java - 使用ExecutorService和Java中的Callable编写文件不起作用

Question

我正在编写一个例程，该例程将从文件中检索URL列表，使用JSoup获取每个URL的内容，找到某些模式，然后将结果写入输出文件(每个分析的URL一个)。

我有一个WebPageAnalysisTask(实现Callable)，现在返回null，但是它将返回一个对象，其中包含处理结果(待完成):

public WebPageAnalyzerTask(String targetUrl, Pattern searchPattern) {
    this.targetUrl = targetUrl;
    this.searchPattern = searchPattern;
}

@Override
public WebPageAnalysisTaskResult call() throws Exception {
    long startTime = System.nanoTime();
    String htmlContent = this.getHtmlContentFromUrl();
    List<String> resultContent = this.getAnalysisResults(htmlContent);

    try (BufferedWriter bw = Files.newBufferedWriter(Paths.get("c:/output", UUID.randomUUID().toString() + ".txt"),
            StandardCharsets.UTF_8, StandardOpenOption.WRITE)) {
        bw.write(parseListToLine(resultContent));
    }

    long endTime = System.nanoTime();
    return null;
}

我正在使用NIO和try-with-resources编写文件。

将使用该任务的代码如下:

/**
 * Starts the analysis of the Web Pages retrieved from the input text file using the provided pattern.
 */
public void startAnalysis() {
    List<String> urlsToBeProcessed = null;

    try (Stream<String> stream = Files.lines(Paths.get(this.inputPath))) {

        urlsToBeProcessed = stream.collect(Collectors.toList());

        if (urlsToBeProcessed != null && urlsToBeProcessed.size() > 0) {
            List<Callable<WebPageAnalysisTaskResult>> pageAnalysisTasks = this
                    .buildPageAnalysisTasksList(urlsToBeProcessed);
            ExecutorService executor = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
            List<Future<WebPageAnalysisTaskResult>> results = executor.invokeAll(pageAnalysisTasks);
            executor.shutdown();
        } else {
            throw new NoContentToProcessException();
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

/**
 * Builds a list of tasks in which each task will be filled with data required for the analysis processing.
 * @param urlsToBeProcessed The list of URLs to be processed.
 * @return A list of tasks that must be handled by an executor service for asynchronous processing.
 */
private List<Callable<WebPageAnalysisTaskResult>> buildPageAnalysisTasksList(List<String> urlsToBeProcessed) {
    List<Callable<WebPageAnalysisTaskResult>> tasks = new ArrayList<>();
    UrlValidator urlValidator = new UrlValidator(ALLOWED_URL_SCHEMES);

    urlsToBeProcessed.forEach(urlAddress -> {
        if (urlValidator.isValid(urlAddress)) {
            tasks.add(new WebPageAnalyzerTask(urlAddress, this.targetPattern));
        }
    });

    return tasks;
}

包含URL列表的文件被读取一次。 ExecutorService为每个URL创建任务，并将异步分析和写入带有结果的文件。

到目前为止，正在读取文件，并且正在分析每个URL的HTML内容并将其保存在String中。但是，该任务未写入文件。所以我想知道那里会发生什么。

有人可以告诉我是否想念东西吗？

提前致谢。

Answer 1

以下try块中可能出现异常

try (BufferedWriter bw = Files.newBufferedWriter(Paths.get("c:/output", UUID.randomUUID().toString() + ".txt"),
        StandardCharsets.UTF_8, StandardOpenOption.WRITE)) {
  bw.write(parseListToLine(resultContent));
}

尝试向其添加 catch块，并在实际发生异常的情况下打印异常，以查看导致该异常的原因

catch (IOException e) {
  // Replace with logger or some kind of error handling in production code
  e.printStackTrace();
}