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玩转java并发工具_玩Java并发

發布時間：2023/12/3 java 47 豆豆

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玩轉java并發工具

最近，我需要將一些文件（每個文件都有JSON格式的對象列表（數組））轉換為每個文件都具有相同數據（對象）的分隔行的文件。這是一次性的任務，很簡單。我使用Java nio的某些功能進行了讀寫。我以最簡單的方式使用了GSON。一個線程在文件上運行，轉換和寫入。整個操作在幾秒鐘內完成。但是，我想并發一點。因此，我增強了可同時工作的工具。

線程數

可運行以讀取文件。

閱讀器線程將提交到ExecutorService。輸出是對象列表（示例中為User），將被放入BlockingQueue。

可運行以寫入文件。

每個可運行對象將從阻塞隊列中輪詢。它將數據行寫入文件。我沒有將編寫器Runnable添加到ExecutorService，而是僅使用它啟動了一個線程。 Runnable具有while(some boolen is true) {...}模式。下面的更多內容...

同步一切

BlockingQueue是這兩種線程的接口。由于writer的runnable在while循環（消費者）中運行，我希望能夠使其停止，以便該工具終止。因此，我為此使用了兩個對象：

信號

讀取輸入文件的循環會增加一個計數器。完成遍歷輸入文件并提交編寫器后，我在主線程中初始化了一個信號燈： semaphore.acquire(numberOfFiles);

在每個可運行的閱讀器中，我釋放了信號量： semaphore.release();

原子布爾

作者的while循環使用AtomicBoolean。只要AtomicBoolean == true，編寫器將繼續。在主線程中，在獲取信號量之后，我將AtomicBoolean設置為false。這使編寫器線程可以終止。

使用Java NIO

為了掃描，讀取和寫入文件系統，我使用了Java NIO的某些功能。

掃描： Files.newDirectoryStream(inputFilesDirectory, "*.json");
開始之前刪除輸出目錄： Files.walkFileTree...
BufferedReader和BufferedWriter： Files.newBufferedReader(filePath); Files.newBufferedWriter(fileOutputPath, Charset.defaultCharset());

一注。為了生成此示例的隨機文件，我使用了apache commons lang： RandomStringUtils.randomAlphabetic
GitHub中的所有代碼。

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;}} }

翻譯自: https://www.javacodegeeks.com/2014/12/playing-with-java-concurrency.html