Merge branch 'eugenp:master' into master

apache-httpclient-2/README.md

@@ -13,4 +13,5 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 - [How To Get Cookies From the Apache HttpClient Response](https://www.baeldung.com/java-apache-httpclient-cookies)
 - [Enabling Logging for Apache HttpClient](https://www.baeldung.com/apache-httpclient-enable-logging)
 - [Apache HttpClient vs. CloseableHttpClient](https://www.baeldung.com/apache-httpclient-vs-closeablehttpclient)
+- [Expand Shortened URLs with Apache HttpClient](https://www.baeldung.com/apache-httpclient-expand-url)
 - More articles: [[<-- prev]](../apache-httpclient)

apache-httpclient-2/src/test/java/com/baeldung/httpclient/expandUrl/HttpClientExpandUrlLiveTest.java

@@ -0,0 +1,126 @@
+package com.baeldung.httpclient.expandUrl;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+
+import java.io.IOException;
+import java.util.List;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+
+import org.apache.commons.lang3.tuple.ImmutablePair;
+import org.apache.commons.lang3.tuple.Pair;
+
+import org.apache.hc.client5.http.classic.methods.HttpHead;
+import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+
+import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.HttpHeaders;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+class HttpClientExpandUrlLiveTest {
+
+    private static CloseableHttpClient httpClient;
+
+    @BeforeAll
+    static void setup() {
+        httpClient = HttpClientBuilder.create()
+            .disableRedirectHandling()
+            .build();
+    }
+
+    @AfterAll
+    static void tearDown() throws IOException {
+        if (httpClient != null) {
+            httpClient.close();
+        }
+    }
+
+    @Test
+    void givenShortenedOnce_whenUrlIsExpanded_thenCorrectResult() throws IOException {
+        final String expectedResult = "https://www.baeldung.com/rest-versioning";
+        final String actualResult = expandSingleLevel("http://bit.ly/3LScTri");
+        assertThat(actualResult, equalTo(expectedResult));
+    }
+
+    @Test
+    void givenShortenedMultiple_whenUrlIsExpanded_thenCorrectResult() throws IOException {
+        final String expectedResult = "https://www.baeldung.com/rest-versioning";
+        final String actualResult = expand("http://t.co/e4rDDbnzmk");
+        assertThat(actualResult, equalTo(expectedResult));
+    }
+
+    private String expand(final String urlArg) throws IOException {
+        String originalUrl = urlArg;
+        String newUrl = expandSingleLevel(originalUrl);
+        while (!originalUrl.equals(newUrl)) {
+            originalUrl = newUrl;
+            newUrl = expandSingleLevel(originalUrl);
+        }
+
+        return newUrl;
+    }
+
+    final String expandSafe(final String urlArg) throws IOException {
+        String originalUrl = urlArg;
+        String newUrl = expandSingleLevelSafe(originalUrl).getRight();
+        final List<String> alreadyVisited = Lists.newArrayList(originalUrl, newUrl);
+        while (!originalUrl.equals(newUrl)) {
+            originalUrl = newUrl;
+            final Pair<Integer, String> statusAndUrl = expandSingleLevelSafe(originalUrl);
+            newUrl = statusAndUrl.getRight();
+            final boolean isRedirect = statusAndUrl.getLeft() == 301 || statusAndUrl.getLeft() == 302;
+            if (isRedirect && alreadyVisited.contains(newUrl)) {
+                throw new IllegalStateException("Likely a redirect loop");
+            }
+            alreadyVisited.add(newUrl);
+        }
+
+        return newUrl;
+    }
+
+    private Pair<Integer, String> expandSingleLevelSafe(final String url) throws IOException {
+        try {
+            HttpHead request = new HttpHead(url);
+            Pair<Integer, String> resp = httpClient.execute(request, response -> {
+                final int statusCode = response.getCode();
+                if (statusCode != 301 && statusCode != 302) {
+                    return new ImmutablePair<>(statusCode, url);
+                }
+                final Header[] headers = response.getHeaders(HttpHeaders.LOCATION);
+                Preconditions.checkState(headers.length == 1);
+                final String newUrl = headers[0].getValue();
+
+                return new ImmutablePair<>(statusCode, newUrl);
+            });
+            return resp;
+        } catch (final IllegalArgumentException uriEx) {
+            return new ImmutablePair<>(500, url);
+        }
+    }
+
+    private String expandSingleLevel(final String url) throws IOException {
+        try {
+            HttpHead request = new HttpHead(url);
+            String expandedUrl = httpClient.execute(request, response -> {
+                final int statusCode = response.getCode();
+                if (statusCode != 301 && statusCode != 302) {
+                    return url;
+                }
+                final Header[] headers = response.getHeaders(HttpHeaders.LOCATION);
+                Preconditions.checkState(headers.length == 1);
+
+                return headers[0].getValue();
+            });
+            return expandedUrl;
+        } catch (final IllegalArgumentException uriEx) {
+            return url;
+        }
+    }
+
+}

