Merge pull request #83 from eugenp/master

update

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/AnnotatedClass.java

@@ -0,0 +1,8 @@
+package com.baeldung.annotations;
+
+import javax.annotation.Generated;
+
+@RetentionAnnotation
+@Generated("Available only on source code")
+public class AnnotatedClass {
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/RetentionAnnotation.java

@@ -0,0 +1,12 @@
+package com.baeldung.annotations;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.TYPE;
+
+@Target(TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface RetentionAnnotation {
+}

core-java-modules/core-java-annotations/src/test/java/com/baeldung/annotations/AnnotatedClassUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.annotations;
+
+import org.junit.Test;
+
+import java.lang.annotation.Annotation;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+public class AnnotatedClassUnitTest {
+
+    @Test
+    public void whenAnnotationRetentionPolicyRuntime_shouldAccess() {
+        AnnotatedClass anAnnotatedClass = new AnnotatedClass();
+        Annotation[] annotations = anAnnotatedClass.getClass().getAnnotations();
+        assertThat(annotations.length, is(1));
+    }
+}

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

@@ -25,7 +25,7 @@
     </dependencies>
 
     <properties>
-        <assertj.version>3.18.0</assertj.version>
+        <assertj.version>3.19.0</assertj.version>
     </properties>
 
 </project>

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/dequestack/ArrayLifoStack.java

@@ -0,0 +1,91 @@
+package com.baeldung.collections.dequestack;
+
+import java.util.ArrayDeque;
+import java.util.Collection;
+import java.util.Deque;
+import java.util.Iterator;
+
+public class ArrayLifoStack<E> implements LifoStack<E> {
+    private final Deque<E> deque = new ArrayDeque<>();
+
+    @Override
+    public void push(E item) {
+        deque.addFirst(item);
+    }
+
+    @Override
+    public E pop() {
+        return deque.removeFirst();
+    }
+
+    @Override
+    public E peek() {
+        return deque.peekFirst();
+    }
+
+    // implementing methods from the Collection interface
+    @Override
+    public int size() {
+        return deque.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return deque.isEmpty();
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        return deque.contains(o);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return deque.iterator();
+    }
+
+    @Override
+    public Object[] toArray() {
+        return deque.toArray();
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+        return deque.toArray(a);
+    }
+
+    @Override
+    public boolean add(E e) {
+        return deque.add(e);
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        return deque.remove(o);
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        return deque.containsAll(c);
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+        return deque.addAll(c);
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+        return deque.removeAll(c);
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+        return deque.retainAll(c);
+    }
+
+    @Override
+    public void clear() {
+        deque.clear();
+    }
+}

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/dequestack/LifoStack.java

@@ -0,0 +1,12 @@
+package com.baeldung.collections.dequestack;
+
+import java.util.Collection;
+
+public interface LifoStack<E> extends Collection<E> {
+
+    E peek();
+
+    E pop();
+
+    void push(E item);
+}

