Merge branch 'master' into thombergs-patch-4

README.md

@@ -14,7 +14,7 @@ Java and Spring Tutorials
 ================
 
 This project is **a collection of small and focused tutorials** - each covering a single and well defined area of development in the Java ecosystem. 
-A strong focus of these is, of course, the Spring Framework - Spring, Spring Boot and Spring Securiyt. 
+A strong focus of these is, of course, the Spring Framework - Spring, Spring Boot and Spring Security. 
 In additional to Spring, the following technologies are in focus: `core Java`, `Jackson`, `HttpClient`, `Guava`. 
 
 

akka-http/README.md

@@ -1,3 +1,3 @@
-### Relevant articles
+## Relevant articles:
 
 - [Introduction to Akka HTTP](https://www.baeldung.com/akka-http)

algorithms-miscellaneous-1/README.md

@@ -12,4 +12,5 @@
 - [Check If a String Contains All The Letters of The Alphabet](https://www.baeldung.com/java-string-contains-all-letters)
 - [Find the Middle Element of a Linked List](http://www.baeldung.com/java-linked-list-middle-element)
 - [Calculate Factorial in Java](https://www.baeldung.com/java-calculate-factorial)
-- [Find Substrings That Are Palindromes in Java](https://www.baeldung.com/java-palindrome-substrings)
+- [Find Substrings That Are Palindromes in Java](https://www.baeldung.com/java-palindrome-substrings)
+- [Find the Longest Substring without Repeating Characters](https://www.baeldung.com/java-longest-substring-without-repeated-characters)

algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/permutation/Permutation.java

@@ -0,0 +1,123 @@
+package com.baeldung.algorithms.permutation;
+
+import java.util.Arrays;
+import java.util.Collections;
+
+public  class Permutation {
+
+    public static <T> void printAllRecursive(T[] elements, char delimiter) {
+        printAllRecursive(elements.length, elements, delimiter);
+    }
+
+    public static <T> void printAllRecursive(int n, T[] elements, char delimiter) {
+
+        if(n == 1) {
+            printArray(elements, delimiter);
+        } else {
+            for(int i = 0; i < n-1; i++) {
+                printAllRecursive(n - 1, elements, delimiter);
+                if(n % 2 == 0) {
+                    swap(elements, i, n-1);
+                } else {
+                    swap(elements, 0, n-1);
+                }
+            }
+            printAllRecursive(n - 1, elements, delimiter);
+        }
+    }
+
+    public static <T> void printAllIterative(int n, T[] elements, char delimiter) {
+
+        int[] indexes = new int[n];
+        for (int i = 0; i < n; i++) {
+            indexes[i] = 0;
+        }
+
+        printArray(elements, delimiter);
+
+        int i = 0;
+        while (i < n) {
+            if (indexes[i] < i) {
+                swap(elements, i % 2 == 0 ?  0: indexes[i], i);
+                printArray(elements, delimiter);
+                indexes[i]++;
+                i = 0;
+            }
+            else {
+                indexes[i] = 0;
+                i++;
+            }
+        }
+    }
+
+    public static <T extends Comparable<T>> void printAllOrdered(T[] elements, char delimiter) {
+
+        Arrays.sort(elements);
+        boolean hasNext = true;
+
+        while(hasNext) {
+            printArray(elements, delimiter);
+            int k = 0, l = 0;
+            hasNext = false;
+            for (int i = elements.length - 1; i > 0; i--) {
+                if (elements[i].compareTo(elements[i - 1]) > 0) {
+                    k = i - 1;
+                    hasNext = true;
+                    break;
+                }
+            }
+
+            for (int i = elements.length - 1; i > k; i--) {
+                if (elements[i].compareTo(elements[k]) > 0) {
+                    l = i;
+                    break;
+                }
+            }
+
+            swap(elements, k, l);
+            Collections.reverse(Arrays.asList(elements).subList(k + 1, elements.length));
+        }
+    }
+
+    public static <T> void printRandom(T[] elements, char delimiter) {
+
+        Collections.shuffle(Arrays.asList(elements));
+        printArray(elements, delimiter);
+    }
+
+    private static <T> void swap(T[] elements, int a, int b) {
+
+        T tmp = elements[a];
+        elements[a] = elements[b];
+        elements[b] = tmp;
+    }
+
+    private static <T> void printArray(T[] elements, char delimiter) {
+
+        String delimiterSpace = delimiter + " ";
+        for(int i = 0; i < elements.length; i++) {
+            System.out.print(elements[i] + delimiterSpace);
+        }
+        System.out.print('\n');
+    }
+
+    public static void main(String[] argv) {
+
+        Integer[] elements = {1,2,3,4};
+
+        System.out.println("Rec:");
+        printAllRecursive(elements, ';');
+
+        System.out.println("Iter:");
+        printAllIterative(elements.length, elements, ';');
+
+        System.out.println("Orderes:");
+        printAllOrdered(elements, ';');
+
+        System.out.println("Random:");
+        printRandom(elements, ';');
+
+        System.out.println("Random:");
+        printRandom(elements, ';');
+    }
+}

algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java

@@ -0,0 +1,16 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class LinkedListFindMiddle {
+
+    public <T> T findMiddle(MyNode<T> head) {
+        MyNode<T> slowPointer = head;
+        MyNode<T> fastPointer = head;
+
+        while (fastPointer.next != null && fastPointer.next.next != null) {
+            fastPointer = fastPointer.next.next;
+            slowPointer = slowPointer.next;
+        }
+        return slowPointer.data;
+    }
+
+}

algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class MyNode<E> {
+    MyNode<E> next;
+    E data;
+
+    public MyNode(E value) {
+        data = value;
+        next = null;
+    }
+
+    public MyNode(E value, MyNode<E> n) {
+        data = value;
+        next = n;
+    }
+
+    public void setNext(MyNode<E> n) {
+        next = n;
+    }
+}

algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java

@@ -0,0 +1,22 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class RotateArray {
+
+    public void rotate(int[] input, int step) {
+        step %= input.length;
+        reverse(input, 0, input.length - 1);
+        reverse(input, 0, step - 1);
+        reverse(input, step, input.length - 1);
+    }
+
+    private void reverse(int[] input, int start, int end) {
+        while (start < end) {
+            int temp = input[start];
+            input[start] = input[end];
+            input[end] = temp;
+            start++;
+            end--;
+        }
+    }
+
+}

algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java

@@ -0,0 +1,38 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class TwoSum {
+
+    public boolean twoSum(int[] input, int targetValue) {
+
+        int pointerOne = 0;
+        int pointerTwo = input.length - 1;
+
+        while (pointerOne < pointerTwo) {
+            int sum = input[pointerOne] + input[pointerTwo];
+
+            if (sum == targetValue) {
+                return true;
+            } else if (sum < targetValue) {
+                pointerOne++;
+            } else {
+                pointerTwo--;
+            }
+        }
+
+        return false;
+    }
+
+    public boolean twoSumSlow(int[] input, int targetValue) {
+
+        for (int i = 0; i < input.length; i++) {
+            for (int j = 1; j < input.length; j++) {
+                if (input[i] + input[j] == targetValue) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+}

algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class LinkedListFindMiddleUnitTest {
+
+    LinkedListFindMiddle linkedListFindMiddle = new LinkedListFindMiddle();
+
+    @Test
+    public void givenLinkedListOfMyNodes_whenLinkedListFindMiddle_thenCorrect() {
+
+        MyNode<String> head = createNodesList(8);
+
+        assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("4");
+
+        head = createNodesList(9);
+
+        assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("5");
+    }
+
+    private static MyNode<String> createNodesList(int n) {
+
+        MyNode<String> head = new MyNode<String>("1");
+        MyNode<String> current = head;
+
+        for (int i = 2; i <= n; i++) {
+            MyNode<String> newNode = new MyNode<String>(String.valueOf(i));
+            current.setNext(newNode);
+            current = newNode;
+        }
+
+        return head;
+    }
+
+}

algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RotateArrayUnitTest {
+
+    private RotateArray rotateArray = new RotateArray();
+
+    private int[] inputArray;
+
+    private int step;
+
+    @Test
+    public void givenAnArrayOfIntegers_whenRotateKsteps_thenCorrect() {
+
+        inputArray = new int[] { 1, 2, 3, 4, 5, 6, 7 };
+        step = 4;
+
+        rotateArray.rotate(inputArray, step);
+
+        assertThat(inputArray).containsExactly(new int[] { 4, 5, 6, 7, 1, 2, 3 });
+    }
+
+}

algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class TwoSumUnitTest {
+
+    private TwoSum twoSum = new TwoSum();
+
+    private int[] sortedArray;
+
+    private int targetValue;
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 12;
+
+        assertTrue(twoSum.twoSumSlow(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairDoesNotExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 20;
+
+        assertFalse(twoSum.twoSumSlow(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSum_thenPairExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 12;
+
+        assertTrue(twoSum.twoSum(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSum_thenPairDoesNotExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 20;
+
+        assertFalse(twoSum.twoSum(sortedArray, targetValue));
+    }
+
+}

apache-spark/pom.xml

@@ -15,16 +15,76 @@
     </parent>
 
     <dependencies>
-        <!-- https://mvnrepository.com/artifact/org.apache.spark/spark-core_2.10 -->
         <dependency>
             <groupId>org.apache.spark</groupId>
-            <artifactId>spark-core_2.10</artifactId>
+            <artifactId>spark-core_2.11</artifactId>
             <version>${org.apache.spark.spark-core.version}</version>
+            <scope>provided</scope>
         </dependency>
+		<dependency>
+    		<groupId>org.apache.spark</groupId>
+    		<artifactId>spark-sql_2.11</artifactId>
+    		<version>${org.apache.spark.spark-sql.version}</version>
+    		<scope>provided</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.spark</groupId>
+			<artifactId>spark-streaming_2.11</artifactId>
+			<version>${org.apache.spark.spark-streaming.version}</version>
+			<scope>provided</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.spark</groupId>
+			<artifactId>spark-streaming-kafka-0-10_2.11</artifactId>
+			<version>${org.apache.spark.spark-streaming-kafka.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>com.datastax.spark</groupId>
+			<artifactId>spark-cassandra-connector_2.11</artifactId>
+			<version>${com.datastax.spark.spark-cassandra-connector.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>com.datastax.spark</groupId>
+			<artifactId>spark-cassandra-connector-java_2.11</artifactId>
+			<version>${com.datastax.spark.spark-cassandra-connector-java.version}</version>
+		</dependency>
     </dependencies>
-
+	<build>
+    	<plugins>
+    	  	<plugin>
+    			<groupId>org.apache.maven.plugins</groupId>
+    			<artifactId>maven-compiler-plugin</artifactId>
+    			<version>3.2</version>
+    			<configuration>
+      				<source>1.8</source>
+      				<target>1.8</target>
+    			</configuration>
+  			</plugin>
+      		<plugin>
+        		<artifactId>maven-assembly-plugin</artifactId>
+        		<executions>
+          			<execution>
+            			<phase>package</phase>
+            			<goals>
+              				<goal>single</goal>
+            			</goals>
+          			</execution>
+        		</executions>
+        		<configuration>
+          			<descriptorRefs>
+            			<descriptorRef>jar-with-dependencies</descriptorRef>
+          			</descriptorRefs>
+        		</configuration>
+      		</plugin>
+   		</plugins>
+  	</build>
     <properties>
-        <org.apache.spark.spark-core.version>2.2.0</org.apache.spark.spark-core.version>
+        <org.apache.spark.spark-core.version>2.3.0</org.apache.spark.spark-core.version>
+        <org.apache.spark.spark-sql.version>2.3.0</org.apache.spark.spark-sql.version>
+        <org.apache.spark.spark-streaming.version>2.3.0</org.apache.spark.spark-streaming.version>
+        <org.apache.spark.spark-streaming-kafka.version>2.3.0</org.apache.spark.spark-streaming-kafka.version>
+        <com.datastax.spark.spark-cassandra-connector.version>2.3.0</com.datastax.spark.spark-cassandra-connector.version>
+        <com.datastax.spark.spark-cassandra-connector-java.version>1.5.2</com.datastax.spark.spark-cassandra-connector-java.version>
     </properties>
 
 </project>

apache-spark/src/main/java/com/baeldung/data/pipeline/Word.java

@@ -0,0 +1,25 @@
+package com.baeldung.data.pipeline;
+
+import java.io.Serializable;
+
+public class Word implements Serializable {
+    private static final long serialVersionUID = 1L;
+    private String word;
+    private int count;
+    Word(String word, int count) {
+        this.word = word;
+        this.count = count;
+    }
+    public String getWord() {
+        return word;
+    }
+    public void setWord(String word) {
+        this.word = word;
+    }
+    public int getCount() {
+        return count;
+    }
+    public void setCount(int count) {
+        this.count = count;
+    }
+}

