From 0aa46996a6ec9c7a1f84e5b9230d446fc1efdf27 Mon Sep 17 00:00:00 2001
From: Vivek Kumar <vivek.ispat@gmail.com>
Date: Tue, 17 Jan 2017 13:31:59 +0530
Subject: [PATCH] BAEL-580 handling exceptions in lambda expressions (#1004)

---
 .../exceptions/LambdaExceptionWrappers.java   | 57 +++++++++++++++++++
 .../lambda/exceptions/ThrowingConsumer.java   |  8 +++
 .../LambdaExceptionWrappersTest.java          | 46 +++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 core-java/src/main/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappers.java
 create mode 100644 core-java/src/main/java/com/baeldung/java8/lambda/exceptions/ThrowingConsumer.java
 create mode 100644 core-java/src/test/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappersTest.java

diff --git a/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappers.java b/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappers.java
new file mode 100644
index 0000000000..64532c8b6f
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappers.java
@@ -0,0 +1,57 @@
+package com.baeldung.java8.lambda.exceptions;
+
+import java.util.function.Consumer;
+
+public class LambdaExceptionWrappers {
+
+    public static Consumer<Integer> lambdaWrapper(Consumer<Integer> consumer) {
+        return i -> {
+            try {
+                consumer.accept(i);
+            } catch (ArithmeticException e) {
+                System.err.println("Arithmetic Exception occured : " + e.getMessage());
+            }
+        };
+    }
+
+    static <T, E extends Exception> Consumer<T> consumerWrapper(Consumer<T> consumer, Class<E> clazz) {
+        return i -> {
+            try {
+                consumer.accept(i);
+            } catch (Exception ex) {
+                try {
+                    E exCast = clazz.cast(ex);
+                    System.err.println("Exception occured : " + exCast.getMessage());
+                } catch (ClassCastException ccEx) {
+                    throw ex;
+                }
+            }
+        };
+    }
+
+    public static <T> Consumer<T> throwingConsumerWrapper(ThrowingConsumer<T, Exception> throwingConsumer) {
+        return i -> {
+            try {
+                throwingConsumer.accept(i);
+            } catch (Exception ex) {
+                throw new RuntimeException(ex);
+            }
+        };
+    }
+
+    public static <T, E extends Exception> Consumer<T> handlingConsumerWrapper(ThrowingConsumer<T, E> throwingConsumer, Class<E> exceptionClass) {
+        return i -> {
+            try {
+                throwingConsumer.accept(i);
+            } catch (Exception ex) {
+                try {
+                    E exCast = exceptionClass.cast(ex);
+                    System.err.println("Exception occured : " + exCast.getMessage());
+                } catch (ClassCastException ccEx) {
+                    throw new RuntimeException(ex);
+                }
+            }
+        };
+    }
+
+}
\ No newline at end of file
diff --git a/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/ThrowingConsumer.java b/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/ThrowingConsumer.java
new file mode 100644
index 0000000000..c5860e7f6b
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java8/lambda/exceptions/ThrowingConsumer.java
@@ -0,0 +1,8 @@
+package com.baeldung.java8.lambda.exceptions;
+
+@FunctionalInterface
+public interface ThrowingConsumer<T, E extends Exception> {
+
+    void accept(T t) throws E;
+
+}
\ No newline at end of file
diff --git a/core-java/src/test/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappersTest.java b/core-java/src/test/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappersTest.java
new file mode 100644
index 0000000000..7b8ee55a27
--- /dev/null
+++ b/core-java/src/test/java/com/baeldung/java8/lambda/exceptions/LambdaExceptionWrappersTest.java
@@ -0,0 +1,46 @@
+package com.baeldung.java8.lambda.exceptions;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static com.baeldung.java8.lambda.exceptions.LambdaExceptionWrappers.*;
+
+public class LambdaExceptionWrappersTest {
+
+    private List<Integer> integers;
+
+    @Before
+    public void init() {
+        integers = Arrays.asList(3, 9, 7, 0, 10, 20);
+    }
+
+    @Test
+    public void whenNoExceptionFromLambdaWrapper_thenSuccess() {
+        integers.forEach(lambdaWrapper(i -> System.out.println(50 / i)));
+    }
+
+    @Test
+    public void whenNoExceptionFromConsumerWrapper_thenSuccess() {
+        integers.forEach(consumerWrapper(i -> System.out.println(50 / i), ArithmeticException.class));
+    }
+
+    @Test(expected = RuntimeException.class)
+    public void whenExceptionFromThrowingConsumerWrapper_thenSuccess() {
+        integers.forEach(throwingConsumerWrapper(i -> writeToFile(i)));
+    }
+
+    @Test
+    public void whenNoExceptionFromHandlingConsumerWrapper_thenSuccess() {
+        integers.forEach(handlingConsumerWrapper(i -> writeToFile(i), IOException.class));
+    }
+
+    void writeToFile(Integer i) throws IOException {
+        if (i == 0) {
+            throw new IOException(); // mock IOException
+        }
+    }
+}