实践中filter的配置
配置一个权限filter，拦截一切没有登录却想访问只有登录后才有的权限页面的url，我的做法如下：
先写上一个filter：
package com.xll.util;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class RightFilter implements Filter {private FilterConfig filterConfig;public void destroy() {}public void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) resp;String uri = request.getRequestURI();System.out.println(uri);String ctx = request.getContextPath();System.out.println(ctx);uri = uri.substring(ctx.length());if (uri.startsWith("/admin")) {if (request.getSession().getAttribute("username") == null) {System.out.println("没有登录");response.sendRedirect("/VoteSystem/index.jsp");System.out.println("xxxxxxxxxxx");return ;} else {chain.doFilter(request, response);}}}public void init(FilterConfig filterConfig) throws ServletException {this.filterConfig = filterConfig;}}<filter><filter-name>RightFilter</filter-name><filter-class>com.xll.util.RightFilter</filter-class></filter><filter-mapping><filter-name>RightFilter</filter-name><url-pattern>/admin/*</url-pattern></filter-mapping><filter><!--定义核心Filter FilterDispatcher --><filter-name>struts2</filter-name><!-- 定义核心Filter的名称 --><filter-class><!--定义核心Filter的实现类 -->org.apache.struts2.dispatcher.FilterDispatcher</filter-class></filter><filter-mapping><filter-name>struts2</filter-name><!--核心Filter的名称 --><url-pattern>/*</url-pattern><!--使用该核心Filter过滤所有的Web请求 --></filter-mapping>