Merge branch 'masterEugen'

.gitignore

@@ -42,3 +42,9 @@ spring-check-if-a-property-is-null/.mvn/wrapper/maven-wrapper.properties
 *.springBeans
 
 20171220-JMeter.csv
+
+.factorypath
+dependency-reduced-pom.xml
+*.so
+*.dylib
+*.dll

cdi/pom.xml

@@ -14,6 +14,24 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-core</artifactId>
+            <version>1.3</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.10.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-context</artifactId>
@@ -42,4 +60,4 @@
         <weld-se-core.version>2.4.1.Final</weld-se-core.version>
     </properties>
 
-</project>
+</project>

cdi/src/main/java/com/baeldung/dependencyinjection/application/FileApplication.java

@@ -0,0 +1,18 @@
+package com.baeldung.dependencyinjection.application;
+
+import com.baeldung.dependencyinjection.imageprocessors.ImageFileProcessor;
+import org.jboss.weld.environment.se.Weld;
+import org.jboss.weld.environment.se.WeldContainer;
+
+public class FileApplication {
+    
+    public static void main(String[] args) {
+        Weld weld = new Weld();
+        WeldContainer container = weld.initialize();
+        ImageFileProcessor imageFileProcessor = container.select(ImageFileProcessor.class).get();
+        System.out.println(imageFileProcessor.openFile("file1.png"));
+        System.out.println(imageFileProcessor.writeFile("file1.png"));
+        System.out.println(imageFileProcessor.saveFile("file1.png"));
+        container.shutdown();
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/factories/TimeLoggerFactory.java

@@ -0,0 +1,14 @@
+package com.baeldung.dependencyinjection.factories;
+
+import com.baeldung.dependencyinjection.loggers.TimeLogger;
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+import javax.enterprise.inject.Produces;
+
+public class TimeLoggerFactory {
+    
+    @Produces
+    public TimeLogger getTimeLogger() {
+        return new TimeLogger(new SimpleDateFormat("HH:mm"), Calendar.getInstance());
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/imagefileeditors/GifFileEditor.java

@@ -0,0 +1,27 @@
+package com.baeldung.dependencyinjection.imagefileeditors;
+
+import com.baeldung.dependencyinjection.qualifiers.GifFileEditorQualifier;
+
+@GifFileEditorQualifier
+public class GifFileEditor implements ImageFileEditor {
+    
+    @Override
+    public String openFile(String fileName) {
+        return "Opening GIF file " + fileName;
+    }
+
+    @Override
+    public String editFile(String fileName) {
+        return "Editing GIF file " + fileName;
+    }
+    
+    @Override
+    public String writeFile(String fileName) {
+        return "Writing GIF file " + fileName;
+    }
+
+    @Override
+    public String saveFile(String fileName) {
+        return "Saving GIF file " + fileName;
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/imagefileeditors/ImageFileEditor.java

@@ -0,0 +1,12 @@
+package com.baeldung.dependencyinjection.imagefileeditors;
+
+public interface ImageFileEditor {
+    
+    String openFile(String fileName);
+    
+    String editFile(String fileName);
+    
+    String writeFile(String fileName);
+    
+    String saveFile(String fileName);
+}

cdi/src/main/java/com/baeldung/dependencyinjection/imagefileeditors/JpgFileEditor.java

@@ -0,0 +1,27 @@
+package com.baeldung.dependencyinjection.imagefileeditors;
+
+import com.baeldung.dependencyinjection.qualifiers.JpgFileEditorQualifier;
+
+@JpgFileEditorQualifier
+public class JpgFileEditor implements ImageFileEditor {
+   
+    @Override
+    public String openFile(String fileName) {
+        return "Opening JPG file " + fileName;
+    }
+
+    @Override
+    public String editFile(String fileName) {
+        return "Editing JPG file " + fileName;
+    }
+    
+    @Override
+    public String writeFile(String fileName) {
+        return "Writing JPG file " + fileName;
+    }
+
+    @Override
+    public String saveFile(String fileName) {
+        return "Saving JPG file " + fileName;
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/imagefileeditors/PngFileEditor.java

