异常类的妙用

以往在使用异常时，只是知道通过异常类的构造方法设置一些出错信息,此外最多就是把引起该异常的原因通过Throwable类的子类一同设置进去。今天在分析springSecurity3.0.5的框架时，看到AuthenticationException这个异常类(用在验证时)的源码，发现这个异常类除了上述常见的用法外，还把Authentication（验证信息）的做为属性放到了异常类中，当验证出错时AuthenticationException抛出时，Authentication（验证信息）一同被抛出了，这样捕获异常的类就能得到更丰富的信息，有些数据还可以通过异常类返回给调用者。看了这样的代码，思路不由地开阔了不少。该类源码如下：

 1 package org.springframework.security.core;
 2 
 3 /**
 4  * Abstract superclass for all exceptions related to an {@link Authentication} object being invalid for whatever
 5  * reason.
 6  *
 7  * @author Ben Alex
 8  */
 9 public abstract class AuthenticationException extends RuntimeException {
10     //~ Instance fields ================================================================================================
11 
12     private Authentication authentication;
13     private Object extraInformation;
14 
15     //~ Constructors ===================================================================================================
16 
17     /**
18      * Constructs an <code>AuthenticationException</code> with the specified message and root cause.
19      *
20      * @param msg the detail message
21      * @param t the root cause
22 */
23     public AuthenticationException(String msg, Throwable t) {
24         super(msg, t);
25     }
26 
27     /**
28      * Constructs an <code>AuthenticationException</code> with the specified message and no root cause.
29      *
30      * @param msg the detail message
31 */
32     public AuthenticationException(String msg) {
33         super(msg);
34     }
35 
36     public AuthenticationException(String msg, Object extraInformation) {
37         super(msg);
38         this.extraInformation = extraInformation;
39     }
40 
41     //~ Methods ========================================================================================================
42 
43     /**
44      * The authentication request which this exception corresponds to (may be <code>null</code>)
45 */
46     public Authentication getAuthentication() {
47         return authentication;
48     }
49 
50     public void setAuthentication(Authentication authentication) {
51         this.authentication = authentication;
52     }
53 
54     /**
55      * Any additional information about the exception. Generally a <code>UserDetails</code> object.
56      *
57      * @return extra information or <code>null</code>
58 */
59     public Object getExtraInformation() {
60         return extraInformation;
61     }
62 
63     public void clearExtraInformation() {
64         this.extraInformation = null;
65     }
66 }

 

下面是在AbstractAuthenticationManager类中被使用到的片断：

 public final Authentication authenticate(Authentication authRequest) throws AuthenticationException {

        try {

            return doAuthentication(authRequest);

        } catch (AuthenticationException e) {

            e.setAuthentication(authRequest);



            if (clearExtraInformation) {

                e.clearExtraInformation();

            }



            throw e;

        }

    }

 通过上述两段源码可以看到，老外在写代码时考虑得很细，在异常类中加入了额外信息后,还提供了一个 clearExtraInformation()方法，用来清除额外信息。