apache-httpclient/src/test/java/com/baeldung/httpclient/HttpClientCancelRequestLiveTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.httpclient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+
+import org.apache.hc.client5.http.classic.methods.HttpGet;
+import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+import org.apache.hc.client5.http.impl.classic.HttpClients;
+import org.apache.hc.core5.http.HttpEntity;
+import org.apache.hc.core5.http.HttpStatus;
+import org.junit.jupiter.api.Test;
+
+class HttpClientCancelRequestLiveTest {
+
+    private static final String SAMPLE_URL = "http://www.github.com";
+
+    @Test
+    void whenRequestIsCanceled_thenCorrect() throws IOException {
+        HttpGet request = new HttpGet(SAMPLE_URL);
+        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
+                httpClient.execute(request, response -> {
+                HttpEntity entity = response.getEntity();
+
+                System.out.println("----------------------------------------");
+                System.out.println(response.getCode());
+                if (entity != null) {
+                    System.out.println("Response content length: " + entity.getContentLength());
+                }
+                System.out.println("----------------------------------------");
+                // Do not feel like reading the response body
+                // Call abort on the request object
+                request.abort();
+
+                assertThat(response.getCode()).isEqualTo(HttpStatus.SC_OK);
+                return response;
+            });
+        }
+    }
+}

apache-httpclient/src/test/java/com/baeldung/httpclient/base/HttpClientLiveTest.java

@@ -1,8 +1,8 @@
 package com.baeldung.httpclient.base;
 
 import com.baeldung.httpclient.ResponseUtil;
+
 import org.apache.http.Header;
-import org.apache.http.HttpEntity;
 import org.apache.http.HttpHeaders;
 import org.apache.http.client.config.RequestConfig;
 import org.apache.http.client.methods.CloseableHttpResponse;
@@ -10,7 +10,6 @@ import org.apache.http.client.methods.HttpGet;
 import org.apache.http.conn.ConnectTimeoutException;
 import org.apache.http.impl.client.CloseableHttpClient;
 import org.apache.http.impl.client.HttpClientBuilder;
-import org.apache.http.impl.client.HttpClients;
 import org.apache.http.impl.conn.BasicHttpClientConnectionManager;
 import org.junit.After;
 import org.junit.Before;
@@ -73,30 +72,4 @@ public class HttpClientLiveTest {
         assertThat(headers, not(emptyArray()));
     }
 
-    // tests - cancel request
-
-    @Test
-    public final void whenRequestIsCanceled_thenCorrect() throws IOException {
-        instance = HttpClients.custom().build();
-        final HttpGet request = new HttpGet(SAMPLE_URL);
-        response = instance.execute(request);
-
-        try {
-            final HttpEntity entity = response.getEntity();
-
-            System.out.println("----------------------------------------");
-            System.out.println(response.getStatusLine());
-            if (entity != null) {
-                System.out.println("Response content length: " + entity.getContentLength());
-            }
-            System.out.println("----------------------------------------");
-
-            // Do not feel like reading the response body
-            // Call abort on the request object
-            request.abort();
-        } finally {
-            response.close();
-        }
-    }
-
 }

apache-httpclient4/README.md

@@ -4,6 +4,7 @@ This module contains articles about Apache HttpClient 4.5
 
 ### Relevant Articles
 
+- [Apache HttpClient – Cancel Request](https://www.baeldung.com/httpclient-cancel-request)
 - [Apache HttpClient with SSL](https://www.baeldung.com/httpclient-ssl)
 - [Apache HttpClient Timeout](https://www.baeldung.com/httpclient-timeout)
 - [Custom HTTP Header with the Apache HttpClient](https://www.baeldung.com/httpclient-custom-http-header)

apache-httpclient4/src/test/java/com/baeldung/httpclient/HttpClientCancelRequestV4LiveTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.httpclient;
+
+import java.io.IOException;
+
+import org.apache.http.HttpEntity;
+import org.apache.http.client.methods.CloseableHttpResponse;
+import org.apache.http.client.methods.HttpGet;
+import org.apache.http.impl.client.CloseableHttpClient;
+import org.apache.http.impl.client.HttpClientBuilder;
+import org.apache.http.impl.client.HttpClients;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class HttpClientCancelRequestV4LiveTest {
+
+    private static final String SAMPLE_URL = "http://www.github.com";
+
+    private CloseableHttpClient instance;
+
+    private CloseableHttpResponse response;
+
+    @Before
+    public final void before() {
+        instance = HttpClientBuilder.create().build();
+    }
+
+    @After
+    public final void after() throws IllegalStateException, IOException {
+        ResponseUtil.closeResponse(response);
+    }
+
+    @Test
+    public final void whenRequestIsCanceled_thenCorrect() throws IOException {
+        instance = HttpClients.custom().build();
+        final HttpGet request = new HttpGet(SAMPLE_URL);
+        response = instance.execute(request);
+
+        try {
+            final HttpEntity entity = response.getEntity();
+
+            System.out.println("----------------------------------------");
+            System.out.println(response.getStatusLine());
+            if (entity != null) {
+                System.out.println("Response content length: " + entity.getContentLength());
+            }
+            System.out.println("----------------------------------------");
+
+            // Do not feel like reading the response body
+            // Call abort on the request object
+            request.abort();
+        } finally {
+            response.close();
+        }
+    }
+}

apache-httpclient4/src/test/java/com/baeldung/httpclient/retry/ApacheHttpClientRetryLiveTest.java

@@ -24,7 +24,7 @@ import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-public class ApacheHttpClientRetryIntegrationTest {
+public class ApacheHttpClientRetryLiveTest {
 
     private Integer requestCounter;
     private CloseableHttpClient httpClient;

aws-modules/aws-lambda-modules/lambda-function/pom.xml

@@ -3,14 +3,14 @@
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
-    <artifactId>lambda</artifactId>
+    <artifactId>lambda-function</artifactId>
     <version>0.1.0-SNAPSHOT</version>
-    <name>lambda</name>
+    <name>lambda-function</name>
     <packaging>jar</packaging>
 
