BAEL-1921 - added example code and unit test for GlobalExceptionHandler (#4646)

* added example code and unit test for GlobalExceptionHandler

* Code for common exceptions

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/Arithmetic.java

@@ -0,0 +1,20 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Arithmetic {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(Arithmetic.class);
+
+    public static void main(String[] args) {
+
+        try {
+            int result = 30 / 0; // Trying to divide by zero
+        } catch (ArithmeticException e) {
+            LOGGER.error("ArithmeticException caught!");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/ArrayIndexOutOfBounds.java

@@ -0,0 +1,24 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ArrayIndexOutOfBounds {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(ArrayIndexOutOfBounds.class);
+
+    public static void main(String[] args) {
+
+        int[] nums = new int[] { 1, 2, 3 };
+
+        try {
+            int numFromNegativeIndex = nums[-1]; // Trying to access at negative index
+            int numFromGreaterIndex = nums[4]; // Trying to access at greater index
+            int numFromLengthIndex = nums[3]; // Trying to access at index equal to size of the array
+        } catch (ArrayIndexOutOfBoundsException e) {
+            LOGGER.error("ArrayIndexOutOfBoundsException caught");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/ClassCast.java

@@ -0,0 +1,36 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class Animal {
+
+}
+
+class Dog extends Animal {
+
+}
+
+class Lion extends Animal {
+
+}
+
+public class ClassCast {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(ClassCast.class);
+
+    public static void main(String[] args) {
+
+        try {
+            Animal animalOne = new Dog(); // At runtime the instance is dog
+            Dog bruno = (Dog) animalOne; // Downcasting
+
+            Animal animalTwo = new Lion(); // At runtime the instance is animal
+            Dog tommy = (Dog) animalTwo; // Downcasting
+        } catch (ClassCastException e) {
+            LOGGER.error("ClassCastException caught!");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/FileNotFound.java

@@ -0,0 +1,25 @@
+package com.baeldung.exceptions;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class FileNotFound {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(FileNotFound.class);
+    
+    public static void main(String[] args) {
+        
+        BufferedReader reader = null;
+        try {
+            reader = new BufferedReader(new FileReader(new File("/invalid/file/location")));
+        } catch (FileNotFoundException e) {
+            LOGGER.error("FileNotFoundException caught!");
+        }
+    }
+    
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/GlobalExceptionHandler.java

@@ -0,0 +1,28 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class GlobalExceptionHandler {
+
+    public static void main(String[] args) {
+
+        Handler globalExceptionHandler = new Handler();
+        Thread.setDefaultUncaughtExceptionHandler(globalExceptionHandler);
+        new GlobalExceptionHandler().performArithmeticOperation(10, 0);
+    }
+
+    public int performArithmeticOperation(int num1, int num2) {
+        return num1/num2;
+    }
+
+}
+
+class Handler implements Thread.UncaughtExceptionHandler {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(Handler.class);
+
+    public void uncaughtException(Thread t, Throwable e) {
+        LOGGER.info("Unhandled exception caught!");
+    }
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/IllegalArgument.java

@@ -0,0 +1,18 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class IllegalArgument {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(IllegalArgument.class);
+
+    public static void main(String[] args) {
+        try {
+            Thread.sleep(-1000);
+        } catch (InterruptedException e) {
+            LOGGER.error("IllegalArgumentException caught!");
+        }
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/IllegalState.java

@@ -0,0 +1,32 @@
+package com.baeldung.exceptions;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class IllegalState {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(IllegalState.class);
+
+    public static void main(String[] args) {
+
+        List<Integer> intList = new ArrayList<>();
+
+        for (int i = 0; i < 10; i++) {
+            intList.add(i);
+        }
+
+        Iterator<Integer> intListIterator = intList.iterator(); // Initialized with index at -1
+
+        try {
+            intListIterator.remove(); // IllegalStateException
+        } catch (IllegalStateException e) {
+            LOGGER.error("IllegalStateException caught!");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/InterruptedExceptionExample.java

@@ -0,0 +1,28 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class ChildThread extends Thread {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(ChildThread.class);
+
+    public void run() {
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            LOGGER.error("InterruptedException caught!");
+        }
+    }
+    
+}
+
+public class InterruptedExceptionExample {
+
+    public static void main(String[] args) throws InterruptedException {
+        ChildThread childThread = new ChildThread();
+        childThread.start();
+        childThread.interrupt();
+    }
+    
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/MalformedURL.java