@@ -0,0 +1,27 @@
+package com.baeldung.dependencyinjection.imagefileeditors;
+
+import com.baeldung.dependencyinjection.qualifiers.PngFileEditorQualifier;
+
+@PngFileEditorQualifier
+public class PngFileEditor implements ImageFileEditor {
+   
+    @Override
+    public String openFile(String fileName) {
+        return "Opening PNG file " + fileName;
+    }
+
+    @Override
+    public String editFile(String fileName) {
+        return "Editing PNG file " + fileName;
+    }
+    
+    @Override
+    public String writeFile(String fileName) {
+        return "Writing PNG file " + fileName;
+    }
+
+    @Override
+    public String saveFile(String fileName) {
+        return "Saving PNG file " + fileName;
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/imageprocessors/ImageFileProcessor.java

@@ -0,0 +1,42 @@
+package com.baeldung.dependencyinjection.imageprocessors;
+
+import com.baeldung.dependencyinjection.loggers.TimeLogger;
+import com.baeldung.dependencyinjection.qualifiers.PngFileEditorQualifier;
+import javax.inject.Inject;
+import com.baeldung.dependencyinjection.imagefileeditors.ImageFileEditor;
+
+public class ImageFileProcessor {
+    
+    private final ImageFileEditor imageFileEditor;
+    private final TimeLogger timeLogger;
+    
+    @Inject
+    public ImageFileProcessor(@PngFileEditorQualifier ImageFileEditor imageFileEditor, TimeLogger timeLogger) {
+        this.imageFileEditor = imageFileEditor;
+        this.timeLogger = timeLogger;
+    }
+    
+    public ImageFileEditor getImageFileditor() {
+        return imageFileEditor;
+    }
+    
+    public TimeLogger getTimeLogger() {
+        return timeLogger;
+    }
+    
+    public String openFile(String fileName) {
+        return imageFileEditor.openFile(fileName) + " at: " + timeLogger.getTime();
+    }
+    
+    public String editFile(String fileName) {
+        return imageFileEditor.editFile(fileName) + " at: " + timeLogger.getTime();
+    }
+     
+    public String writeFile(String fileName) {
+        return imageFileEditor.writeFile(fileName) + " at: " + timeLogger.getTime();
+    }
+    
+    public String saveFile(String fileName) {
+        return imageFileEditor.saveFile(fileName)+ " at: " + timeLogger.getTime();
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/loggers/TimeLogger.java

@@ -0,0 +1,19 @@
+package com.baeldung.dependencyinjection.loggers;
+
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+
+public class TimeLogger {
+    
+    private final SimpleDateFormat dateFormat;
+    private final Calendar calendar;
+    
+    public TimeLogger(SimpleDateFormat dateFormat, Calendar calendar) {
+        this.dateFormat = dateFormat;
+        this.calendar = calendar;
+    }
+    
+    public String getTime() {
+        return dateFormat.format(calendar.getTime());
+    }
+}

cdi/src/main/java/com/baeldung/dependencyinjection/qualifiers/GifFileEditorQualifier.java

@@ -0,0 +1,12 @@
+package com.baeldung.dependencyinjection.qualifiers;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import javax.inject.Qualifier;
+
+@Qualifier
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE, ElementType.PARAMETER})
+public @interface GifFileEditorQualifier {}

cdi/src/main/java/com/baeldung/dependencyinjection/qualifiers/JpgFileEditorQualifier.java

@@ -0,0 +1,12 @@
+package com.baeldung.dependencyinjection.qualifiers;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import javax.inject.Qualifier;
+
+@Qualifier
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE, ElementType.PARAMETER})
+public @interface JpgFileEditorQualifier {}

cdi/src/main/java/com/baeldung/dependencyinjection/qualifiers/PngFileEditorQualifier.java

@@ -0,0 +1,12 @@
+package com.baeldung.dependencyinjection.qualifiers;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import javax.inject.Qualifier;
+
+@Qualifier
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE, ElementType.PARAMETER})
+public @interface PngFileEditorQualifier {}

cdi/src/test/java/com/baeldung/test/dependencyinjection/GifFileEditorUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.imagefileeditors.GifFileEditor;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class GifFileEditorUnitTest {
+    
+    private static GifFileEditor gifFileEditor;
+    
+    
+    @BeforeClass
+    public static void setGifFileEditorInstance() {
+        gifFileEditor = new GifFileEditor();
+    }
+    
+    @Test
+    public void givenGifFileEditorlInstance_whenCalledopenFile_thenOneAssertion() {
+        assertThat(gifFileEditor.openFile("file1.gif")).isEqualTo("Opening GIF file file1.gif");
+    }
+    
+    @Test
+    public void givenGifFileEditorlInstance_whenCallededitFile_thenOneAssertion() {
+        assertThat(gifFileEditor.editFile("file1.gif")).isEqualTo("Editing GIF file file1.gif");
+    }
+    
+    @Test
+    public void givenGifFileEditorInstance_whenCalledwriteFile_thenOneAssertion() {
+        assertThat(gifFileEditor.writeFile("file1.gif")).isEqualTo("Writing GIF file file1.gif");
+    }
+    
+    @Test
+    public void givenGifFileEditorInstance_whenCalledsaveFile_thenOneAssertion() {
+        assertThat(gifFileEditor.saveFile("file1.gif")).isEqualTo("Saving GIF file file1.gif");
+    }
+}

cdi/src/test/java/com/baeldung/test/dependencyinjection/ImageProcessorUnitTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.imagefileeditors.GifFileEditor;
+import com.baeldung.dependencyinjection.imagefileeditors.JpgFileEditor;
+import com.baeldung.dependencyinjection.imagefileeditors.PngFileEditor;
+import com.baeldung.dependencyinjection.imageprocessors.ImageFileProcessor;
+import com.baeldung.dependencyinjection.loggers.TimeLogger;
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.jboss.weld.environment.se.Weld;
+import org.jboss.weld.environment.se.WeldContainer;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class ImageProcessorUnitTest {
+    
+    private static ImageFileProcessor imageFileProcessor;
+    private static SimpleDateFormat dateFormat;
+    private static Calendar calendar;
+    
+    
+    @BeforeClass
+    public static void setImageProcessorInstance() {
+        Weld weld = new Weld();
+        WeldContainer container = weld.initialize();
+        imageFileProcessor = container.select(ImageFileProcessor.class).get();
+        container.shutdown();
+    }
+    
+    @BeforeClass
+    public static void setSimpleDateFormatInstance() {
+        dateFormat = new SimpleDateFormat("HH:mm");
+    }
+    
+    @BeforeClass
+    public static void setCalendarInstance() {
+        calendar = Calendar.getInstance();
+    }
+    
+    @Test
+    public void givenImageProcessorInstance_whenInjectedPngFileEditorandTimeLoggerInstances_thenTwoAssertions() {
+        assertThat(imageFileProcessor.getImageFileditor()).isInstanceOf(PngFileEditor.class);
+        assertThat(imageFileProcessor.getTimeLogger()).isInstanceOf(TimeLogger.class);
+    }
+    
+    @Test
+    public void givenImageProcessorInstance_whenCalledopenFile_thenOneAssertion() {
+        String currentTime = dateFormat.format(calendar.getTime());
+        assertThat(imageFileProcessor.openFile("file1.png")).isEqualTo("Opening PNG file file1.png at: " + currentTime);
+    }
+    
+    @Test
+    public void givenImageProcessorInstance_whenCallededitFile_thenOneAssertion() {
+        String currentTime = dateFormat.format(calendar.getTime());
+        assertThat(imageFileProcessor.editFile("file1.png")).isEqualTo("Editing PNG file file1.png at: " + currentTime);
+    }
+    
+    @Test
+    public void givenImageProcessorInstance_whenCalledwriteFile_thenOneAssertion() {
+        String currentTime = dateFormat.format(calendar.getTime());
+        assertThat(imageFileProcessor.writeFile("file1.png")).isEqualTo("Writing PNG file file1.png at: " + currentTime);
+    }
+    
+    @Test
+    public void givenImageProcessorInstance_whenCalledsaveFile_thenOneAssertion() {
+        String currentTime = dateFormat.format(calendar.getTime());
+        assertThat(imageFileProcessor.saveFile("file1.png")).isEqualTo("Saving PNG file file1.png at: " + currentTime);
+    }
+}