     <parent>
         <groupId>com.baeldung</groupId>
-        <artifactId>aws-lambda</artifactId>
+        <artifactId>aws-lambda-modules</artifactId>
         <version>1.0.0-SNAPSHOT</version>
     </parent>
 

aws-modules/aws-lambda-modules/pom.xml

@@ -3,8 +3,8 @@
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
-    <artifactId>aws-lambda</artifactId>
-    <name>aws-lambda</name>
+    <artifactId>aws-lambda-modules</artifactId>
+    <name>aws-lambda-modules</name>
     <packaging>pom</packaging>
 
     <parent>
@@ -14,9 +14,9 @@
     </parent>
 
     <modules>
-        <module>lambda</module>
-        <module>shipping-tracker/ShippingFunction</module>
-        <module>todo-reminder/ToDoFunction</module>
+        <module>lambda-function</module>
+        <module>shipping-tracker-lambda/ShippingFunction</module>
+        <module>todo-reminder-lambda/ToDoFunction</module>
     </modules>
 
 </project>

aws-modules/aws-lambda-modules/shipping-tracker-lambda/ShippingFunction/pom.xml

@@ -9,7 +9,7 @@
 
     <parent>
         <groupId>com.baeldung</groupId>
-        <artifactId>aws-lambda</artifactId>
+        <artifactId>aws-lambda-modules</artifactId>
         <version>1.0.0-SNAPSHOT</version>
         <relativePath>../../</relativePath>
     </parent>

aws-modules/aws-lambda-modules/todo-reminder-lambda/ToDoFunction/pom.xml

@@ -8,6 +8,13 @@
     <name>ToDoFunction</name>
     <packaging>jar</packaging>
 
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>aws-lambda-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../</relativePath>
+    </parent>
+
     <dependencies>
         <dependency>
             <groupId>com.amazonaws</groupId>

aws-modules/aws-lambda-modules/todo-reminder-lambda/ToDoFunction/src/test/java/com/baeldung/lambda/todo/AppUnitTest.java

@@ -21,7 +21,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.verify;
 
 @RunWith(MockitoJUnitRunner.class)
-public class AppTest {
+public class AppUnitTest {
 
     @Mock(answer = Answers.RETURNS_DEEP_STUBS)
     private Context mockContext;

aws-modules/aws-lambda-modules/todo-reminder-lambda/ToDoFunction/src/test/java/com/baeldung/lambda/todo/service/ToDoReaderServiceUnitTest.java

@@ -7,7 +7,7 @@ import uk.org.webcompere.systemstubs.rules.SystemOutRule;
 
 import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
 
-public class ToDoReaderServiceTest {
+public class ToDoReaderServiceUnitTest {
 
     @Rule
     public SystemOutRule systemOutRule = new SystemOutRule();

aws-modules/aws-s3/README.md

@@ -7,3 +7,4 @@ This module contains articles about Simple Storage Service (S3) on AWS
 - [AWS S3 with Java](https://www.baeldung.com/aws-s3-java)
 - [Multipart Uploads in Amazon S3 with Java](https://www.baeldung.com/aws-s3-multipart-upload)
 - [Using the JetS3t Java Client With Amazon S3](https://www.baeldung.com/jets3t-amazon-s3)
+- [Check if a Specified Key Exists in a Given S3 Bucket Using Java](https://www.baeldung.com/java-aws-s3-check-specified-key-exists)

aws-modules/pom.xml

@@ -15,7 +15,7 @@
 
     <modules>
         <module>aws-app-sync</module>
-        <module>aws-lambda</module>
+        <module>aws-lambda-modules</module>
         <module>aws-miscellaneous</module>
         <module>aws-reactive</module>
         <module>aws-s3</module>

checker-framework/pom.xml

@@ -3,9 +3,9 @@
     xmlns="http://maven.apache.org/POM/4.0.0"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
     <modelVersion>4.0.0</modelVersion>
-    <artifactId>checker-plugin</artifactId>
+    <artifactId>checker-framework</artifactId>
     <version>1.0-SNAPSHOT</version>
-    <name>checker-plugin</name>
+    <name>checker-framework</name>
     <packaging>jar</packaging>
 
     <parent>

core-java-modules/core-java-19/README.md

@@ -1,3 +1,4 @@
 ## Relevant Articles
 - [Record Patterns in Java 19](https://www.baeldung.com/java-19-record-patterns)
 - [Structured Concurrency in Java 19](https://www.baeldung.com/java-structured-concurrency)
+- [Possible Root Causes for High CPU Usage in Java](https://www.baeldung.com/java-high-cpu-usage-causes)

core-java-modules/core-java-8-2/README.md

@@ -11,4 +11,6 @@ This module contains articles about Java 8 core features
 - [Convert Between Byte Array and UUID in Java](https://www.baeldung.com/java-byte-array-to-uuid)
 - [Create a Simple “Rock-Paper-Scissors” Game in Java](https://www.baeldung.com/java-rock-paper-scissors)
 - [VarArgs vs Array Input Parameters in Java](https://www.baeldung.com/varargs-vs-array)
+- [Lambda Expression vs. Anonymous Inner Class](https://www.baeldung.com/java-lambdas-vs-anonymous-class)
+- [Java Helper vs. Utility Classes](https://www.baeldung.com/java-helper-vs-utility-classes)
 - [[<-- Prev]](/core-java-modules/core-java-8)

core-java-modules/core-java-8-datetime-2/README.md

@@ -2,4 +2,5 @@
 
 - [Generating Random Dates in Java](https://www.baeldung.com/java-random-dates)
 - [Creating a LocalDate with Values in Java](https://www.baeldung.com/java-creating-localdate-with-values)
+- [Parsing Date Strings with Varying Formats](https://www.baeldung.com/java-parsing-dates-many-formats)
 - [[<-- Prev]](/core-java-modules/core-java-datetime-java8-1)

core-java-modules/core-java-8-datetime-2/src/main/java/com/baeldung/parsingDates/SimpleDateTimeFormat.java

