Question

我有3个任务要做：

首先：下载htmlFile -------- \同时在同一个执行官中，它工作正常。
第二：解压缩html文件--------- /
第三：下载图片------＆gt;在另一个执行器中，我需要下载分为5个文件的图像，为此我使用的是FixedThreadPool（5），换句话说，5个paralel下载。

但是当我点击下载时，我的图像下载开始时没有等待htmlDownload完成，我怎么能对我的executorPool等待我的另一个执行者singleThread？

主类：

ExecutorService e = Executors.newSingleThreadExecutor();

            //Download HTML and Unzip Threads
            typeDownloaded = "html";
            DownloadUtil.downloadHtml(e, this, dns, port, uuid, filePathHtmlDownload, cookies, typeDownloaded);
            UnzipUtil.unZipHtml(e, this, filePathHtmlDownload, outputFolder, typeDownloaded);
            typeDownloaded = "images";
            DownloadUtil.downloadImages(e, this, dns, port, numImg, uuid, cookies, typeDownloaded);

我的DownloadUtil类：

public class DownloadUtil {

    private static Logger log = Logger.getLogger(LoginLocalServiceImpl.class.getName());

    public static void downloadHtml(Executor e, MainViewController controller, String dns, int port,
            String offlineUUID, String filePath, Map<String, String> cookies, String type) throws IOException {

        String urlHtml = "http://" + dns + ":" + port + Constants.TARGET_SERVICE_DOWNLOADFILES + offlineUUID;

        System.out.println(urlHtml);

        e.execute(new DownloaderTask(controller, urlHtml, filePath, cookies, type));

    }

    public static void downloadImages(Executor e, MainViewController controller, String dns, int port, int numImg,
            String uuid, Map<String, String> cookies, String type) throws SystemException, IOException {

        String filePath;
        String urlImages;

        if (numImg == 1) {
            filePath = System.getProperty("user.home") + File.separator + "Documents" + File.separator + "TargetApp" + File.separator + "TempImageDownload.zip";
            urlImages = "http://" + dns + ":" + port + Constants.TARGET_SERVICE_DOWNLOADIMAGES + uuid;
            e.execute(new DownloaderTask(controller, urlImages, filePath, cookies, type));

        } else {

            ExecutorService exec = Executors.newFixedThreadPool(numImg);

            for (int i = 0; i < numImg; i++) {
                filePath = System.getProperty("user.home") + File.separator + "Documents" + File.separator + "TargetApp" + File.separator + "TempImage" + i + "Download.zip";
                urlImages = "http://" + dns + ":" + port + Constants.TARGET_SERVICE_DOWNLOADIMAGES + uuid + "/?pos=" + (i);
                exec.execute(new DownloaderTask(controller, urlImages, filePath, cookies, type));

            }

        }


    }
}

Answer 1

您可以延迟提交图像下载任务，直到html下载完成，如下所示：

    final ExecutorService htmlDownloadExecutor = Executors.newSingleThreadExecutor();
    final ExecutorService imageDownloadExecutor = Executors.newFixedThreadPool(5);
    ...
    //Download HTML and Unzip Threads
    typeDownloaded = "html";
    final DownloaderTask htmlTask = DownloadUtil.downloadHtml(mainViewController, dns, port, uuid, filePathHtmlDownload, cookies, typeDownloaded);
    typeDownloaded = "images";
    final List<DownloaderTask> imageTasks = DownloadUtil.downloadImages(mainViewController, dns, port, numImg, uuid, cookies, typeDownloaded);

    // submit the html download escape
    htmlDownloadExecutor.execute(new Runnable() {
        @Override
        public void run() {
            // first run the html task
            htmlTask.run();
            // now submit the image tasks to run
            for (DownloaderTask imageTask : imageTasks) {
                imageDownloadExecutor.execute(imageTask);
            }

        }
    });

帮助函数已更改为返回任务实例，然后在适当的情况下将任务实例提交给相应的执行程序服务实例。 html下载任务立即提交下载html，一旦下载完成，下载图像的任务就会被提交。此解决方案中没有涉及线程阻塞操作（CountDownLatch.await（）），因此它应该具有更高的可伸缩性/高性能。

Answer 2

Google的Guava有ListenableFuture，它将在完成任务后执行其他任务。另一种方法是使用CountDownLatch让图像下载线程等待，但这会在等待时占用这些线程。

我怎样才能做一个执行程序FixedThreadPool等待另一个执行程序SingleThreadExecutor？

2 个答案: