多线程处理中Future的妙用

java 中Future是一个将来对象，里面保存这线程处理结果，它像一个提货凭证，拿着它你能够随时去提取结果。在两种状况下，离开Future几乎很难办。一种状况是拆分订单，好比你的应用收到一个批量订单，此时若是要求最快的处理订单，那么须要并发处理，并发的结果若是收集，这个问题若是本身去编程将很是繁琐，此时能够使用CompletionService解决这个问题。CompletionService将Future收集到一个队列里，能够按结果处理完成的前后顺序进队。另一种状况是，若是你须要并发去查询一些东西（好比爬虫），并发查询只要有一个结果返回，你就认为查询到了，而且结束查询，这时也须要用CompletionService和Future来解决。直接上代码更直观：

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class CompletionServiceTest {
	
	static int numThread =100;
	static ExecutorService executor = Executors.newFixedThreadPool(numThread);

	public static void main(String[] args) throws Exception{
		//data表示批量任务
		int[] data =new int[100];
		for(int i=1;i<100000;i++){
			int idx =i % 100;
			data[idx] =i;
			if(i%100==0){ 
				testCompletionService(data);
				data =new int[100];
			}
		}
	}
	
	private static void testCompletionService(int [] data) throws Exception{		
		CompletionService<Object> ecs = new ExecutorCompletionService<Object>(executor);
		for(int i=0;i<data.length;i++){
			final Integer t=data[i];
			ecs.submit(new Callable<Object>() {
				public Object call() {
					try {
						Thread.sleep(new Random().nextInt(1000));
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					return t;
				}
			});
		}
		//CompletionService会按处理完后顺序返回结果
		List<Object> res =new ArrayList<Object>();
		for(int i = 0;i<data.length;i++ ){
			Future<Object> f = ecs.take();
			res.add(f.get());
		}				
		System.out.println(Thread.currentThread().getName()+":"+res);
	}
	
	private static void testBasicFuture(int [] data) throws Exception{		
		List<Future<Object>> res =new ArrayList<Future<Object>>();
		for(int i=0;i<data.length;i++){
			final Integer t=data[i];
			Future<Object> future=executor.submit(new Callable<Object>() {
				public Object call() {
					return t;
				}
			});
			res.add(future);
		}		
		
		for(int i = 0;i<res.size();i++ ){
			Future<Object> f = res.get(i);
			Object rObject =f.get();
			System.out.print(":"+rObject);
		}				
		System.out.println("LN");
	}
}