@@ -0,0 +1,20 @@
+package com.baeldung.parsingDates;
+
+import java.util.Arrays;
+import java.util.List;
+import org.joda.time.LocalDate;
+import org.joda.time.format.DateTimeFormat;
+
+public class SimpleDateTimeFormat {
+
+    public static LocalDate parseDate(String date) {
+        List<String> patternList = Arrays.asList("MM/dd/yyyy", "dd.MM.yyyy", "yyyy-MM-dd");
+        for (String pattern : patternList) {
+            try {
+                return DateTimeFormat.forPattern(pattern).parseLocalDate(date);
+            } catch (IllegalArgumentException e) {
+            }
+        }
+        return null;
+    }
+}

core-java-modules/core-java-8-datetime-2/src/main/java/com/baeldung/parsingDates/SimpleDateTimeFormater.java

@@ -0,0 +1,17 @@
+package com.baeldung.parsingDates;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeFormatterBuilder;
+
+public class SimpleDateTimeFormater {
+
+    public static LocalDate parseDate(String date) {
+        DateTimeFormatterBuilder dateTimeFormatterBuilder = new DateTimeFormatterBuilder()
+                .append(DateTimeFormatter.ofPattern("[MM/dd/yyyy]" + "[dd-MM-yyyy]" + "[yyyy-MM-dd]"));
+
+        DateTimeFormatter dateTimeFormatter = dateTimeFormatterBuilder.toFormatter();
+
+        return LocalDate.parse(date, dateTimeFormatter);
+    }
+}

core-java-modules/core-java-8-datetime-2/src/main/java/com/baeldung/parsingDates/SimpleDateUtils.java

@@ -0,0 +1,18 @@
+package com.baeldung.parsingDates;
+
+import java.text.ParseException;
+import java.util.Date;
+import org.apache.commons.lang3.time.DateUtils;
+
+public class SimpleDateUtils {
+
+    public static Date parseDate(String date) {
+        try {
+            return DateUtils.parseDateStrictly(date,
+                    new String[]{"yyyy/MM/dd", "dd/MM/yyyy", "yyyy-MM-dd"});
+        } catch (ParseException ex) {
+            return null;
+        }
+    }
+
+}

core-java-modules/core-java-8-datetime-2/src/main/java/com/baeldung/parsingDates/SimpleParseDate.java

@@ -0,0 +1,19 @@
+package com.baeldung.parsingDates;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.List;
+
+public class SimpleParseDate {
+
+    public Date parseDate(String dateString, List<String> formatStrings) {
+        for (String formatString : formatStrings) {
+            try {
+                return new SimpleDateFormat(formatString).parse(dateString);
+            } catch (ParseException e) {
+            }
+        }
+        return null;
+    }
+}

core-java-modules/core-java-8-datetime-2/src/test/java/com/baeldung/parsingDates/SimpleParseDateUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.parsingDates;
+
+import com.baeldung.parsingDates.SimpleDateTimeFormat;
+import com.baeldung.parsingDates.SimpleDateTimeFormater;
+import com.baeldung.parsingDates.SimpleDateUtils;
+import com.baeldung.parsingDates.SimpleParseDate;
+import java.time.format.DateTimeParseException;
+import java.util.Arrays;
+import org.junit.*;
+import static org.junit.Assert.*;
+import org.joda.time.LocalDate;
+
+public class SimpleParseDateUnitTest {
+
+    @Test
+    public void whenInvalidInput_thenGettingUnexpectedResult() {
+        SimpleParseDate simpleParseDate = new SimpleParseDate();
+        String date = "2022-40-40";
+        assertEquals("Sat May 10 00:00:00 UTC 2025", simpleParseDate.parseDate(date, Arrays.asList("MM/dd/yyyy", "dd.MM.yyyy", "yyyy-MM-dd")).toString());
+    }
+
+    @Test
+    public void whenInvalidDate_thenAssertThrows() {
+        SimpleDateTimeFormater simpleDateTimeFormater = new SimpleDateTimeFormater();
+        assertEquals(java.time.LocalDate.parse("2022-12-04"), simpleDateTimeFormater.parseDate("2022-12-04"));
+        assertThrows(DateTimeParseException.class, () -> simpleDateTimeFormater.parseDate("2022-13-04"));
+    }
+
+    @Test
+    public void whenDateIsCorrect_thenParseCorrect() {
+        SimpleDateUtils simpleDateUtils = new SimpleDateUtils();
+        assertNull(simpleDateUtils.parseDate("53/10/2014"));
+        assertEquals("Wed Sep 10 00:00:00 UTC 2014", simpleDateUtils.parseDate("10/09/2014").toString());
+    }
+
+    @Test
+    public void whenDateIsCorrect_thenResultCorrect() {
+        SimpleDateTimeFormat simpleDateTimeFormat = new SimpleDateTimeFormat();
+        assertNull(simpleDateTimeFormat.parseDate("53/10/2014"));
+        assertEquals(LocalDate.parse("2014-10-10"), simpleDateTimeFormat.parseDate("2014-10-10"));
+    }
+
+}

