Struts2中的异常处理

<p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><strong><span style="font-size: 12px; color: rgb(255, 0, 0);">因为在Action的execute方法声明时就抛出了Exception异常，所以我们无需再execute方法中捕捉异常，仅需在struts.xml 中配置异常处理。</span></strong></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">为了使用Struts2的异常处理机制，必须打开Struts2的异常映射功能，这需要<strong><span style="color: rgb(255, 0, 0);">exception拦截器</span></strong>。在struts-default.xml文件中已经开启了exception拦截器。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<strong><span style="font-size: 16px; color: rgb(255, 0, 0);">声明式异常捕捉</span></strong></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">Struts2的异常处理机制是通过在struts.xml文件中配置<exception-mapping……/>元素完成的，配置该元素时，需要指定两个属性：
<strong><span style="color: rgb(255, 0, 0);">exception</span></strong>：指定该异常类型的完全限定名。
<span style="color: rgb(255, 0, 0);"><strong>result</strong></span>：指定逻辑视图名。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 12px;">根据<exception-mapping…../>元素出现位置的不同，异常映射又可分为两种：</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"><strong><span style="color: rgb(255, 0, 0);">局部异常映射</span></strong>：将<exception-mapping… />元素作为<action…/>元素的子元素配置；
<span style="color: rgb(255, 0, 0);"><strong>全局异常映射</strong></span>：将<exception-mapping… />元素作为<global-exception-mappings… />元素的子元素配置；</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">全局异常映射对所有的Action都有效，但局部异常映射仅对该异常映射所在的Action有效。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">如果局部异常映射和全局异常映射配置了同一个异常类型，在<action…./>元素内的<strong><span style="color: rgb(255, 0, 0);">局部异常映射将覆盖全局异常映射</span></strong>。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 16px; color: rgb(255, 0, 0);"><strong>Struts.xml</strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">  <package name="ssh2" extends="struts-default"></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">     </span><strong><span style="font-size: 12px; color: rgb(255, 0, 0);"><global-results>
           <result name="sql">/exception.jsp</result>
           <result name="root">/exception.jsp</result>
     </global-results></span></strong></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px; color: rgb(255, 0, 0);"><strong>     <global-exception-mappings>
           <exception-mapping exception="java.sql.SQLException" result="sql"/>
           <exception-mapping exception="java.lang.Exception" result="root"/>
     </global-exception-mappings></strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">     <action name="login" class="loginAction">
         <result>/welcome.jsp</result>
         </span><span style="font-size: 12px;"><strong><span style="color: rgb(255, 0, 0);"><result name="nullPointer">/nullPointer.jsp</result>
         <exception-mapping exception="java.lang.NullPointerException" result="nullPointer"/>
</span></strong>      </action></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">  </package></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 16px; color: rgb(255, 0, 0);"><strong>Action</strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">   public class loginAction extends ActionSupport
   {
        public String add() throws SQLException
        {
             return "toadd";
        }
   }
  
<strong><span style="color: rgb(255, 0, 0);">有异常往外抛即可。你也可以在方法里面抛，比如throw SQLException。</span></strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">我们可以使用Struts2的标签输出异常信息：</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">输出异常的message属性信息:<s:property value="exception.message" /></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">输出异常堆栈信息:<s:property value="exceptionStack" />。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 12px;">有了处理系统异常的基础，我们来看一看<strong><span style="font-size: 16px; color: rgb(255, 0, 0);">自定义异常</span></strong>：</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">package com.exception ;</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">public class MyException extends Exception 
{
 
    private String message;
 
    public MyException(String message)
    {
           super(message);
           this.message = message ;
    }</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">    public String getMessage() {
          return message;
    }</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">    public void setMessage(String message) {
           this.message = message;
    }
}</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 12px;">public String execute() throws Exception
{
    if(!"hello".equals(usename) || !"world".equals(password))
    {
            </span><span style="font-size: 12px;"><strong><span style="color: rgb(255, 0, 0);"> throw new MyException("用户名或密码错误，您发现了吧！");
</span></strong>    }
    return "success" ;
}</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;">
<span style="font-size: 12px;"><strong><span style="font-size: 16px; color: rgb(255, 0, 0);">在action配置中的异常处理
</span></strong>    
<struts>
   <package name="struts2" extends="struts-default">       
      <action name="login" class="com.struts2.LoginAction">
            <strong><span style="color: rgb(255, 0, 0);"><exception-mapping result="myex" </span></strong></span><span style="font-size: 12px;"><span style="color: rgb(255, 0, 0);"><strong>exception="com.exception.MyException">          
            </exception-mapping>
            <result name="myex">/error.jsp</result>
</strong></span>            <result name="success">/result.jsp</result>
      </action>
   </package> 
</struts></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 16px; color: rgb(255, 0, 0);"><strong>在全局配置中的异常处理</strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"><struts>
   <package name="struts2" extends="struts-default">
      </span><span style="font-size: 12px;"><strong><span style="color: rgb(255, 0, 0);"><global-results>
          <result name="myexception1">/error.jsp</result>
      </global-results>
      
      <global-exception-mappings>
          <exception-mapping result="myexception1"
               exception="com.exception.MyException">           
          </exception-mapping>
      </global-exception-mappings>
</span></strong>     
      <action name="login" class="com.struts2.LoginAction">
            <result name="success">/result.jsp</result>
      </action>
   </package>
</struts></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 16px; color: rgb(255, 0, 0);"><strong>错误页面error.jsp</strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"><%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="s"  uri="/struts-tags"%>  
<html>
  <body>
    <!-- 这个exception 是 exception="com.exception.MyException" -->
    <s:property value="exception.message"/>
  </body>
</html></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"></span>
<span style="font-size: 16px; color: rgb(255, 0, 0);"><strong>总结</strong></span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">局部异常处理比全局异常处理高，并且可覆盖全局异常处理，如果定义了全局异常映射，那么会对所有的Action生效，反之定义了局部异常映射则会对当前Action生效，</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;">如果在全局区域和局部区域定义了相同的异常映射，首先去局部异常区域找result结果页面，如果找到了，则直接跳转到错误结果页面，不管全局有没有相同的结果，都被局部所覆盖，如果在局部区域没找到，则去全局区域找。</span></p><p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px; font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-size: 12px;"> </span></p>