防止网站恶意刷新

import java.io.IOException;   
import java.util.concurrent.ConcurrentHashMap;   
import java.util.concurrent.CopyOnWriteArrayList;   
  
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;   
import javax.servlet.http.HttpServletResponse;   
  
  
public class RefreshFilter implements Filter {   
       
    @Override  
    public void doFilter(ServletRequest request, ServletResponse response,   
            FilterChain chain) throws IOException, ServletException {   
           
        filter((HttpServletRequest) request,(HttpServletResponse) response, chain);   
    }   
       
    private void filter(HttpServletRequest request, HttpServletResponse response,   
            FilterChain chain) throws IOException, ServletException {   
           
        String requestURI = request.getRequestURI();   
        Cache cache = Cache.getInstance();   
        cache.increment(requestURI);   
        if(cache.isUpCount(requestURI)) {   
            response.getWriter().println("到达次数，不允许请求，请稍候再试");   
            return;   
        }   
        chain.doFilter(request, response);   
    }   
       
       
  
  
    @Override  
    public void destroy() {   
           
    }   
  
    @Override  
    public void init(FilterConfig config) throws ServletException {   
           
    }   
       
    //缓存   
    private static class Cache {   
           
        private static final ConcurrentHashMap<String, CopyOnWriteArrayList<Long>> map = new ConcurrentHashMap<String, CopyOnWriteArrayList<Long>>();   
        private static final long EXPIRE_TIME = 1000 * 20L;   
        private static final long CLEAR_TIME = 1000 * 2L;   
        private static final int MAX_REFRESH_COUNT = 20;   
           
        private static final Cache cache = new Cache();   
           
        private Cache() {   
            new Thread(new ClearCacheRunnable()).start();   
        }   
           
        public static Cache getInstance() {   
            return cache;   
        }   
           
           
        //增长指定URL的点击次数   
        public void increment(String key) {   
            CopyOnWriteArrayList<Long> list = map.get(key);   
            if(list == null) {   
                map.put(key, new CopyOnWriteArrayList<Long>());   
            }   
            map.get(key).add(new Long(System.currentTimeMillis()));   
        }   
           
        //是否到达指定数量   
        public boolean isUpCount(String key) {   
            CopyOnWriteArrayList<Long> list = map.get(key);   
            if(list == null) {   
                return false;   
            }   
            return list.size() > MAX_REFRESH_COUNT;   
        }   
           
        //清理过期数据线程   
        private static class ClearCacheRunnable implements Runnable {   
            @Override  
            public void run() {   
                while(true) {   
                    try {   
                        Thread.sleep(Cache.CLEAR_TIME);   
                        clear();   
                    } catch (InterruptedException e) {   
                        e.printStackTrace();   
                    }   
                }   
            }   
  
            private void clear() {   
                for(String key : map.keySet()) {   
                    CopyOnWriteArrayList<Long> list = map.get(key);   
                    for(Long date : list) {   
                        if(System.currentTimeMillis() - date > Cache.EXPIRE_TIME) {   
                            System.out.println(list.remove(date));   
                        }   
                    }   
                }   
            }   
        }   
    }   
       
       
}