@@ -0,0 +1,25 @@
+package com.baeldung.exceptions;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MalformedURL {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(MalformedURL.class);
+
+    public static void main(String[] args) {
+
+        URL baeldungURL = null;
+
+        try {
+            baeldungURL = new URL("malformedurl");
+        } catch (MalformedURLException e) {
+            LOGGER.error("MalformedURLException caught!");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/NullPointer.java

@@ -0,0 +1,36 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class NullPointer {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(NullPointer.class);
+
+    public static void main(String[] args) {
+
+        Person personObj = null;
+
+        try {
+            String name = personObj.personName; // Accessing the field of a null object
+            personObj.personName = "Jon Doe"; // Modifying the field of a null object
+        } catch (NullPointerException e) {
+            LOGGER.error("NullPointerException caught!");
+        }
+
+    }
+}
+
+class Person {
+
+    public String personName;
+
+    public String getPersonName() {
+        return personName;
+    }
+
+    public void setPersonName(String personName) {
+        this.personName = personName;
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/NumberFormat.java

@@ -0,0 +1,23 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class NumberFormat {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(NumberFormat.class);
+
+    public static void main(String[] args) {
+
+        String str1 = "100ABCD";
+
+        try {
+            int x = Integer.parseInt(str1); // Converting string with inappropriate format
+            int y = Integer.valueOf(str1);
+        } catch (NumberFormatException e) {
+            LOGGER.error("NumberFormatException caught!");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/ParseExceptionExample.java

@@ -0,0 +1,25 @@
+package com.baeldung.exceptions;
+
+import java.text.DateFormat;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ParseExceptionExample {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(ParseExceptionExample.class);
+
+    public static void main(String[] args) {
+
+        DateFormat format = new SimpleDateFormat("MM, dd, yyyy");
+
+        try {
+            format.parse("01, , 2010");
+        } catch (ParseException e) {
+            LOGGER.error("ParseException caught!");
+        }
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/exceptions/StringIndexOutOfBounds.java

@@ -0,0 +1,23 @@
+package com.baeldung.exceptions;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class StringIndexOutOfBounds {
+
+    private static Logger LOGGER = LoggerFactory.getLogger(StringIndexOutOfBounds.class);
+    
+    public static void main(String[] args) {
+
+        String str = "Hello World";
+
+        try {
+            char charAtNegativeIndex = str.charAt(-1); // Trying to access at negative index
+            char charAtLengthIndex = str.charAt(11); // Trying to access at index equal to size of the string
+        } catch (StringIndexOutOfBoundsException e) {
+           LOGGER.error("StringIndexOutOfBoundsException caught");
+        }
+
+    }
+
+}

core-java-modules/core-java-reflection/src/test/java/com/baeldung/reflection/exceptions/GlobalExceptionHandlerUnitTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.exceptions;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+import org.slf4j.LoggerFactory;
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.classic.spi.LoggingEvent;
+import ch.qos.logback.core.Appender;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
+
+@RunWith(MockitoJUnitRunner.class)
+public class GlobalExceptionHandlerUnitTest {
+
+    @Mock
+    private Appender<ILoggingEvent> mockAppender;
+
+    @Captor
+    private ArgumentCaptor<LoggingEvent> captorLoggingEvent;
+
+    @Before
+    public void setup() {
+        final Logger logger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
+        logger.addAppender(mockAppender);
+
+        Handler globalExceptionHandler = new Handler();
+        Thread.setDefaultUncaughtExceptionHandler(globalExceptionHandler);
+    }
+
+    @After
+    public void teardown() {
+        final Logger logger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
+        logger.detachAppender(mockAppender);
+    }
+
+    @Test
+    public void whenArithmeticException_thenUseUncaughtExceptionHandler() throws InterruptedException {
+
+        Thread globalExceptionHandlerThread = new Thread() {
+            public void run() {
+                GlobalExceptionHandler globalExceptionHandlerObj = new GlobalExceptionHandler();
+                globalExceptionHandlerObj.performArithmeticOperation(99, 0);
+            }
+        };
+
+        globalExceptionHandlerThread.start();
+        globalExceptionHandlerThread.join();
+
+        verify(mockAppender).doAppend(captorLoggingEvent.capture());
+        LoggingEvent loggingEvent = captorLoggingEvent.getValue();
+
+        assertThat(loggingEvent.getLevel()).isEqualTo(Level.INFO);
+        assertThat(loggingEvent.getFormattedMessage()).isEqualTo("Unhandled exception caught!");
+    }
+
+}