对于Java Web中的Filter和Interceptor的理解
<p>写在前面：因为部门项目中有用户登录验证方面的需求，故而学习了一下相关的验证技术，本文仅是作者个人学习的心得，由于水平有限，如有错误之处还请指出、见谅。</p> <h3><strong>1. 背景</strong></h3> <p>在设计web应用的时候，用户登录/注册是必不可少的功能，对用户登录信息进行验证的方法也是多种多样，大致可以认为如下模式：前端验证+后台验证。根据笔者的经验，一般会在前端进行一些例如是否输入数据、输入的数据的格式是否正确等一系列的验证，在后台会查询数据库进行验证。</p> <p>一般在后台进行验证的时候，都会选择使用Servlet的Filter作为拦截器，本文主要介绍Servlet的Filter，然后再拿它跟Spring MVC的HnadlerInterceptor进行对比。</p> <h3><strong>2. Filter</strong></h3> <p><strong>2.1 什么是Filter</strong></p> <p>Servlet作为Java Web的基础，它的一个比较核心也被广泛应用的功能就是Filter，又叫拦截器。顾名思义，拦截器就是起到拦截作用的。一般情况下，用户从客户端发出请求到服务器后，整个的流程是：</p> <p>HttpRequest ----> Filter ----> Servlet ----> Controller/Action/... ----> Filter ----> HttpResponse</p> <p>根据上面的流程可以看出，Filter的作用就是在用户请求到达Servlet之前，进行拦截。在拦截到用户的请求后，我们可以实现一些自定义的业务逻辑，例如之前说到的对用户登录信息进行验证。Filter还可以在服务器响应到达客户端之前对响应的数据进行修改，本文主要介绍第一个功能。</p> <p><strong>2.2 Filter的工作原理</strong></p> <p>Filter跟Servlet一样都是由服务器负责创建和销毁的，在web应用程序启动时，服务器会根据应用程序的web.xml文件中的配置信息调用 public void init(FilterConfig filterConfig) throws ServletException 方法来初始化Filter，在web应用程序被移除或者是服务器关闭时，会调用 public void destroy() 来销毁Filter。在一个应用程序中一个Filter只会被创建和销毁一次，在进行完初始化之后，Filter中声明了 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException 方法，用来实现一些需要在拦截完成之后的业务逻辑。</p> <p>注意到上面的 doFilter() 方法的参数中，有 chain 这个参数，它是传递过来的拦截链对象，里面包含了用户定义的一系列的拦截器，这些拦截器根据其在web.xml中定义的顺序依次被执行。当用户的信息验证通过或者当前拦截器不起作用时，我们可以执行 chain.doFilter() 方法来跳过当前拦截器来执行拦截器链中的下一个拦截器。</p> <p><strong>2.3 自己实现Filter</strong></p> <p>自己实现Filter时，需要继承接口 javax.servlet.Filter 并且实现相关的方法。</p> <p><strong>2.3.1所用到的工具：</strong></p> <p>IDE: IntelliJ IDEA</p> <p>构建工具：gradle</p> <p>本地服务器：Tomcat</p> <p><strong>2.3.2 具体代码</strong></p> <p>build.gradle</p> <pre> <code class="language-java">group 'xiangang.wei' version '1.0-SNAPSHOT' apply plugin: 'java' apply plugin: 'war' sourceCompatibility = 1.8 repositories { jcenter() mavenCentral() } dependencies { testCompile group: 'junit', name: 'junit', version: '4.11' // servlet-api compile group: 'javax.servlet', name: 'servlet-api', version: '2.5' }</code></pre> <p>web.xml</p> <pre> <code class="language-java"><?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> <filter> <filter-name>loginValidation</filter-name> <filter-class>filter.LoginValidation</filter-class> <init-param> <param-name>redirectPath</param-name> <param-value>/index.jsp</param-value> </init-param> <init-param> <param-name>disableloginValidation</param-name> <param-value>N</param-value> </init-param> <init-param> <param-name>logonString</param-name> <param-value>/index.jsp</param-value> </init-param> </filter> <filter-mapping> <filter-name>loginValidation</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app></code></pre> <p>web.xml中<init-param>标签被用来配置Filter的初始化时使用的参数，其中<param-name>标签表示参数的名字，可以是自己定义的任何名字，<param-value>标签表示对应的初始化参数的值。上面的初始化参数中， redirectPath 定义了当验证不成功时页面重定向的的路径， logonString 定义了拦截器拦截的指定URL。 <filter-mapping> 标签定义了拦截器的拦截模式，在 <url-pattern> 标签定义了拦截模式，上面的 /* 表示拦截所有。它和之前定义的指定拦截的URL标签结合起来使用。</p> <p>index.jsp</p> <pre> <code class="language-java"><%-- Created by IntelliJ IDEA. User: xiangang Date: 2016/11/21 Time: 下午3:42 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>用户登陆界面</title> <style type="text/css"> div{ margin: auto; border: gray 1px solid; width: 70%; } </style> </head> <body> <div> <form action="success.jsp" method="post"> <table> <tr> <td>用户名：<input type="text" name="name" /></td> </tr> <tr> <td>密 码：<input type="password" name="password" /></td> </tr> <tr> <td><input type="submit" value="提交" /></td> <td><input type="reset" value="重置" /></td> </tr> </table> </form> </div> </body> </html></code></pre> <p>Filter对应的实现类：</p> <p>LoginValidation.java</p> <pre> <code class="language-java">package filter; import javax.servlet.*; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; /** * Created by xiangang on 2016/11/21. */ public class LoginValidation implements Filter{ public FilterConfig config; public static boolean isContains(String url, String[] regx){ boolean flag = false; for (int i = 0;i<regx.length;i++){ if (url.indexOf(regx[i])!=-1){ flag = true; return flag; } } return flag; } @Override public void init(FilterConfig filterConfig) throws ServletException { this.config = filterConfig; } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest httpServletRequest= (HttpServletRequest)request; HttpServletResponse httpServletResponse = (HttpServletResponse)response; String name = httpServletRequest.getParameter("name"); String password = httpServletRequest.getParameter("password"); String redirectPath=httpServletRequest.getContextPath()+config.getInitParameter("redirectPath"); String logonString = config.getInitParameter("logonString"); String[] logonList = logonString.split(";"); if (isContains(httpServletRequest.getRequestURI(),logonList)){ chain.doFilter(request,response); return; } if ("Y".equals(config.getInitParameter("disableloginValidation"))){ chain.doFilter(request,response); return; } if ("root".equals(name) && "admin".equals(password)){ chain.doFilter(request,response); return; }else{ httpServletResponse.sendRedirect(redirectPath); return; } } @Override public void destroy() { this.config = null; } }</code></pre> <p>登录成功之后的页面：</p> <p>success.jsp</p> <pre> <code class="language-java"><%-- Created by IntelliJ IDEA. User: xiangang Date: 2016/11/21 Time: 下午3:56 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>登录成功！</title> </head> <body> 欢迎！ </body> </html></code></pre> <p>配置好Tomcat之后，开启应用程序：</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/b3410d0cb867e302bc278d14c1d9f5a5.png"></p> <p style="text-align:center"><img src="https://simg.open-open.com/show/dd23d14c16b30bdbd8fc92b8c7e9f324.png"></p> <p>登录失败时不会跳转，仍然会停留在原页面。</p> <h3><strong>3. Interceptor</strong></h3> <p>之前提到的Filter是Servlet层面的拦截器，在许多的Java Web框架中，都实现了自己的拦截器Interceptor。例如Struts2中的Interceptor、Spring MVC中的HandlerInterceptor等。相比于Filter,框架中的Interceptor的产生作用的时间和位置不一样，下面描述了应用了Spring MVC中的HandlerInterceptor的web请求流程：</p> <p>HttpRequest ----> DispactherServlet ----> HandlerInterceptor ---->Controller----> HandlerInterceptor ----> HttpResponse</p> <p>两者的主要区别在于Filter起作用的时机是在请求到达Servlet之前，二HandlerInterceptor其作用的时机是在DispactherServlet接收到用户请求完成请求到相应的Handler映射之后。虽然都先于在具体的业务逻辑执行，但是还是存在一些差异。Filter面对的是所有的请求，而HandlerInterceptor是面对具体的Controller。Filter总是先于HandlerInterceptor发挥作用，在Filter中甚至可以中断请求，从而使它无法到达相应的Servlet。而且两者的配置也不一样，Filter是在web.xml中进行配置，HandlerInterceptor是在具体的applicationContext.xml中进行配置。</p> <p><strong>3.1 HandlerInterceptor的工作原理</strong></p> <p>分析源码，发现HandlerInterceptor接口中声明了如下几个方法：</p> <pre> <code class="language-java">public interface HandlerInterceptor { /** * Intercept the execution of a handler. Called after HandlerMapping determined * an appropriate handler object, but before HandlerAdapter invokes the handler. * <p>DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can decide to abort the execution chain, * typically sending a HTTP error or writing a custom response. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler chosen handler to execute, for type and/or instance evaluation * @return {@code true} if the execution chain should proceed with the * next interceptor or the handler itself. Else, DispatcherServlet assumes * that this interceptor has already dealt with the response itself. * @throws Exception in case of errors */ boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception; /** * Intercept the execution of a handler. Called after HandlerAdapter actually * invoked the handler, but before the DispatcherServlet renders the view. * Can expose additional model objects to the view via the given ModelAndView. * <p>DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can post-process an execution, * getting applied in inverse order of the execution chain. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param modelAndView the {@code ModelAndView} that the handler returned * (can also be {@code null}) * @throws Exception in case of errors */ void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception; /** * Callback after completion of request processing, that is, after rendering * the view. Will be called on any outcome of handler execution, thus allows * for proper resource cleanup. * <p>Note: Will only be called if this interceptor's {@code preHandle} * method has successfully completed and returned {@code true}! * <p>As with the {@code postHandle} method, the method will be invoked on each * interceptor in the chain in reverse order, so the first interceptor will be * the last to be invoked. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param ex exception thrown on handler execution, if any * @throws Exception in case of errors */ void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception; }</code></pre> <p>这三个方法分别会在具体的HandlerController方法执行之前，执行成功之后，和执行完成之后被执行。</p> <p><strong>3.2 自己实现HandlerInterceptor</strong></p> <p>Spring MVC框架采用了适配器的开发模式，使用一个抽象的类 HandlerInterceptorAdapter 实现 HandlerInterceptor 接口，这样当我们需要自己实现HandlerInterceptor时，我们可以继承 HandlerInterceptorAdapter 这样我们就不用全部实现这三个方法，而可以选择性的实现自己需要的方法。</p> <p><strong>3.2.1所用到的工具：</strong></p> <p>IDE: IntelliJ IDEA</p> <p>构建工具：gradle</p> <p>本地服务器：Tomcat</p> <p><strong>3.2.2具体的代码：</strong></p> <p>build.gradle</p> <pre> <code class="language-java">group 'xiangang.wei' version '1.0-SNAPSHOT' apply plugin: 'java' apply plugin: 'war'source Compatibility = 1.8 repositories { jcenter() mavenCentral() } dependencies { testCompile group: 'junit', name: 'junit', version: '4.11' // servlet-api compile group: 'javax.servlet', name: 'servlet-api', version: '2.5' //spring相关 compile group: 'org.springframework', name: 'spring-webmvc', version: '4.3.3.RELEASE' compile group: 'org.springframework', name: 'spring-orm', version: '4.3.3.RELEASE' compile group: 'org.springframework', name: 'spring-aspects', version: '4.3.3.RELEASE' compile group: 'org.springframework.security', name: 'spring-security-config', version: '3.2.0.RELEASE' compile group: 'org.springframework.security', name: 'spring-security-taglibs', version: '3.2.0.RELEASE' compile 'org.springframework.security:spring-security-web:3.2.0.RELEASE' //hibernate相关 compile 'org.hibernate:hibernate-core:4.3.6.Final' //mysql compile group: 'mysql', name: 'mysql-connector-java', version: '5.1.39' //springData compile group: 'org.springframework.data', name: 'spring-data-jpa', version: '1.10.3.RELEASE' // https://mvnrepository.com/artifact/log4j/log4j日志 compile group: 'log4j', name: 'log4j', version: '1.2.17' //json解析相关 compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.5.4' compile group: 'com.fasterxml.jackson.core', name: 'jackson-core', version: '2.5.4' }</code></pre> <p>web.xml</p> <pre> <code class="language-java"><?