Java异常处理

在java8使用lambda表达式的时候，不可避免的要调用异常处理机制，下面主要记录受检异常与非受检异常在lambda中的处理。

一、非受检异常处理

例子如下所示：

 1 public static void testUncheckedException(){
 2         List<Integer> integers = Arrays.asList(5, 10, 11, 32, 40, 60);
 3         integers.forEach(i ->{
 4             try {
 5                 System.out.println(50 / i);
 6             } catch (ArithmeticException e) {
 7                 System.err.println("Arithmetic Exception occurred : " + e.getMessage());
 8             }
 9         });
10  }

编写包装方法来进行处理：

 1 /**
 2  * @param consumer 接收一个泛型的参数T，然后调用accept，对这个参数做一系列的操作
 3  */
 4 private static Consumer<Integer> lambdaWrapper(Consumer<Integer> consumer) {
 5         return i -> {
 6             try {
 7                 System.out.println("accepted value is : "+i);
 8                 consumer.accept(i);
 9             } catch (ArithmeticException e) {
10                 System.err.println("Arithmetic Exception occurred : " + e.getMessage());
11             }
12         };
13 }

1 public static void testUncheckedException1(){
2         List<Integer> integers = Arrays.asList(5, 10, 11, 32, 40, 60);
3         integers.forEach(lambdaWrapper(i-> System.out.println(50/i)));
4 }

对方法加以改进并对异常进行抛出：

 1 private static <T, E extends Exception> Consumer<T> consumerWrapper(Consumer<T> consumer, Class<E> clazz) {
 2         return i -> {
 3             try {
 4                 consumer.accept(i);
 5             } catch (Exception e) {
 6                 try {
 7                     E eCast = clazz.cast(e);
 8                     System.err.println("Exception occurred : " + eCast.getMessage());
 9                 } catch (ClassCastException ccEx) {
10                     throw e;
11                 }
12             }
13         };
14 }

1 public static void testUncheckedException2(){
2         List<Integer> integers = Arrays.asList(5, 10, 11, 32, 40, 60);
3         integers.forEach(
4                 consumerWrapper(
5                         i -> System.out.println(50 / i),
6                         ArithmeticException.class));
7 }

二、受检异常处理

例子如下所示：

 1 private static void writeToFile(String string) throws IOException {
 2         File file = new File("c:/newfile.txt");
 3 
 4         try (FileOutputStream fop = new FileOutputStream(file)) {
 5 
 6             if (!file.exists()) {
 7                 file.createNewFile();
 8             }
 9 
10             byte[] contentInBytes = string.getBytes();
11 
12             fop.write(contentInBytes);
13             fop.flush();
14             fop.close();
15 
16             System.out.println("Done");
17 
18         }
19 }
20 
21 public static void testCheckedException(){
22         List<String> integers = Arrays.asList("3", "9", "7", "0", "10", "20");
23         integers.forEach(i -> {
24             try {
25                 writeToFile(i);
26             } catch (IOException e) {
27                 throw new RuntimeException(e);
28             }
29         });
30 }

可以首先编写一个可以抛出异常的函数式接口：

1 @FunctionalInterface
2 public interface ThrowingConsumer<T, E extends Exception> {
3     void accept(T t) throws E;
4 }

 1 private static <T> Consumer<T> throwingConsumerWrapper(ThrowingConsumer<T, Exception> throwingConsumer) {
 2         return i -> {
 3             try {
 4                 throwingConsumer.accept(i);
 5             } catch (Exception e) {
 6                 throw new RuntimeException(e);
 7             }
 8         };
 9 }
10 
11 public static void testCheckedException1(){
12         List<String> stringS = Arrays.asList("3", "9", "7", "0", "10", "20");
13         stringS.forEach(throwingConsumerWrapper(ExceptionHandler::writeToFile));
14 }

进行优化改造：

 1 private static <T, E extends Exception> Consumer<T> handlingConsumerWrapper(
 2             ThrowingConsumer<T, E> throwingConsumer, Class<E> exceptionClass) {
 3         return i -> {
 4             try {
 5                 throwingConsumer.accept(i);
 6             } catch (Exception ex) {
 7                 try {
 8                     E exCast = exceptionClass.cast(ex);
 9                     System.err.println("Exception occurred : " + exCast.getMessage());
10                 } catch (ClassCastException ccEx) {
11                     throw new RuntimeException(ex);
12                 }
13             }
14         };
15 }
16 
17 public static void testCheckedException2(){
18         List<String> stringList = Arrays.asList("3", "9", "7", "0", "10", "20");
19         stringList.forEach(handlingConsumerWrapper(ExceptionHandler::writeToFile, IOException.class));
20 }

参考原文地址为：http://www.baeldung.com/java-lambda-exceptions