apache-spark/src/main/java/com/baeldung/data/pipeline/WordCountingApp.java

@@ -0,0 +1,116 @@
+package com.baeldung.data.pipeline;
+
+import static com.datastax.spark.connector.japi.CassandraJavaUtil.javaFunctions;
+import static com.datastax.spark.connector.japi.CassandraJavaUtil.mapToRow;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.kafka.clients.consumer.ConsumerRecord;
+import org.apache.kafka.common.serialization.StringDeserializer;
+import org.apache.log4j.Level;
+import org.apache.log4j.Logger;
+import org.apache.spark.SparkConf;
+import org.apache.spark.api.java.JavaPairRDD;
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.function.FlatMapFunction;
+import org.apache.spark.api.java.function.Function;
+import org.apache.spark.api.java.function.Function2;
+import org.apache.spark.api.java.function.PairFunction;
+import org.apache.spark.api.java.function.VoidFunction;
+import org.apache.spark.streaming.Durations;
+import org.apache.spark.streaming.api.java.JavaDStream;
+import org.apache.spark.streaming.api.java.JavaInputDStream;
+import org.apache.spark.streaming.api.java.JavaPairDStream;
+import org.apache.spark.streaming.api.java.JavaStreamingContext;
+import org.apache.spark.streaming.kafka010.ConsumerStrategies;
+import org.apache.spark.streaming.kafka010.KafkaUtils;
+import org.apache.spark.streaming.kafka010.LocationStrategies;
+
+import scala.Tuple2;
+
+public class WordCountingApp {
+
+    @SuppressWarnings("serial")
+    public static void main(String[] args) throws InterruptedException {
+        Logger.getLogger("org")
+            .setLevel(Level.OFF);
+        Logger.getLogger("akka")
+            .setLevel(Level.OFF);
+
+        Map<String, Object> kafkaParams = new HashMap<>();
+        kafkaParams.put("bootstrap.servers", "localhost:9092");
+        kafkaParams.put("key.deserializer", StringDeserializer.class);
+        kafkaParams.put("value.deserializer", StringDeserializer.class);
+        kafkaParams.put("group.id", "use_a_separate_group_id_for_each_stream");
+        kafkaParams.put("auto.offset.reset", "latest");
+        kafkaParams.put("enable.auto.commit", false);
+
+        Collection<String> topics = Arrays.asList("messages");
+
+        SparkConf sparkConf = new SparkConf();
+        sparkConf.setMaster("local[2]");
+        sparkConf.setAppName("WordCountingApp");
+        sparkConf.set("spark.cassandra.connection.host", "127.0.0.1");
+
+        JavaStreamingContext streamingContext = new JavaStreamingContext(sparkConf, Durations.seconds(1));
+
+        JavaInputDStream<ConsumerRecord<String, String>> messages = KafkaUtils.createDirectStream(streamingContext, LocationStrategies.PreferConsistent(), ConsumerStrategies.<String, String> Subscribe(topics, kafkaParams));
+
+        JavaPairDStream<String, String> results = messages.mapToPair(new PairFunction<ConsumerRecord<String, String>, String, String>() {
+            @Override
+            public Tuple2<String, String> call(ConsumerRecord<String, String> record) {
+                return new Tuple2<>(record.key(), record.value());
+            }
+        });
+
+        JavaDStream<String> lines = results.map(new Function<Tuple2<String, String>, String>() {
+            @Override
+            public String call(Tuple2<String, String> tuple2) {
+                return tuple2._2();
+            }
+        });
+
+        JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
+            @Override
+            public Iterator<String> call(String x) {
+                return Arrays.asList(x.split("\\s+"))
+                    .iterator();
+            }
+        });
+
+        JavaPairDStream<String, Integer> wordCounts = words.mapToPair(new PairFunction<String, String, Integer>() {
+            @Override
+            public Tuple2<String, Integer> call(String s) {
+                return new Tuple2<>(s, 1);
+            }
+        })
+            .reduceByKey(new Function2<Integer, Integer, Integer>() {
+                @Override
+                public Integer call(Integer i1, Integer i2) {
+                    return i1 + i2;
+                }
+            });
+
+        wordCounts.foreachRDD(new VoidFunction<JavaPairRDD<String, Integer>>() {
+            @Override
+            public void call(JavaPairRDD<String, Integer> javaRdd) throws Exception {
+                Map<String, Integer> wordCountMap = javaRdd.collectAsMap();
+                for (String key : wordCountMap.keySet()) {
+                    List<Word> words = Arrays.asList(new Word(key, wordCountMap.get(key)));
+                    JavaRDD<Word> rdd = streamingContext.sparkContext()
+                        .parallelize(words);
+                    javaFunctions(rdd).writerBuilder("vocabulary", "words", mapToRow(Word.class))
+                        .saveToCassandra();
+                }
+            }
+        });
+
+        streamingContext.start();
+        streamingContext.awaitTermination();
+    }
+}

apache-spark/src/main/java/com/baeldung/data/pipeline/WordCountingAppWithCheckpoint.java

@@ -0,0 +1,140 @@
+package com.baeldung.data.pipeline;
+
+import static com.datastax.spark.connector.japi.CassandraJavaUtil.javaFunctions;
+import static com.datastax.spark.connector.japi.CassandraJavaUtil.mapToRow;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.kafka.clients.consumer.ConsumerRecord;
+import org.apache.kafka.common.serialization.StringDeserializer;
+import org.apache.log4j.Level;
+import org.apache.log4j.Logger;
+import org.apache.spark.SparkConf;
+import org.apache.spark.api.java.JavaPairRDD;
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.api.java.Optional;
+import org.apache.spark.api.java.function.FlatMapFunction;
+import org.apache.spark.api.java.function.Function;
+import org.apache.spark.api.java.function.Function2;
+import org.apache.spark.api.java.function.Function3;
+import org.apache.spark.api.java.function.PairFunction;
+import org.apache.spark.api.java.function.VoidFunction;
+import org.apache.spark.streaming.Durations;
+import org.apache.spark.streaming.State;
+import org.apache.spark.streaming.StateSpec;
+import org.apache.spark.streaming.api.java.JavaDStream;
+import org.apache.spark.streaming.api.java.JavaInputDStream;
+import org.apache.spark.streaming.api.java.JavaMapWithStateDStream;
+import org.apache.spark.streaming.api.java.JavaPairDStream;
+import org.apache.spark.streaming.api.java.JavaStreamingContext;
+import org.apache.spark.streaming.kafka010.ConsumerStrategies;
+import org.apache.spark.streaming.kafka010.KafkaUtils;
+import org.apache.spark.streaming.kafka010.LocationStrategies;
+
+import scala.Tuple2;
+
+public class WordCountingAppWithCheckpoint {
+
+    public static JavaSparkContext sparkContext;
+
+    @SuppressWarnings("serial")
+    public static void main(String[] args) throws InterruptedException {
+
+        Logger.getLogger("org")
+            .setLevel(Level.OFF);
+        Logger.getLogger("akka")
+            .setLevel(Level.OFF);
+
+        Map<String, Object> kafkaParams = new HashMap<>();
+        kafkaParams.put("bootstrap.servers", "localhost:9092");
+        kafkaParams.put("key.deserializer", StringDeserializer.class);
+        kafkaParams.put("value.deserializer", StringDeserializer.class);
+        kafkaParams.put("group.id", "use_a_separate_group_id_for_each_stream");
+        kafkaParams.put("auto.offset.reset", "latest");
+        kafkaParams.put("enable.auto.commit", false);
+
+        Collection<String> topics = Arrays.asList("messages");
+
+        SparkConf sparkConf = new SparkConf();
+        sparkConf.setMaster("local[2]");
+        sparkConf.setAppName("WordCountingAppWithCheckpoint");
+        sparkConf.set("spark.cassandra.connection.host", "127.0.0.1");
+
+        JavaStreamingContext streamingContext = new JavaStreamingContext(sparkConf, Durations.seconds(1));
+
+        sparkContext = streamingContext.sparkContext();
+
+        streamingContext.checkpoint("./.checkpoint");
+
+        JavaInputDStream<ConsumerRecord<String, String>> messages = KafkaUtils.createDirectStream(streamingContext, LocationStrategies.PreferConsistent(), ConsumerStrategies.<String, String> Subscribe(topics, kafkaParams));
+
+        JavaPairDStream<String, String> results = messages.mapToPair(new PairFunction<ConsumerRecord<String, String>, String, String>() {
+            @Override
+            public Tuple2<String, String> call(ConsumerRecord<String, String> record) {
+                return new Tuple2<>(record.key(), record.value());
+            }
+        });
+
+        JavaDStream<String> lines = results.map(new Function<Tuple2<String, String>, String>() {
+            @Override
+            public String call(Tuple2<String, String> tuple2) {
+                return tuple2._2();
+            }
+        });
+
+        JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
+            @Override
+            public Iterator<String> call(String x) {
+                return Arrays.asList(x.split("\\s+"))
+                    .iterator();
+            }
+        });
+
+        JavaPairDStream<String, Integer> wordCounts = words.mapToPair(new PairFunction<String, String, Integer>() {
+            @Override
+            public Tuple2<String, Integer> call(String s) {
+                return new Tuple2<>(s, 1);
+            }
+        })
+            .reduceByKey(new Function2<Integer, Integer, Integer>() {
+                @Override
+                public Integer call(Integer i1, Integer i2) {
+                    return i1 + i2;
+                }
+            });
+
+        Function3<String, Optional<Integer>, State<Integer>, Tuple2<String, Integer>> mappingFunc = (word, one, state) -> {
+            int sum = one.orElse(0) + (state.exists() ? state.get() : 0);
+            Tuple2<String, Integer> output = new Tuple2<>(word, sum);
+            state.update(sum);
+            return output;
+        };
+
+        JavaPairRDD<String, Integer> initialRDD = JavaPairRDD.fromJavaRDD(sparkContext.emptyRDD());
+
+        JavaMapWithStateDStream<String, Integer, Integer, Tuple2<String, Integer>> cumulativeWordCounts = wordCounts.mapWithState(StateSpec.function(mappingFunc)
+            .initialState(initialRDD));
+
+        cumulativeWordCounts.foreachRDD(new VoidFunction<JavaRDD<Tuple2<String, Integer>>>() {
+            @Override
+            public void call(JavaRDD<Tuple2<String, Integer>> javaRdd) throws Exception {
+                List<Tuple2<String, Integer>> wordCountList = javaRdd.collect();
+                for (Tuple2<String, Integer> tuple : wordCountList) {
+                    List<Word> words = Arrays.asList(new Word(tuple._1, tuple._2));
+                    JavaRDD<Word> rdd = sparkContext.parallelize(words);
+                    javaFunctions(rdd).writerBuilder("vocabulary", "words", mapToRow(Word.class))
+                        .saveToCassandra();
+                }
+            }
+        });
+
+        streamingContext.start();
+        streamingContext.awaitTermination();
+    }
+}

