(17)Struts2_异常处理: exception-mapping 元素

谁践踏了优雅 2021-10-06 14:14 294阅读 0赞

### **异常处理: exception-mapping 元素** ###

#### 在action方法中添加 ####

int i=1/0;

#### 请求action后，结果为： ####

![这里写图片描述][20160904104149756]

--------------------

#### 在struts.xml中添加异常处理：exception-mapping元素 ####

<action name="czy_save" class="com.qbz.struts2_02.GG_CZY" method="save">
                <exception-mapping result="ArithmeticException" exception="java.lang.ArithmeticException"></exception-mapping>
                <result name="ArithmeticException">/WEB-INF/page/Input.jsp</result>
    
                <result name="save">/WEB-INF/page/Show.jsp</result>
            </action>

#### 此时，页面将直接跳转到Input.jsp： ####

![这里写图片描述][20160904104651349]

#### 在Input.jsp加入标签显示exception信息： ####

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
    <%@ taglib prefix="s" uri="/struts-tags" %>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
      </head>
      <body>
      <form action="czy_save.action" method="post">
          <s:debug></s:debug><br>
          <s:property value="exception"/><br>
          <s:property value="exception.message"/><br>
           编号：<input type="text" name="dlh"/><br>
           姓名：<input type="text" name="name"/><br>
           部门：<input type="text" name="bmmc"/><br>
           <input type="submit" value="保存"/>
       </form>
      </body>
    </html>

#### 请求action后的页面效果： ####

![这里写图片描述][20160904105259323]

#### 点击 Debug ： ####

![这里写图片描述][20160904110122445]

#### 可见，对象栈的 栈顶 是异常对象，所以在上面页面没用下标就直接读取属性。ExceptionHolder有两个属性，一个是exceptionStack，一个是exception。 ####

--------------------

#### 我们来看，Struts2是如何做到异常映射处理的。 ####

#### 在struts\_default.xml中查看： ####

#### 我们的package的父类struts-default中引用的默认拦截器 ####

<default-interceptor-ref name="defaultStack"/>

![这里写图片描述][20160904111127115]

#  #

![这里写图片描述][20160904111142880]

#### ctrl+shift+t 查看 ExceptionMappingInterceptor 源码 ####

public class ExceptionMappingInterceptor extends AbstractInterceptor { 
    
        //省略......
    
        @Override
        public String intercept(ActionInvocation invocation) throws Exception {
            String result;
    
            try {
                result = invocation.invoke();
            } catch (Exception e) {
                if (isLogEnabled()) {
                    handleLogging(e);
                }
                List<ExceptionMappingConfig> exceptionMappings = invocation.getProxy().getConfig().getExceptionMappings();
                ExceptionMappingConfig mappingConfig = this.findMappingFromExceptions(exceptionMappings, e);
                if (mappingConfig != null && mappingConfig.getResult()!=null) {
                    Map parameterMap = mappingConfig.getParams();
                    // create a mutable HashMap since some interceptors will remove parameters, and parameterMap is immutable
                    invocation.getInvocationContext().setParameters(new HashMap<String, Object>(parameterMap));
                    result = mappingConfig.getResult();
                    publishException(invocation, new ExceptionHolder(e));
                } else {
                    throw e;
                }
            }
    
            return result;
        }
    
        //省略......
    
        /** * Default implementation to handle ExceptionHolder publishing. Pushes given ExceptionHolder on the stack. * Subclasses may override this to customize publishing. * * @param invocation The invocation to publish Exception for. * @param exceptionHolder The exceptionHolder wrapping the Exception to publish. */
        protected void publishException(ActionInvocation invocation, ExceptionHolder exceptionHolder) {
            invocation.getStack().push(exceptionHolder);
        }
    
    }

#### 可见，当catch到异常之后**publishException(invocation, new ExceptionHolder(e))**把异常压入了栈中。 ####

--------------------

#### 每个action是不是都要配置异常处理呢？当然不用，下面来看**global-exception-mappings**、**global-results** 。 ####

#### 在struts.xml中配置如下： ####

<global-results>
                <result name="ArithmeticException">/WEB-INF/page/Input.jsp</result>
            </global-results>
    
            <global-exception-mappings>
                <exception-mapping result="ArithmeticException" exception="java.lang.ArithmeticException"></exception-mapping>
            </global-exception-mappings>

[20160904104149756]: /images/20211006/9da8e7ac00a248c8b153f8155a336a57.png
[20160904104651349]: /images/20211006/e9d5a1c046924dc084024efc613552a1.png
[20160904105259323]: /images/20211006/82e2c9ea2a9f499d86259e10c93879fd.png
[20160904110122445]: /images/20211006/a4a1d50a24fb4fee836e0d5d37d62003.png
[20160904111127115]: /images/20211006/11c49c629b684dd6939b52cb676f3158.png
[20160904111142880]: /images/20211006/438cccd294a04da995e11f2a1d146b0d.png