cdi/src/test/java/com/baeldung/test/dependencyinjection/JpgFileEditorUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.imagefileeditors.JpgFileEditor;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class JpgFileEditorUnitTest {
+    
+    private static JpgFileEditor jpgFileUtil;
+    
+    
+    @BeforeClass
+    public static void setJpgFileEditorInstance() {
+        jpgFileUtil = new JpgFileEditor();
+    }
+    
+    @Test
+    public void givenJpgFileEditorInstance_whenCalledopenFile_thenOneAssertion() {
+        assertThat(jpgFileUtil.openFile("file1.jpg")).isEqualTo("Opening JPG file file1.jpg");
+    }
+    
+    @Test
+    public void givenJpgFileEditorlInstance_whenCallededitFile_thenOneAssertion() {
+        assertThat(jpgFileUtil.editFile("file1.gif")).isEqualTo("Editing JPG file file1.gif");
+    }
+    
+    @Test
+    public void givenJpgFileEditorInstance_whenCalledwriteFile_thenOneAssertion() {
+        assertThat(jpgFileUtil.writeFile("file1.jpg")).isEqualTo("Writing JPG file file1.jpg");
+    }
+    
+    @Test
+    public void givenJpgFileEditorInstance_whenCalledsaveFile_thenOneAssertion() {
+        assertThat(jpgFileUtil.saveFile("file1.jpg")).isEqualTo("Saving JPG file file1.jpg");
+    }
+}

cdi/src/test/java/com/baeldung/test/dependencyinjection/PngFileEditorUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.imagefileeditors.PngFileEditor;
+import com.baeldung.dependencyinjection.qualifiers.PngFileEditorQualifier;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+@PngFileEditorQualifier
+public class PngFileEditorUnitTest {
+    
+    private static PngFileEditor pngFileEditor;
+    
+    
+    @BeforeClass
+    public static void setPngFileEditorInstance() {
+        pngFileEditor = new PngFileEditor();
+    }
+    
+    @Test
+    public void givenPngFileEditorInstance_whenCalledopenFile_thenOneAssertion() {
+        assertThat(pngFileEditor.openFile("file1.png")).isEqualTo("Opening PNG file file1.png");
+    }
+    
+    @Test
+    public void givenPngFileEditorInstance_whenCallededitFile_thenOneAssertion() {
+        assertThat(pngFileEditor.editFile("file1.png")).isEqualTo("Editing PNG file file1.png");
+    }
+    
+    @Test
+    public void givenPngFileEditorInstance_whenCalledwriteFile_thenOneAssertion() {
+        assertThat(pngFileEditor.writeFile("file1.png")).isEqualTo("Writing PNG file file1.png");
+    }
+    
+    @Test
+    public void givenPngFileEditorInstance_whenCalledsaveFile_thenOneAssertion() {
+        assertThat(pngFileEditor.saveFile("file1.png")).isEqualTo("Saving PNG file file1.png");
+    }
+}

cdi/src/test/java/com/baeldung/test/dependencyinjection/TimeLoggerFactoryUnitTest.java

