我這里需要通過多線程去處理數據，然后在所有數據都處理完成后再往下執行。這里就用到了CountDownLatch。把countdownlatch作為參數傳入到每個線程類里，在線程中處理完數據后執行countdown方法。在所有countdownlatch歸零后，其await方法結束阻塞狀態而往下執行。

具體代碼如下：

將多線程任務提交線程池

@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;}//通過定時任務調用的fetch方法，為了避免定時任務在多次執行中失效，通異步指定線程池的方式進行調用@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;}//作為參數將CountDownLatch傳入InnerRunner innerRunner = new InnerRunner(downLatch, tagNew);executor.execute(innerRunner);}try {//等待線程執行完畢,如果十分鐘后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線程類

private class InnerRunner implements Runnable {private CountDownLatch downLatch;private FetchTag tag;private InnerRunner(CountDownLatch downLatch, FetchTag tag) {this.downLatch = downLatch;this.tag = tag;}@Overridepublic void run() { //將countDown方法移入到具體方法中的finally塊中，以保證即使在拋出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();}}

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