五个有用的过滤器

     一、使浏览器不缓存页面的过滤器   
      import javax.servlet.*;   
      import javax.servlet.http.HttpServletResponse;   
      import java.io.IOException;   
        
      /**
      * 用于的使 Browser 不缓存页面的过滤器
      */  
      public class ForceNoCacheFilter implements Filter {   
        
      public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain filterChain) throws IOException, ServletException   
      {   
          ((HttpServletResponse)
      response).setHeader("Cache-Control","no-cache");   
          ((HttpServletResponse) response).setHeader("Pragma","no-cache");   
          ((HttpServletResponse) response).setDateHeader ("Expires", -1);   
          filterChain.doFilter(request, response);   
      }   
        
      public void destroy()   
      {   
      }   
        
           public void init(FilterConfig filterConfig) throws ServletException  
      
      {   
      }   
      }   
        
      二、检测用户是否登陆的过滤器   
        
      import javax.servlet.*;   
      import javax.servlet.http.HttpServletRequest;   
      import javax.servlet.http.HttpServletResponse;   
      import javax.servlet.http.HttpSession;   
      import java.util.List;   
      import java.util.ArrayList;   
      import java.util.StringTokenizer;   
      import java.io.IOException;   
        
      /**
      * 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面

      * 配置参数

      * checkSessionKey 需检查的在 Session 中保存的关键字

      * redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath

      * notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath

      */  
      public class CheckLoginFilter   
      implements Filter   
      {   
           protected FilterConfig filterConfig = null;   
           private String redirectURL = null;   
           private List notCheckURLList = new ArrayList();   
           private String sessionKey = null;   
        
      public void doFilter(ServletRequest servletRequest, ServletResponse
      servletResponse, FilterChain filterChain) throws IOException,
      ServletException   
      {   
          HttpServletRequest request = (HttpServletRequest) servletRequest;   
          HttpServletResponse response = (HttpServletResponse) servletResponse; 
       
        
           HttpSession session = request.getSession();   
         if(sessionKey == null)   
          {   
           filterChain.doFilter(request, response);   
          return;   
          }   
         if((!checkRequestURIIntNotFilterList(request)) &&
      session.getAttribute(sessionKey) == null)   
          {   
           response.sendRedirect(request.getContextPath() + redirectURL);   
          return;   
          }   
          filterChain.doFilter(servletRequest, servletResponse);   
      }   
        
      public void destroy()   
      {   
          notCheckURLList.clear();   
      }   
        
      private boolean checkRequestURIIntNotFilterList(HttpServletRequest
      request)   
      {   
          String uri = request.getServletPath() + (request.getPathInfo() == null
      ? "" : request.getPathInfo());   
         return notCheckURLList.contains(uri);   
      }   
        
      public void init(FilterConfig filterConfig) throws ServletException   
      {   
         this.filterConfig = filterConfig;   
          redirectURL = filterConfig.getInitParameter("redirectURL");   
          sessionKey = filterConfig.getInitParameter("checkSessionKey");   
        
          String notCheckURLListStr =
      filterConfig.getInitParameter("notCheckURLList");   
        
         if(notCheckURLListStr != null)   
          {   
           StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");   

           notCheckURLList.clear();   
          while(st.hasMoreTokens())   
           {   
            notCheckURLList.add(st.nextToken());   
           }   
          }   
      }   
      }   
        
      三、字符编码的过滤器   
        
      import javax.servlet.*;   
      import java.io.IOException;   
        
      /**
      * 用于设置 HTTP 请求字符编码的过滤器，通过过滤器参数encoding指明使用何种字符编码,用于处理Html Form请求参数的中文问题
      */  
      public class CharacterEncodingFilter   
      implements Filter   
      {   
      protected FilterConfig filterConfig = null;   
      protected String encoding = "";   
        
      public void doFilter(ServletRequest servletRequest, ServletResponse
      servletResponse, FilterChain filterChain) throws IOException,
      ServletException   
      {   
               if(encoding != null)   
                 servletRequest.setCharacterEncoding(encoding);   
                filterChain.doFilter(servletRequest, servletResponse);   
      }   
        
      public void destroy()   
      {   
          filterConfig = null;   
          encoding = null;   
      }   
        
           public void init(FilterConfig filterConfig) throws ServletException  
      
      {   
                this.filterConfig = filterConfig;   
               this.encoding = filterConfig.getInitParameter("encoding");   
        
      }   
      }   
        
      四、资源保护过滤器   
        
        
      package catalog.view.util;   
        
      import javax.servlet.Filter;   
      import javax.servlet.FilterConfig;   
      import javax.servlet.ServletRequest;   
      import javax.servlet.ServletResponse;   
      import javax.servlet.FilterChain;   
      import javax.servlet.ServletException;   
      import javax.servlet.http.HttpServletRequest;   
      import java.io.IOException;   
      import java.util.Iterator;   
      import java.util.Set;   
      import java.util.HashSet;   
      //   
      import org.apache.commons.logging.Log;   
      import org.apache.commons.logging.LogFactory;   
        
