在Java中使用ExecutorService和Callable编写文件不起作用
我正在编写一个例程,它将从文件中检索URL列表,使用JSoup获取每个URL的内容,查找某些模式并将结果写入输出文件(一个用于分析每个URL)。在Java中使用ExecutorService和Callable编写文件不起作用
我有一个WebPageAnalysisTask(实现可赎回)和现在它返回null,但它会返回保存处理结果的对象(做):
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;
}
我写该文件使用NIO并尝试使用资源。
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;
}
文件保存的URL列表被读取一次。 ExecutorService为每个URL创建任务,并将异步分析和写入结果文件。
现在正在读取文件,并且每个URL的HTML内容正在被分析并保存在一个字符串中。但是,该任务不是写入文件。所以我想知道那里会发生什么。
有人可以告诉我,如果我错过了什么吗?
在此先感谢。
也许你在下面try
块得到一个例外
try (BufferedWriter bw = Files.newBufferedWriter(Paths.get("c:/output", UUID.randomUUID().toString() + ".txt"),
StandardCharsets.UTF_8, StandardOpenOption.WRITE)) {
bw.write(parseListToLine(resultContent));
}
尝试将catch
块添加到它,并打印异常,如果事情确实发生,看看是什么原因呢
catch (IOException e) {
// Replace with logger or some kind of error handling in production code
e.printStackTrace();
}
我的耻辱!我完全忘记了catch块,之后我发现在尝试在不存在的目录中写入文件时发生IOException。谢谢! –
由于该任务将在类WebPageAnalyzerTask
中的方法call()
上运行错误,所以您应该检查List<Future<WebPageAnalysisTaskResult>> results = executor.invokeAll(pageAnalysisTasks);
的结果并确定任务运行时发生了什么错误。
for (Future<WebPageAnalysisTaskResult> future : results) {
try {
future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
您正在使用'java.io.BufferedWriter'写入文件,而不是NIO。 – EJP