core-java-11/README.md

@@ -2,4 +2,4 @@
 
 - [Java 11 Single File Source Code](https://www.baeldung.com/java-single-file-source-code)
 - [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
-
+- [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)

core-java-8/README.md

@@ -33,3 +33,8 @@
 - [Java Primitives versus Objects](https://www.baeldung.com/java-primitives-vs-objects)
 - [How to Use if/else Logic in Java 8 Streams](https://www.baeldung.com/java-8-streams-if-else-logic)
 - [How to Replace Many if Statements in Java](https://www.baeldung.com/java-replace-if-statements)
+- [Java @Override Annotation](https://www.baeldung.com/java-override)
+- [Java @SuppressWarnings Annotation](https://www.baeldung.com/java-suppresswarnings)
+- [Java @SafeVarargs Annotation](https://www.baeldung.com/java-safevarargs)
+- [Java @Deprecated Annotation](https://www.baeldung.com/java-deprecated)
+- [Java 8 Predicate Chain](https://www.baeldung.com/java-predicate-chain)

core-java-9/src/main/java/com/baeldung/java9/set/UnmodifiableSet.java

@@ -0,0 +1,44 @@
+package com.baeldung.java9.set;
+
+import com.google.common.collect.ImmutableSet;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+public class UnmodifiableSet {
+
+    public static void main(String[] args) {
+
+        Set<String> set = new HashSet<>();
+        set.add("Canada");
+        set.add("USA");
+
+        coreJDK(set);
+        guavaOf();
+        copyOf(set);
+        java9Of();
+    }
+
+    private static void java9Of() {
+        Set<String> immutable = Set.of("Canada", "USA");
+        System.out.println(immutable);
+    }
+
+    private static void guavaOf() {
+        Set<String> immutable = ImmutableSet.of("Canada", "USA");
+        System.out.println(immutable);
+    }
+
+    private static void copyOf(Set<String> set) {
+        Set<String> immutable = ImmutableSet.copyOf(set);
+        set.add("Costa Rica");
+        System.out.println(immutable);
+    }
+
+    private static void coreJDK(Set<String> set) {
+        Set<String> unmodifiableSet = Collections.unmodifiableSet(set);
+        set.add("Costa Rica");
+        System.out.println(unmodifiableSet);
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/SetExamplesUnitTest.java

@@ -1,5 +1,7 @@
 package com.baeldung.java9;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Set;
 import org.junit.Test;
 
@@ -23,4 +25,14 @@ public class SetExamplesUnitTest {
         Set<Integer> intSet = Set.of(intArray);
         assertEquals(intSet.size(), intArray.length);
     }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void testUnmodifiableSet() {
+        Set<String> set = new HashSet<>();
+        set.add("Canada");
+        set.add("USA");
+
+        Set<String> unmodifiableSet = Collections.unmodifiableSet(set);
+        unmodifiableSet.add("Costa Rica");
+    }
 }

core-java-arrays/README.md

@@ -13,3 +13,4 @@
 - [How to Invert an Array in Java](http://www.baeldung.com/java-invert-array)
 - [Array Operations in Java](http://www.baeldung.com/java-common-array-operations)
 - [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
+- [Sorting Arrays in Java](https://www.baeldung.com/java-sorting-arrays)

core-java-collections-list/README.md

@@ -24,4 +24,5 @@
 - [Java List Initialization in One Line](https://www.baeldung.com/java-init-list-one-line)
 - [Ways to Iterate Over a List in Java](https://www.baeldung.com/java-iterate-list)
 - [ClassCastException: Arrays$ArrayList cannot be cast to ArrayList](https://www.baeldung.com/java-classcastexception-arrays-arraylist)
-- [Flattening Nested Collections in Java](http://www.baeldung.com/java-flatten-nested-collections)
+- [Flattening Nested Collections in Java](http://www.baeldung.com/java-flatten-nested-collections)
+- [Intersection of Two Lists in Java](https://www.baeldung.com/java-lists-intersection)

core-java-collections-list/src/main/java/com/baeldung/list/multidimensional/ArrayListOfArrayList.java

@@ -6,11 +6,11 @@ public class ArrayListOfArrayList {
 
     public static void main(String args[]) {
 
-        int numVertices = 3;
+        int vertexCount = 3;
-        ArrayList<ArrayList<Integer>> graph = new ArrayList<>(numVertices);
+        ArrayList<ArrayList<Integer>> graph = new ArrayList<>(vertexCount);
 
         //Initializing each element of ArrayList with ArrayList
-        for(int i=0; i< numVertices; i++) {
+        for(int i = 0; i< vertexCount; i++) {
             graph.add(new ArrayList<Integer>());
         }
 
@@ -21,13 +21,14 @@ public class ArrayListOfArrayList {
         graph.get(1).add(0);
         graph.get(2).add(1);
         graph.get(0).add(2);
-      
+
-        //Printing all the edges
+        vertexCount = graph.size();
-        for(int vertexNo=0; vertexNo<numVertices; vertexNo++) {
+        for(int i = 0; i < vertexCount; i++) {
-            int edgeCount = graph.get(vertexNo).size();
+            int edgeCount = graph.get(i).size();
-            ArrayList<Integer> listOfVertices = graph.get(vertexNo);
+            for(int j = 0; j < edgeCount; j++) {
-            for(int i=0; i<edgeCount; i++) {
+                Integer startVertex = i;
-                System.out.println("Vertex "+vertexNo+" is connected to vetex "+listOfVertices.get(i));
+                Integer endVertex = graph.get(i).get(j);
+                System.out.printf("Vertex %d is connected to vertex %d%n", startVertex, endVertex);
             }
         }
     }

core-java-collections-list/src/main/java/com/baeldung/list/multidimensional/ThreeDimensionalArrayList.java

