
+    @Benchmark
+    public int[] systemArrayCopyBenchmark() {
+        int[] target = new int[SIZE];
+        System.arraycopy(src, 0, target, 0, SIZE);
+        return target;
+    }
+
+    @Benchmark
+    public int[] arraysCopyOfBenchmark() {
+        return Arrays.copyOf(src, SIZE);
+    }
+}

core-java-modules/core-java-arrays-sorting/pom.xml

@@ -78,4 +78,5 @@
         <guava.version>28.2-jre</guava.version>
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
+
 </project>

core-java-modules/core-java-collections-maps-3/README.md

@@ -8,5 +8,5 @@ This module contains articles about Map data structures in Java.
 - [The Map.computeIfAbsent() Method](https://www.baeldung.com/java-map-computeifabsent)
 - [Collections.synchronizedMap vs. ConcurrentHashMap](https://www.baeldung.com/java-synchronizedmap-vs-concurrenthashmap)
 - [Java HashMap Load Factor](https://www.baeldung.com/java-hashmap-load-factor)
-- [Converting java.util.Properties to HashMap](https://www.baeldung.com/java-convert-properties-to-hashmap)
+- [Converting Java Properties to HashMap](https://www.baeldung.com/java-convert-properties-to-hashmap)
 - More articles: [[<-- prev]](/core-java-modules/core-java-collections-maps-2)

core-java-modules/core-java-collections-maps-4/README.md

@@ -0,0 +1,6 @@
+## Java Collections Cookbooks and Examples
+
+This module contains articles about Map data structures in Java.
+
+### Relevant Articles: 
+- [Using a Custom Class as a Key in a Java HashMap](https://www.baeldung.com/custom-key-hashmap)

core-java-modules/core-java-collections-maps-4/pom.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-collections-maps-4</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-collections-maps-4</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-surefire-plugin</artifactId>
+                    <version>3.0.0-M5</version>
+                    <configuration>
+                        <!-- those tests are not made for CI purposes, but for manual testing -->
+                        <groups>!performance</groups>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+
+</project>

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/maps/CoordinateKey.java

@@ -0,0 +1,39 @@
+package com.baeldung.maps;
+
+import java.util.Objects;
+
+public class CoordinateKey {
+
+    private final int x;
+    private final int y;
+    private final int hashCode;
+
+    public CoordinateKey(int x, int y) {
+        this.x = x;
+        this.y = y;
+        this.hashCode = Objects.hash(x, y);
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        CoordinateKey that = (CoordinateKey) o;
+        return x == that.x && y == that.y;
+    }
+
+    @Override
+    public int hashCode() {
+        return this.hashCode;
+    }
+}

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/maps/CoordinateMutableKey.java

@@ -0,0 +1,45 @@
+package com.baeldung.maps;
+
+import java.util.Objects;
+
+public class CoordinateMutableKey {
+
+    private int x;
+    private int y;
+
+    public CoordinateMutableKey(int x, int y) {
+        this.x = x;
+        this.y = y;
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    public void setY(int y) {
+        this.y = y;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        CoordinateMutableKey that = (CoordinateMutableKey) o;
+        return x == that.x && y == that.y;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(x, y);
+    }
+}

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/maps/CoordinateSlowKey.java

@@ -0,0 +1,13 @@
+package com.baeldung.maps;
+
+public class CoordinateSlowKey extends CoordinateKey {
+
+    public CoordinateSlowKey(int x, int y) {
+        super(x, y);
+    }
+
+    @Override
+    public int hashCode() {
+        return 1;
+    }
+}

core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/maps/CoordinateKeyUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.maps;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+import java.awt.*;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+public class CoordinateKeyUnitTest {
+
+    private Map<CoordinateKey, Color> pixels = new HashMap<>();
+
+    @Test
+    void testOptimalKey() {
+        // setup
+        CoordinateKey coord = new CoordinateKey(1, 2);
+        pixels.put(coord, Color.CYAN);
+        // read out color correctly
+        assertEquals(Color.CYAN, pixels.get(coord));
+    }
+
+    @Test
+    void testSlowKey() {
+        // setup
+        CoordinateKey coord = new CoordinateSlowKey(1, 2);
+        pixels.put(coord, Color.CYAN);
+        // read out color correctly
+        assertEquals(Color.CYAN, pixels.get(coord));
+    }
+
+    // Performance Test Parameters - change here
+    private static final int MAX_X = 100;
+    private static final int MAX_Y = 100;
+    private static final int COUNT_OF_QUERIES = 1000;
+    private static final int QUERY_X = 1;
+    private static final int QUERY_Y = 1;
+
+    @Tag("performance")
+    @Test
+    void testKeyPerformance() {
+        // generate some sample keys and values
+        for (int x = 0; x < MAX_X; x++) {
+            for (int y = 0; y < MAX_Y; y++) {
+                pixels.put(new CoordinateKey(x, y), new Color(x % 255, y % 255, (x + y) % 255));
+            }
+        }
+        // read out multiple times and measure time
+        CoordinateKey coord = new CoordinateKey(QUERY_X, QUERY_Y);
+        long t1 = System.currentTimeMillis();
+        for (int i = 0; i < COUNT_OF_QUERIES; i++) {
+            assertNotNull(pixels.get(coord));
+        }
+        long t2 = System.currentTimeMillis();
+        System.out.printf("Optimal key performance: %d ms%n", t2 - t1);
+    }
+
+    @Tag("performance")
+    @Test
+    void testSlowKeyPerformance() {
+        // generate some sample keys and values
+        for (int x = 0; x < MAX_X; x++) {
+            for (int y = 0; y < MAX_Y; y++) {
+                pixels.put(new CoordinateSlowKey(x, y), new Color(x % 255, y % 255, (x + y) % 255));
+            }
+        }
+        // read out multiple times and measure time
+        CoordinateKey coord = new CoordinateSlowKey(QUERY_X, QUERY_Y);
+        long t1 = System.currentTimeMillis();
+        for (int i = 0; i < COUNT_OF_QUERIES; i++) {
+            assertNotNull(pixels.get(coord));
+        }
+        long t2 = System.currentTimeMillis();
+        System.out.printf("Slow key performance: %d ms%n", t2 - t1);
+    }
+
+}

