我這裡需要通過多執行緒去處理資料，然後在所有資料都處理完成後再往下執行。這裡就用到了CountDownLatch。把countdownlatch作為引數傳入到每個執行緒類裡，線上程中處理完資料後執行countdown方法。在所有countdownlatch歸零後，其await方法結束阻塞狀態而往下執行。

具體程式碼如下：

將多執行緒任務提交執行緒池

   @Bean(name = "ggnews_executor")
	public Executor postExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(1);
		executor.setMaxPoolSize(1);
		executor.setQueueCapacity(1);
		executor.setKeepAliveSeconds(120);
		executor.setThreadNamePrefix("executor-");
		executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
		return executor;
	}
	//通過定時任務呼叫的fetch方法，為了避免定時任務在多次執行中失效，通非同步指定執行緒池的方式進行呼叫
	@Async("ggnews_executor")
	public void fetch() {
		if(fetchFlag.getAndSet(false)) {
			List<FetchTag> tags = fetchTagService.selectFetchTagList(fetchTag);
			CountDownLatch downLatch = new CountDownLatch(tags.size());
			for (FetchTag tag : tags) {
				FetchTag tagNew;
				try {
					tagNew =(FetchTag) tag.clone();
				} catch (Throwable e) {
					log.error("",e);
					continue;
				}
        //作為引數將CountDownLatch傳入
				InnerRunner innerRunner = new InnerRunner(downLatch,tagNew);
				executor.execute(innerRunner);
			}
			try {
        //等待執行緒執行完畢,如果十分鐘後還沒結束也會停止阻塞狀態
				downLatch.await(10,TimeUnit.MINUTES);
				fetchFlag.getAndSet(true);
			} catch (Throwable e) {
				log.error("fetch()方法發生錯誤:{}",e);
				fetchFlag.getAndSet(true);
				//e.printStackTrace();
			} finally {
				fetchFlag.getAndSet(true);
			}
		} else {
			log.info("=======上次抓取尚未結束=========");
		}
	}

InnerRunner為要執行具體任務的執行緒類

private class InnerRunner implements Runnable {
		private CountDownLatch downLatch;
		private FetchTag tag;
		private InnerRunner(CountDownLatch downLatch,FetchTag tag) {
			this.downLatch = downLatch;
			this.tag = tag;
		}
		@Override
		public void run() {
      //將countDown方法移入到具體方法中的finally塊中，以保證即使在丟擲異常的情況下也算執行了此次任務，countdown會被執行
			fetchGG(tag.getTag(),downLatch);
			//downLatch.countDown();
			this.tag = null;
		}
	}

private static final String GOOGLE_URL_IN = "https://news.google.com/rss/search?hl=hi&gl=IN&ceid=IN:hi&q=";
public void fetchGG(String tag,CountDownLatch downLatch) {
		try {
			Document document = Jsoup.parse(new URL(GOOGLE_URL_IN + URLEncoder.encode("\"" + tag + "\"","utf-8")),30000);
			Elements elements = document.getElementsByTag("item");
			int rank = 1;
			for (Element element : elements) {
				
				String sourceTitle = element.getElementsByTag("title").get(0).text();
				log.info("source title:" + sourceTitle);
			}
		} catch (Throwable e) {
			log.info("fetch google url error",e);
		} finally {
      //肯定會被執行
			downLatch.countDown();
		}
	}

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支援我們。