core-java-modules/core-java-collections-4/src/test/java/com/baeldung/collections/dequestack/StackVsDequeUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.collections.dequestack;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.Iterator;
+import java.util.Stack;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class StackVsDequeUnitTest {
+
+    @Test
+    void givenAStack_whenAccessByIndex_thenElementCanBeRead() {
+        Stack<String> myStack = new Stack<>();
+        myStack.push("I am the 1st element."); //index 0
+        myStack.push("I am the 2nd element."); //index 1
+        myStack.push("I am the 3rd element."); //index 2
+        //access by index
+        assertThat(myStack.get(0)).isEqualTo("I am the 1st element.");
+    }
+
+    @Test
+    void givenAStack_whenIterate_thenFromBottomToTop() {
+        Stack<String> myStack = new Stack<>();
+        myStack.push("I am at the bottom.");
+        myStack.push("I am in the middle.");
+        myStack.push("I am at the top.");
+
+        Iterator<String> it = myStack.iterator();
+
+        assertThat(it).toIterable().containsExactly(
+          "I am at the bottom.",
+          "I am in the middle.",
+          "I am at the top.");
+    }
+
+    @Test
+    void givenAStack_whenAddOrRemoveByIndex_thenElementCanBeAddedOrRemoved() {
+        Stack<String> myStack = new Stack<>();
+        myStack.push("I am the 1st element.");
+        myStack.push("I am the 3rd element.");
+
+        assertThat(myStack.size()).isEqualTo(2);
+
+        //insert by index
+        myStack.add(1, "I am the 2nd element.");
+        assertThat(myStack.size()).isEqualTo(3);
+        assertThat(myStack.get(1)).isEqualTo("I am the 2nd element.");
+        //remove by index
+        myStack.remove(1);
+        assertThat(myStack.size()).isEqualTo(2);
+    }
+
+    @Test
+    void givenADeque_whenAddOrRemoveLastElement_thenTheLastElementCanBeAddedOrRemoved() {
+        Deque<String> myStack = new ArrayDeque<>();
+        myStack.push("I am the 1st element.");
+        myStack.push("I am the 2nd element.");
+        myStack.push("I am the 3rd element.");
+
+        assertThat(myStack.size()).isEqualTo(3);
+
+        //insert element to the bottom of the stack
+        myStack.addLast("I am the NEW element.");
+        assertThat(myStack.size()).isEqualTo(4);
+        assertThat(myStack.peek()).isEqualTo("I am the 3rd element.");
+
+        //remove element from the bottom of the stack
+        String removedStr = myStack.removeLast();
+        assertThat(myStack.size()).isEqualTo(3);
+        assertThat(removedStr).isEqualTo("I am the NEW element.");
+    }
+
+    @Test
+    void givenADeque_whenIterate_thenFromTopToBottom() {
+        Deque<String> myStack = new ArrayDeque<>();
+        myStack.push("I am at the bottom.");
+        myStack.push("I am in the middle.");
+        myStack.push("I am at the top.");
+
+        Iterator<String> it = myStack.iterator();
+
+        assertThat(it).toIterable().containsExactly(
+          "I am at the top.",
+          "I am in the middle.",
+          "I am at the bottom.");
+    }
+}

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

@@ -7,4 +7,5 @@ This module contains articles about Map data structures in Java.
 - [Comparing Two HashMaps in Java](https://www.baeldung.com/java-compare-hashmaps)
 - [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)
 - More articles: [[<-- prev]](/core-java-modules/core-java-collections-maps-2)

core-java-modules/core-java-jpms/decoupling-pattern2/consumermodule/pom.xml

@@ -17,7 +17,7 @@
     <dependencies>
         <dependency>
             <groupId>com.baeldung.servicemodule</groupId>
-            <artifactId>servicemodule</artifactId>
+            <artifactId>servicemodule2</artifactId>
             <version>${servicemodule.version}</version>
         </dependency>
         <dependency>
@@ -41,4 +41,4 @@
         <providermodule.version>1.0</providermodule.version>
     </properties>
 
-</project>
+</project>

core-java-modules/core-java-lang-oop-generics/README.md

@@ -8,3 +8,4 @@ This module contains articles about generics in Java
 - [Raw Types in Java](https://www.baeldung.com/raw-types-java)
 - [Super Type Tokens in Java Generics](https://www.baeldung.com/java-super-type-tokens)
 - [Java Warning “unchecked conversion”](https://www.baeldung.com/java-unchecked-conversion)
+- [Java Warning “Unchecked Cast”](https://www.baeldung.com/java-warning-unchecked-cast)

core-java-modules/core-java-lang-oop-generics/src/main/java/com/baeldung/uncheckedcast/UncheckedCast.java

@@ -0,0 +1,26 @@
+package com.baeldung.uncheckedcast;
+
+import java.time.LocalDate;
+import java.time.Month;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.Map;
+
+public class UncheckedCast {
+    public static Map getRawMap() {
+        Map rawMap = new HashMap();
+        rawMap.put("date 1", LocalDate.of(2021, Month.FEBRUARY, 10));
+        rawMap.put("date 2", LocalDate.of(1992, Month.AUGUST, 8));
+        rawMap.put("date 3", LocalDate.of(1976, Month.NOVEMBER, 18));
+        return rawMap;
+    }
+
+    public static Map getRawMapWithMixedTypes() {
+        Map rawMap = new HashMap();
+        rawMap.put("date 1", LocalDate.of(2021, Month.FEBRUARY, 10));
+        rawMap.put("date 2", LocalDate.of(1992, Month.AUGUST, 8));
+        rawMap.put("date 3", LocalDate.of(1976, Month.NOVEMBER, 18));
+        rawMap.put("date 4", new Date());
+        return rawMap;
+    }
+}

