Javaマルチスレッドの使用を記録する

public List listThreads(List list, final int nThreads ) {
		final List fileList = new ArrayList<>();
		if (list == null || list.isEmpty()) {
			return null;
		}
//		long start = System.currentTimeMillis();
		int size = list.size();
		ExecutorService executorService = Executors.newFixedThreadPool(nThreads); //  


		List> futures = new ArrayList>(nThreads);
		for (int i = 0; i < nThreads; i++) {


			//  ， 
			final List subList;


			if (i == (nThreads - 1)) {
				subList = list.subList(size / nThreads * i, size);
			} else {
				subList = list.subList(size / nThreads * i, size / nThreads * (i + 1));
			}
			Callable task = new Callable() {
				
				public String call() throws Exception {
					int size = 0;
					for (String str : subList) {
						size++;
						//  
						Thread.sleep(200);


//						 System.out.println(size*nThreads+"/");
					}
					return String.valueOf(size);
				}
			};


			futures.add(executorService.submit(task));
		}
//		for (Future future : futures) {
//			 ret.append(future.get());  
//			 ret.length(future.get());
//		}
		executorService.shutdown();
		while (true) {
			if (executorService.isTerminated()) {
//				System.out.println(" ，   " + String.valueOf((System.currentTimeMillis() - start) / 1000) + "   ！");
//				FileNamesAndNumber.getFileNamesAndNumber(ApiTestManagerForThread.pathname);
				break;
			}
			try {
				Thread.sleep(200);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		System.out.println(" ");
		return fileList;


	}