@@ -12,9 +12,9 @@ public class ThreeDimensionalArrayList {
         ArrayList< ArrayList< ArrayList<String> > > space = new ArrayList<>(x_axis_length);
 
         //Initializing each element of ArrayList with ArrayList< ArrayList<String> >
-        for(int i=0; i< x_axis_length; i++) {
+        for(int i = 0; i < x_axis_length; i++) {
             space.add(new ArrayList< ArrayList<String> >(y_axis_length));
-            for(int j =0; j< y_axis_length; j++) {
+            for(int j = 0; j < y_axis_length; j++) {
                 space.get(i).add(new ArrayList<String>(z_axis_length));
             }
         }
@@ -33,9 +33,9 @@ public class ThreeDimensionalArrayList {
         space.get(1).get(1).add(1,"Yellow");
 
         //Printing colors for all the points
-        for(int i=0; i<x_axis_length; i++) {
+        for(int i = 0; i < x_axis_length; i++) {
-            for(int j=0; j<y_axis_length; j++) {
+            for(int j = 0; j < y_axis_length; j++) {
-                for(int k=0; k<z_axis_length; k++) {
+                for(int k = 0; k < z_axis_length; k++) {
                     System.out.println("Color of point ("+i+","+j+","+k+") is :"+space.get(i).get(j).get(k));
                 }
             }

core-java-collections/README.md

@@ -28,4 +28,6 @@
 - [Combining Different Types of Collections in Java](https://www.baeldung.com/java-combine-collections)
 - [Sorting in Java](http://www.baeldung.com/java-sorting)
 - [Join and Split Arrays and Collections in Java](http://www.baeldung.com/java-join-and-split)
-- [A Guide to EnumMap](https://www.baeldung.com/java-enum-map)
+- [A Guide to EnumMap](https://www.baeldung.com/java-enum-map)
+- [A Guide to Iterator in Java](http://www.baeldung.com/java-iterator)
+- [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)

core-java-io/README.md

@@ -35,3 +35,5 @@
 - [Guide to Java OutputStream](https://www.baeldung.com/java-outputstream)
 - [Reading a CSV File into an Array](https://www.baeldung.com/java-csv-file-array)
 - [Guide to BufferedReader](https://www.baeldung.com/java-buffered-reader)
+- [How to Get the File Extension of a File in Java](http://www.baeldung.com/java-file-extension)
+- [Getting a File’s Mime Type in Java](http://www.baeldung.com/java-file-mime-type)

core-java-io/pom.xml

@@ -160,6 +160,17 @@
             <version>${opencsv.version}</version>
             <scope>test</scope>
         </dependency>
+        <!-- Mime Type Resolution Libraries -->
+        <dependency>
+            <groupId>org.apache.tika</groupId>
+            <artifactId>tika-core</artifactId>
+            <version>${tika.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>net.sf.jmimemagic</groupId>
+            <artifactId>jmimemagic</artifactId>
+            <version>${jmime-magic.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -264,6 +275,9 @@
         <esapi.version>2.1.0.1</esapi.version>
         <jmh-generator-annprocess.version>1.19</jmh-generator-annprocess.version>
         <async-http-client.version>2.4.5</async-http-client.version>
+        <!-- Mime Type Libraries -->
+        <tika.version>1.18</tika.version>
+        <jmime-magic.version>0.1.5</jmime-magic.version>
     </properties>
 
 </project>

core-java-lang/README.md

@@ -33,3 +33,5 @@
 - [How to Separate Double into Integer and Decimal Parts](https://www.baeldung.com/java-separate-double-into-integer-decimal-parts)
 - [“Sneaky Throws” in Java](http://www.baeldung.com/java-sneaky-throws)
 - [Retrieving a Class Name in Java](https://www.baeldung.com/java-class-name)
+- [Java Compound Operators](https://www.baeldung.com/java-compound-operators)
+- [Guide to Java Packages](https://www.baeldung.com/java-packages)

core-java-security/README.md

@@ -0,0 +1,11 @@
+## Core Java Security 
+
+### Relevant Articles: 
+- [MD5 Hashing in Java](http://www.baeldung.com/java-md5)
+- [Guide to the Cipher Class](http://www.baeldung.com/java-cipher-class)
+- [Introduction to SSL in Java](http://www.baeldung.com/java-ssl)
+- [Java KeyStore API](http://www.baeldung.com/java-keystore)
+- [Encrypting and Decrypting Files in Java](http://www.baeldung.com/java-cipher-input-output-stream)
+- [Hashing a Password in Java](https://www.baeldung.com/java-password-hashing)
+- [SSL Handshake Failures](https://www.baeldung.com/java-ssl-handshake-failures)
+- [SHA-256 Hashing in Java](https://www.baeldung.com/sha-256-hashing-java)

core-java-security/pom.xml

@@ -0,0 +1,55 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-security</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-security</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>${commons-codec.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.bouncycastle</groupId>
+            <artifactId>bcprov-jdk15on</artifactId>
+            <version>${bouncycastle.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+
+        <!-- util -->
+        <commons-lang3.version>3.8.1</commons-lang3.version>
+        <bouncycastle.version>1.55</bouncycastle.version>
+        <commons-codec.version>1.10</commons-codec.version>
+
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+      
+    </properties>
+
+</project>

core-java-security/src/main/resources/logback.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <logger name="org.springframework" level="WARN" />
+    <logger name="org.springframework.transaction" level="WARN" />
+
+    <!-- in order to debug some marshalling issues, this needs to be TRACE -->
+    <logger name="org.springframework.web.servlet.mvc" level="WARN" />
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java/README.md