core-java-modules/core-java-lang-oop-generics/src/test/java/com/baeldung/uncheckedcast/UncheckedCastUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.uncheckedcast;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.LocalDate;
+import java.time.Month;
+import java.util.Map;
+
+public class UncheckedCastUnitTest {
+
+    @Test
+    public void givenRawMap_whenCastToTypedMap_shouldHaveCompilerWarning() {
+        Map<String, LocalDate> castFromRawMap = (Map<String, LocalDate>) UncheckedCast.getRawMap();
+        Assert.assertEquals(3, castFromRawMap.size());
+        Assert.assertEquals(castFromRawMap.get("date 2"), LocalDate.of(1992, Month.AUGUST, 8));
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenMixTypedRawMap_whenCastToTypedMap_shouldThrowClassCastException() {
+        Map<String, LocalDate> castFromRawMap = (Map<String, LocalDate>) UncheckedCast.getRawMapWithMixedTypes();
+        Assert.assertEquals(4, castFromRawMap.size());
+        Assert.assertTrue(castFromRawMap.get("date 4").isAfter(castFromRawMap.get("date 3")));
+    }
+}

core-java-modules/core-java-nio-2/pom.xml

@@ -14,5 +14,12 @@
         <version>0.0.1-SNAPSHOT</version>
         <relativePath>../</relativePath>
     </parent>
-
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.6.1</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
 </project>

core-java-modules/core-java-nio-2/src/test/java/com/baeldung/selector/SelectorManualTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.selector;
+
+import org.junit.Test;
+import java.io.IOException;
+import java.nio.channels.Pipe;
+import java.nio.channels.SelectableChannel;
+import java.nio.channels.Selector;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import static java.nio.channels.SelectionKey.OP_READ;
+
+public class SelectorManualTest {
+
+    @Test
+    public void whenWakeUpCalledOnSelector_thenBlockedThreadReturns() throws IOException, InterruptedException {
+        Pipe pipe = Pipe.open();
+
+        Selector selector = Selector.open();
+        SelectableChannel channel = pipe.source();
+        channel.configureBlocking(false);
+        channel.register(selector, OP_READ);
+
+        List<String> invocationStepsTracker = Collections.synchronizedList(new ArrayList<>());
+
+        CountDownLatch latch = new CountDownLatch(1);
+
+        Thread thread = new Thread(() -> {
+            invocationStepsTracker.add(">> Count down");
+            latch.countDown();
+            try {
+                invocationStepsTracker.add(">> Start select");
+                selector.select();
+                invocationStepsTracker.add(">> End select");
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        });
+
+        invocationStepsTracker.add(">> Start await");
+        thread.start();
+        latch.await();
+        invocationStepsTracker.add(">> End await");
+
+        invocationStepsTracker.add(">> Wakeup thread");
+
+        selector.wakeup();
+        channel.close();
+
+        assertThat(invocationStepsTracker)
+          .containsExactly(
+            ">> Start await",
+            ">> Count down",
+            ">> Start select",
+            ">> End await",
+            ">> Wakeup thread",
+            ">> End select"
+          );
+    }
+}

docker/README.md

@@ -3,3 +3,4 @@
 - [Introduction to Docker Compose](https://www.baeldung.com/docker-compose)
 - [Reusing Docker Layers with Spring Boot](https://www.baeldung.com/docker-layers-spring-boot)
 - [Running Spring Boot with PostgreSQL in Docker Compose](https://www.baeldung.com/spring-boot-postgresql-docker)
+- [How To Configure Java Heap Size Inside a Docker Container](https://www.baeldung.com/ops/docker-jvm-heap-size)

docker/heap-sizing/Dockerfile

@@ -0,0 +1,4 @@
+FROM openjdk:8u92-jdk-alpine
+COPY /src /src/
+RUN mkdir /app && ls /src && javac /src/main/java/com/baeldung/docker/heapsizing/PrintXmxXms.java -d /app
+CMD java -version && java $JAVA_OPTS -cp /app com.baeldung.docker.heapsizing.PrintXmxXms

docker/heap-sizing/pom.xml

@@ -0,0 +1,61 @@
+<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.4.2</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+    <groupId>com.baeldung.docker</groupId>
+    <artifactId>heap-sizing</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>heap-sizing</name>
+    <description>Demo project for Spring Boot</description>
+    <properties>
+        <java.version>11</java.version>
+    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-webflux</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+                <configuration>
+                    <image>
+                        <name>heapsizing-demo</name>
+                    </image>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>com.google.cloud.tools</groupId>
+                <artifactId>jib-maven-plugin</artifactId>
+                <version>2.7.1</version>
+
+                <configuration>
+                    <to>
+                        <image>heapsizing-demo-jib</image>
+                    </to>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

docker/heap-sizing/src/main/java/com/baeldung/docker/heapsizing/HeapSizingApplication.java