core-java-modules/core-java-9-jigsaw/README.md

@@ -8,5 +8,5 @@ This module contains articles about Project Jigsaw and the Java Platform Module
 - [A Guide to Java 9 Modularity](https://www.baeldung.com/java-9-modularity)
 - [Java 9 java.lang.Module API](https://www.baeldung.com/java-9-module-api)
 - [Java 9 Illegal Reflective Access Warning](https://www.baeldung.com/java-illegal-reflective-access)
-
+- [Java Modularity and Unit Testing](https://www.baeldung.com/java-modularity-unit-testing)
 

core-java-modules/core-java-9-jigsaw/compile-library-core-module.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+javac -d mods/com.baeldung.library.core $(find library-core/src/main -name "*.java")

core-java-modules/core-java-9-jigsaw/compile-library-core-tests.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+javac --class-path outDir/library-core/:\
+libs/junit-jupiter-engine-5.9.2.jar:\
+libs/junit-platform-engine-1.9.2.jar:\
+libs/apiguardian-api-1.1.2.jar:\
+libs/junit-jupiter-params-5.9.2.jar:\
+libs/junit-jupiter-api-5.9.2.jar:\
+libs/opentest4j-1.2.0.jar:\
+libs/junit-platform-commons-1.9.2.jar \
+-d outDir/library-test library-core/src/test/java/com/baeldung/library/core/LibraryUnitTest.java

core-java-modules/core-java-9-jigsaw/compile-library-core-with-tests.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+javac --class-path libs/junit-jupiter-engine-5.9.2.jar:\
+libs/junit-platform-engine-1.9.2.jar:\
+libs/apiguardian-api-1.1.2.jar:\
+libs/junit-jupiter-params-5.9.2.jar:\
+libs/junit-jupiter-api-5.9.2.jar:\
+libs/opentest4j-1.2.0.jar:\
+libs/junit-platform-commons-1.9.2.jar \
+-d outDir/library-core \
+library-core/src/main/java/com/baeldung/library/core/Book.java \
+library-core/src/main/java/com/baeldung/library/core/Library.java \
+library-core/src/main/java/com/baeldung/library/core/Main.java \
+library-core/src/test/java/com/baeldung/library/core/LibraryUnitTest.java

core-java-modules/core-java-9-jigsaw/compile-library-core.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+javac --class-path libs/junit-jupiter-engine-5.9.2.jar:\
+libs/junit-platform-engine-1.9.2.jar:\
+libs/apiguardian-api-1.1.2.jar:\
+libs/junit-jupiter-params-5.9.2.jar:\
+libs/junit-jupiter-api-5.9.2.jar:\
+libs/opentest4j-1.2.0.jar:\
+libs/junit-platform-commons-1.9.2.jar \
+-d outDir/library-core \
+library-core/src/main/java/com/baeldung/library/core/Book.java \
+library-core/src/main/java/com/baeldung/library/core/Library.java \
+library-core/src/main/java/com/baeldung/library/core/Main.java

core-java-modules/core-java-9-jigsaw/compile-library-test-module.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+javac --module-path mods:libs -d mods/com.baeldung.library.test $(find library-test/src/test -name "*.java")

core-java-modules/core-java-9-jigsaw/download-junit-dependencies.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+wget -P libs/ https://repo1.maven.org/maven2/org/apiguardian/apiguardian-api/1.1.2/apiguardian-api-1.1.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/opentest4j/opentest4j/1.2.0/opentest4j-1.2.0.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/platform/junit-platform-commons/1.9.2/junit-platform-commons-1.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/platform/junit-platform-engine/1.9.2/junit-platform-engine-1.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/platform/junit-platform-reporting/1.9.2/junit-platform-reporting-1.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/platform/junit-platform-console/1.9.2/junit-platform-console-1.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/platform/junit-platform-launcher/1.9.2/junit-platform-launcher-1.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/jupiter/junit-jupiter-engine/5.9.2/junit-jupiter-engine-5.9.2.jar /
+wget -P libs/ https://repo1.maven.org/maven2/org/junit/jupiter/junit-jupiter-params/5.9.2/junit-jupiter-params-5.9.2.jar

core-java-modules/core-java-9-jigsaw/library-core/pom.xml

@@ -0,0 +1,55 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-9-jigsaw</artifactId>
+    <version>0.2-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>library-core</artifactId>
+
+  <properties>
+    <maven.compiler.source>19</maven.compiler.source>
+    <maven.compiler.target>19</maven.compiler.target>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <version>5.9.2</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <version>5.9.2</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.8.1</version>
+        <configuration>
+          <release>9</release>
+        </configuration>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.0.0-M5</version>
+        <configuration>
+          <useModulePath>false</useModulePath>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

core-java-modules/core-java-9-jigsaw/library-core/src/main/java/com/baeldung/library/core/Book.java

