Java countDownLatch如何实现多线程任务阻塞等待

我这里需要通过多线程去处理数据，然后在所有数据都处理完成后再往下执行。这里就用到了CountDownLatch。把countdownlatch作为参数传入到每个线程类里，在线程中处理完数据后执行countdown方法。在所有countdownlatch归零后，其await方法结束阻塞状态而往下执行。

具体代码如下：

将多线程任务提交线程池

@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;}//通过定时任务调用的fetch方法，为了避免定时任务在多次执行中失效，通异步指定线程池的方式进行调用@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;}//作为参数将CountDownLatch传入InnerRunner innerRunner = new InnerRunner(downLatch, tagNew);executor.execute(innerRunner);}try {//等待线程执行完毕,如果十分钟后还没结束也会停止阻塞状态downLatch.await(10,TimeUnit.MINUTES);fetchFlag.getAndSet(true);} catch (Throwable e) {log.error('fetch()方法发生错误:{}', e);fetchFlag.getAndSet(true);//e.printStackTrace();} finally {fetchFlag.getAndSet(true);}} else {log.info('=======上次抓取尚未结束=========');}}

InnerRunner为要执行具体任务的线程类

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() { //将countDown方法移入到具体方法中的finally块中，以保证即使在抛出异常的情况下也算执行了此次任务，countdown会被执行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 { //肯定会被执行downLatch.countDown();}}

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