      /**
      * This Filter class handle the security of the application.
      *
      * It should be configured inside the web.xml.
      *
      * @author Derek Y. Shen
      */  
      public class SecurityFilter implements Filter {   
      //the login page uri   
      private static final String LOGIN_PAGE_URI = "login.jsf";   
        
      //the logger object   
      private Log logger = LogFactory.getLog(this.getClass());   
        
      //a set of restricted resources   
      private Set restrictedResources;   
        
      /**
         * Initializes the Filter.
         */  
      public void init(FilterConfig filterConfig) throws ServletException {   
        this.restrictedResources = new HashSet();   
        this.restrictedResources.add("/createProduct.jsf");   
        this.restrictedResources.add("/editProduct.jsf");   
        this.restrictedResources.add("/productList.jsf");   
      }   
        
      /**
         * Standard doFilter object.
         */  
      public void doFilter(ServletRequest req, ServletResponse res, FilterChain
      chain)   
         throws IOException, ServletException {   
        this.logger.debug("doFilter");   
           
         String contextPath = ((HttpServletRequest)req).getContextPath();   
         String requestUri = ((HttpServletRequest)req).getRequestURI();   
           
        this.logger.debug("contextPath = " + contextPath);   
        this.logger.debug("requestUri = " + requestUri);   
           
        if (this.contains(requestUri, contextPath) &&
      !this.authorize((HttpServletRequest)req)) {   
         this.logger.debug("authorization failed");   
         
      ((HttpServletRequest)req).getRequestDispatcher(LOGIN_PAGE_URI).forward(req,
      res);   
         }   
        else {   
         this.logger.debug("authorization succeeded");   
          chain.doFilter(req, res);   
         }   
      }   
        
      public void destroy() {}   
        
      private boolean contains(String value, String contextPath) {   
         Iterator ite = this.restrictedResources.iterator();   
           
        while (ite.hasNext()) {   
          String restrictedResource = (String)ite.next();   
            
         if ((contextPath + restrictedResource).equalsIgnoreCase(value)) {   
          return true;   
          }   
         }   
           
        return false;   
      }   
        
      private boolean authorize(HttpServletRequest req) {   
        
                    //处理用户登录   
             /* UserBean user =
      (UserBean)req.getSession().getAttribute(BeanNames.USER_BEAN);
        
         if (user != null && user.getLoggedIn()) {
          //user logged in
          return true;
         }
         else {
          return false;
         }*/  
      }   
      }  
      五 利用Filter限制用户浏览权限

      在一个系统中通常有多个权限的用户。不同权限用户的可以浏览不同的页面。使用Filter进行判断不仅省下了代码量，而且如果要更改的话只需要在Filter文件里动下就可以。

      以下是Filter文件代码：

      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;   
        
      public class RightFilter implements Filter {   
        
          public void destroy() {   
                 
           }   
        
          public void doFilter(ServletRequest sreq, ServletResponse sres,
      FilterChain arg2) throws IOException, ServletException {   
              // 获取uri地址   
               HttpServletRequest request=(HttpServletRequest)sreq;   
               String uri = request.getRequestURI();   
               String ctx=request.getContextPath();   
               uri = uri.substring(ctx.length());   
              //判断admin级别网页的浏览权限   
              if(uri.startsWith("/admin")) {   
                  if(request.getSession().getAttribute("admin")==null) {   
                       request.setAttribute("message","您没有这个权限");   
                      
      request.getRequestDispatcher("/login.jsp").forward(sreq,sres);   
                      return;   
                   }   
               }   
              //判断manage级别网页的浏览权限   
              if(uri.startsWith("/manage")) {   
                  //这里省去   
                   }   
               }   
              //下面还可以添加其他的用户权限，省去。   
        
           }   
        
          public void init(FilterConfig arg0) throws ServletException {   
                 
           }   
        
      }

      <!-- 判断页面的访问权限 -->  
        <filter>  
           <filter-name>RightFilter</filter-name>  
            <filter-class>cn.itkui.filter.RightFilter</filter-class>  
        </filter>  
        <filter-mapping>  
            <filter-name>RightFilter</filter-name>  
            <url-pattern>/admin/*</url-pattern>  
        </filter-mapping>  
        <filter-mapping>  
            <filter-name>RightFilter</filter-name>  
            <url-pattern>/manage/*</url-pattern>  
        </filter-mapping>  

      在web.xml中加入Filter的配置，如下：
      <filter>  

              <filter-name>EncodingAndCacheflush</filter-name>  
              <filter-class>EncodingAndCacheflush</filter-class>  
              <init-param>  
                  <param-name>encoding</param-name>  
                  <param-value>UTF-8</param-value>  
              </init-param>  
          </filter>  
          <filter-mapping>  
              <filter-name>EncodingAndCacheflush</filter-name>  
              <url-pattern>/*</url-pattern>  
          </filter-mapping>  
      要传递参数的时候最好使用form进行传参，如果使用链接的话当中文字符的时候过滤器转码是不会起作用的，还有就是页面上

      form的method也要设置为post，不然过滤器也起不了作用。