BAEL-3840 Suppressed Exceptions in Java

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/suppressed/ExceptionalResource.java

@@ -0,0 +1,13 @@
+package com.baeldung.suppressed;
+
+public class ExceptionalResource implements AutoCloseable {
+    
+    public void processSomething() {
+        throw new NullPointerException("Thrown from processSomething()");
+    }
+
+    @Override
+    public void close() throws Exception {
+        throw new NullPointerException("Thrown from close()");
+    }
+}

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/suppressed/SuppressedExceptionsDemo.java

@@ -0,0 +1,42 @@
+package com.baeldung.suppressed;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+
+public class SuppressedExceptionsDemo {
+
+    public static void demoSuppressedException(String filePath) throws IOException {
+        FileInputStream fileIn = null;
+        try {
+            fileIn = new FileInputStream(filePath);
+        } catch (IOException e) {
+            
+        } finally {
+            fileIn.close();
+        }
+    }
+    
+    public static void demoAddSuppressedException(String filePath) throws IOException {
+        Throwable firstException = null;
+        FileInputStream fileIn = null;
+        try {
+            fileIn = new FileInputStream(filePath);
+        } catch (IOException e) {
+            firstException = e;
+        } finally {
+            try {
+                fileIn.close();
+            } catch (NullPointerException npe) {
+                if (firstException != null) {
+                    npe.addSuppressed(firstException);
+                }
+            }
+        }
+    }
+    
+    public static void demoExceptionalResource() throws Exception {
+        try (ExceptionalResource exceptionalResource = new ExceptionalResource()) {
+            exceptionalResource.processSomething();
+        }
+    }
+}

core-java-modules/core-java-exceptions-2/src/test/java/com/baeldung/suppressed/SuppressedExceptionsUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.suppressed;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import org.junit.Test;
+import static org.hamcrest.CoreMatchers.instanceOf;
+
+public class SuppressedExceptionsUnitTest {
+
+    @Test(expected = NullPointerException.class)
+    public void givenNonExistentFileName_whenAttemptFileOpen_thenNullPointerException() throws IOException {
+        SuppressedExceptionsDemo.demoSuppressedException("/non-existent-path/non-existent-file.txt");
+    }
+    
+    @Test
+    public void givenNonExistentFileName_whenAttemptFileOpenStoreSuppressed_thenSuppressedExceptionAvailable() {
+        try {
+            SuppressedExceptionsDemo.demoAddSuppressedException("/non-existent-path/non-existent-file.txt");
+        } catch (Exception e) {
+            assertEquals(1, e.getSuppressed().length);
+            assertThat(e.getSuppressed()[0], instanceOf(FileNotFoundException.class));
+        }
+    }
+    
+    @Test
+    public void whenUsingExceptionalResource_thenSuppressedExceptionAvailable() {
+        try {
+            SuppressedExceptionsDemo.demoExceptionalResource();
+        } catch (Exception e) {
+            assertEquals("Thrown from processSomething()", e.getMessage());
+            assertEquals(1, e.getSuppressed().length);
+            assertEquals("Thrown from close()", e.getSuppressed()[0].getMessage());
+        }
+    }
+}