多線程處理中Future的妙用

java 中Future是一個將來對象，裏面保存這線程處理結果，它像一個提貨憑證，拿着它你能夠隨時去提取結果。在兩種狀況下，離開Future幾乎很難辦。一種狀況是拆分訂單，好比你的應用收到一個批量訂單，此時若是要求最快的處理訂單，那麼須要併發處理，併發的結果若是收集，這個問題若是本身去編程將很是繁瑣，此時能夠使用CompletionService解決這個問題。CompletionService將Future收集到一個隊列裏，能夠按結果處理完成的前後順序進隊。另一種狀況是，若是你須要併發去查詢一些東西（好比爬蟲），併發查詢只要有一個結果返回，你就認爲查詢到了，而且結束查詢，這時也須要用CompletionService和Future來解決。直接上代碼更直觀：

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表示批量任務
		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會按處理完後順序返回結果
		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");
	}
}