五种有用的过滤器

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。