@@ -0,0 +1,19 @@
+package com.baeldung.docker.heapsizing;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+import java.util.logging.Logger;
+
+import static com.baeldung.docker.heapsizing.PrintXmxXms.logMemory;
+
+@SpringBootApplication
+public class HeapSizingApplication {
+    private static final Logger logger = Logger.getLogger(HeapSizingApplication.class.getName());
+
+    public static void main(String[] args) {
+        SpringApplication.run(HeapSizingApplication.class, args);
+        logMemory(logger);
+    }
+
+}

docker/heap-sizing/src/main/java/com/baeldung/docker/heapsizing/PrintXmxXms.java

@@ -0,0 +1,36 @@
+package com.baeldung.docker.heapsizing;
+
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryMXBean;
+import java.lang.management.MemoryPoolMXBean;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class PrintXmxXms {
+
+    private static final Logger logger = Logger.getLogger(PrintXmxXms.class.getName());
+
+    public static void main(String[] args) {
+        logMemory(logger);
+    }
+
+    /**
+     * We're reusing this method in HeapSizingApplication, therefore this method was extracted
+     * to avoid repetition.
+     */
+    static void logMemory(Logger logger) {
+        float mb = 1024f * 1024f;
+        MemoryMXBean memoryBean = ManagementFactory.getMemoryMXBean();
+
+        // xmx controls the maximum size of the memory allocation pool,
+        // which includes the heap, the garbage collector's survivor space, and other pools.
+        float xmx = memoryBean.getHeapMemoryUsage().getMax() / mb;
+        float xms = memoryBean.getHeapMemoryUsage().getInit() / mb;
+        logger.log(Level.INFO, "Initial Memory (xms) : {0}mb", xms);
+        logger.log(Level.INFO, "Max Memory (xmx) : {0}mb", xmx);
+
+        for (MemoryPoolMXBean mp : ManagementFactory.getMemoryPoolMXBeans()) {
+            logger.log(Level.INFO, "Pool: {0} (type {1}) = {2}", new Object[]{ mp.getName(), mp.getType(), mp.getUsage().getMax() / mb });
+        }
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/Member.java

@@ -0,0 +1,6 @@
+package com.baeldung.map.hashing;
+
+class Member {
+    Integer id;
+    String name;
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithBadHashing.java

@@ -0,0 +1,8 @@
+package com.baeldung.map.hashing;
+
+public class MemberWithBadHashing extends Member {
+    @Override
+    public int hashCode() {
+        return name.hashCode();
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithGuavaHashing.java

@@ -0,0 +1,18 @@
+package com.baeldung.map.hashing;
+
+import com.google.common.base.Charsets;
+import com.google.common.hash.HashFunction;
+import com.google.common.hash.Hashing;
+
+public class MemberWithGuavaHashing extends Member {
+    @Override
+    public int hashCode() {
+        HashFunction hashFunction = Hashing.murmur3_32();
+        return hashFunction.newHasher()
+                .putInt(id)
+                .putString(name, Charsets.UTF_8)
+                .hash().hashCode();
+    }
+
+
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithId.java

@@ -0,0 +1,18 @@
+package com.baeldung.map.hashing;
+
+public class MemberWithId extends Member {
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        MemberWithId that = (MemberWithId) o;
+
+        return id.equals(that.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id;
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithIdAndName.java

@@ -0,0 +1,23 @@
+package com.baeldung.map.hashing;
+
+import java.util.Objects;
+
+public class MemberWithIdAndName extends Member {
+    public static final int PRIME = 31;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        MemberWithObjects that = (MemberWithObjects) o;
+        return Objects.equals(id, that.id) &&
+                Objects.equals(name, that.name);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = id.hashCode();
+        result = PRIME * result + (name == null ? 0  : name.hashCode());
+        return result;
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithObjects.java

