Java中异步处理机制的应用场景有哪些

package org.wit.ff.ch3;import java.io.BufferedWriter;import java.io.File;import java.io.FileWriter;import java.io.IOException;import java.util.Scanner;import java.util.concurrent.BlockingQueue;import java.util.concurrent.CountDownLatch;import java.util.concurrent.LinkedBlockingQueue;import java.util.concurrent.TimeUnit;public class AsyncHandler {  private CountDownLatch latch;  private volatile boolean handleFinish;  private volatile boolean sendFinish;  private BlockingQueue<String> queue; private BufferedWriter bw; public AsyncHandler(CountDownLatch latch) {  this.latch = latch;    queue = new LinkedBlockingQueue<String>();  File file = new File("E:/hello.txt");  try {   bw = new BufferedWriter(new FileWriter(file));  } catch (IOException e) {   throw new RuntimeException(e);  } } public void handle() {  // 模拟性能瓶颈的执行过程,3s处理一条消息.  new Thread() {   public void run() {    while (!handleFinish) {     try {      TimeUnit.SECONDS.sleep(3);     } catch (InterruptedException e1) {      // 不做处理.     }     String s = queue.peek();     if (s != null) {      queue.poll();      try {       bw.write(s);       bw.newLine();      } catch (IOException e) {      }     }     // 若队列为空并且消息发送完成.     if (queue.isEmpty() && sendFinish) {      // 计数器1->0      latch.countDown();      // 让处理过程结束.      handleFinish = true;      break;     }    }   }  }.start(); }  public void sendFinish() {  sendFinish = true; }  public void release() {  System.out.println("release!");  if (bw != null) {   try {    bw.close();   } catch (IOException e) {    // TODO 打印日志.   }  }  //其实使用queue = null就够了.  if (queue != null) {   queue.clear();   queue = null;  } }  public void sendMsg(String text) {  if (text != null && !text.isEmpty()) {   queue.add(text);  } } public static void main(String[] args) {  CountDownLatch latch = new CountDownLatch(1);  AsyncHandler handler = new AsyncHandler(latch);  handler.handle();  // 做一次检查.  Scanner scanner = new Scanner(System.in);  while (true) {   String text = scanner.next();   // 若用户选择退出.   if ("exit".equals(text)) {    // 表示消息已经发送完成.    handler.sendFinish();    break;   }   handler.sendMsg(text);  }  try {   // 阻塞主线程等待消息写入到本地文件完成.   latch.await();  } catch (InterruptedException e) {   e.printStackTrace();  }  // 释放资源 文件流,队列.  handler.release();  // 关闭控制台输入.  scanner.close(); }}