core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/maps/CoordinateMutableKeyUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.maps;
+
+import org.junit.jupiter.api.Test;
+
+import java.awt.*;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+public class CoordinateMutableKeyUnitTest {
+
+    @Test
+    void testKeyMutable() {
+        // setup
+        Map<CoordinateMutableKey, Color> pixels = new HashMap<>();
+        CoordinateMutableKey coord = new CoordinateMutableKey(1, 2);
+        pixels.put(coord, Color.CYAN);
+        // read out color correctly
+        assertEquals(Color.CYAN, pixels.get(coord));
+        // change key's hashcode should result in null value
+        coord.setX(10);
+        assertNull(pixels.get(coord));
+    }
+
+}

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

@@ -3,6 +3,6 @@
 ### Relevant Articles:
 
 - [Read and Write User Input in Java](http://www.baeldung.com/java-console-input-output)
-- [Formatting with printf() in Java](https://www.baeldung.com/java-printstream-printf)
+- [Formatting Output with printf() in Java](https://www.baeldung.com/java-printstream-printf)
 - [ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)
 - [System.console() vs. System.out](https://www.baeldung.com/java-system-console-vs-system-out)

core-java-modules/core-java-date-operations-1/pom.xml

@@ -26,7 +26,6 @@
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
         </dependency>
-
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>

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

@@ -11,3 +11,4 @@ This module contains articles about parsing and formatting Java date and time ob
 - [Display All Time Zones With GMT And UTC in Java](http://www.baeldung.com/java-time-zones)
 - [Convert between String and Timestamp](https://www.baeldung.com/java-string-to-timestamp)
 - [Convert String to Date in Java](http://www.baeldung.com/java-string-to-date)
+- [Format a Milliseconds Duration to HH:MM:SS](https://www.baeldung.com/java-ms-to-hhmmss)

core-java-modules/core-java-datetime-string/pom.xml

@@ -75,7 +75,7 @@
 
     <properties>
         <commons-validator.version>1.6</commons-validator.version>
-        <joda-time.version>2.10</joda-time.version>
+        <joda-time.version>2.10.10</joda-time.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
         <maven.compiler.source>1.9</maven.compiler.source>

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/formatduration/FormatDurationUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.formatduration;
+
+import org.apache.commons.lang3.time.DurationFormatUtils;
+import org.joda.time.Period;
+import org.junit.Test;
+
+import java.time.Duration;
+import java.util.concurrent.TimeUnit;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class FormatDurationUnitTest {
+
+
+    @Test
+    public void givenInterval_WhenFormatInterval_formatDuration() {
+        long HH = TimeUnit.MILLISECONDS.toHours(38114000);
+        long MM = TimeUnit.MILLISECONDS.toMinutes(38114000) % 60;
+        long SS = TimeUnit.MILLISECONDS.toSeconds(38114000) % 60;
+        String timeInHHMMSS = String.format("%02d:%02d:%02d", HH, MM, SS);
+
+        assertThat(timeInHHMMSS).isEqualTo("10:35:14");
+    }
+
+    @Test
+    public void givenInterval_WhenFormatUsingDuration_formatDuration() {
+        Duration duration = Duration.ofMillis(38114000);
+        long seconds = duration.getSeconds();
+        long HH = seconds / 3600;
+        long MM = (seconds % 3600) / 60;
+        long SS = seconds % 60;
+        String timeInHHMMSS =  String.format("%02d:%02d:%02d", HH, MM, SS);
+        assertThat(timeInHHMMSS).isEqualTo("10:35:14");
+    }
+
+
+    @Test
+    public void givenInterval_WhenFormatDurationUsingApacheCommons_formatDuration() {
+        assertThat(DurationFormatUtils.formatDuration(38114000, "HH:mm:ss"))
+          .isEqualTo("10:35:14");
+    }
+
+    @Test
+    public void givenInterval_WhenFormatDurationUsingJodaTime_formatDuration() {
+        org.joda.time.Duration duration = new org.joda.time.Duration(38114000);
+        Period period = duration.toPeriod();
+        long HH = period.getHours();
+        long MM = period.getMinutes();
+        long SS = period.getSeconds();
+
+        String timeInHHMMSS = String.format("%02d:%02d:%02d", HH, MM, SS);
+        assertThat(timeInHHMMSS).isEqualTo("10:35:14");
+    }
+}

core-java-modules/core-java-exceptions-3/pom.xml

@@ -36,4 +36,5 @@
         <!-- testing -->
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
+
 </project>

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

@@ -13,4 +13,5 @@ This module contains articles about core Java input/output(IO) conversions.
 - [Java – Write a Reader to File](https://www.baeldung.com/java-write-reader-to-file)
 - [Java – Reader to Byte Array](https://www.baeldung.com/java-convert-reader-to-byte-array)
 - [Java – Reader to InputStream](https://www.baeldung.com/java-convert-reader-to-inputstream)
+- [Java String to InputStream](https://www.baeldung.com/convert-string-to-input-stream)
 - More articles: [[next -->]](/core-java-modules/core-java-io-conversions-2)

core-java-modules/core-java-io/src/main/resources/logback.xml

@@ -9,6 +9,7 @@
 
     <logger name="org.springframework" level="WARN" />
     <logger name="org.springframework.transaction" level="WARN" />
+    <logger name="net.sf.jmimemagic" level="WARN" />
 
