玩Java并发

最近，我需要将一些文件（每个文件都有JSON格式的对象列表（数组））转换为每个文件都具有相同数据（对象）的分隔行的文件。这是一次性的任务，很简单。我使用Java nio的某些功能进行了读写。我以最简单的方式使用了GSON。一个线程在文件上运行，转换和写入。整个操作在几秒钟内完成。但是，我想并发一点。因此，我增强了可同时工作的工具。

线程数

可运行以读取文件。

阅读器线程将提交到ExecutorService。输出是对象列表（示例中为User），将被放入BlockingQueue。

可运行以写入文件。

每个可运行对象将从阻塞队列中轮询。它将数据行写入文件。我没有将编写器Runnable添加到ExecutorService，而是仅使用它启动了一个线程。 Runnable具有while(some boolen is true) {...}模式。有关以下内容的更多信息...

同步一切

BlockingQueue是这两种线程的接口。由于writer的runnable在while循环（消费者）中运行，我希望能够使其停止，以便该工具终止。因此，我为此使用了两个对象：

信号

读取输入文件的循环会增加一个计数器。完成遍历输入文件并提交编写器后，我在主线程中初始化了一个信号灯： semaphore.acquire(numberOfFiles);

在每个可运行的阅读器中，我释放了信号量： semaphore.release();

原子布尔

作者的while循环使用AtomicBoolean。只要AtomicBoolean == true，编写器将继续。在主线程中，在获取信号量之后，我将AtomicBoolean设置为false。这使编写器线程可以终止。

使用Java NIO

为了扫描，读取和写入文件系统，我使用了Java NIO的某些功能。

扫描： Files.newDirectoryStream(inputFilesDirectory, "*.json");
开始之前删除输出目录： Files.walkFileTree...
BufferedReader和BufferedWriter： Files.newBufferedReader(filePath); Files.newBufferedWriter(fileOutputPath, Charset.defaultCharset());

一注。为了生成此示例的随机文件，我使用了apache commons lang： RandomStringUtils.randomAlphabetic
GitHub中的所有代码。

public class JsonArrayToJsonLines {private final static Path inputFilesDirectory = Paths.get("src\\main\\resources\\files");private final static Path outputDirectory = Paths.get("src\\main\\resources\\files\\output");private final static Gson gson = new Gson();private final BlockingQueue<EntitiesData> entitiesQueue = new LinkedBlockingQueue<>();private AtomicBoolean stillWorking = new AtomicBoolean(true);private Semaphore semaphore = new Semaphore(0);int numberOfFiles = 0;private JsonArrayToJsonLines() {}public static void main(String[] args) throws IOException, InterruptedException {new JsonArrayToJsonLines().process();}private void process() throws IOException, InterruptedException {deleteFilesInOutputDir();final ExecutorService executorService = createExecutorService();DirectoryStream<Path> directoryStream = Files.newDirectoryStream(inputFilesDirectory, "*.json");for (int i = 0; i < 2; i++) {new Thread(new JsonElementsFileWriter(stillWorking, semaphore, entitiesQueue)).start();}directoryStream.forEach(new Consumer<Path>() {@Overridepublic void accept(Path filePath) {numberOfFiles++;executorService.submit(new OriginalFileReader(filePath, entitiesQueue));}});semaphore.acquire(numberOfFiles);stillWorking.set(false);shutDownExecutor(executorService);}private void deleteFilesInOutputDir() throws IOException {Files.walkFileTree(outputDirectory, new SimpleFileVisitor<Path>() {@Overridepublic FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {Files.delete(file);return FileVisitResult.CONTINUE;}});}private ExecutorService createExecutorService() {int numberOfCpus = Runtime.getRuntime().availableProcessors();return Executors.newFixedThreadPool(numberOfCpus);}private void shutDownExecutor(final ExecutorService executorService) {executorService.shutdown();try {if (!executorService.awaitTermination(120, TimeUnit.SECONDS)) {executorService.shutdownNow();}if (!executorService.awaitTermination(120, TimeUnit.SECONDS)) {}} catch (InterruptedException ex) {executorService.shutdownNow();Thread.currentThread().interrupt();}}private static final class OriginalFileReader implements Runnable {private final Path filePath;private final BlockingQueue<EntitiesData> entitiesQueue;private OriginalFileReader(Path filePath, BlockingQueue<EntitiesData> entitiesQueue) {this.filePath = filePath;this.entitiesQueue = entitiesQueue;}@Overridepublic void run() {Path fileName = filePath.getFileName();try {BufferedReader br = Files.newBufferedReader(filePath);User[] entities = gson.fromJson(br, User[].class);System.out.println("---> " + fileName);entitiesQueue.put(new EntitiesData(fileName.toString(), entities));} catch (IOException | InterruptedException e) {throw new RuntimeException(filePath.toString(), e);}}}private static final class JsonElementsFileWriter implements Runnable {private final BlockingQueue<EntitiesData> entitiesQueue;private final AtomicBoolean stillWorking;private final Semaphore semaphore;private JsonElementsFileWriter(AtomicBoolean stillWorking, Semaphore semaphore,BlockingQueue<EntitiesData> entitiesQueue) {this.stillWorking = stillWorking;this.semaphore = semaphore;this.entitiesQueue = entitiesQueue;}@Overridepublic void run() {while (stillWorking.get()) {try {EntitiesData data = entitiesQueue.poll(100, TimeUnit.MILLISECONDS);if (data != null) {try {String fileOutput = outputDirectory.toString() + File.separator + data.fileName;Path fileOutputPath = Paths.get(fileOutput);BufferedWriter writer = Files.newBufferedWriter(fileOutputPath, Charset.defaultCharset());for (User user : data.entities) {writer.append(gson.toJson(user));writer.newLine();}writer.flush();System.out.println("=======================================>>>>> " + data.fileName);} catch (IOException e) {throw new RuntimeException(data.fileName, e);} finally {semaphore.release();}}} catch (InterruptedException e1) {}}}}private static final class EntitiesData {private final String fileName;private final User[] entities;private EntitiesData(String fileName, User[] entities) {this.fileName = fileName;this.entities = entities;}}
}