简介
Spring 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。
应用场景:
- 日志记录
- 权限检查
- 性能监控
- 通用行为
拦截器接口
package org.springframework.web.servlet;
public interface HandlerInterceptor {
boolean preHandle(
HttpServletRequest request, HttpServletResponse response,
Object handler)
throws Exception;
void postHandle(
HttpServletRequest request, HttpServletResponse response,
Object handler, ModelAndView modelAndView)
throws Exception;
void afterCompletion(
HttpServletRequest request, HttpServletResponse response,
Object handler, Exception ex)
throws Exception;
}
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(如我们上一章的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;
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。
拦截器适配器
有时候我们可能只需要实现三个回调方法中的某一个,如果实现HandlerInterceptor接口的话,三个方法必须实现,不管你需不需要,此时spring提供了一个HandlerInterceptorAdapter适配器(一种适配器设计模式的实现),允许我们只实现需要的回调方法。
public abstract class HandlerInterceptorAdapter implements HandlerInterceptor {
//省略代码 此处所以三个回调方法都是空实现,preHandle返回true。
}
运行流程
- 正常流程:
- 中断流程:
DispatcherServlet工作流程
//doDispatch方法
//1、处理器拦截器的预处理(正序执行)
HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
if (interceptors != null) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
//1.1、失败时触发afterCompletion的调用
triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
return;
}
interceptorIndex = i;//1.2、记录当前预处理成功的索引
}
}
//2、处理器适配器调用我们的处理器
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
//当我们返回null或没有返回逻辑视图名时的默认视图名翻译(详解4.15.5 RequestToViewNameTranslator)
if (mv != null && !mv.hasView()) {
mv.setViewName(getDefaultViewName(request));
}
//3、处理器拦截器的后处理(逆序)
if (interceptors != null) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
}
}
//4、视图的渲染
if (mv != null && !mv.wasCleared()) {
render(mv, processedRequest, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
//5、触发整个请求处理完毕回调方法afterCompletion
triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
注:以上是流程的简化代码,中间省略了部分代码,不完整。
// triggerAfterCompletion方法
private void triggerAfterCompletion(HandlerExecutionChain mappedHandler, int interceptorIndex,
HttpServletRequest request, HttpServletResponse response, Exception ex) throws Exception {
// 5、触发整个请求处理完毕回调方法afterCompletion (逆序从1.2中的预处理成功的索引处的拦截器执行)
if (mappedHandler != null) {
HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
if (interceptors != null) {
for (int i = interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
try {
interceptor.afterCompletion(request, response, mappedHandler.getHandler(), ex);
}
catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
}
}
入门
正常流程
拦截器实现
package cn.javass.chapter5.web.interceptor;
//省略import
public class HandlerInterceptor1 extends HandlerInterceptorAdapter {//此处一般继承HandlerInterceptorAdapter适配器即可
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
System.out.println("===========HandlerInterceptor1 preHandle");
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
System.out.println("===========HandlerInterceptor1 postHandle");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
System.out.println("===========HandlerInterceptor1 afterCompletion");
}
}
控制器
package cn.javass.chapter5.web.controller;
//省略import
public class TestController implements Controller {
@Override
public ModelAndView handleRequest(HttpServletRequest req, HttpServletResponse resp) throws Exception {
System.out.println("===========TestController");
return new ModelAndView("test");
}
}
spring配置
<bean name="/test" class="cn.javass.chapter5.web.controller.TestController"/>
<bean id="handlerInterceptor1"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor1"/>
<bean id="handlerInterceptor2"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor2"/>
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
<property name="interceptors">
<list>
<ref bean="handlerInterceptor1"/>
<ref bean="handlerInterceptor2"/>
</list>
</property>
</bean>
interceptors:指定拦截器链,拦截器的执行顺序就是此处添加拦截器的顺序;
视图页面
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%System.out.println("==========test.jsp");%>
test page
测试输出
===========HandlerInterceptor1 preHandle
===========HandlerInterceptor2 preHandle
===========TestController
===========HandlerInterceptor2 postHandle
===========HandlerInterceptor1 postHandle
==========test.jsp
===========HandlerInterceptor2 afterCompletion
===========HandlerInterceptor1 afterCompletion
中断流程
拦截器
HandlerInterceptor3和HandlerInterceptor4 与 之前的 HandlerInteceptor1和HandlerInterceptor2一样,只是在HandlerInterceptor4的preHandle方法返回false:
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
System.out.println("===========HandlerInterceptor1 preHandle");
onse.getWriter().print("break");//流程中断的话需要我们进行响应的处理
return false;//返回false表示流程中断
控制器
流程中断不会执行到控制器,使用之前的TestController控制器。
spring配置文件
bean id="handlerInterceptor3"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor3"/>
<bean id="handlerInterceptor4"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor4"/>
<bean id="handlerInterceptor3"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor3"/>
<bean id="handlerInterceptor4"
class="cn.javass.chapter5.web.interceptor.HandlerInterceptor4"/>
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
<property name="interceptors">
<list>
<ref bean="handlerInterceptor3"/>
<ref bean="handlerInterceptor4"/>
</list>
</property>
</bean>
测试输出
===========HandlerInterceptor3 preHandle
===========HandlerInterceptor4 preHandle
===========HandlerInterceptor3 afterCompletion