@@ -0,0 +1,15 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.factories.TimeLoggerFactory;
+import com.baeldung.dependencyinjection.loggers.TimeLogger;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class TimeLoggerFactoryUnitTest {
+    
+    @Test
+    public void givenTimeLoggerFactory_whenCalledgetTimeLogger_thenOneAssertion() {
+        TimeLoggerFactory timeLoggerFactory = new TimeLoggerFactory();
+        assertThat(timeLoggerFactory.getTimeLogger()).isInstanceOf(TimeLogger.class);
+    }
+}

cdi/src/test/java/com/baeldung/test/dependencyinjection/TimeLoggerUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.test.dependencyinjection;
+
+import com.baeldung.dependencyinjection.loggers.TimeLogger;
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class TimeLoggerUnitTest {
+    
+    
+    @Test
+    public void givenTimeLoggerInstance_whenCalledgetLogTime_thenOneAssertion() {
+        SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm");
+        Calendar calendar = Calendar.getInstance();
+        TimeLogger timeLogger = new TimeLogger(dateFormat, calendar);
+        String currentTime = dateFormat.format(calendar.getTime());
+        assertThat(timeLogger.getTime()).isEqualTo(currentTime);
+    }
+}

core-java-io/pom.xml

@@ -220,6 +220,7 @@
                     <excludes>
                         <exclude>**/*LiveTest.java</exclude>
                         <exclude>**/*IntegrationTest.java</exclude>
+                        <exclude>**/*IntTest.java</exclude>
                         <exclude>**/*LongRunningUnitTest.java</exclude>
                         <exclude>**/*ManualTest.java</exclude>
                     </excludes>
@@ -289,6 +290,7 @@
                                     </excludes>
                                     <includes>
                                         <include>**/*IntegrationTest.java</include>
+                                        <include>**/*IntTest.java</include>
                                     </includes>
                                 </configuration>
                             </execution>

core-java-sun/pom.xml

@@ -353,6 +353,7 @@
                                     </excludes>
                                     <includes>
                                         <include>**/*IntegrationTest.java</include>
+                                        <include>**/*IntTest.java</include>
                                     </includes>
                                 </configuration>
                             </execution>

core-java/pom.xml

@@ -222,6 +222,7 @@
                     <excludes>
                         <exclude>**/*LiveTest.java</exclude>
                         <exclude>**/*IntegrationTest.java</exclude>
+                        <exclude>**/*IntTest.java</exclude>
                         <exclude>**/*LongRunningUnitTest.java</exclude>
                         <exclude>**/*ManualTest.java</exclude>
                     </excludes>
@@ -387,6 +388,7 @@
                                     </excludes>
                                     <includes>
                                         <include>**/*IntegrationTest.java</include>
+                                        <include>**/*IntTest.java</include>
                                     </includes>
                                 </configuration>
                             </execution>

core-java/src/main/java/com/baeldung/immutableobjects/Currency.java

@@ -0,0 +1,18 @@
+package com.baeldung.immutableobjects;
+
+public final class Currency {
+
+    private final String value;
+    
+    private Currency(String currencyValue) {
+        value = currencyValue;
+    }
+    
+    public String getValue() {
+        return value;
+    }
+    
+    public static Currency of(String value) {
+        return new Currency(value);
+    }
+}

core-java/src/main/java/com/baeldung/immutableobjects/Money.java

@@ -0,0 +1,20 @@
+package com.baeldung.immutableobjects;
+
+// 4. Immutability in Java
+public final class Money {
+    private final double amount;
+    private final Currency currency;
+
+    public Money(double amount, Currency currency) {
+        this.amount = amount;
+        this.currency = currency;
+    }
+
+    public Currency getCurrency() {
+        return currency;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+}

