五个有用的过滤器 Filter

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。