SpringMVC拦截器

Spring Web MVC的处理器拦截器类似于Servlet开发中的过滤器Filter，用于对处理器进行预处理和后处理。

一.拦截器的接口

自定义拦截器需要实现HandlerInterceptor接口

package org.springframework.web.servlet;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public abstract interface HandlerInterceptor
{
public abstract boolean preHandle(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse, Object paramObject)
throws Exception;

public abstract void postHandle(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse, Object paramObject, ModelAndView paramModelAndView)
throws Exception;

public abstract void afterCompletion(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse, Object paramObject, Exception paramException)
throws Exception;
}

1. preHandle：预处理回调方法，实现处理器的预处理（如登录检查），第三个参数为响应的处理器（如Controller实现）；
   返回值：true表示继续流程（如调用下一个拦截器或处理器）；
   false表示流程中断（如登录检查失败），不会继续调用其他的拦截器或处理器，此时我们需要通过response来产生响应；
2. postHandle：后处理回调方法，实现处理器的后处理（但在渲染视图之前），此时我们可以通过modelAndView（模型和视图对象）对模型数据进行处理或对视图进行处理，modelAndView也可能为null。
3. afterCompletion：整个请求处理完毕回调方法，即在视图渲染完毕时回调，如性能监控中我们可以在此记录结束时间并输出消耗时间，还可以进行一些资源清理，类似于try-catch-finally中的finally，但仅调用处理器执行链中preHandle返回true的拦截器的afterCompletion。

二.拦截器处理流程

方法解析：

　　第一个方法preHandle尤其重要，他可以根据返回值

　　改变请求往下的流程，起着先导作用，第二个方法posHandle，他可以在

　　请求通过处理器后，紧接着做一系列的操作，最后经过最后一个方法

　　afterCompletion，进行客户端的响应。
　　##三.多拦截器demo
1.自定义拦截器1

package org.springmvc.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class MyInterceptor implements HandlerInterceptor {

public void afterCompletion(HttpServletRequest request,
HttpServletResponse response, Object handler, Exception arg3)
throws Exception {
System.out.println("MyInterceptor.afterCompletion");
}

public void postHandle(HttpServletRequest request,
HttpServletResponse response, Object handler,
ModelAndView modelAndView) throws Exception {
System.out.println("MyInterceptor.postHandle");

}

public boolean preHandle(HttpServletRequest request,
HttpServletResponse response, Object handler) throws Exception {
System.out.println("MyInterceptor.preHandle");
return true;
}

}

2.自定义拦截器2

package org.springmvc.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class MyInterceptor2 implements HandlerInterceptor {

public void afterCompletion(HttpServletRequest request,
HttpServletResponse response, Object handler, Exception arg3)
throws Exception {
System.out.println("MyInterceptor.afterCompletion2");
}

public void postHandle(HttpServletRequest request,
HttpServletResponse response, Object handler,
ModelAndView modelAndView) throws Exception {
System.out.println("MyInterceptor.postHandle2");

}

public boolean preHandle(HttpServletRequest request,
HttpServletResponse response, Object handler) throws Exception {
System.out.println("MyInterceptor.preHandle2");
return true;
}

}

3.在springmvc.xml文件中配置拦截器

<!-- 自动扫描的包名 -->
<context:component-scan base-package="org.springmvc.controller" /> 
<!-- 拦截器 -->
<mvc:interceptors>
<mvc:interceptor>
<mvc:mapping path="/*" />
<bean class="org.springmvc.interceptor.MyInterceptor"></bean>
</mvc:interceptor>

<mvc:interceptor>
<mvc:mapping path="/*"/>
<bean class="org.springmvc.interceptor.MyInterceptor2"></bean>
</mvc:interceptor>
</mvc:interceptors>

<!-- 视图解释类 -->
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/" />
<property name="suffix" value=".jsp" />
</bean>

4.控制器

@RequestMapping("helloworld")
public String testHelloWorld(){
System.out.println("hello world");
return "success";
}

5.jsp文件

<a href="helloworld">helloworld</a>

6.控制台打印

MyInterceptor.preHandle
MyInterceptor.preHandle2
hello world
MyInterceptor.postHandle2
MyInterceptor.postHandle
MyInterceptor.afterCompletion2
MyInterceptor.afterCompletion

7.多拦截器时请求流程