SpringMVC interceptor and exception handling mechanism

concept

SpringMVC interceptors are similar to filters and are used for pre- and post-processing

Connecting interceptors into a chain in a certain order is the interceptor chain.

The difference between interceptors and filters

A quick start with interceptors

1. Create an interceptor class to implement the HandlerInterceptor interface

2. Configure interceptor

   <!--    配置拦截器-->
       <mvc:interceptors>
           <mvc:interceptor>
   <!--            对那些资源执行拦截操作,这是对所有资源执行-->
               <mvc:mapping path="/**/"/>
               <bean class="com.myspring.interceptor.MyHandlerInterceptor"></bean>
           </mvc:interceptor>
       </mvc:interceptors>
   

3. Test the interception effect of the interceptor

   package com.myspring.interceptor;
   
   import org.springframework.web.servlet.HandlerInterceptor;
   import org.springframework.web.servlet.ModelAndView;
   
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   public class MyHandlerInterceptor implements HandlerInterceptor {
   //    覆盖三个方法
   //在目标方法(控制类中对应方法)执行前执行
       @Override
       public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
           String param = request.getParameter("param");
           if("yes".equals(param)){
               //        返回值为false不放行，true放行
               return true;
           }
           else {
               request.getRequestDispatcher("/error.js").forward(request,response);
               return  false;
           }
       }
   //在目标方法执行之后，视图返回之前执行
       @Override
       public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
           modelAndView.addObject("name","xiaoming");
       }
   //在整个流程都执行完毕后执行
       @Override
       public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
           
       }
   }
   

Execution of the three methods: Configure the two interceptors in the configuration file as 1 and 2. The execution order is: preHandle of 1 > preHandle of 2 > postHandle of 2 > postHandle of 1 > afterCompletion of 2 > afterCompletion of 1

SpringMVC exception handling mechanism

As shown in the picture:

Two ways to handle exceptions:

• Simple exception handler SimpleMappingExceptionResolver using springmvc
• Use Spring's exception handling interface HandlerExceptionResolver to customize your own exception handler

SimpleMappingExceptionResolver

It mainly requires mapping configuration of corresponding exceptions and views.

In the springmvc configuration file:

    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
<!--        默认错误页面-->
        <property name="defaultErrorView" value="error"/>
        <property name="exceptionMappings">
            <map>
                <entry key="java.lang.ClassCastException" value="error1"/>
                <entry key="java.lang.ClassNotFoundException" value="error2"/>
            </map>
        </property>
    </bean>

HandlerExceptionResolver custom exception handler

1. Create an exception handler class to implement HandlerExceptionResolver

   public class MyExceptionResolver implements HandlerExceptionResolver {
       @Override
       //参数Exception是异常对象，返回值是你要跳转的错误页面
       public ModelAndView resolveException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) {
           ModelAndView modelAndView = new ModelAndView();
           if(e instanceof  Exception){
   
           }
           modelAndView.setViewName("error.jsp");
           return modelAndView;
       }
   }
   

2. Configure exception handler

   <bean class="com.myspring.domain.MyExceptionResolver"/>
   

   XML copy full screen

3. Write exception page