     <!-- in order to debug some marshalling issues, this needs to be TRACE -->
     <logger name="org.springframework.web.servlet.mvc" level="WARN" />

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

@@ -76,6 +76,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-dependency-plugin</artifactId>
+                <version>${maven-dependency-plugin.version}</version>
                 <executions>
                     <execution>
                         <id>copy-dependencies</id>
@@ -106,6 +107,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-assembly-plugin</artifactId>
+                <version>${maven-assembly-plugin.version}</version>
                 <executions>
                     <execution>
                         <phase>package</phase>
@@ -383,6 +385,8 @@
         <maven-jar-plugin.version>3.0.2</maven-jar-plugin.version>
         <onejar-maven-plugin.version>1.4.4</onejar-maven-plugin.version>
         <maven-shade-plugin.version>3.1.1</maven-shade-plugin.version>
+        <maven-assembly-plugin.version>3.3.0</maven-assembly-plugin.version>
+        <maven-dependency-plugin.version>3.2.0</maven-dependency-plugin.version>
         <spring-boot-maven-plugin.version>2.0.3.RELEASE</spring-boot-maven-plugin.version>
         <source.version>1.8</source.version>
         <target.version>1.8</target.version>

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/isinstancevsisassignablefrom/IsInstanceIsAssignableFromUnitTest.java

@@ -8,7 +8,30 @@ import org.junit.Test;
 public class IsInstanceIsAssignableFromUnitTest {
 
     @Test
-    public void whenUsingIsInstanceProperly_desiredResultsHappen() {
+    public void whenUsingInstanceOfProperly_thenDesiredResultsHappen() {
+        Shape shape = new Triangle();
+        Triangle triangle = new Triangle();
+        IsoscelesTriangle isoscelesTriangle = new IsoscelesTriangle();
+        Shape nonspecificShape = null;
+
+        assertTrue(shape instanceof Shape);
+        assertTrue(triangle instanceof Shape);
+        assertTrue(isoscelesTriangle instanceof Shape);
+        assertFalse(nonspecificShape instanceof Shape);
+
+        assertTrue(shape instanceof Triangle);
+        assertTrue(triangle instanceof Triangle);
+        assertTrue(isoscelesTriangle instanceof Triangle);
+        assertFalse(nonspecificShape instanceof Triangle);
+
+        assertFalse(shape instanceof IsoscelesTriangle);
+        assertFalse(triangle instanceof IsoscelesTriangle);
+        assertTrue(isoscelesTriangle instanceof IsoscelesTriangle);
+        assertFalse(nonspecificShape instanceof IsoscelesTriangle);
+    }
+
+    @Test
+    public void whenUsingIsInstanceProperly_thenDesiredResultsHappen() {
         Shape shape = new Triangle();
         Triangle triangle = new Triangle();
         IsoscelesTriangle isoscelesTriangle = new IsoscelesTriangle();
@@ -33,7 +56,7 @@ public class IsInstanceIsAssignableFromUnitTest {
     }
 
     @Test
-    public void whenUsingIsAssignableFromProperly_desiredResultsHappen() {
+    public void whenUsingIsAssignableFromProperly_thenDesiredResultsHappen() {
         Shape shape = new Triangle();
         Triangle triangle = new Triangle();
         IsoscelesTriangle isoscelesTriangle = new IsoscelesTriangle();
@@ -64,4 +87,31 @@ public class IsInstanceIsAssignableFromUnitTest {
         assertTrue(isoscelesTriangle2.getClass().isAssignableFrom(isoscelesTriangle2.getClass()));
     }
 
+    @Test(expected = NullPointerException.class)
+    public void whenUsingNull_thenDesiredResultsHappen() {
+        assertFalse(null instanceof Shape);
+        assertFalse(Shape.class.isInstance(null));
+        assertFalse(Shape.class.isAssignableFrom(null)); // NullPointerException
+    }
+
+    @Test
+    public void whenUsingPrimitiveType_thenDesiredResultsHappen() {
+        //assertFalse(10 instanceof int); // illegal
+        assertFalse(int.class.isInstance(10));
+        assertTrue(Integer.class.isInstance(10));
+        assertTrue(int.class.isAssignableFrom(int.class));
+        assertFalse(float.class.isAssignableFrom(int.class));
+    }
+
+    @Test
+    public void whenUsingClassInstanceVariable_thenDesiredResultsHappen() {
+        Shape shape = new Triangle();
+        Triangle triangle = new Triangle();
+        Class<?> clazz = shape.getClass();
+
+        //assertFalse(triangle instanceof clazz); // illegal
+        assertTrue(clazz.isInstance(triangle));
+        assertTrue(clazz.isAssignableFrom(triangle.getClass()));
+    }
+
 }

core-java-modules/core-java-lang-4/README.md

@@ -8,3 +8,4 @@ This module contains articles about core features in the Java language
 - [Java Objects.hash() vs Objects.hashCode()](https://www.baeldung.com/java-objects-hash-vs-objects-hashcode)
 - [Referencing a Method in Javadoc Comments](https://www.baeldung.com/java-method-in-javadoc)
 - [Tiered Compilation in JVM](https://www.baeldung.com/jvm-tiered-compilation)
+- [Fixing the “Declared package does not match the expected package” Error](https://www.baeldung.com/java-declared-expected-package-error)

