作用：拦截器是SpringMVC中用来拦截控制器方法的一类组件。其他(比如静态资源)概不拦截！
SpringMVC拦截器的相关流程：
1、编写拦截器：实现HandlerInterceptor接口，编写preHandle、postHandle、afterCompletion的相关内容(不要求每个方法都写！)
2、在SpringMVC的配置文件中配置拦截器：
<mvc:interceptors> <mvc:interceptor> <mvc:mapping path="/**"/> <bean class="cn.liuxingchang.interceptor.MyInterceptor" /> </mvc:interceptor> </mvc:interceptors>完了。
关于 <mvc:mapping />的说明：
1、 <mvc:mapping path="/**"/>表示拦截所有请求路径；
2、 <mvc:mapping path="/user/*" />可以拦截诸如"/user/update"这样的路径！不符合这种格式的不拦截。
关于<mvc:exclude-mapping />的说明：
<mvc:exclude-mapping path="/user/**" />表示像"/user/**"这样的不拦截，其他都拦截！
您可能又会问了：/* 和 /** 有区别吗？
当然有，有关这二者的比较，可参考：/* /** #SpringMVC拦截器中/*和/**的区别 @FDDLC
拦截器里可以实现3个方法：preHandle、postHandle、afterCompletion。如果有多个拦截器，执行顺序如下：
关于拦截器的说明如下：
1、preHandle的返回值：如果是true，代表放行，如上图正常走流程；如果是false，执行链中止，相当于断路，由图可知controller也不会再执行了；另外，false的情况可以指定响应页面。
2、postHandle也可以指定响应页面。
3、afterCompletion表示响应完了，所以在这个方法里不能再提定响应页面，否则控制台会报：Cannot forward after response has been committed
最后附上源码：
项目结构：
pom.xml的内容：
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.example</groupId> <artifactId>P061_interceptor</artifactId> <version>1.0-SNAPSHOT</version> <packaging>war</packaging> <name>P061_interceptor Maven Webapp</name> <!-- FIXME change it to the project's website --> <url>http://www.example.com</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>1.7</maven.compiler.source> <maven.compiler.target>1.7</maven.compiler.target> </properties> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.1.8.RELEASE</version> </dependency> <dependency> <groupId>org.apache.tomcat</groupId> <artifactId>servlet-api</artifactId> <version>6.0.36</version> </dependency> </dependencies> <build> <finalName>P061_interceptor</finalName> <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) --> <plugins> <plugin> <artifactId>maven-clean-plugin</artifactId> <version>3.1.0</version> </plugin> <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging --> <plugin> <artifactId>maven-resources-plugin</artifactId> <version>3.0.2</version> </plugin> <plugin> <artifactId>maven-compiler-plugin</artifactId> <version>3.8.0</version> </plugin> <plugin> <artifactId>maven-surefire-plugin</artifactId> <version>2.22.1</version> </plugin> <plugin> <artifactId>maven-war-plugin</artifactId> <version>3.2.2</version> </plugin> <plugin> <artifactId>maven-install-plugin</artifactId> <version>2.5.2</version> </plugin> <plugin> <artifactId>maven-deploy-plugin</artifactId> <version>2.8.2</version> </plugin> </plugins> </pluginManagement> </build> </project>
web.xml的内容：
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" > <web-app> <display-name>Archetype Created Web Application</display-name> <servlet> <servlet-name>dispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <!--关联springmvc.xml，让其中的配置生效！--> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:springmvc.xml</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>dispatcherServlet</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app>
springmvc.xml的内容：
<?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:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="cn.liuxingchang" /> <mvc:annotation-driven /> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="viewResolver"> <property name="prefix" value="/WEB-INF/pages/"></property> <property name="suffix" value=".jsp"></property> </bean> <mvc:interceptors> <mvc:interceptor> <mvc:mapping path="/**"/> <bean class="cn.liuxingchang.interceptor.MyInterceptor" /> </mvc:interceptor> <mvc:interceptor> <mvc:mapping path="/**"/> <bean class="cn.liuxingchang.interceptor.MyInterceptor2" /> </mvc:interceptor> </mvc:interceptors> </beans>
index.jsp的内容：
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <body> <a href="test?name=Tom">test</a> </body> </html>
success.jsp的内容：
<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %> <html> <head> <title>Title</title> </head> <body> <% System.out.println("success"); %> <h3>success</h3> </body> </html>
login.jsp的内容：
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h3>请登录！</h3> </body> </html>
MyInterceptor.java的内容：
package cn.liuxingchang.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 MyInterceptor implements HandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { System.out.println("preHandle"); return true; } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { System.out.println("postHandle"); } @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { System.out.println("afterCompletion"); } }
MyInterceptor2.java的内容：
package cn.liuxingchang.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 MyInterceptor2 implements HandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { System.out.println("preHandle2"); return true; } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { System.out.println("postHandle2"); } @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { System.out.println("afterCompletion2"); } }
HelloController.java的内容：
package cn.liuxingchang.controller; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; @Controller public class HelloController { @RequestMapping("/test") public String test() { System.out.println("controller"); return "success"; } }