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> <!--框架默认帮我们配置好了ApplicationContext的实现类(org.springframework.web.context.support.XmlWebApplicationContext),不需要自己手动配置--> <!--配置ApplicationContext需要加载的配置文件--> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:databaseAccess.xml,classpath:service.xml</param-value> </context-param> <!--ApplicationContext的加载和关闭--> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <!--配置字符过滤器,防止出现中文乱码--> <filter> <filter-name>CharacterEncodingFilter</filter-name> <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <!--配置Spring MVC的前置控制器--> <servlet> <servlet-name>dispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:dispatcherServlet.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dispatcherServlet</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app></code></pre> <p>涉及到HandlerInterceptor的配置文件 dispatcherServlet.xml</p> <pre> <code class="language-java"><?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: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/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <!--开启注解--> <mvc:annotation-driven/> <!--添加需要扫描的包--> <context:component-scan base-package="ims" use-default-filters="false"> <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </context:component-scan> <!--添加HandlerInterceptor--> <mvc:interceptors> <mvc:interceptor> <mvc:mapping path="/user/**"/> <bean class="ims.handlerInterceptor.LoginInterceptor"/> </mvc:interceptor> <mvc:interceptor> <mvc:mapping path="/register/**"/> <bean class="ims.handlerInterceptor.RegisterInterceptor"/> </mvc:interceptor> </mvc:interceptors> <!--添加试图解析器--> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/views/"/> <property name="suffix" value=".jsp"/> </bean> </beans></code></pre> <p>配置HandlerInterceptor有两种方式，一种是如上面所示，这张方式配置的HandlerInterceptor可以指定具体的拦截路径，另外一种方式是直接在 <mvc:interceptors> 中使用<bean>标签进行配置： <bean class="ims.handlerInterceptor.LoginInterceptor"/> 按照这种方式配置的HandlerInterceptor会对所有的路径进行拦截。</p> <p>具体的Interceptor实现类：</p> <p>LoginInterceptor.java</p> <pre> <code class="language-java">package ims.handlerInterceptor; import ims.service.UserService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.stereotype.Service; import org.springframework.web.servlet.handler.HandlerInterceptorAdapter; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; /** * Created by xiangang on 16/11/17. */ public class LoginInterceptor extends HandlerInterceptorAdapter { @Autowired private UserService userService; @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { boolean flag = true; HttpSession session = request.getSession(); if (session.getAttribute("user") == null) { String userName = request.getParameter("userName"); String password = request.getParameter("password"); flag = userService.selectByUserName(userName, password); if (flag){ session.setAttribute("user",userName); } } if (!flag){ response.sendRedirect("index.jsp"); } return flag; } }</code></pre> <p>具体的运行结果这里也就不再贴图了，实现的效果跟之前的Filter是一致的。</p> <h3> </h3> <p> </p> <p>来自：http://www.jianshu.com/p/39c0cfe25997</p> <p> </p> 本文由用户 Ellie30M 自行上传分享，仅供网友学习交流。所有权归原作者，若您的权利被侵害，请联系管理员。
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