@@ -0,0 +1,52 @@
+package com.baeldung.library.core;
+
+import java.util.Objects;
+
+public class Book {
+
+    private String title;
+    private String author;
+
+    public Book(String title, String author) {
+        this.title = title;
+        this.author = author;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+
+    @Override
+    public String toString() {
+        return "Book [title=" + title + ", author=" + author + "]";
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        final Book book = (Book) o;
+
+        if (!Objects.equals(title, book.title)) {
+            return false;
+        }
+        return Objects.equals(author, book.author);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = title != null ? title.hashCode() : 0;
+        result = 31 * result + (author != null ? author.hashCode() : 0);
+        return result;
+    }
+}

core-java-modules/core-java-9-jigsaw/library-core/src/main/java/com/baeldung/library/core/Library.java

@@ -0,0 +1,25 @@
+package com.baeldung.library.core;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Library {
+
+    private List<Book> books = new ArrayList<>();
+
+    public void addBook(Book book) {
+        books.add(book);
+    }
+
+    public List<Book> getBooks() {
+        return books;
+    }
+
+    void removeBook(Book book) {
+        books.remove(book);
+    }
+
+    protected void removeBookByAuthor(String author) {
+        books.removeIf(book -> book.getAuthor().equals(author));
+    }
+}

core-java-modules/core-java-9-jigsaw/library-core/src/main/java/com/baeldung/library/core/Main.java

@@ -0,0 +1,16 @@
+package com.baeldung.library.core;
+
+public class Main {
+
+    public static void main(String[] args) {
+        Library library = new Library();
+        library.addBook(new Book("The Lord of the Rings", "J.R.R. Tolkien"));
+        library.addBook(new Book("The Hobbit", "J.R.R. Tolkien"));
+        library.addBook(new Book("The Silmarillion", "J.R.R. Tolkien"));
+        library.addBook(new Book("The Chronicles of Narnia", "C.S. Lewis"));
+        library.addBook(new Book("The Lion, the Witch and the Wardrobe", "C.S. Lewis"));
+        System.out.println("Welcome to our library!");
+        System.out.println("We have the following books:");
+        library.getBooks().forEach(System.out::println);
+    }
+}

core-java-modules/core-java-9-jigsaw/library-core/src/main/java/module-info.java

@@ -0,0 +1,3 @@
+module com.baeldung.library.core {
+    exports com.baeldung.library.core;
+}

core-java-modules/core-java-9-jigsaw/library-core/src/test/java/com/baeldung/library/core/LibraryUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.library.core;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class LibraryUnitTest {
+
+    @Test
+    void givenEmptyLibrary_whenAddABook_thenLibraryHasOneBook() {
+        Library library = new Library();
+        Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+        library.addBook(theLordOfTheRings);
+        int expected = 1;
+        int actual = library.getBooks().size();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void givenTheLibraryWithABook_whenRemoveABook_thenLibraryIsEmpty() {
+        Library library = new Library();
+        Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+        library.addBook(theLordOfTheRings);
+        library.removeBook(theLordOfTheRings);
+        int expected = 0;
+        int actual = library.getBooks().size();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void givenTheLibraryWithSeveralBook_whenRemoveABookByAuthor_thenLibraryHasNoBooksByTheAuthor() {
+        Library library = new Library();
+        Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+        Book theHobbit = new Book("The Hobbit", "J.R.R. Tolkien");
+        Book theSilmarillion = new Book("The Silmarillion", "J.R.R. Tolkien");
+        Book theHungerGames = new Book("The Hunger Games", "Suzanne Collins");
+        library.addBook(theLordOfTheRings);
+        library.addBook(theHobbit);
+        library.addBook(theSilmarillion);
+        library.addBook(theHungerGames);
+        library.removeBookByAuthor("J.R.R. Tolkien");
+        int expected = 1;
+        int actual = library.getBooks().size();
+        assertEquals(expected, actual);
+    }
+
+}

core-java-modules/core-java-9-jigsaw/library-test/src/test/java/com/baeldung/library/test/LibraryUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.library.test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.baeldung.library.core.Book;
+import com.baeldung.library.core.Library;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import org.junit.jupiter.api.Test;
+
+class LibraryUnitTest {
+
+    @Test
+    void givenEmptyLibrary_whenAddABook_thenLibraryHasOneBook() {
+        Library library = new Library();
+        Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+        library.addBook(theLordOfTheRings);
+        int expected = 1;
+        int actual = library.getBooks().size();
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    void givenTheLibraryWithABook_whenRemoveABook_thenLibraryIsEmpty()
+        throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
+        Library library = new Library();
+        Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+        library.addBook(theLordOfTheRings);
+        Method removeBook = Library.class.getDeclaredMethod("removeBook", Book.class);
+        removeBook.setAccessible(true);
+        removeBook.invoke(library, theLordOfTheRings);
+        int expected = 0;
+        int actual = library.getBooks().size();
+        assertEquals(expected, actual);
+    }
+@Test
+void givenTheLibraryWithSeveralBook_whenRemoveABookByAuthor_thenLibraryHasNoBooksByTheAuthor() {
+    TestLibrary library = new TestLibrary();
+    Book theLordOfTheRings = new Book("The Lord of the Rings", "J.R.R. Tolkien");
+    Book theHobbit = new Book("The Hobbit", "J.R.R. Tolkien");
+    Book theSilmarillion = new Book("The Silmarillion", "J.R.R. Tolkien");
+    Book theHungerGames = new Book("The Hunger Games", "Suzanne Collins");
+    library.addBook(theLordOfTheRings);
+    library.addBook(theHobbit);
+    library.addBook(theSilmarillion);
+    library.addBook(theHungerGames);
+    library.removeBookByAuthor("J.R.R. Tolkien");
+    int expected = 1;
+    int actual = library.getBooks().size();
+    assertEquals(expected, actual);
+}
+
+}

core-java-modules/core-java-9-jigsaw/library-test/src/test/java/com/baeldung/library/test/TestLibrary.java

