高效并发缓存

package concurrent;

import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

/**
 * 高效并发缓存
 * @author user
 *
 */
public class MemoryCacheTest {

	private final ConcurrentHashMap<String, Future<String>> cache = new ConcurrentHashMap<String, Future<String>>();

	public void query(String dataId) throws InterruptedException, ExecutionException{
		while(true){
			Future<String> future = cache.get(dataId);
			if(future == null){
				System.err.println("not have querying ........");
				Callable<String> call = new Callable<String>() {
					@Override
					public String call() throws Exception {
						System.err.println("非常耗时的操作！！！！！begin");
						Thread.sleep(5000);
						System.err.println("非常耗时的操作！！！！！end");
						return "大大的數據！";
					}
				};
				FutureTask<String> futureTask = new FutureTask<String>(call);
				if(null == cache.putIfAbsent(dataId, futureTask)){
					future = futureTask;
					futureTask.run();
				}
			}
			Thread.sleep(1000);
			System.err.println(future.get());
		}
	}

	/**
	 * @param args
	 * @throws ExecutionException 
	 * @throws InterruptedException 
	 */
	public static void main(String[] args) throws InterruptedException, ExecutionException {
		MemoryCacheTest test = new MemoryCacheTest();
		test.query("1");
	}

}