详解Javaweb应用使用限流处理大量的并发请求

public class ServiceFilter implements Filter {		private static final int MAX_COUNT = 20;		private AtomicInteger filterCount = 0;	public void doFilter(ServletRequest request, ServletResponse response,			FilterChain chain) throws IOException, ServletException {		System.out.println("before"+filterCount);		if(filterCount > MAX_COUNT) {			//请求个数太多，跳转到排队页面			request.getRequestDispatcher("index.jsp").forward(request, response);		} else {			//请求个数加1			filterCount.incrementAndGet();			chain.doFilter(request, response);			//访问结束，请求个数减1			filterCount.decrementAndGet();		}	}

public class RateLimiterUtils {	private static Logger logger = LoggerFactory.getLogger(RateLimiterUtils.class);	private static final ConcurrentHashMap<String, RateLimiter> resourceLimitMap = 			new ConcurrentHashMap<String, RateLimiter>();		/**	 * 限流	 * @param resource 需要限流的对象的标识	 * @return true表示得到了许可，没有达到限流阀值，false表示得不到许可，达到了限流阀值。	 * @author: hejinen	 * @date:2016年10月19日 上午11:08:49	 */	public static boolean rateLimit(String resource) {		RateLimiter limit = getRateLimit(resource);		return limit.tryAcquire();	}    /**	 * 获取某个需限流对象的RateLimiter，如不存在则创建新的	 * @param resouce 需要限流的对象标识	 */	public static RateLimiter getRateLimit(String resource) {		RateLimiter limit = resourceLimitMap.get(resource);			if(limit == null) {			synchronized(RateLimiterUtils.class) {				limit = resourceLimitMap.get(resource);				double qps = getQpsByResource(resource);				if(limit == null) {					limit = RateLimiter.create(qps);					resourceLimitMap.put(resource, limit);					LoggerUtil.info(RateLimiterUtils.class, "create rate limiter for key:{0},QPS:{1}", resource,qps);				}			}		}		return resourceLimitMap.get(resource);	}}