方法1：

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
  
public class Main {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch doneSignal = new CountDownLatch(100);
        ExecutorService e = Executors.newFixedThreadPool(100);
        for (int i = 0; i < 100; i++) {
            e.execute(new A(doneSignal));
        }
        doneSignal.await();// wait for all to finish
        System.out.println("OK!");
        e.shutdown();
    }
}
  
class A implements Runnable {
    private CountDownLatch doneSignal;
  
    public A(CountDownLatch doneSignal) {
        this.doneSignal = doneSignal;
    }
  
    public void run() {
        System.out.println("test");
        try {
            Thread.sleep(1000L);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        doneSignal.countDown();
    }
}
 

方法2：

		ExecutorService exec = Executors.newCachedThreadPool();
		
		List<ImageUploadRunnable> tasks = new ArrayList<ImageUploadRunnable>();
		tasks.add(new ImageUploadRunnable(180, savefile,url));
		tasks.add(new ImageUploadRunnable(100, savefile,url));
		tasks.add(new ImageUploadRunnable(60, savefile,url));
		tasks.add(new ImageUploadRunnable(30, savefile,url));
		List<Future<String>> futureList = exec.invokeAll(tasks, 8l, TimeUnit.SECONDS);
		//
		
		for (int i = 0, size = futureList.size(); i < size; i++) {

			Future<String> fu = futureList.get(i);
			String s = fu.get(3l, TimeUnit.SECONDS);
			System.out.println(s);
		}
					
		exec.shutdown();
 

public class ImageUploadRunnable implements Callable<String> {
	
	private File file;
	private int num;
	private String url;
//	private CountDownLatch doneSignal;
	
	public ImageUploadRunnable(int num, File file, String url){
		this.num = num;
		this.file = file;
//		this.doneSignal = doneSignal;
		this.url = url;
	}

	
	public String call() throws Exception {

		String result = "aaaa";
		return result;
	}

}
 

主要用的是CountDownLatch 的特性

方法2：主要用的是exec.invokeAll