@@ -0,0 +1,19 @@
+package com.baeldung.map.hashing;
+
+import java.util.Objects;
+
+public class MemberWithObjects extends Member {
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        MemberWithObjects that = (MemberWithObjects) o;
+        return Objects.equals(id, that.id) &&
+                Objects.equals(name, that.name);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, name);
+    }
+}

java-collections-maps-3/src/test/java/com/baeldung/map/hashing/HashingUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.map.hashing;
+
+import com.google.common.base.Stopwatch;
+import org.junit.jupiter.api.Test;
+
+import java.time.Duration;
+import java.util.HashMap;
+import java.util.SplittableRandom;
+import java.util.function.Supplier;
+
+public class HashingUnitTest {
+
+    public static final int SAMPLES = 1000000;
+    private SplittableRandom random = new SplittableRandom();
+
+    private String[] names = {"John", "Adam", "Suzie"};
+
+    @Test
+    void givenPrimitiveByteArrayKey_whenRetrievingFromMap_shouldRetrieveDifferentObjects() {
+        // bad hashing example is prohibitively slow for bigger samples
+//        Duration[] badHashing = testDuration(MemberWithBadHashing::new);
+        Duration[] withId = testDuration(MemberWithId::new);
+        Duration[] withObjects = testDuration(MemberWithObjects::new);
+        Duration[] withIdAndName = testDuration(MemberWithIdAndName::new);
+
+//        System.out.println("Inserting with bad hashing:");
+//        System.out.println(badHashing[0]);
+//        System.out.println("Getting with bad hashing:");
+//        System.out.println(badHashing[1]);
+
+        System.out.println("Inserting with id hashing:");
+        System.out.println(withId[0]);
+        System.out.println("Getting with id hashing:");
+        System.out.println(withId[1]);
+
+        System.out.println("Inserting with id and name hashing:");
+        System.out.println(withIdAndName[0]);
+        System.out.println("Getting with id and name hashing:");
+        System.out.println(withIdAndName[1]);
+
+        System.out.println("Inserting with Objects hashing:");
+        System.out.println(withObjects[0]);
+        System.out.println("Getting with Objects hashing:");
+        System.out.println(withObjects[1]);
+    }
+
+    private String randomName() {
+        return names[random.nextInt(2)];
+    }
+
+    private <T extends Member> Duration[] testDuration(Supplier<T> factory) {
+        HashMap<T, String> map = new HashMap<>();
+        Stopwatch stopwatch = Stopwatch.createUnstarted();
+
+        stopwatch.start();
+        for(int i = 0; i < SAMPLES; i++) {
+            T member = factory.get();
+            member.id = i;
+            member.name = randomName();
+            map.put(member, member.name);
+        }
+        stopwatch.stop();
+        Duration elapsedInserting = stopwatch.elapsed();
+        stopwatch.reset();
+
+        stopwatch.start();
+        for (T key : map.keySet()) {
+            map.get(key);
+        }
+        stopwatch.stop();
+        Duration elapsedGetting = stopwatch.elapsed();
+        stopwatch.reset();
+
+        return new Duration[]{elapsedInserting, elapsedGetting};
+    }
+}

jmeter/README.md

@@ -7,7 +7,7 @@ It contains the code of a simple API for some CRUD operations built using Spring
 
 - Maven
 - JDK 8
-- MongoDB
+- MongoDB (Note: for the Write Extracted Data to a File Using JMeter example MongoDB is not required)
 
