java Nio 异步操作(三)

    xiaoxiao2025-09-25  89

    异步channel API

    主要引入三个异步类: AsynchronousFileChannel,AsynchronousSocketChannel, and AsynchronousServerSocketChannel.

    AsynchronousFileChannel跟FileChannel区别:不保存全局的position和offset,可以制定访问位置,也支持并发访问文件不同。 AsynchronousServerSocketChannel AsynchronousSocketChannel:能够绑定到一个制定线程池的组中,这个线程池能够用future或者CompletionHandler来对执行结果进行处理, AsynchronousChannelGroup:执行异步IO的java线程池的组类, AsynchronousChannelGroup.java: public static AsynchronousChannelGroup withFixedThreadPool(int nThreads, ThreadFactory threadFactory) public static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor,int initialSize) public static AsynchronousChannelGroup withThreadPool(ExecutorService executor)​​​ 我们看使用示例 [java] view plain copy package com.mime;    import java.io.IOException;  import java.net.InetSocketAddress;  import java.net.StandardSocketOptions;  import java.nio.ByteBuffer;  import java.nio.channels.AsynchronousChannelGroup;  import java.nio.channels.AsynchronousFileChannel;  import java.nio.channels.AsynchronousServerSocketChannel;  import java.nio.channels.AsynchronousSocketChannel;  import java.nio.channels.CompletionHandler;  import java.nio.channels.FileLock;  import java.nio.charset.Charset;  import java.nio.file.Path;  import java.nio.file.Paths;  import java.nio.file.StandardOpenOption;  import java.util.ArrayList;  import java.util.List;  import java.util.Set;  import java.util.TreeSet;  import java.util.concurrent.Callable;  import java.util.concurrent.ExecutionException;  import java.util.concurrent.ExecutorService;  import java.util.concurrent.Executors;  import java.util.concurrent.Future;  import java.util.concurrent.ThreadLocalRandom;    public class NIO2AsynchronousFileChannel {      public static void main(String[] args) {                    asyFile();          asyFileChannel2();          asyServerSocketChannel();      }        // 异步文件读写示例      public static void asyFile() {          ByteBuffer buffer = ByteBuffer.allocate(100);          String encoding = System.getProperty("file.encoding");          Path path = Paths.get("/tmp""store.txt");          try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel                  .open(path, StandardOpenOption.READ)) {              Future<Integer> result = asynchronousFileChannel.read(buffer, 0);              // 读超时控制              // int count = result.get(100, TimeUnit.NANOSECONDS);                while (!result.isDone()) {                  System.out.println("Do something else while reading ...");              }              System.out.println("Read done: " + result.isDone());              System.out.println("Bytes read: " + result.get());                // 使用CompletionHandler回调接口异步读取文件              final Thread current = Thread.currentThread();              asynchronousFileChannel.read(buffer, 0,                      "Read operation status ...",                      new CompletionHandler<Integer, Object>() {                          @Override                          public void completed(Integer result, Object attachment) {                              System.out.println(attachment);                              System.out.print("Read bytes: " + result);                              current.interrupt();                          }                            @Override                          public void failed(Throwable exc, Object attachment) {                              System.out.println(attachment);                              System.out.println("Error:" + exc);                              current.interrupt();                          }                      });            } catch (Exception ex) {              System.err.println(ex);          }          buffer.flip();          System.out.print(Charset.forName(encoding).decode(buffer));          buffer.clear();            // 异步文件写示例          ByteBuffer buffer1 = ByteBuffer                  .wrap("The win keeps Nadal at the top of the heap in men's"                          .getBytes());          Path path1 = Paths.get("/tmp""store.txt");          try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel                  .open(path1, StandardOpenOption.WRITE)) {              Future<Integer> result = asynchronousFileChannel                      .write(buffer1, 100);              while (!result.isDone()) {                  System.out.println("Do something else while writing ...");              }              System.out.println("Written done: " + result.isDone());              System.out.println("Bytes written: " + result.get());                // file lock              Future<FileLock> featureLock = asynchronousFileChannel.lock();              System.out.println("Waiting for the file to be locked ...");              FileLock lock = featureLock.get();              if (lock.isValid()) {                  Future<Integer> featureWrite = asynchronousFileChannel.write(                          buffer, 0);                  System.out.println("Waiting for the bytes to be written ...");                  int written = featureWrite.get();                  // or, use shortcut                  // int written = asynchronousFileChannel.write(buffer,0).get();                  System.out.println("I’ve written " + written + " bytes into "                          + path.getFileName() + " locked file!");                  lock.release();              }                // asynchronousFileChannel.lock("Lock operation status:", new              // CompletionHandler<FileLock, Object>() ;            } catch (Exception ex) {              System.err.println(ex);          }      }        // public static AsynchronousFileChannel open(Path file, Set<? extends      // OpenOption> options,ExecutorService executor, FileAttribute<?