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/bookstore/Book.java

@@ -0,0 +1,21 @@
+// The next line is commented out to avoid the code to fail the build.
+// package com.baeldung;
+
+/**
+* If the below package declaration is commented out and the above incorrect package 
+* declaration is uncommented, then the problem will replicate.
+*/
+package com.baeldung.bookstore;
+
+public class Book {
+
+    private String title;
+    private String author;
+    private long isbn;
+    
+    public Book(String title, String author, long isbn) {
+        this.title = title;
+        this.author = author;
+        this.isbn = isbn;
+    }
+}

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/bookstore/LibraryAdmin.java

@@ -0,0 +1,14 @@
+package com.baeldung.bookstore;
+
+import java.util.Random;
+
+public class LibraryAdmin {
+
+    public Book createBook(String title, String author) {
+
+        final long isbn = new Random().nextLong();
+
+        return new Book(title, author, isbn);
+    }
+    
+}

core-java-modules/core-java-lang-oop-types/pom.xml

@@ -25,6 +25,7 @@
             <version>${commons-codec.version}</version>
         </dependency>
     </dependencies>
+
     <properties>
         <commons-codec.version>1.15</commons-codec.version>
     </properties>

core-java-modules/core-java-networking-3/README.md

@@ -8,4 +8,5 @@ This module contains articles about networking in Java
 - [Downloading Email Attachments in Java](https://www.baeldung.com/java-download-email-attachments)
 - [Connection Timeout vs. Read Timeout for Java Sockets](https://www.baeldung.com/java-socket-connection-read-timeout)
 - [Find Whether an IP Address Is in the Specified Range or Not in Java](https://www.baeldung.com/java-check-ip-address-range)
+- [Find the IP Address of a Client Connected to a Server](https://www.baeldung.com/java-client-get-ip-address)
 - [[<-- Prev]](/core-java-modules/core-java-networking-2)

core-java-modules/core-java-networking-3/src/main/java/com/baeldung/clientaddress/ApplicationClient.java

@@ -0,0 +1,39 @@
+package com.baeldung.clientaddress;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+
+public class ApplicationClient {
+
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void connect(String ip, int port) throws IOException {
+        clientSocket = new Socket(ip, port);
+        out = new PrintWriter(clientSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+    }
+
+    public void sendGreetings(String msg) throws IOException {
+        out.println(msg);
+        String reply = in.readLine();
+        System.out.println("Reply received from the server :: " + reply);
+    }
+
+    public void disconnect() throws IOException {
+        in.close();
+        out.close();
+        clientSocket.close();
+    }
+
+    public static void main(String[] args) throws IOException {
+        ApplicationClient client = new ApplicationClient();
+        client.connect(args[0], Integer.parseInt(args[1])); // IP address and port number of the server
+        client.sendGreetings(args[2]); // greetings message
+        client.disconnect();
+    }
+}

core-java-modules/core-java-networking-3/src/main/java/com/baeldung/clientaddress/ApplicationServer.java

@@ -0,0 +1,51 @@
+package com.baeldung.clientaddress;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.InetSocketAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class ApplicationServer {
+
+    private ServerSocket serverSocket;
+    private Socket connectedSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void startServer(int port) throws IOException {
+        serverSocket = new ServerSocket(port);
+        connectedSocket = serverSocket.accept();
+
+        InetSocketAddress socketAddress = (InetSocketAddress) connectedSocket.getRemoteSocketAddress();
+        String clientIpAddress = socketAddress.getAddress()
+            .getHostAddress();
+        System.out.println("IP address of the connected client :: " + clientIpAddress);
+
+        out = new PrintWriter(connectedSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(connectedSocket.getInputStream()));
+        String msg = in.readLine();
+        System.out.println("Message received from the client :: " + msg);
+        out.println("Hello Client !!");
+
+        closeIO();
+        stopServer();
+    }
+
+    private void closeIO() throws IOException {
+        in.close();
+        out.close();
+    }
+
+    private void stopServer() throws IOException {
+        connectedSocket.close();
+        serverSocket.close();
+    }
+
+    public static void main(String[] args) throws IOException {
+        ApplicationServer server = new ApplicationServer();
+        server.startServer(5000);
+    }
+}

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

@@ -13,5 +13,6 @@ This module contains articles about working with the operating system (OS) in Ja
 - [Pattern Search with Grep in Java](http://www.baeldung.com/grep-in-java)
 - [How to Run a Shell Command in Java](http://www.baeldung.com/run-shell-command-in-java)
 - [Taking Screenshots Using Java](https://www.baeldung.com/java-taking-screenshots)
+- [Java Sound API – Capturing Microphone](https://www.baeldung.com/java-sound-api-capture-mic)
 
 This module uses Java 9, so make sure to have the JDK 9 installed to run it.

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

@@ -16,6 +16,12 @@
 	</parent>
 
 	<dependencies>
+	    <dependency>
+		    <groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit-jupiter-engine.version}</version>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.apache.commons</groupId>
 			<artifactId>commons-collections4</artifactId>
@@ -88,6 +94,7 @@
 		<guava.version>25.1-jre</guava.version>
 		<unix4j.version>0.4</unix4j.version>
 		<grep4j.version>1.8.7</grep4j.version>
+		<junit-jupiter-engine.version>5.7.2</junit-jupiter-engine.version>
 	</properties>
 
 </project>

core-java-modules/core-java-os/src/main/java/com/baeldung/example/soundapi/App.java