@@ -5,7 +5,6 @@
 ### Relevant Articles: 
 - [Java Timer](http://www.baeldung.com/java-timer-and-timertask)
 - [How to Run a Shell Command in Java](http://www.baeldung.com/run-shell-command-in-java)
-- [MD5 Hashing in Java](http://www.baeldung.com/java-md5)
 - [How to Print Screen in Java](http://www.baeldung.com/print-screen-in-java)
 - [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
 - [Getting Started with Java Properties](http://www.baeldung.com/java-properties)
@@ -23,44 +22,27 @@
 - [Difference between URL and URI](http://www.baeldung.com/java-url-vs-uri)
 - [Creating a Java Compiler Plugin](http://www.baeldung.com/java-build-compiler-plugin)
 - [Quick Guide to Java Stack](http://www.baeldung.com/java-stack)
-- [Guide to java.util.Formatter](http://www.baeldung.com/java-string-formatter)
-- [Guide to the Cipher Class](http://www.baeldung.com/java-cipher-class)
 - [Compiling Java *.class Files with javac](http://www.baeldung.com/javac)
-- [A Guide to Iterator in Java](http://www.baeldung.com/java-iterator)
 - [Introduction to Javadoc](http://www.baeldung.com/javadoc)
 - [Guide to the Externalizable Interface in Java](http://www.baeldung.com/java-externalizable)
-- [A Practical Guide to DecimalFormat](http://www.baeldung.com/java-decimalformat)
 - [How to Detect the OS Using Java](http://www.baeldung.com/java-detect-os)
 - [ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)
 - [What is the serialVersionUID?](http://www.baeldung.com/java-serial-version-uid)
 - [A Guide to the ResourceBundle](http://www.baeldung.com/java-resourcebundle)
 - [Class Loaders in Java](http://www.baeldung.com/java-classloaders)
-- [Introduction to SSL in Java](http://www.baeldung.com/java-ssl)
-- [Java KeyStore API](http://www.baeldung.com/java-keystore)
 - [Double-Checked Locking with Singleton](http://www.baeldung.com/java-singleton-double-checked-locking)
 - [Guide to Java Clock Class](http://www.baeldung.com/java-clock)
 - [Importance of Main Manifest Attribute in a Self-Executing JAR](http://www.baeldung.com/java-jar-executable-manifest-main-class)
-- [How to Get the File Extension of a File in Java](http://www.baeldung.com/java-file-extension)
 - [Java Global Exception Handler](http://www.baeldung.com/java-global-exception-handler)
-- [Encrypting and Decrypting Files in Java](http://www.baeldung.com/java-cipher-input-output-stream)
 - [How to Get the Size of an Object in Java](http://www.baeldung.com/java-size-of-object)
 - [Guide to Java Instrumentation](http://www.baeldung.com/java-instrumentation)
-- [Getting a File’s Mime Type in Java](http://www.baeldung.com/java-file-mime-type)
 - [Common Java Exceptions](http://www.baeldung.com/java-common-exceptions)
 - [Throw Exception in Optional in Java 8](https://www.baeldung.com/java-optional-throw-exception)
-- [Add a Character to a String at a Given Position](https://www.baeldung.com/java-add-character-to-string)
-- [Calculating the nth Root in Java](https://www.baeldung.com/java-nth-root)
-- [Convert Double to String, Removing Decimal Places](https://www.baeldung.com/java-double-to-string)
-- [ZoneOffset in Java](https://www.baeldung.com/java-zone-offset)
-- [Hashing a Password in Java](https://www.baeldung.com/java-password-hashing)
 - [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
-- [A Guide to SimpleDateFormat](https://www.baeldung.com/java-simple-date-format)
+- [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
-- [SSL Handshake Failures](https://www.baeldung.com/java-ssl-handshake-failures)
-- [Changing the Order in a Sum Operation Can Produce Different Results?](https://www.baeldung.com/java-floating-point-sum-order)
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)
 - [Guide to Character Encoding](https://www.baeldung.com/java-char-encoding)
-- [Calculate the Area of a Circle in Java](https://www.baeldung.com/java-calculate-circle-area)
-- [A Guide to the Java Math Class](https://www.baeldung.com/java-lang-math)
 - [Graphs in Java](https://www.baeldung.com/java-graphs)
 - [Console I/O in Java](http://www.baeldung.com/java-console-input-output)
+- [Formatting with printf() in Java](https://www.baeldung.com/java-printstream-printf)

core-java/pom.xml

@@ -24,11 +24,6 @@
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
         </dependency>
-        <dependency>
-            <groupId>org.bouncycastle</groupId>
-            <artifactId>bcprov-jdk15on</artifactId>
-            <version>${bouncycastle.version}</version>
-        </dependency>
         <dependency>
             <groupId>org.unix4j</groupId>
             <artifactId>unix4j-command</artifactId>
@@ -75,12 +70,6 @@
             <version>${assertj-core.version}</version>
             <scope>test</scope>
         </dependency>
-
-        <dependency>
-            <groupId>commons-codec</groupId>
-            <artifactId>commons-codec</artifactId>
-            <version>${commons-codec.version}</version>
-        </dependency>
         <dependency>
             <groupId>org.javamoney</groupId>
             <artifactId>moneta</artifactId>
@@ -126,17 +115,6 @@
             <artifactId>h2</artifactId>
             <version>${h2database.version}</version>
         </dependency>
-        <!-- Mime Type Resolution Libraries -->
-        <dependency>
-            <groupId>org.apache.tika</groupId>
-            <artifactId>tika-core</artifactId>
-            <version>${tika.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>net.sf.jmimemagic</groupId>
-            <artifactId>jmimemagic</artifactId>
-            <version>${jmime-magic.version}</version>
-        </dependency>
         <!-- instrumentation -->
         <dependency>
             <groupId>org.javassist</groupId>
@@ -477,8 +455,6 @@
 
         <!-- util -->
         <commons-lang3.version>3.5</commons-lang3.version>
-        <bouncycastle.version>1.55</bouncycastle.version>
-        <commons-codec.version>1.10</commons-codec.version>
         <commons-io.version>2.5</commons-io.version>
         <commons-math3.version>3.6.1</commons-math3.version>
         <decimal4j.version>1.0.3</decimal4j.version>
@@ -509,9 +485,6 @@
         <spring-boot-maven-plugin.version>2.0.3.RELEASE</spring-boot-maven-plugin.version>
         <exec-maven-plugin.version>1.6.0</exec-maven-plugin.version>
         <icu4j.version>61.1</icu4j.version>
-        <!-- Mime Type Libraries -->
-        <tika.version>1.18</tika.version>
-        <jmime-magic.version>0.1.5</jmime-magic.version>
         <!-- instrumentation -->
         <javaassist.version>3.21.0-GA</javaassist.version>
         

core-java/src/main/java/com/baeldung/curltojava/JavaCurlExamples.java

@@ -0,0 +1,29 @@
+package com.baeldung.curltojava;
+
+import java.io.BufferedInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class JavaCurlExamples {
+
+    public static String inputStreamToString(InputStream inputStream) {
+        final int bufferSize = 8 * 1024;
+        byte[] buffer = new byte[bufferSize];
+        final StringBuilder builder = new StringBuilder();
+        try (BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream, bufferSize)) {
+            while (bufferedInputStream.read(buffer) != -1) {
+                builder.append(new String(buffer));
+            }
+        } catch (IOException ex) {
+            Logger.getLogger(JavaCurlExamples.class.getName()).log(Level.SEVERE, null, ex);
+        }
+        return builder.toString();
+    }
+
+    public static void consumeInputStream(InputStream inputStream) {
+        inputStreamToString(inputStream);
+    }
+
+}