core-java/src/test/java/com/baeldung/extension/ExtensionUnitTest.java

@@ -19,8 +19,7 @@ public class ExtensionUnitTest {
     public void getExtension_whenStringHandle_thenExtensionIsTrue() {
         String expectedExtension = "java";
         Optional<String> actualExtension = extension.getExtensionByStringHandling("Demo.java");
-        Assert.assertTrue(actualExtension.isPresent());
+        Assert.assertEquals(expectedExtension, actualExtension.get());
-        actualExtension.ifPresent(ext -> Assert.assertEquals(expectedExtension,ext));
     }
 
     @Test

core-java/src/test/java/com/baeldung/immutableobjects/ImmutableObjectsUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.immutableobjects;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+
+public class ImmutableObjectsUnitTest {
+
+    @Test
+    public void whenCallingStringReplace_thenStringDoesNotMutate() {
+        // 2. What's an Immutable Object?
+        final String name = "baeldung";
+        final String newName = name.replace("dung", "----");
+
+        assertEquals("baeldung", name);
+        assertEquals("bael----", newName);
+    }
+
+    public void whenReassignFinalValue_thenCompilerError() {
+        // 3. The final Keyword in Java (1)
+        final String name = "baeldung";
+        // name = "bael...";
+    }
+
+    @Test
+    public void whenAddingElementToList_thenSizeChange() {
+        // 3. The final Keyword in Java (2)
+        final List<String> strings = new ArrayList<>();
+        assertEquals(0, strings.size());
+        strings.add("baeldung");
+        assertEquals(1, strings.size());
+    }
+}

custom-pmd/src/main/java/org/baeldung/pmd/UnitTestNamingConventionRule.java

@@ -11,6 +11,7 @@ public class UnitTestNamingConventionRule extends AbstractJavaRule {
 
     private static List<String> allowedEndings = Arrays.asList(
       "IntegrationTest",
+      "IntTest",
       "ManualTest",
       "JdbcTest",
       "LiveTest",

javax-servlets/src/main/java/com/baeldung/servlets/ErrorHandlerServlet.java

@@ -0,0 +1,34 @@
+package com.baeldung.servlets;
+
+import javax.servlet.annotation.*;
+import javax.servlet.http.*;
+import java.io.*;
+import java.util.*;
+
+import static javax.servlet.RequestDispatcher.*;
+
+@WebServlet(urlPatterns = "/errorHandler")
+public class ErrorHandlerServlet extends HttpServlet {
+
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
+            throws IOException {
+        resp.setContentType("text/html; charset=utf-8");
+        try (PrintWriter writer = resp.getWriter()) {
+            writer.write("<html><head><title>Error description</title></head><body>");
+            writer.write("<h2>Error description</h2>");
+            writer.write("<ul>");
+            Arrays.asList(ERROR_STATUS_CODE, ERROR_EXCEPTION_TYPE, ERROR_MESSAGE)
+                    .forEach(e ->
+                            writer.write("<li>" + e + ":" + req.getAttribute(e) + " </li>")
+                    );
+            writer.write("</ul>");
+            writer.write("</html></body>");
+        }
+
+        Exception exception = (Exception) req.getAttribute(ERROR_EXCEPTION);
+        if (IllegalArgumentException.class.isInstance(exception)) {
+            getServletContext().log("Error on an application argument", exception);
+        }
+    }
+}

javax-servlets/src/main/java/com/baeldung/servlets/RandomErrorServlet.java

@@ -0,0 +1,13 @@
+package com.baeldung.servlets;
+
+import javax.servlet.annotation.*;
+import javax.servlet.http.*;
+
+@WebServlet(urlPatterns = "/randomError")
+public class RandomErrorServlet extends HttpServlet {
+
+    @Override
+    protected void doGet(HttpServletRequest req, final HttpServletResponse resp) {
+        throw new IllegalStateException("Random error");
+    }
+}