@@ -0,0 +1,34 @@
+package com.baeldung.example.soundapi;
+
+import javax.sound.sampled.AudioFileFormat;
+import javax.sound.sampled.AudioFormat;
+
+public class App {
+    public static void main(String[] args) throws Exception {
+
+        AudioFormat format = buildAudioFormatInstance();
+
+        SoundRecorder soundRecorder = new SoundRecorder();
+        soundRecorder.build(format);
+
+        System.out.println("Start recording ....");
+        soundRecorder.start();
+        Thread.sleep(20000);
+        soundRecorder.stop();
+
+        WaveDataUtil wd = new WaveDataUtil();
+        Thread.sleep(3000);
+        wd.saveToFile("/SoundClip", AudioFileFormat.Type.WAVE, soundRecorder.getAudioInputStream());
+    }
+
+    public static AudioFormat buildAudioFormatInstance() {
+        ApplicationProperties aConstants = new ApplicationProperties();
+        AudioFormat.Encoding encoding = aConstants.ENCODING;
+        float rate = aConstants.RATE;
+        int channels = aConstants.CHANNELS;
+        int sampleSize = aConstants.SAMPLE_SIZE;
+        boolean bigEndian = aConstants.BIG_ENDIAN;
+
+        return new AudioFormat(encoding, rate, sampleSize, channels, (sampleSize / 8) * channels, rate, bigEndian);
+    }
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/example/soundapi/ApplicationProperties.java

@@ -0,0 +1,10 @@
+package com.baeldung.example.soundapi;
+import javax.sound.sampled.AudioFormat;
+
+public class ApplicationProperties {
+    public final AudioFormat.Encoding ENCODING = AudioFormat.Encoding.PCM_SIGNED;
+    public final float RATE = 44100.0f;
+    public final int CHANNELS = 1;
+    public final int SAMPLE_SIZE = 16;
+    public final boolean BIG_ENDIAN = true;
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/example/soundapi/SoundRecorder.java

@@ -0,0 +1,123 @@
+package com.baeldung.example.soundapi;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import javax.sound.sampled.AudioFormat;
+import javax.sound.sampled.AudioInputStream;
+import javax.sound.sampled.AudioSystem;
+import javax.sound.sampled.DataLine;
+import javax.sound.sampled.TargetDataLine;
+
+public class SoundRecorder implements Runnable {
+    private AudioInputStream audioInputStream;
+    private AudioFormat format;
+    public Thread thread;
+    private double duration;
+
+    public SoundRecorder() {
+        super();
+    }
+
+    public SoundRecorder(AudioFormat format) {
+        this.format = format;
+    }
+
+    public SoundRecorder build(AudioFormat format) {
+        this.format = format;
+        return this;
+    }
+
+    public void start() {
+        thread = new Thread(this);
+        thread.setName("Capture Microphone");
+        thread.start();
+    }
+
+    public void stop() {
+        thread = null;
+    }
+
+    @Override
+    public void run() {
+        duration = 0;
+
+        try (final ByteArrayOutputStream out = new ByteArrayOutputStream(); final TargetDataLine line = getTargetDataLineForRecord();) {
+
+            int frameSizeInBytes = format.getFrameSize();
+            int bufferLengthInFrames = line.getBufferSize() / 8;
+            final int bufferLengthInBytes = bufferLengthInFrames * frameSizeInBytes;
+            buildByteOutputStream(out, line, frameSizeInBytes, bufferLengthInBytes);
+            this.audioInputStream = new AudioInputStream(line);
+            setAudioInputStream(convertToAudioIStream(out, frameSizeInBytes));
+            audioInputStream.reset();
+        } catch (IOException ex) {
+            ex.printStackTrace();
+        } catch (Exception ex) {
+            ex.printStackTrace();
+            return;
+        }
+    }
+
+    public void buildByteOutputStream(final ByteArrayOutputStream out, final TargetDataLine line, int frameSizeInBytes, final int bufferLengthInBytes) throws IOException {
+        final byte[] data = new byte[bufferLengthInBytes];
+        int numBytesRead;
+
+        line.start();
+        while (thread != null) {
+            if ((numBytesRead = line.read(data, 0, bufferLengthInBytes)) == -1) {
+                break;
+            }
+            out.write(data, 0, numBytesRead);
+        }
+    }
+
+    private void setAudioInputStream(AudioInputStream aStream) {
+        this.audioInputStream = aStream;
+    }
+
+    public AudioInputStream convertToAudioIStream(final ByteArrayOutputStream out, int frameSizeInBytes) {
+        byte audioBytes[] = out.toByteArray();
+        ByteArrayInputStream bais = new ByteArrayInputStream(audioBytes);
+        AudioInputStream audioStream = new AudioInputStream(bais, format, audioBytes.length / frameSizeInBytes);
+        long milliseconds = (long) ((audioInputStream.getFrameLength() * 1000) / format.getFrameRate());
+        duration = milliseconds / 1000.0;
+        System.out.println("Recorded duration in seconds:" + duration);
+        return audioStream;
+    }
+
+    public TargetDataLine getTargetDataLineForRecord() {
+        TargetDataLine line;
+        DataLine.Info info = new DataLine.Info(TargetDataLine.class, format);
+        if (!AudioSystem.isLineSupported(info)) {
+            return null;
+        }
+        try {
+            line = (TargetDataLine) AudioSystem.getLine(info);
+            line.open(format, line.getBufferSize());
+        } catch (final Exception ex) {
+            return null;
+        }
+        return line;
+    }
+
+    public AudioInputStream getAudioInputStream() {
+        return audioInputStream;
+    }
+
+    public AudioFormat getFormat() {
+        return format;
+    }
+
+    public void setFormat(AudioFormat format) {
+        this.format = format;
+    }
+
+    public Thread getThread() {
+        return thread;
+    }
+
+    public double getDuration() {
+        return duration;
+    }
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/example/soundapi/WaveDataUtil.java

