Java 抑制異常示例 · HowToDoInJava 中文系列教程

# Java 抑制異常示例 > 原文： [https://howtodoinjava.com/java7/java-suppressed-exceptions/](https://howtodoinjava.com/java7/java-suppressed-exceptions/) 顧名思義， [**被抑制的異常**](https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html#suppressed-exceptions "suppressed-exceptions")是在代碼中引發的異常，但是以某種方式被忽略了。如果您記得[`try-catch-finally`](https://howtodoinjava.com/java7/automatic-resource-management-with-try-with-resources-in-java-7/)塊的執行順序以及它們如何返回任何值或異常，那么您會記得，如果`try`中引發了異常，則也將抑制`finally`塊中引發的**異常**。在 Java 7 之前的版本中，您通過記錄日志了解了這些異常（如果已實現），但是一旦`finally`塊結束，您就無法控制這些類型的異常。好吧，借助 Java 7 中的[**新特性**](https://howtodoinjava.com/java7/java-7-changes-features-and-enhancements/ "java 7 features")，您還可以控制這些受抑制的異常。 ```java Table of contents 1\. What are suppressed exceptions? 2\. Suppressed exception example 3\. Demonstration in different scenarios ``` ## 1\. 什么是禁止的異常？在 Java 7 中，遇到抑制異常的最常見用例是 **try-with-resources** 語句。當我們在`try`塊中遇到異常時，應用程序將嘗試關閉資源。如果它遇到關閉`AutoCloseable`資源時可能發生的多個異常，則會將其他異常作為**抑制的異常**附加到主要異常上。為了支持抑制的異常，在 JDK 7 中向[`Throwable`](https://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html "Throwable")類（`Exception`和`Error`類的父級）添加了新的構造器和兩個新方法。 ```java Throwable.getSupressed(); // Returns Throwable[] Throwable.addSupressed(aThrowable); ``` ## 2\. 抑制異常的例子例如，在寫入輸出流時，可以從`try`塊引發一個異常，當`try-with-resources`語句嘗試關閉流時，可以從該異常中引發最多兩個異常。如果從`try`塊引發一個異常，并且從`try-with-resources`語句引發一個或多個異常，則將從`try-with-resources`語句引發的那些異常抑制，并且由該塊引發的異常由`closeStream()`方法拋出。您可以通過從`try`塊引發的異常中調用`Throwable.getSuppressed()`方法來檢索這些受抑制的異常。 ## 3\. 在不同情況下的示例例如，我正在編寫一個自動關閉的資源（即`DirtyResource.java`），無論我們嘗試訪問它還是關閉它，它都會引發異常。這樣，當以不同方式訪問時，我們將能夠看到不同的行為。 ```java public class DirtyResource implements AutoCloseable { /** * Need to call this method if you want to access this resource * @throws RuntimeException no matter how you call this method * */ public void accessResource() { throw new RuntimeException("I wanted to access this resource. Bad luck. Its dirty resource !!!"); } /** * The overridden closure method from AutoCloseable interface * @throws Exception which is thrown during closure of this dirty resource * */ @Override public void close() throws Exception { throw new NullPointerException("Remember me. I am your worst nightmare !! I am Null pointer exception !!"); } } ``` #### 3.1 抑制異常之前的特性 ```java package com.howtodoinjava.demo.core; import static java.lang.System.err; public class SuppressedExceptionDemoWithTryFinallyPrevious { /** * Executable member function demonstrating suppressed exceptions * One exception is lost if not added in suppressed exceptions list */ public static void memberFunction() throws Exception { DirtyResource resource= new DirtyResource(); try { resource.accessResource(); } finally { resource.close(); } } public static void main(String[] arguments) throws Exception { try { memberFunction(); } catch(Exception ex) { err.println("Exception encountered: " + ex.toString()); final Throwable[] suppressedExceptions = ex.getSuppressed(); final int numSuppressed = suppressedExceptions.length; if (numSuppressed > 0) { err.println("tThere are " + numSuppressed + " suppressed exceptions:"); for (final Throwable exception : suppressedExceptions) { err.println("tt" + exception.toString()); } } } } } Output: Exception encountered: java.lang.NullPointerException: Remember me. I am your worst nightmare !! I am Null pointer exception !! ``` 如您所見，僅捕獲了一個異常，而第二個`RuntimeException`被抑制。 #### 3.2 在 Java 7 中抑制異常之后 ```java package com.howtodoinjava.demo.core; import static java.lang.System.err; public class SuppressedExceptionDemoWithTryFinallyNew { /** * Executable member function demonstrating suppressed exceptions * Suppressed expression is added back in primary exception */ public static void memberFunction() throws Exception { Throwable th = null; DirtyResource resource= new DirtyResource(); try { resource.accessResource(); } catch(Exception e) { th = e; } finally { try { resource.close(); } catch(Exception e) { if(th != null) { e.addSuppressed(th); //Add to primary exception throw e; } } } } /** * Executable function demonstrating suppressed exceptions. */ public static void main(String[] arguments) throws Exception { try { memberFunction(); } catch(Exception ex) { err.println("Exception encountered: " + ex.toString()); final Throwable[] suppressedExceptions = ex.getSuppressed(); final int numSuppressed = suppressedExceptions.length; if (numSuppressed > 0) { err.println("tThere are " + numSuppressed + " suppressed exceptions:"); for (final Throwable exception : suppressedExceptions) { err.println("tt" + exception.toString()); } } } } } Output: Exception encountered: java.lang.NullPointerException: Remember me. I am your worst nightmare !! I am Null pointer exception !! There are 1 suppressed exceptions: java.lang.RuntimeException: I wanted to access this resource. Bad luck. Its dirty resource !!! ``` 在這里，在`catch`塊中，我們可以訪問兩個異常。一個作為主要異常，第二個作為受抑制異常。 #### 3.3 成員函數中的`try-with-resource`塊并捕獲異常 ```java package com.howtodoinjava.demo.core; import static java.lang.System.err; public class SuppressedExceptionDemoWithTryCatch { public static void memberFunction() throws Exception { try (DirtyResource resource= new DirtyResource()) { resource.accessResource(); } } /** * Executable member function demonstrating suppressed exceptions using try-with-resources */ public static void main(String[] arguments) throws Exception { try { memberFunction(); } catch(Exception ex) { err.println("Exception encountered: " + ex.toString()); final Throwable[] suppressedExceptions = ex.getSuppressed(); final int numSuppressed = suppressedExceptions.length; if (numSuppressed > 0) { err.println("tThere are " + numSuppressed + " suppressed exceptions:"); for (final Throwable exception : suppressedExceptions) { err.println("tt" + exception.toString()); } } } } } Output: Exception encountered: java.lang.RuntimeException: I wanted to access this resource. Bad luck. Its dirty resource !!! There are 1 suppressed exceptions: java.lang.NullPointerException: Remember me. I am your worst nightmare !! I am Null pointer exception !! ``` 太好了！在成員函數中使用`try-with-resource`時，我們能夠看到這兩種異常。 #### 3.4 默認`try-with-resource`塊 ```java package com.howtodoinjava.demo.core; public class SuppressedExceptionDemoWithTryWithResource { /** * Demonstrating suppressed exceptions using try-with-resources */ public static void main(String[] arguments) throws Exception { try (DirtyResource resource= new DirtyResource()) { resource.accessResource(); } } } Output: Exception in thread "main" java.lang.RuntimeException: I wanted to access this resource. Bad luck. Its dirty resource !!! at DirtyResource.accessResource(DirtyResource.java:9) at SuppressedExceptionDemoWithTryWithResource.main(SuppressedExceptionDemoWithTryWithResource.java:12) Suppressed: java.lang.NullPointerException: Remember me. I am your worst nightmare !! I am Null pointer exception !! at DirtyResource.close(DirtyResource.java:19) at SuppressedExceptionDemoWithTryWithResource.main(SuppressedExceptionDemoWithTryWithResource.java:13) ``` 好吧，非常高興看到包含**抑制異常**的完整信息的輸出。學習愉快！