12.2、拦截器配置和执行顺序

拦截器已在上一节介绍，下面直接示例演示。
一、web.xml配置

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://xmlns.jcp.org/xml/ns/javaee"    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"    id="WebApp_ID" version="3.1">    <!-- The front controller of this Spring Web application, responsible for handling all application requests -->    <!--配置spring xml的寻找路径-->    <servlet>        <servlet-name>springDispatcherServlet</servlet-name>        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>        <init-param>            <param-name>contextConfigLocation</param-name>            <param-value>classpath:springmvc.xml</param-value>        </init-param>        <load-on-startup>1</load-on-startup>    </servlet>    <!-- Map all requests to the DispatcherServlet for handling -->    <servlet-mapping>        <servlet-name>springDispatcherServlet</servlet-name>        <url-pattern>/</url-pattern>    </servlet-mapping></web-app>

二、spring配置文件

<?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:aop="http://www.springframework.org/schema/aop"    xmlns:context="http://www.springframework.org/schema/context"    xmlns:mvc="http://www.springframework.org/schema/mvc"    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">    <context:component-scan base-package="com.lzj.springmvc"></context:component-scan>    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">        <property name="prefix" value="/WEB-INF/views/"></property>        <property name="suffix" value=".jsp"></property>    </bean>    <mvc:interceptors>        <!-- <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>         -->        <mvc:interceptor>            <!--表示拦截根目录下的所有请求-->            <mvc:mapping path="/*"/>            <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>        </mvc:interceptor>    </mvc:interceptors></beans>

三、创建拦截器

package com.lzj.springmvc.interceptors;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.web.servlet.HandlerInterceptor;import org.springframework.web.servlet.ModelAndView;public class FirstInterceptor implements HandlerInterceptor{    @Override    public void afterCompletion(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, Exception arg3)            throws Exception {        System.out.println("FirstInterceptor -> afterCompletion");    }    @Override    public void postHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, ModelAndView arg3)            throws Exception {        System.out.println("FirstInterceptor -> postHandle");    }    @Override    public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {        System.out.println("FirstInterceptor -> preHandle");        return true;    }}

四、创建一个index.jsp请求，其内容为：

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

五、创建控制器
用于截获index.jsp中的hello world请求

@Controller@RequestMapping("/springMVC")public class TestSpringMVC {    @RequestMapping("/testRequestMapping")    public String testRequestMapping(){        System.out.println("testRequestMapping");        return "success";    }}

当点击index.jsp中的请求连接时，拦截器拦截请求，执行preHandle方法，然后控制器截获请求，执行控制器testRequestMapping方法，当控制器执行结束后并返回时，拦截器拦截请求，执行postHandle方法，最后释放资源，执行afterCompletion。输出结果如下：

preHandlehello worldpostHandleafterCompletion

拦截器配置方法：spring中拦截器除了上面的配置方法

        <!-- <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>         -->        <mvc:interceptor>            <!--表示拦截根目录下的所有请求-->            <mvc:mapping path="/*"/>            <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>        </mvc:interceptor>    </mvc:interceptors>

还可以按如下配置：

<mvc:interceptors>        <!-- <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>         -->        <mvc:interceptor>            <!--表示根目录下的所有请求都不拦截-->            <mvc:exclude-mapping path="/*"/>            <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>        </mvc:interceptor>    </mvc:interceptors>

拦截器执行顺序：如果有多个拦截器，那么多个拦截器执行的顺序是什么？在上面代码的基础上创建一个SecondInterceptor

package com.lzj.springmvc.interceptors;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.web.servlet.HandlerInterceptor;import org.springframework.web.servlet.ModelAndView;public class SecondInterceptor implements HandlerInterceptor{    @Override    public void afterCompletion(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, Exception arg3)            throws Exception {        System.out.println("SecondInterceptor -> afterCompletion");    }    @Override    public void postHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, ModelAndView arg3)            throws Exception {        System.out.println("SecondInterceptor -> postHandle");    }    @Override    public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {        System.out.println("SecondInterceptor -> preHandle");        return true;    }}

spring的配置文件为

    <mvc:interceptors>        <mvc:interceptor>            <mvc:mapping path="/*"/>            <bean class="com.lzj.springmvc.interceptors.FirstInterceptor"></bean>        </mvc:interceptor>        <mvc:interceptor>            <mvc:mapping path="/*"/>            <bean class="com.lzj.springmvc.interceptors.SecondInterceptor"></bean>        </mvc:interceptor>    </mvc:interceptors>

当执行index.jsp中hello world请求时，console中打印出：

        FirstInterceptor -> preHandle        SecondInterceptor -> preHandle        hello world        SecondInterceptor -> postHandle        FirstInterceptor -> postHandle        SecondInterceptor -> afterCompletion        FirstInterceptor -> afterCompletion

但是如果当FirstInterceptor 拦截器中preHandle返回false时，

public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {        System.out.println("FirstInterceptor -> preHandle");        return false;    }

此时console中只输出：

FirstInterceptor -> preHandle

此时过滤在第一个过滤器的preHandle方法就已经返回了，不会再执行第一个过滤器的postHandle和afterCompletion方法，也不会再执行后面的过滤器。

如果第FirstInterceptor 种的preHandle返回true，SecondInterceptor 中的preHandle返回false的话，执行index.jsp中的请求，console中输出：

FirstInterceptor -> preHandleSecondInterceptor -> preHandleFirstInterceptor -> afterCompletion