@@ -0,0 +1,34 @@
+package com.baeldung.example.soundapi;
+
+import java.io.File;
+
+import javax.sound.sampled.AudioFileFormat;
+import javax.sound.sampled.AudioInputStream;
+import javax.sound.sampled.AudioSystem;
+
+public class WaveDataUtil {
+    public boolean saveToFile(String name, AudioFileFormat.Type fileType, AudioInputStream audioInputStream) {
+        System.out.println("Saving...");
+        if (null == name || null == fileType || audioInputStream == null) {
+            return false;
+        }
+        File myFile = new File(name + "." + fileType.getExtension());
+        try {
+            audioInputStream.reset();
+        } catch (Exception e) {
+            return false;
+        }
+        int i = 0;
+        while (myFile.exists()) {
+            String temp = "" + i + myFile.getName();
+            myFile = new File(temp);
+        }
+        try {
+            AudioSystem.write(audioInputStream, fileType, myFile);
+        } catch (Exception ex) {
+            return false;
+        }
+        System.out.println("Saved " + myFile.getAbsolutePath());
+        return true;
+    }
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/java9/process/ProcessAPIEnhancements.java

@@ -0,0 +1,101 @@
+package com.baeldung.java9.process;
+
+import java.io.IOException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.stream.Stream;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ProcessAPIEnhancements {
+
+    static Logger log = LoggerFactory.getLogger(ProcessAPIEnhancements.class);
+
+    public static void main(String[] args) throws IOException, InterruptedException, ExecutionException {
+        infoOfCurrentProcess();
+        infoOfLiveProcesses();
+        infoOfSpawnProcess();
+        infoOfExitCallback();
+        infoOfChildProcess();
+    }
+
+    private static void infoOfCurrentProcess() {
+        ProcessHandle processHandle = ProcessHandle.current();
+        ProcessHandle.Info processInfo = processHandle.info();
+
+        log.info("PID: " + processHandle.pid());
+        log.info("Arguments: " + processInfo.arguments());
+        log.info("Command: " + processInfo.command());
+        log.info("Instant: " + processInfo.startInstant());
+        log.info("Total CPU duration: " + processInfo.totalCpuDuration());
+        log.info("User: " + processInfo.user());
+    }
+
+    private static void infoOfSpawnProcess() throws IOException {
+
+        String javaCmd = ProcessUtils.getJavaCmd().getAbsolutePath();
+        ProcessBuilder processBuilder = new ProcessBuilder(javaCmd, "-version");
+        Process process = processBuilder.inheritIO().start();
+        ProcessHandle processHandle = process.toHandle();
+        ProcessHandle.Info processInfo = processHandle.info();
+
+        log.info("PID: " + processHandle.pid());
+        log.info("Arguments: " + processInfo.arguments());
+        log.info("Command: " + processInfo.command());
+        log.info("Instant: " + processInfo.startInstant());
+        log.info("Total CPU duration: " + processInfo.totalCpuDuration());
+        log.info("User: " + processInfo.user());
+    }
+
+    private static void infoOfLiveProcesses() {
+        Stream<ProcessHandle> liveProcesses = ProcessHandle.allProcesses();
+        liveProcesses.filter(ProcessHandle::isAlive)
+            .forEach(ph -> {
+                log.info("PID: " + ph.pid());
+                log.info("Instance: " + ph.info().startInstant());
+                log.info("User: " + ph.info().user());
+            });
+    }
+
+    private static void infoOfChildProcess() throws IOException {
+        int childProcessCount = 5;
+        for (int i = 0; i < childProcessCount; i++) {
+            String javaCmd = ProcessUtils.getJavaCmd()
+              .getAbsolutePath();
+            ProcessBuilder processBuilder
+              = new ProcessBuilder(javaCmd, "-version");
+            processBuilder.inheritIO().start();
+        }
+
+        Stream<ProcessHandle> children = ProcessHandle.current()
+          .children();
+        children.filter(ProcessHandle::isAlive)
+          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
+            .command()));
+        Stream<ProcessHandle> descendants = ProcessHandle.current()
+          .descendants();
+        descendants.filter(ProcessHandle::isAlive)
+          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
+            .command()));
+    }
+
+    private static void infoOfExitCallback() throws IOException, InterruptedException, ExecutionException {
+        String javaCmd = ProcessUtils.getJavaCmd()
+          .getAbsolutePath();
+        ProcessBuilder processBuilder
+          = new ProcessBuilder(javaCmd, "-version");
+        Process process = processBuilder.inheritIO()
+          .start();
+        ProcessHandle processHandle = process.toHandle();
+
+        log.info("PID: {} has started", processHandle.pid());
+        CompletableFuture<ProcessHandle> onProcessExit = processHandle.onExit();
+        onProcessExit.get();
+        log.info("Alive: " + processHandle.isAlive());
+        onProcessExit.thenAccept(ph -> {
+            log.info("PID: {} has stopped", ph.pid());
+        });
+    }
+
+}

core-java-modules/core-java-os/src/test/java/com/baeldung/example/soundapi/AppUnitTest.java

