Spring拦截器

一.拦截器：Interceptor
拦截器的作用：对请求进行拦截、判断，最终选择放行或者拦截。
在SpringMVC中，拦截器的第1次会出现在调用Controller的方法之前。

在拦截器中，共有3个抽象方法需要被实现，分别是：preHandle()、postHandle()、afterCompletion()，其中，preHandle()会在调用Controller中的方法之前被执行，该方法返回boolean值，如果返回true，则表示放行，返回false表示拦截，postHandle()和afterCompletion()会在Controller执行结果之后被调用！

二.使用拦截器的步骤
1.自定义拦截器类，实现HandlerInterceptor接口
2.在Spring的配置文件中，添加节点，进行配置
如果需要匹配所有资源，则需要使用 /**。

<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/*" />
        <mvc:exclude-mapping path="/login.do"/>
        <mvc:exclude-mapping path="/handleLogin.do"/>
        <bean class="cn.tedu.spring.interceptor.SessionInterceptor"></bean>
    </mvc:interceptor>
</mvc:interceptors>

3.使用拦截器实现判断是否登录
public boolean preHandle( HttpServletRequest request, 
        HttpServletResponse response, Object handler)throws Exception {
    // 获取Session
    HttpSession session = request.getSession();
    // 检查Session
    // 例如存在规则：登录后Session中一定有username
    if (session.getAttribute("username") == null) {
        // Session中没有登录数据，则重定向到登录
        response.sendRedirect("login.do");
        // 不允许放行，此次请求将被拦截
        return false;
    } else {
        // Session中有登录数据，则正常放行
        return true;
    }
}

三.实例

1.spring配置文件applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"
	xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop"
	xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:util="http://www.springframework.org/schema/util"
	xmlns:jpa="http://www.springframework.org/schema/data/jpa"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsd
        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
        http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd">
        
    <context:component-scan base-package="cn.tedu.spring"/>
	<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		<property name="prefix" value="/WEB-INF/jsp/"/>
		<property name="suffix" value=".jsp"/>
	</bean>
        
	<mvc:interceptors>
		<mvc:interceptor>
			<mvc:mapping path="/*"/>
			<mvc:exclude-mapping path="/login.do"/>
			<mvc:exclude-mapping path="/handlerLogin.do"/>
			<bean class="cn.tedu.spring.interceptor.SessionInterceptor"></bean>
		</mvc:interceptor>
	</mvc:interceptors>
</beans>

2.web.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
  <display-name>DAY06-01-SpringMVC-Interceptor</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
 	<servlet-name>SpringMVC</servlet-name>
 	<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 	<init-param>
 		<param-name>contextConfigLocation</param-name>
 		<param-value>classpath:applicationContext.xml</param-value>
 	</init-param>
 	<load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
 	<servlet-name>SpringMVC</servlet-name>
 	<url-pattern>*.do</url-pattern>
 </servlet-mapping>
</web-app>

3.WEB-INF下jsp文件里的文件

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Spring MVC - Interceptor</title>
</head>
<body>
	<form action="handlerLogin.do" method="post">
		<input type="submit" value="登录"/>
	</form>
</body>
</html>

4.拦截器类

package cn.tedu.spring.interceptor;

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

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



public class SessionInterceptor implements HandlerInterceptor{

	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
		System.out.println("SessionInterceptor.preHandle()");
		System.out.println("\tag0=:"+request);
		System.out.println("\tag1=:"+response);
		System.out.println("\tag2=:"+handler);
		//获取Session
		HttpSession session = request.getSession();;
		// 检查Session
		// 例如存在规则：登录后Session中一定有username
		if (session.getAttribute("username") == null) {
			// Session中没有登录数据，则重定向到登录
			response.sendRedirect("login.do");
			// 不允许放行，此次请求将被拦截
			return false;
		} else {
			// Session中有登录数据，则正常放行
			return true;
		}
	}
	
	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView arg3)
			throws Exception {
		
	}
	
	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception arg3)
			throws Exception {
		
	}
}

5.控制器类

package cn.tedu.spring.controller;

import javax.servlet.http.HttpSession;
import javax.websocket.Session;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class UserController {
	@RequestMapping("reg.do")
	public String showReg() {
		System.out.println("UserController.showReg()");
		return "reg";
	}
	@RequestMapping("login.do")
	public String showLogin() {
		System.out.println("UserController.showLogin()");
		return "login";
	}
	@RequestMapping("index.do")
	public String showIndex() {
		System.out.println("UserController.showIndex()");
		return "index";
	}
	@RequestMapping("user_info.do")
	public String showUserInfo() {
		System.out.println("UserController.showUserInfo()");
		return "user_info";
	}
	@RequestMapping("handlerLogin.do")
	public String handlerLogin(HttpSession session) {
		System.out.println("UserController.showhandlerLogin()");
		session.setAttribute("username", "rose");
		return "index";
	}
}