core-java/src/test/java/com/baeldung/curltojava/JavaCurlExamplesUnitTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.curltojava;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class JavaCurlExamplesUnitTest {
+
+
+    @Test
+    public void givenCommand_whenCalled_thenProduceZeroExitCode() throws IOException {
+        String command = "curl --location --request GET \"https://postman-echo.com/get?foo1=bar1&foo2=bar2\"";
+        ProcessBuilder processBuilder = new ProcessBuilder(command.replaceAll("\"", "").split(" "));
+        processBuilder.directory(new File("/home/"));
+        Process process = processBuilder.start();
+        InputStream inputStream = process.getInputStream();
+        // Consume the inputStream so the process can exit
+        JavaCurlExamples.consumeInputStream(inputStream);
+        int exitCode = process.exitValue();
+        
+        Assert.assertEquals(0, exitCode);
+    }
+    
+    @Test
+    public void givenNewCommands_whenCalled_thenCheckIfIsAlive() throws IOException {
+        String command = "curl --location --request GET \"https://postman-echo.com/get?foo1=bar1&foo2=bar2\"";
+        ProcessBuilder processBuilder = new ProcessBuilder(command.replaceAll("\"", "").split(" "));
+        processBuilder.directory(new File("/home/"));
+        Process process = processBuilder.start();
+        
+        // Re-use processBuilder
+        processBuilder.command(new String[]{"newCommand", "arguments"});
+        
+        Assert.assertEquals(true, process.isAlive());
+    }
+
+    @Test
+    public void whenRequestGet_thenReturnSuccessResponseCode() throws IOException {
+        String url = "https://postman-echo.com/get?foo1=bar1&foo2=bar2";
+        URL urlObj = new URL(url);
+        HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();
+        connection.setDoOutput(true);
+        connection.setInstanceFollowRedirects(false);
+        connection.setRequestMethod("GET");
+        connection.connect();
+        
+        Assert.assertEquals(HttpURLConnection.HTTP_OK, connection.getResponseCode());
+    }
+
+}

core-java/src/test/java/com/baeldung/string/StringReplaceAndRemoveUnitTest.java

@@ -1,83 +0,0 @@
-package com.baeldung.string;
-
-
-import org.apache.commons.lang3.StringUtils;
-import org.junit.Test;
-
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
-
-public class StringReplaceAndRemoveUnitTest {
-
-
-    @Test
-    public void givenTestStrings_whenReplace_thenProcessedString() {
-
-        String master = "Hello World Baeldung!";
-        String target = "Baeldung";
-        String replacement = "Java";
-        String processed = master.replace(target, replacement);
-        assertTrue(processed.contains(replacement));
-        assertFalse(processed.contains(target));
-
-    }
-
-    @Test
-    public void givenTestStrings_whenReplaceAll_thenProcessedString() {
-
-        String master2 = "Welcome to Baeldung, Hello World Baeldung";
-        String regexTarget= "(Baeldung)$";
-        String replacement = "Java";
-        String processed2 = master2.replaceAll(regexTarget, replacement);
-        assertTrue(processed2.endsWith("Java"));
-
-    }
-
-    @Test
-    public void givenTestStrings_whenStringBuilderMethods_thenProcessedString() {
-
-        String master = "Hello World Baeldung!";
-        String target = "Baeldung";
-        String replacement = "Java";
-
-        int startIndex = master.indexOf(target);
-        int stopIndex = startIndex + target.length();
-
-        StringBuilder builder = new StringBuilder(master);
-
-
-        builder.delete(startIndex, stopIndex);
-        assertFalse(builder.toString().contains(target));
-
-
-        builder.replace(startIndex, stopIndex, replacement);
-        assertTrue(builder.toString().contains(replacement));
-
-
-    }
-
-
-    @Test
-    public void givenTestStrings_whenStringUtilsMethods_thenProcessedStrings() {
-
-        String master = "Hello World Baeldung!";
-        String target = "Baeldung";
-        String replacement = "Java";
-
-        String processed = StringUtils.replace(master, target, replacement);
-        assertTrue(processed.contains(replacement));
-
-        String master2 = "Hello World Baeldung!";
-        String target2 = "baeldung";
-        String processed2 = StringUtils.replaceIgnoreCase(master2, target2, replacement);
-        assertFalse(processed2.contains(target));
-
-    }
-
-
-
-
-
-
-
-}

core-kotlin/README.md

@@ -47,3 +47,7 @@
 - [Dependency Injection for Kotlin with Injekt](https://www.baeldung.com/kotlin-dependency-injection-with-injekt)
 - [Implementing a Binary Tree in Kotlin](https://www.baeldung.com/kotlin-binary-tree)
 - [Generate a Random Alphanumeric String in Kotlin](https://www.baeldung.com/kotlin-random-alphanumeric-string)
+- [Kotlin Contracts](https://www.baeldung.com/kotlin-contracts)
+- [Operator Overloading in Kotlin](https://www.baeldung.com/kotlin-operator-overloading)
+- [Inline Classes in Kotlin](https://www.baeldung.com/kotlin-inline-classes)
+- [Creating Java static final Equivalents in Kotlin](https://www.baeldung.com/kotlin-java-static-final)

gson/README.md

@@ -9,3 +9,4 @@
 - [Exclude Fields from Serialization in Gson](http://www.baeldung.com/gson-exclude-fields-serialization)
 - [Save Data to a JSON File with Gson](https://www.baeldung.com/gson-save-file)
 - [Convert JSON to a Map Using Gson](https://www.baeldung.com/gson-json-to-map)
+- [Working with Primitive Values in Gson](https://www.baeldung.com/java-gson-primitives)

guava/README.md

@@ -18,4 +18,3 @@
 - [Hamcrest Text Matchers](http://www.baeldung.com/hamcrest-text-matchers)
 - [Quick Guide to the Guava RateLimiter](http://www.baeldung.com/guava-rate-limiter)
 - [Hamcrest File Matchers](https://www.baeldung.com/hamcrest-file-matchers)
-- [SHA-256 Hashing in Java](https://www.baeldung.com/sha-256-hashing-java)

java-collections-maps/README.md

@@ -17,3 +17,5 @@
 - [Finding the Highest Value in a Java Map](https://www.baeldung.com/java-find-map-max)
 - [Merging Two Maps with Java 8](https://www.baeldung.com/java-merge-maps)
 - [How to Check If a Key Exists in a Map](https://www.baeldung.com/java-map-key-exists)
+- [Comparing Two HashMaps in Java](https://www.baeldung.com/java-compare-hashmaps)
+- [Immutable Map Implementations in Java](https://www.baeldung.com/java-immutable-maps) 

java-dates/README.md

@@ -26,3 +26,5 @@
 - [Format ZonedDateTime to String](https://www.baeldung.com/java-format-zoned-datetime-string)
 - [Convert Between java.time.Instant and java.sql.Timestamp](https://www.baeldung.com/java-time-instant-to-java-sql-timestamp)
 - [Convert between String and Timestamp](https://www.baeldung.com/java-string-to-timestamp)
+- [A Guide to SimpleDateFormat](https://www.baeldung.com/java-simple-date-format)
+- [ZoneOffset in Java](https://www.baeldung.com/java-zone-offset)

java-dates/src/test/java/com/baeldung/date/DateDiffUnitTest.java

@@ -8,6 +8,8 @@ import java.time.Duration;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.Period;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
 import java.time.temporal.ChronoUnit;
 import java.util.Date;
 import java.util.Locale;

java-numbers/README.md

@@ -13,3 +13,9 @@
 - [Find All Pairs of Numbers in an Array That Add Up to a Given Sum](http://www.baeldung.com/java-algorithm-number-pairs-sum)
 - [Java – Random Long, Float, Integer and Double](http://www.baeldung.com/java-generate-random-long-float-integer-double)
 - [Using Math.sin with Degrees](https://www.baeldung.com/java-math-sin-degrees)
+- [A Practical Guide to DecimalFormat](http://www.baeldung.com/java-decimalformat)
+- [Calculating the nth Root in Java](https://www.baeldung.com/java-nth-root)
+- [Convert Double to String, Removing Decimal Places](https://www.baeldung.com/java-double-to-string)
+- [Changing the Order in a Sum Operation Can Produce Different Results?](https://www.baeldung.com/java-floating-point-sum-order)
+- [Calculate the Area of a Circle in Java](https://www.baeldung.com/java-calculate-circle-area)
+- [A Guide to the Java Math Class](https://www.baeldung.com/java-lang-math)