@@ -0,0 +1,10 @@
+package com.baeldung.library.test;
+
+import com.baeldung.library.core.Library;
+
+public class TestLibrary extends Library {
+    @Override
+    public void removeBookByAuthor(final String author) {
+        super.removeBookByAuthor(author);
+    }
+}

core-java-modules/core-java-9-jigsaw/library-test/src/test/java/module-info.java

@@ -0,0 +1,5 @@
+module com.baeldung.library.test {
+    requires com.baeldung.library.core;
+    requires org.junit.jupiter.api;
+    opens com.baeldung.library.test to org.junit.platform.commons;
+}

core-java-modules/core-java-9-jigsaw/pom.xml

@@ -5,6 +5,10 @@
     <modelVersion>4.0.0</modelVersion>
     <artifactId>core-java-9-jigsaw</artifactId>
     <name>core-java-9-jigsaw</name>
+    <packaging>pom</packaging>
+    <modules>
+        <module>library-core</module>
+    </modules>
 
     <parent>
         <groupId>com.baeldung</groupId>

core-java-modules/core-java-9-jigsaw/run-library-core-module-with-patch.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+java --module-path mods:libs \
+--add-modules com.baeldung.library.core \
+--add-opens com.baeldung.library.core/com.baeldung.library.core=org.junit.platform.commons \
+--add-reads com.baeldung.library.core=org.junit.jupiter.api \
+--patch-module com.baeldung.library.core=outDir/library-test \
+--module org.junit.platform.console --select-class com.baeldung.library.core.LibraryUnitTest

core-java-modules/core-java-9-jigsaw/run-library-core-module.sh

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+java --module-path mods --module com.baeldung.library.core/com.baeldung.library.core.Main

core-java-modules/core-java-9-jigsaw/run-library-test-class-path.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+java --module-path libs \
+org.junit.platform.console.ConsoleLauncher \
+--classpath ./outDir/library-core \
+--select-class com.baeldung.library.core.LibraryUnitTest

core-java-modules/core-java-9-jigsaw/run-library-test-module-path.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+java --module-path mods:libs \
+--add-modules com.baeldung.library.test \
+--add-opens com.baeldung.library.core/com.baeldung.library.core=com.baeldung.library.test \
+org.junit.platform.console.ConsoleLauncher --select-class com.baeldung.library.test.LibraryUnitTest

core-java-modules/core-java-collections-maps/src/test/java/com/baeldung/map/ImmutableMapUnitTest.java

@@ -1,84 +1,126 @@
 package com.baeldung.map;
 
-import com.google.common.collect.ImmutableMap;
-import org.junit.jupiter.api.Test;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.util.AbstractMap;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
-import static org.junit.jupiter.api.Assertions.*;
+import org.hamcrest.collection.IsMapContaining;
+import org.junit.jupiter.api.Test;
 
+import com.google.common.collect.ImmutableMap;
 
-public class ImmutableMapUnitTest {
+class ImmutableMapUnitTest {
 
-	@Test
-	public void whenCollectionsUnModifiableMapMethod_thenOriginalCollectionChangesReflectInUnmodifiableMap() {
+    @Test
+    void whenCollectionsUnModifiableMapMethod_thenOriginalCollectionChangesReflectInUnmodifiableMap() {
 
-		Map<String, String> mutableMap = new HashMap<>();
-		mutableMap.put("USA", "North America");
+        Map<String, String> mutableMap = new HashMap<>();
+        mutableMap.put("USA", "North America");
 
-		Map<String, String> unmodifiableMap = Collections.unmodifiableMap(mutableMap);
-		assertThrows(UnsupportedOperationException.class, () -> unmodifiableMap.put("Canada", "North America"));
+        Map<String, String> unmodifiableMap = Collections.unmodifiableMap(mutableMap);
+        assertThrows(UnsupportedOperationException.class, () -> unmodifiableMap.put("Canada", "North America"));
 
-		mutableMap.remove("USA");
-		assertFalse(unmodifiableMap.containsKey("USA"));
+        mutableMap.remove("USA");
+        assertFalse(unmodifiableMap.containsKey("USA"));
 
-		mutableMap.put("Mexico", "North America");
-		assertTrue(unmodifiableMap.containsKey("Mexico"));
-	}
+        mutableMap.put("Mexico", "North America");
+        assertTrue(unmodifiableMap.containsKey("Mexico"));
+    }
 
-	@Test
-	@SuppressWarnings("deprecation")
-	public void whenGuavaImmutableMapFromCopyOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+    @Test
+    @SuppressWarnings("deprecation")
+    void whenGuavaImmutableMapFromCopyOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
 
-		Map<String, String> mutableMap = new HashMap<>();
-		mutableMap.put("USA", "North America");
+        Map<String, String> mutableMap = new HashMap<>();
+        mutableMap.put("USA", "North America");
 
-		ImmutableMap<String, String> immutableMap = ImmutableMap.copyOf(mutableMap);
-		assertTrue(immutableMap.containsKey("USA"));
+        ImmutableMap<String, String> immutableMap = ImmutableMap.copyOf(mutableMap);
+        assertTrue(immutableMap.containsKey("USA"));
 