 ### Running
 
@@ -36,6 +36,14 @@ Or create a new one via a POST:
 $ curl -X POST -H "Content-Type:application/json" -d '{ "firstName" : "Dassi", "lastName" : "Orleando", "phoneNumber": "+237 545454545", "email": "[email protected]" }' localhost:8080/students
 ```
 
+### Available UUID API
+
+You can view the test response using curl:
+
+```bash
+$ curl localhost:8080/api/uuid
+```
+
 Now with default configurations it will be available at: [http://localhost:8080](http://localhost:8080)
 
 Enjoy it :)

jmeter/src/main/java/com/baeldung/controller/RetrieveUuidController.java

@@ -0,0 +1,18 @@
+package com.baeldung.controller;
+
+import com.baeldung.model.Response;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.UUID;
+
+import static java.lang.String.format;
+
+@RestController
+public class RetrieveUuidController {
+
+    @GetMapping("/api/uuid")
+    public Response uuid() {
+        return new Response(format("Test message... %s.", UUID.randomUUID()));
+    }
+}

jmeter/src/main/java/com/baeldung/model/Response.java

@@ -0,0 +1,40 @@
+package com.baeldung.model;
+
+import java.time.Instant;
+import java.util.UUID;
+
+public class Response {
+    private Instant timestamp;
+    private UUID uuid;
+    private String message;
+
+    public Response(String message) {
+        this.timestamp = Instant.now();
+        this.uuid = UUID.randomUUID();
+        this.message = message;
+    }
+
+    public Instant getTimestamp() {
+        return timestamp;
+    }
+
+    public void setTimestamp(Instant timestamp) {
+        this.timestamp = timestamp;
+    }
+
+    public UUID getUuid() {
+        return uuid;
+    }
+
+    public void setUuid(UUID uuid) {
+        this.uuid = uuid;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+}

jmeter/src/main/resources/FileExtractionExample.jmx

@@ -0,0 +1,124 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<jmeterTestPlan version="1.2" properties="5.0" jmeter="5.4.1">
+  <hashTree>
+    <TestPlan guiclass="TestPlanGui" testclass="TestPlan" testname="Test Plan" enabled="true">
+      <stringProp name="TestPlan.comments">To run this test plan you must also be running the Spring application &quot;JmeterApplication&quot; That can be found in this directory</stringProp>
+      <boolProp name="TestPlan.functional_mode">false</boolProp>
+      <boolProp name="TestPlan.tearDown_on_shutdown">true</boolProp>
+      <boolProp name="TestPlan.serialize_threadgroups">false</boolProp>
+      <elementProp name="TestPlan.user_defined_variables" elementType="Arguments" guiclass="ArgumentsPanel" testclass="Arguments" testname="User Defined Variables" enabled="true">
+        <collectionProp name="Arguments.arguments"/>
+      </elementProp>
+      <stringProp name="TestPlan.user_define_classpath"></stringProp>
+    </TestPlan>
+    <hashTree>
+      <ThreadGroup guiclass="ThreadGroupGui" testclass="ThreadGroup" testname="Thread Group" enabled="true">
+        <stringProp name="ThreadGroup.on_sample_error">continue</stringProp>
+        <elementProp name="ThreadGroup.main_controller" elementType="LoopController" guiclass="LoopControlPanel" testclass="LoopController" testname="Loop Controller" enabled="true">
+          <boolProp name="LoopController.continue_forever">false</boolProp>
+          <stringProp name="LoopController.loops">1</stringProp>
+        </elementProp>
+        <stringProp name="ThreadGroup.num_threads">1</stringProp>
+        <stringProp name="ThreadGroup.ramp_time">1</stringProp>
+        <boolProp name="ThreadGroup.scheduler">false</boolProp>
+        <stringProp name="ThreadGroup.duration"></stringProp>
+        <stringProp name="ThreadGroup.delay"></stringProp>
+        <boolProp name="ThreadGroup.same_user_on_next_iteration">true</boolProp>
+      </ThreadGroup>
+      <hashTree>
+        <HTTPSamplerProxy guiclass="HttpTestSampleGui" testclass="HTTPSamplerProxy" testname="Call GET Test endpoint " enabled="true">
+          <elementProp name="HTTPsampler.Arguments" elementType="Arguments" guiclass="HTTPArgumentsPanel" testclass="Arguments" testname="User Defined Variables" enabled="true">
+            <collectionProp name="Arguments.arguments"/>
+          </elementProp>
+          <stringProp name="HTTPSampler.domain">localhost</stringProp>
+          <stringProp name="HTTPSampler.port">8080</stringProp>
+          <stringProp name="HTTPSampler.protocol">http</stringProp>
+          <stringProp name="HTTPSampler.contentEncoding"></stringProp>
+          <stringProp name="HTTPSampler.path">/api/test</stringProp>
+          <stringProp name="HTTPSampler.method">GET</stringProp>
+          <boolProp name="HTTPSampler.follow_redirects">true</boolProp>
+          <boolProp name="HTTPSampler.auto_redirects">false</boolProp>
+          <boolProp name="HTTPSampler.use_keepalive">true</boolProp>
+          <boolProp name="HTTPSampler.DO_MULTIPART_POST">false</boolProp>
+          <stringProp name="HTTPSampler.embedded_url_re"></stringProp>
+          <stringProp name="HTTPSampler.connect_timeout"></stringProp>
+          <stringProp name="HTTPSampler.response_timeout"></stringProp>
+        </HTTPSamplerProxy>
+        <hashTree>
+          <JSONPostProcessor guiclass="JSONPostProcessorGui" testclass="JSONPostProcessor" testname="JSON Extractor" enabled="true">
+            <stringProp name="JSONPostProcessor.referenceNames">message</stringProp>
+            <stringProp name="JSONPostProcessor.jsonPathExprs">$.message</stringProp>
+            <stringProp name="JSONPostProcessor.match_numbers">1</stringProp>
+            <boolProp name="JSONPostProcessor.compute_concat">true</boolProp>
+            <stringProp name="JSONPostProcessor.defaultValues">NOT_FOUND</stringProp>
+          </JSONPostProcessor>
+          <hashTree/>
+          <BeanShellPostProcessor guiclass="TestBeanGUI" testclass="BeanShellPostProcessor" testname="Response to file using BeanShell PostProcessor" enabled="true">
+            <stringProp name="filename"></stringProp>
+            <stringProp name="parameters"></stringProp>
+            <boolProp name="resetInterpreter">false</boolProp>
+            <stringProp name="script">FileWriter fWriter = new FileWriter(&quot;<path>/result.txt&quot;, true);
+BufferedWriter buff = new BufferedWriter(fWriter);
+
+buff.write(&quot;Response Code : &quot; + ctx.getPreviousResult().getResponseCode());
+buff.write(System.getProperty(&quot;line.separator&quot;));
+buff.write(&quot;Response Headers : &quot; + ctx.getPreviousResult().getResponseHeaders());
+buff.write(System.getProperty(&quot;line.separator&quot;));
+buff.write(&quot;Response Body : &quot; + new String(ctx.getPreviousResult().getResponseData()));
+
+buff.write(&quot;More complex extraction : &quot; + vars.get(&quot;message&quot;));
+
+buff.close();
+fWriter.close();</stringProp>
+          </BeanShellPostProcessor>
+          <hashTree/>
+          <ResultSaver guiclass="ResultSaverGui" testclass="ResultSaver" testname="Response to file using file write Listener" enabled="true">
+            <stringProp name="FileSaver.filename">response</stringProp>
+            <boolProp name="FileSaver.errorsonly">false</boolProp>
+            <boolProp name="FileSaver.successonly">false</boolProp>
+            <boolProp name="FileSaver.skipsuffix">false</boolProp>
+            <boolProp name="FileSaver.skipautonumber">false</boolProp>
+          </ResultSaver>
+          <hashTree/>
+        </hashTree>
+        <ResultCollector guiclass="ViewResultsFullVisualizer" testclass="ResultCollector" testname="View Results Tree" enabled="true">
+          <boolProp name="ResultCollector.error_logging">false</boolProp>
+          <objProp>
+            <name>saveConfig</name>
+            <value class="SampleSaveConfiguration">
+              <time>true</time>
+              <latency>true</latency>
+              <timestamp>true</timestamp>
+              <success>true</success>
+              <label>true</label>
+              <code>true</code>
+              <message>true</message>
+              <threadName>true</threadName>
+              <dataType>true</dataType>
+              <encoding>false</encoding>
+              <assertions>true</assertions>
+              <subresults>true</subresults>
+              <responseData>false</responseData>
+              <samplerData>false</samplerData>
+              <xml>false</xml>
+              <fieldNames>true</fieldNames>
+              <responseHeaders>false</responseHeaders>
+              <requestHeaders>false</requestHeaders>
+              <responseDataOnError>false</responseDataOnError>
+              <saveAssertionResultsFailureMessage>true</saveAssertionResultsFailureMessage>
+              <assertionsResultsToSave>0</assertionsResultsToSave>
+              <bytes>true</bytes>
+              <sentBytes>true</sentBytes>
+              <url>true</url>
+              <threadCounts>true</threadCounts>
+              <idleTime>true</idleTime>
+              <connectTime>true</connectTime>
+            </value>
+          </objProp>
+          <stringProp name="filename"></stringProp>
+        </ResultCollector>
+        <hashTree/>
+      </hashTree>
+    </hashTree>
+  </hashTree>
+</jmeterTestPlan>