java-streams/README.md

@@ -14,3 +14,4 @@
 - [Primitive Type Streams in Java 8](http://www.baeldung.com/java-8-primitive-streams)
 - [Stream Ordering in Java](https://www.baeldung.com/java-stream-ordering)
 - [Introduction to Protonpack](https://www.baeldung.com/java-protonpack)
+- [Java Stream Filter with Lambda Expression](https://www.baeldung.com/java-stream-filter-lambda)

java-strings/README.md

@@ -45,3 +45,7 @@
 - [Remove or Replace part of a String in Java](https://www.baeldung.com/java-remove-replace-string-part)
 - [Replace a Character at a Specific Index in a String in Java](https://www.baeldung.com/java-replace-character-at-index)
 - [Convert a Comma Separated String to a List in Java](https://www.baeldung.com/java-string-with-separator-to-list)
+- [Guide to java.util.Formatter](http://www.baeldung.com/java-string-formatter)
+- [Add a Character to a String at a Given Position](https://www.baeldung.com/java-add-character-to-string)
+- [Remove Leading and Trailing Characters from a String](https://www.baeldung.com/java-remove-trailing-characters)
+- [Concatenating Strings In Java](https://www.baeldung.com/java-strings-concatenation)

java-strings/src/test/java/com/baeldung/string/formatter/DateToStringFormatterUnitTest.java

@@ -1,7 +1,6 @@
 package com.baeldung.string.formatter;
 
-import org.junit.BeforeClass;
+import static org.junit.Assert.assertEquals;
-import org.junit.Test;
 
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
@@ -11,9 +10,11 @@ import java.time.ZoneId;
 import java.time.format.DateTimeFormatter;
 import java.util.Calendar;
 import java.util.Date;
+import java.util.Locale;
 import java.util.TimeZone;
 
-import static org.junit.Assert.assertEquals;
+import org.junit.BeforeClass;
+import org.junit.Test;
 
 public class DateToStringFormatterUnitTest {
 
@@ -40,7 +41,7 @@ public class DateToStringFormatterUnitTest {
     @Test
     public void whenDateConvertedUsingDateFormatToString_thenCorrect() {
         String formattedDate = DateFormat
-          .getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT)
+          .getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT, Locale.US)
           .format(date);
 
         assertEquals(EXPECTED_STRING_DATE, formattedDate);

java-strings/src/test/java/com/baeldung/string/interview/LocaleUnitTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.string.interview;
+
+import java.math.BigDecimal;
+import java.text.NumberFormat;
+import java.util.Locale;
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class LocaleUnitTest {
+    @Test
+    public void whenUsingLocal_thenCorrectResultsForDifferentLocale() {
+        Locale usLocale = Locale.US;
+        BigDecimal number = new BigDecimal(102_300.456d);
+         
+        NumberFormat usNumberFormat = NumberFormat.getCurrencyInstance(usLocale); 
+        assertEquals(usNumberFormat.format(number), "$102,300.46");
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringAnagramUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.interview;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+
+import org.junit.Test;
+
+public class StringAnagramUnitTest {
+    public boolean isAnagram(String s1, String s2) {
+        if(s1.length() != s2.length())
+            return false;
+            
+        char[] arr1 = s1.toCharArray();
+        char[] arr2 = s2.toCharArray();
+        
+        Arrays.sort(arr1);
+        Arrays.sort(arr2);
+        
+        return Arrays.equals(arr1, arr2);
+    }
+    
+    @Test
+    public void whenTestAnagrams_thenTestingCorrectly() {
+        assertThat(isAnagram("car", "arc")).isTrue();
+        assertThat(isAnagram("west", "stew")).isTrue();
+        assertThat(isAnagram("west", "east")).isFalse();
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringChangeCaseUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.string.interview;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class StringChangeCaseUnitTest {
+    @Test
+    public void givenString_whenChangingToUppercase_thenCaseChanged() {
+        String s = "Welcome to Baeldung!";
+        assertEquals("WELCOME TO BAELDUNG!", s.toUpperCase());
+    }
+    
+
+    @Test
+    public void givenString_whenChangingToLowerrcase_thenCaseChanged() {
+        String s = "Welcome to Baeldung!";
+        assertEquals("welcome to baeldung!", s.toLowerCase());
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringCountOccurrencesUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.string.interview;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class StringCountOccurrencesUnitTest {
+    public int countOccurrences(String s, char c) {
+        int count = 0;
+        for (int i = 0; i < s.length(); i++) {
+            if (s.charAt(i) == c) {
+                count++;
+            }
+        }
+        return count;
+    }
+
+    @Test
+    public void givenString_whenCountingFrequencyOfChar_thenCountCorrect() {
+        assertEquals(3, countOccurrences("united states", 't'));
+    }
+
+    public void givenString_whenUsingJava8_thenCountingOfCharCorrect() {
+        String str = "united states";
+        long count = str.chars().filter(ch -> (char)ch == 't').count();
+        assertEquals(3, count);
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringFormatUnitTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.string.interview;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class StringFormatUnitTest {
+    @Test
+    public void givenString_whenUsingStringFormat_thenStringFormatted() {
+        String title = "Baeldung"; 
+        String formatted = String.format("Title is %s", title);
+        assertEquals(formatted, "Title is Baeldung");
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringInternUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.string.interview;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class StringInternUnitTest {
+    @Test
+    public void whenCallingStringIntern_thenStringsInterned() {
+        String s1 = "Baeldung";
+        String s2 = new String("Baeldung");
+        String s3 = new String("Baeldung").intern();
+         
+        assertThat(s1 == s2).isFalse();
+        assertThat(s1 == s3).isTrue();
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringJoinerUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.string.interview;
+
+import java.util.StringJoiner;
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class StringJoinerUnitTest {
+    @Test
+    public void whenUsingStringJoiner_thenStringsJoined() {
+        StringJoiner joiner = new StringJoiner(",", "[", "]");
+        joiner.add("Red")
+          .add("Green")
+          .add("Blue");
+         
+        assertEquals(joiner.toString(), "[Red,Green,Blue]");
+    }
+}

java-strings/src/test/java/com/baeldung/string/interview/StringPalindromeUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.interview;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class StringPalindromeUnitTest {
+    
+    public boolean isPalindrome(String text) {
+        int forward = 0;
+        int backward = text.length() - 1;
+        while (backward > forward) {
+            char forwardChar = text.charAt(forward++);
+            char backwardChar = text.charAt(backward--);
+            if (forwardChar != backwardChar)
+                return false;
+        }
+        return true;
+    }
+    
+    @Test
+    public void givenIsPalindromeMethod_whenCheckingString_thenFindIfPalindrome() {
+        assertThat(isPalindrome("madam")).isTrue();
+        assertThat(isPalindrome("radar")).isTrue();
+        assertThat(isPalindrome("level")).isTrue();
+
+        assertThat(isPalindrome("baeldung")).isFalse();
+    }
+}