第12章 通过异常处理错误

12.6 捕获所有异常

12.6.1 栈轨迹

java.lang.Throwable接口（java.lang.Excpetion实现了该接口）中的getStackTrace()方法返回栈轨迹的数组，我们来看一下它的使用。

 1 import static java.lang.System.out;
 2 public class WhoCalled {
 3   static void f(){
 4     try {
 5       throw new Exception();
 6     }
 7     catch (Exception e) {
 8       for(StackTraceElement ste : e.getStackTrace())
 9         out.println(ste.getClassName() + "." + ste.getMethodName() + "()@" + ste.getFileName() + ":" + ste.getLineNumber());
10     }
11   }
12   static void g() {f();}
13   static void h() {g();}
14   public static void main(String args[]){
15     f();
16     out.println("---------------");
17     g();
18     out.println("---------------");
19     h();
20   }
21 }/*
22 WhoCalled.f()@WhoCalled.java:5
23 WhoCalled.main()@WhoCalled.java:15
24 ---------------
25 WhoCalled.f()@WhoCalled.java:5
26 WhoCalled.g()@WhoCalled.java:12
27 WhoCalled.main()@WhoCalled.java:17
28 ---------------
29 WhoCalled.f()@WhoCalled.java:5
30 WhoCalled.g()@WhoCalled.java:12
31 WhoCalled.h()@WhoCalled.java:13
32 WhoCalled.main()@WhoCalled.java:19
33 */

12.6.2 重新抛出异常

Exception的fillInStackTrace方法重新消除原来的栈轨迹，从该方法的调用点开始重新记录栈轨迹。一般配合Re-throw来使用。

 1 import static java.lang.System.err;
 2 public class ReThrow {
 3   static void f() throws Exception{
 4     try {
 5       throw new Exception();
 6     }
 7     catch (Exception e) {
 8       throw e;
 9     }
10   }
11   static void g() throws Exception{
12     try {
13       throw new Exception();
14     }
15     catch (Exception e) {
16       throw (Exception)e.fillInStackTrace();
17     }
18   }
19   public static void main(String args[]){
20     try{
21       f();
22     }
23     catch(Exception e) {
24       e.printStackTrace();
25     }
26     err.println("---------------");
27     try{
28       g();
29     }
30     catch(Exception e) {
31       e.printStackTrace();
32     }
33   }
34 }/*Output:
35 java.lang.Exception
36     at ReThrow.f(ReThrow.java:5)
37     at ReThrow.main(ReThrow.java:21)
38 ---------------
39 java.lang.Exception
40     at ReThrow.g(ReThrow.java:16)
41     at ReThrow.main(ReThrow.java:28)
42 */

 

12.6.3 异常链

 1 class MyException extends Exception{
 2     MyException(String s){
 3         super(s);
 4     }
 5 }
 6 public class Cause {
 7     public static void main(String[] args) {
 8         try {
 9             try {
10                 throw new Exception("Test");
11             }
12             catch (Exception e) {
13                 throw new MyException("Exception Without Original Cause");
14             }
15         }
16         catch (MyException e) {
17             e.printStackTrace();
18         }
19         try {
20             try {
21                 throw new java.lang.NullPointerException();
22             }
23             catch (Exception e) {
24                 MyException mye = new MyException("Exception With Original Cause");
25                 mye.initCause(e);
26                 throw mye;
27             }
28         }
29         catch (MyException e) {
30             e.printStackTrace();
31         }
32     }
33 }/*
34 MyException: Exception Without Original Cause
35     at Cause.main(Cause.java:13)
36 MyException: Exception With Original Cause
37     at Cause.main(Cause.java:24)
38 Caused by: java.lang.NullPointerException
39     at Cause.main(Cause.java:21)
40 */

 

12.8 使用finally进行清理

 1 import static java.lang.System.out;
 2 import java.util.*;
 3 public class Test {
 4   public static void main(String args[]){
 5     Random r = new Random();
 6     int i = r.nextInt(3);
 7     try{
 8       switch(i) {
 9       case 0:
10         out.println("Case 0");
11         break;
12       case 1:
13         out.println("Case 1");
14         break;
15       case 2:
16         out.println("Case 2");
17         return;
18       default:
19         out.println("Case Default");
20         return;
21       }
22     }
23     finally {
24       out.println("Clean up");
25     }
26   }
27 }/*
28 In output you will always see "Clean up"
29 */

 

 

posted on 2013-05-03 12:55  peter9606  阅读(172)  评论(0)  编辑  收藏  举报

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