@@ -0,0 +1,75 @@
+package com.baeldung.example.soundapi;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+import java.io.ByteArrayOutputStream;
+
+import javax.sound.sampled.AudioFileFormat;
+import javax.sound.sampled.AudioFormat;
+import javax.sound.sampled.TargetDataLine;
+
+public class AppUnitTest {
+
+    AudioFormat af = App.buildAudioFormatInstance();
+    SoundRecorder soundRecorder = new SoundRecorder();
+
+    @Test
+    public void Given_SoundRecorderObject_When_Run_Then_ThrowsNoException() {
+
+        soundRecorder.build(af);
+        try {
+            soundRecorder.start();
+            Thread.sleep(20000);
+            soundRecorder.stop();
+        } catch (InterruptedException ex) {
+            fail("Exception: " + ex);
+        }
+
+    }
+
+    @Test
+    public void Given_AudioFormatObject_When_NotNull_Then_ReturnsTargetDataLine() {
+        soundRecorder.setFormat(af);
+        Assertions.assertDoesNotThrow(() -> soundRecorder.getTargetDataLineForRecord());
+    }
+
+    @Test
+    public void Given_TargetLineDataObject_When_Run_Then_GeneratesOutputStream() {
+
+        soundRecorder.setFormat(af);
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        TargetDataLine tLine = soundRecorder.getTargetDataLineForRecord();
+
+        int frameSizeInBytes = af.getFrameSize();
+        int bufferLengthInFrames = tLine.getBufferSize() / 8;
+        final int bufferLengthInBytes = bufferLengthInFrames * frameSizeInBytes;
+
+        Assertions.assertDoesNotThrow(
+                () -> soundRecorder.buildByteOutputStream(out, tLine, frameSizeInBytes, bufferLengthInBytes));
+    }
+
+    @Test
+    public void Given_AudioInputStream_When_NotNull_Then_SaveToWavFile() {
+        soundRecorder.setFormat(af);
+        soundRecorder.build(af);
+        try {
+            soundRecorder.start();
+            Thread.sleep(20000);
+            soundRecorder.stop();
+            WaveDataUtil wd = new WaveDataUtil();
+            Thread.sleep(3000);
+            boolean saveFile = wd.saveToFile("/SoundClip", AudioFileFormat.Type.WAVE,
+                    soundRecorder.getAudioInputStream());
+
+            assertEquals(saveFile, true);
+
+        } catch (InterruptedException ex) {
+            fail("Exception: " + ex);
+        }
+
+    }
+
+}

core-java-modules/core-java-os/src/test/java/com/baeldung/java9/process/ProcessAPIEnhancementsUnitTest.java

@@ -1,132 +0,0 @@
-package com.baeldung.java9.process;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertTrue;
-
-import java.io.IOException;
-import java.util.concurrent.CompletableFuture;
-import java.util.stream.Stream;
-
-import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * Created by sanaulla on 2/23/2017.
- */
-
-public class ProcessAPIEnhancementsUnitTest {
-
-    Logger log = LoggerFactory.getLogger(ProcessAPIEnhancementsUnitTest.class);
-
-    // @Test
-    // OS / Java version dependent
-    public void givenCurrentProcess_whenInvokeGetInfo_thenSuccess() throws IOException {
-        ProcessHandle processHandle = ProcessHandle.current();
-        ProcessHandle.Info processInfo = processHandle.info();
-        assertNotNull(processHandle.pid());
-        assertEquals(true, processInfo.arguments()
-          .isPresent());
-        assertEquals(true, processInfo.command()
-          .isPresent());
-        assertTrue(processInfo.command()
-          .get()
-          .contains("java"));
-
-        assertEquals(true, processInfo.startInstant()
-          .isPresent());
-        assertEquals(true, processInfo.totalCpuDuration()
-          .isPresent());
-        assertEquals(true, processInfo.user()
-          .isPresent());
-    }
-
-    // @Test
-    // OS / Java version dependent
-    public void givenSpawnProcess_whenInvokeGetInfo_thenSuccess() throws IOException {
-
-        String javaCmd = ProcessUtils.getJavaCmd()
-          .getAbsolutePath();
-        ProcessBuilder processBuilder = new ProcessBuilder(javaCmd, "-version");
-        Process process = processBuilder.inheritIO()
-          .start();
-        ProcessHandle processHandle = process.toHandle();
-        ProcessHandle.Info processInfo = processHandle.info();
-        assertNotNull(processHandle.pid());
-        assertEquals(true, processInfo.arguments()
-          .isPresent());
-        assertEquals(true, processInfo.command()
-          .isPresent());
-        assertTrue(processInfo.command()
-          .get()
-          .contains("java"));
-        assertEquals(true, processInfo.startInstant()
-          .isPresent());
-        assertEquals(false, processInfo.totalCpuDuration()
-          .isPresent());
-        assertEquals(true, processInfo.user()
-          .isPresent());
-    }
-
-    // @Test
-    // OS / Java version dependent
-    public void givenLiveProcesses_whenInvokeGetInfo_thenSuccess() {
-        Stream<ProcessHandle> liveProcesses = ProcessHandle.allProcesses();
-        liveProcesses.filter(ProcessHandle::isAlive)
-            .forEach(ph -> {
-                assertNotNull(ph.pid());
-                assertEquals(true, ph.info()
-                  .startInstant()
-                  .isPresent());
-                assertEquals(true, ph.info()
-                  .user()
-                  .isPresent());
-            });
-    }
-
-    // @Test
-    // OS / Java version dependent
-    public void givenProcess_whenGetChildProcess_thenSuccess() throws IOException {
-        int childProcessCount = 5;
-        for (int i = 0; i < childProcessCount; i++) {
-            String javaCmd = ProcessUtils.getJavaCmd()
-              .getAbsolutePath();
-            ProcessBuilder processBuilder
-              = new ProcessBuilder(javaCmd, "-version");
-            processBuilder.inheritIO().start();
-        }
-
-        Stream<ProcessHandle> children = ProcessHandle.current()
-          .children();
-        children.filter(ProcessHandle::isAlive)
-          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
-            .command()));
-        Stream<ProcessHandle> descendants = ProcessHandle.current()
-          .descendants();
-        descendants.filter(ProcessHandle::isAlive)
-          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
-            .command()));
-    }
-
-    // @Test
-    // OS / Java version dependent
-    public void givenProcess_whenAddExitCallback_thenSuccess() throws Exception {
-        String javaCmd = ProcessUtils.getJavaCmd()
-          .getAbsolutePath();
-        ProcessBuilder processBuilder
-          = new ProcessBuilder(javaCmd, "-version");
-        Process process = processBuilder.inheritIO()
-          .start();
-        ProcessHandle processHandle = process.toHandle();
-
-        log.info("PID: {} has started", processHandle.pid());
-        CompletableFuture<ProcessHandle> onProcessExit = processHandle.onExit();
-        onProcessExit.get();
-        assertEquals(false, processHandle.isAlive());
-        onProcessExit.thenAccept(ph -> {
-            log.info("PID: {} has stopped", ph.pid());
-        });
-    }
-
-}

core-java-modules/core-java-security-3/README.md

@@ -5,4 +5,5 @@ This module contains articles about core Java Security
 ### Relevant Articles:
 
