Filter

属于转帖：http://www.iteye.com/topic/211147

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。