Web App struts框架里实现Filter

　　1 web.xml里添加filter配置信息。
　　<filter>
　　<filter-name>Authentication</filter-name>
　　<filter-class>
　　com.nova.colimas.web.filters.AuthenticationFilter
　　</filter-class>
　　<init-param>
　　<param-name>onError</param-name>
　　<param-value>/pages/index.jsp</param-value>
　　</init-param>
　　</filter>
　　<filter-mapping>
　　<filter-name>Authentication</filter-name>
　　<url-pattern>/protect/*</url-pattern>
　　</filter-mapping>
　　<filter-class>定义使用com.nova.colimas.web.filters.AuthenticationFilter类执行过滤Action。
　　<init-param>当验证失败后Forward到/pages/index.jsp
　　<filter-mapping>只有当地址包括/protect/时运行filter类
　　
　　2 实现com.nova.colimas.web.filters.AuthenticationFilter
　　package com.nova.colimas.web.filters;
　　import java.io.IOException;
　　import javax.servlet.RequestDispatcher;
　　import javax.servlet.ServletException;
　　import javax.servlet.http.*;
　　import javax.servlet.Filter;import javax.servlet.FilterChain;
　　import javax.servlet.FilterConfig;
　　import com.nova.colimas.web.bean.UserBean;
　　import javax.servlet.ServletRequest;
　　import javax.servlet.ServletResponse;import org.apache.struts.Globals;
　　import org.apache.struts.action.*;
　　import com.nova.colimas.web.constants.Constants;
　　/**
　　* Filter implementation for user authentication。必须实现Filter接口
　　* @author tyrone * @version $Id: AuthenticationFilter.java,v 1.0
　　*/public class AuthenticationFilter implements Filter{
　　/**
　　* filterConfig will store the reference of FilterConfig
　　*/　 private FilterConfig filterConfig;
　　private String onErrorUrl;
　　/**
　　* store the reference of the FilterConfig.
　　* @param config FilterConfig object
　　* @throws ServletException
　　*/　 public void init(FilterConfig config) throws ServletException
　　{//获得验证失败forward地址
　　filterConfig = config;
　　onErrorUrl=filterConfig.getInitParameter("onError");
　　if (onErrorUrl==null || "".equals(onErrorUrl)){
　　onErrorUrl="/pages/index.jsp";
　　}
　　}
　　/**
　　* User Authentication is　done. If User is authenticated successful then
　　* control is transferred to logon URI
　　* @param ServletRequest Request
　　* @param ServletRequest Response
　　* @param FilterChain Filter Chain
　　* @throws ServletException,IOException
　　*/　 public void doFilter(ServletRequest request, ServletResponse response, FilterChain next)
　　throws IOException, ServletException
　　{
　　HttpServletRequest httpRequest = (HttpServletRequest)request;
　　HttpServletResponse httpResponse=(HttpServletResponse)response;
　　// Current session
　　HttpSession httpSession = httpRequest.getSession();
　　//Session里是否有用户信息。
　　if (httpSession.getAttribute(Constants.USER_KEY) == null)
　　{
　　ActionErrors errors=new ActionErrors();
　　errors.add(ActionErrors.GLOBAL_ERROR,
　　new ActionError("error authentication"));
　　httpRequest.setAttribute(Globals.ERROR_KEY,errors);
　　//没有，验证失败forward到/pages/index.jsp
　　httpRequest.getRequestDispatcher(onErrorUrl).forward(httpRequest,httpResponse);
　　}else//成果过滤Action结束
　　next.doFilter(request,response);
　　}
　　/**
　　* destroy() method is called by the servlet container
　　*/　 public void destroy()
　　{
　　}
　　}