 - [Secret Key and String Conversion in Java](https://www.baeldung.com/java-secret-key-to-string)
+- [Enabling Unlimited Strength Cryptography in Java](https://www.baeldung.com/jce-enable-unlimited-strength)
 - More articles: [[<-- prev]](/core-java-modules/core-java-security-2)

core-java-modules/core-java-security-3/src/test/java/com/baeldung/cryptography/CryptographyStrengthUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.cryptography;
+
+import org.junit.Test;
+
+import java.security.NoSuchAlgorithmException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class CryptographyStrengthUnitTest {
+    private static final int UNLIMITED_KEY_SIZE = 2147483647;
+
+    @Test
+    public void whenDefaultCheck_thenUnlimitedReturned() throws NoSuchAlgorithmException {
+        int maxKeySize = javax.crypto.Cipher.getMaxAllowedKeyLength("AES");
+        assertThat(maxKeySize).isEqualTo(UNLIMITED_KEY_SIZE);
+    }
+}

core-java-modules/core-java-string-algorithms-3/pom.xml

@@ -32,6 +32,11 @@
             <artifactId>junit-jupiter</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>commons-validator</groupId>
+            <artifactId>commons-validator</artifactId>
+            <version>${validator.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -59,6 +64,7 @@
     <properties>
         <assertj.version>3.6.1</assertj.version>
         <guava.version>28.1-jre</guava.version>
+        <validator.version>1.7</validator.version>
     </properties>
 
 </project>

core-java-modules/core-java-string-algorithms-3/src/main/java/com/baeldung/emailvalidation/EmailValidation.java

@@ -0,0 +1,12 @@
+package com.baeldung.emailvalidation;
+
+import java.util.regex.Pattern;
+
+public class EmailValidation {
+
+    public static boolean patternMatches(String emailAddress, String regexPattern) {
+        return Pattern.compile(regexPattern)
+            .matcher(emailAddress)
+            .matches();
+    }
+}

core-java-modules/core-java-string-algorithms-3/src/test/java/com/baeldung/emailvalidation/EmailValidationUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.emailvalidation;
+
+import static org.junit.Assert.assertTrue;
+import org.apache.commons.validator.routines.EmailValidator;
+import org.junit.Test;
+
+public class EmailValidationUnitTest {
+
+    private String emailAddress;
+    private String regexPattern;
+
+    @Test
+    public void testUsingEmailValidator() {
+        emailAddress = "username@domain.com";
+        assertTrue(EmailValidator.getInstance()
+            .isValid(emailAddress));
+    }
+
+    @Test
+    public void testUsingSimpleRegex() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^(.+)@(\\S+)$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testUsingStrictRegex() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^(?=.{1,64}@)[A-Za-z0-9_-]+(\\.[A-Za-z0-9_-]+)*@" 
+            + "[^-][A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testUsingUnicodeRegex() {
+        emailAddress = "用户名@领域.电脑";
+        regexPattern = "^(?=.{1,64}@)[\\p{L}0-9_-]+(\\.[\\p{L}0-9_-]+)*@" 
+            + "[^-][\\p{L}0-9-]+(\\.[\\p{L}0-9-]+)*(\\.[\\p{L}]{2,})$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testUsingRFC5322Regex() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^[a-zA-Z0-9_!#$%&'*+/=?`{|}~^.-]+@[a-zA-Z0-9.-]+$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testRestrictDots() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+(?:\\.[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+)*@" 
+            + "[a-zA-Z0-9-]+(?:\\.[a-zA-Z0-9-]+)*$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testOwaspValidation() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^[a-zA-Z0-9_+&*-]+(?:\\.[a-zA-Z0-9_+&*-]+)*@(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,7}$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+
+    @Test
+    public void testTopLevelDomain() {
+        emailAddress = "username@domain.com";
+        regexPattern = "^[\\w!#$%&'*+/=?`{|}~^-]+(?:\\.[\\w!#$%&'*+/=?`{|}~^-]+)*" 
+            + "@(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,6}$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+    
+    @Test
+    public void testGmailSpecialCase() {
+        emailAddress = "username+something@domain.com";
+        regexPattern = "^(?=.{1,64}@)[A-Za-z0-9\\+_-]+(\\.[A-Za-z0-9\\+_-]+)*@" 
+            + "[^-][A-Za-z0-9\\+-]+(\\.[A-Za-z0-9\\+-]+)*(\\.[A-Za-z]{2,})$";
+        assertTrue(EmailValidation.patternMatches(emailAddress, regexPattern));
+    }
+}

core-java-modules/core-java-string-operations-3/README.md

@@ -5,3 +5,4 @@
 - [Split Java String by Newline](https://www.baeldung.com/java-string-split-by-newline)
 - [Split a String in Java and Keep the Delimiters](https://www.baeldung.com/java-split-string-keep-delimiters)
 - [Validate String as Filename in Java](https://www.baeldung.com/java-validate-filename)
+- [Count Spaces in a Java String](https://www.baeldung.com/java-string-count-spaces)