五个常用的过滤器

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");   
  
}   
}