分享几个常用过滤器

一、非常优秀的AJAX中文问题解决过滤器

public class AjaxEncodeFilter extends HttpServlet implements Filter {

        /**
     * AJAX使用中的字符过滤器，解决中文问题
     */
    private static final long serialVersionUID = 1L;

        public void doFilter(ServletRequest servletRequest,  
                          ServletResponse servletResponse, FilterChain filterChain)  
                          throws IOException, ServletException {  
                    /*  if (logger.isDebugEnabled()) {  
                        logger.debug("doFilter(ServletRequest, ServletResponse, FilterChain) - start"); //$NON-NLS-1$  
                     }  */
              
                     HttpServletRequest request = (HttpServletRequest) servletRequest;  
                     HttpServletResponse response = (HttpServletResponse) servletResponse;  
              
                  String requestedWith = request.getHeader("x-requested-with");  
                    String type = request.getContentType();  
                   if (requestedWith != null && "XMLHttpRequest".equals(requestedWith)  
                           && null != type  
                            && "application/x-www-form-urlencoded".equals(type)) {  
                         // logger.info("This's ajax post.set encode is UTF-8.");  
                        request.setCharacterEncoding("UTF-8");  
                           response.setCharacterEncoding("UTF-8");  
                          request.getParameterMap();  
                     }  
               
                     filterChain.doFilter(request, response);  
              
                 /*  if (logger.isDebugEnabled()) {  
                         logger.debug("doFilter(ServletRequest, ServletResponse, FilterChain) - end"); //$NON-NLS-1$  
                       }  */
                  }

        public void init(FilterConfig arg0) throws ServletException {
            // TODO Auto-generated method stub
            
        }  
}

二、普通字符编码过滤器

package com.test.util;

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"); 

} 
} 

三、检测是否登录过滤器

package com.test.util;

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<p> 
* 配置参数<p> 
* checkSessionKey 需检查的在 Session 中保存的关键字<br/> 
* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath<br/> 
* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath<br/> 
*/ 
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()); 
    } 
   } 
} 
} 

四、不缓存页面的过滤器

package com.test.util;

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.HttpServletResponse;



/** 
* 用于的使 Browser 不缓存页面的过滤器 
*/ 
public class MyFilter 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 {} 
} 

过滤器的使用需要先了解过滤器的执行过程
1、执行init（）方法初始化过滤器一些参数，FilterConfig获取配置文件

2、执行doFilter（）方法，filterChain.doFilter（）向下继续传递

3、销毁destroy（）

必须配置在web.xml中：

  <filter-name>encodingFilter</filter-name>
  <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
  <init-param>
  <param-name>encoding</param-name>
  <param-value>GBK</param-value>
  </init-param>
  <init-param>
  <param-name>forceEncoding</param-name>
  <param-value>true</param-value>
  </init-param>
  </filter>

<filter-mapping>
  <filter-name>encodingFilter</filter-name>
  <url-pattern>/*</url-pattern>
  </filter-mapping>

init-param即过滤器初始化中FilterConfig读取的值，可以有多过

filter-name 必须与 filter-mapping 的 filter-name保持一致，其它的不解释。