>... attrs)      // throws IOException      private static Set withOptions() {          final Set options = new TreeSet<>();          options.add(StandardOpenOption.READ);          return options;      }        // 使用AsynchronousFileChannel.open(path, withOptions(),      // taskExecutor))这个API对异步文件IO的处理      public static void asyFileChannel2() {          final int THREADS = 5;          ExecutorService taskExecutor = Executors.newFixedThreadPool(THREADS);          String encoding = System.getProperty("file.encoding");          List<Future<ByteBuffer>> list = new ArrayList<>();          int sheeps = 0;          Path path = Paths.get("/tmp",                  "store.txt");          try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel                  .open(path, withOptions(), taskExecutor)) {              for (int i = 0; i < 50; i++) {                  Callable<ByteBuffer> worker = new Callable<ByteBuffer>() {                      @Override                      public ByteBuffer call() throws Exception {                          ByteBuffer buffer = ByteBuffer                                  .allocateDirect(ThreadLocalRandom.current()                                          .nextInt(100200));                          asynchronousFileChannel.read(buffer, ThreadLocalRandom                                  .current().nextInt(0100));                          return buffer;                      }                  };                  Future<ByteBuffer> future = taskExecutor.submit(worker);                  list.add(future);              }              // this will make the executor accept no new threads              // and finish all existing threads in the queue              taskExecutor.shutdown();              // wait until all threads are finished              while (!taskExecutor.isTerminated()) {                  // do something else while the buffers are prepared                  System.out                          .println("Counting sheep while filling up some buffers!So far I counted: "                                  + (sheeps += 1));              }              System.out.println("\nDone! Here are the buffers:\n");              for (Future<ByteBuffer> future : list) {                  ByteBuffer buffer = future.get();                  System.out.println("\n\n" + buffer);                  System.out                          .println("______________________________________________________");                  buffer.flip();                  System.out.print(Charset.forName(encoding).decode(buffer));                  buffer.clear();              }          } catch (Exception ex) {              System.err.println(ex);          }      }        //异步server socket channel io处理示例      public static void asyServerSocketChannel() {                    //使用threadGroup  //      AsynchronousChannelGroup threadGroup = null;  //      ExecutorService executorService = Executors  //      .newCachedThreadPool(Executors.defaultThreadFactory());  //      try {  //      threadGroup = AsynchronousChannelGroup.withCachedThreadPool(executorService, 1);  //      } catch (IOException ex) {  //      System.err.println(ex);  //      }  //      AsynchronousServerSocketChannel asynchronousServerSocketChannel =  //              AsynchronousServerSocketChannel.open(threadGroup);                    final int DEFAULT_PORT = 5555;          final String IP = "127.0.0.1";          ExecutorService taskExecutor = Executors.newCachedThreadPool(Executors                  .defaultThreadFactory());          // create asynchronous server socket channel bound to the default group          try (AsynchronousServerSocketChannel asynchronousServerSocketChannel = AsynchronousServerSocketChannel                  .open()) {              if (asynchronousServerSocketChannel.isOpen()) {                  // set some options                  asynchronousServerSocketChannel.setOption(                          StandardSocketOptions.SO_RCVBUF, 4 * 1024);                  asynchronousServerSocketChannel.setOption(                          StandardSocketOptions.SO_REUSEADDR, true);                  // bind the server socket channel to local address                  asynchronousServerSocketChannel.bind(new InetSocketAddress(IP,                          DEFAULT_PORT));                  // display a waiting message while ... waiting clients                  System.out.println("Waiting for connections ...");                  while (true) {                      Future<AsynchronousSocketChannel> asynchronousSocketChannelFuture = asynchronousServerSocketChannel.accept();                      //使用CompletionHandler来处理IO事件  //                  asynchronousServerSocketChannel.accept(null, new CompletionHandler<AsynchronousSocketChannel, Void>()                       //client使用CompletionHandler来处理IO事件                      //asynchronousSocketChannel.connect(new InetSocketAddress(IP, DEFAULT_PORT), null,new CompletionHandler<Void, Void>()                       try {                          final AsynchronousSocketChannel asynchronousSocketChannel = asynchronousSocketChannelFuture                                  .get();                          Callable<String> worker = new Callable<String>() {                              @Override                              public String call() throws Exception {                                  String host = asynchronousSocketChannel                                          .getRemoteAddress().toString();                                  System.out.println("Incoming connection from: "                                          + host);                                  final ByteBuffer buffer = ByteBuffer                                          .allocateDirect(1024);                                  // transmitting data                                  while (asynchronousSocketChannel.read(buffer)                                          .get() != -1) {                                      buffer.flip();                                  }                                  asynchronousSocketChannel.write(buffer).get();                                  if (buffer.hasRemaining()) {                                      buffer.compact();                                  } else {                                      buffer.clear();                                  }                                  asynchronousSocketChannel.close();                                  System.out.println(host                                          + " was successfully served!");                                  return host;                              }                          };                          taskExecutor.submit(worker);                      } catch (InterruptedException | ExecutionException ex) {                          System.err.println(ex);                          System.err.println("\n Server is shutting down ...");                          // this will make the executor accept no new threads                          // and finish all existing threads in the queue                          taskExecutor.shutdown();                          // wait until all threads are finished                          while (!taskExecutor.isTerminated()) {                          }                          break;                      }                  }              } else {                  System.out                          .println("The asynchronous server-socket channel cannot be opened!");              }          } catch (IOException ex) {              System.err.println(ex);          }        }  }   输出: [html] view plain copy 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