-		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+        assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
 
-		mutableMap.remove("USA");
-		assertTrue(immutableMap.containsKey("USA"));
+        mutableMap.remove("USA");
+        assertTrue(immutableMap.containsKey("USA"));
 
-		mutableMap.put("Mexico", "North America");
-		assertFalse(immutableMap.containsKey("Mexico"));
-	}
+        mutableMap.put("Mexico", "North America");
+        assertFalse(immutableMap.containsKey("Mexico"));
+    }
 
-	@Test
-	@SuppressWarnings("deprecation")
-	public void whenGuavaImmutableMapFromBuilderMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+    @Test
+    @SuppressWarnings("deprecation")
+    void whenGuavaImmutableMapFromBuilderMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
 
-		Map<String, String> mutableMap = new HashMap<>();
-		mutableMap.put("USA", "North America");
+        Map<String, String> mutableMap = new HashMap<>();
+        mutableMap.put("USA", "North America");
 
-		ImmutableMap<String, String> immutableMap = ImmutableMap.<String, String>builder()
-				.putAll(mutableMap)
-				.put("Costa Rica", "North America")
-				.build();
-		assertTrue(immutableMap.containsKey("USA"));
-		assertTrue(immutableMap.containsKey("Costa Rica"));
+        ImmutableMap<String, String> immutableMap = ImmutableMap.<String, String>builder()
+            .putAll(mutableMap)
+            .put("Costa Rica", "North America")
+            .build();
+        assertTrue(immutableMap.containsKey("USA"));
+        assertTrue(immutableMap.containsKey("Costa Rica"));
 
-		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+        assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
 
-		mutableMap.remove("USA");
-		assertTrue(immutableMap.containsKey("USA"));
+        mutableMap.remove("USA");
+        assertTrue(immutableMap.containsKey("USA"));
 
-		mutableMap.put("Mexico", "North America");
-		assertFalse(immutableMap.containsKey("Mexico"));
-	}
+        mutableMap.put("Mexico", "North America");
+        assertFalse(immutableMap.containsKey("Mexico"));
+    }
 
-	@Test
-	@SuppressWarnings("deprecation")
-	public void whenGuavaImmutableMapFromOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+    @Test
+    @SuppressWarnings("deprecation")
+    void whenGuavaImmutableMapFromOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
 
-		ImmutableMap<String, String> immutableMap = ImmutableMap.of("USA", "North America", "Costa Rica", "North America");
-		assertTrue(immutableMap.containsKey("USA"));
-		assertTrue(immutableMap.containsKey("Costa Rica"));
+        ImmutableMap<String, String> immutableMap = ImmutableMap.of("USA", "North America", "Costa Rica", "North America");
+        assertTrue(immutableMap.containsKey("USA"));
+        assertTrue(immutableMap.containsKey("Costa Rica"));
 
-		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
-	}
+        assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+    }
+
+    @Test
+    @SuppressWarnings("deprecation")
+    void givenGuavaImmutableMapFromOfEntriesMethodwhenModifyEntry_thenThrowUnsupportedOperationException() {
+
+        ImmutableMap<Integer, String> immutableMap = ImmutableMap.ofEntries(new AbstractMap.SimpleEntry<>(1, "USA"), new AbstractMap.SimpleEntry<>(2, "Canada"));
+
+        assertThrows(UnsupportedOperationException.class, () -> immutableMap.put(2, "Mexico"));
+    }
+
+    @Test
+    void givenEntrieswhenCreatingGuavaImmutableMapFromOfEntriesMethod_thenCorrect() {
+
+        ImmutableMap<Integer, String> immutableMap = ImmutableMap.ofEntries(new AbstractMap.SimpleEntry<>(1, "USA"));
+
+        assertEquals(1, immutableMap.size());
+        assertThat(immutableMap, IsMapContaining.hasEntry(1, "USA"));
+    }
+
+    @Test
+    void givenGuavaImmutableMapFromOfEntriesMethodwhenEntryKeyExists_thenThrowIllegalArgumentException() {
+
+        assertThrows(IllegalArgumentException.class, () -> ImmutableMap.ofEntries(new AbstractMap.SimpleEntry<>(1, "USA"), new AbstractMap.SimpleEntry<>(1, "Canada")));
+    }
+
+    @Test
+    void givenGuavaImmutableMapFromOfEntriesMethodwhenEntryKeyIsNull_thenThrowNullPointerException() {
+
+        assertThrows(NullPointerException.class, () -> ImmutableMap.ofEntries(new AbstractMap.SimpleEntry<>(null, "USA")));
+    }
+
+    @Test
+    void givenGuavaImmutableMapFromOfEntriesMethodwhenEntryValueIsNull_thenThrowNullPointerException() {
+
+        assertThrows(NullPointerException.class, () -> ImmutableMap.ofEntries(new AbstractMap.SimpleEntry<>(1, null)));
+    }
 
 }

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

@@ -0,0 +1,6 @@
+## Core Java Compiler
+
+### Relevant Articles: 
+
+- [Compiling Java *.class Files with javac](http://www.baeldung.com/javac)
+- [Illegal Character Compilation Error](https://www.baeldung.com/java-illegal-character-error)

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

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-compiler</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-compiler</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.google.gdata</groupId>
+            <artifactId>core</artifactId>
+            <version>${gdata.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <gdata.version>1.47.1</gdata.version>
+    </properties>
+
+</project>