Javaweb应用使用限流处理大量的并发请求详解

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);
	}
}