Java异步处理机制实例详解

package org.wit.ff.ch2;
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;
/**
 * 
 * 
 * 简单异步处理示例.
 * 
 * 
 * @author F.Fang
 * @version $Id: AsyncHandler.java, v 0.1 2014年10月23日 下午11:37:54 F.Fang Exp $
 */
public class AsyncHandler {
 /**
  * 控制资源释放.
  */
 private CountDownLatch latch;
 /**
  * 处理完成标识.
  */
 private volatile boolean handleFinish;
 /**
  * 消息写入本地文件完成.
  */
 private volatile boolean sendFinish;
 /**
  * 阻塞队列.
  */
 private BlockingQueue queue;
 private BufferedWriter bw;
 public AsyncHandler(CountDownLatch latch) {
  this.latch = latch;
  /**
   * 使用链表实现.
   */
  queue = new LinkedBlockingQueue();
  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();
 }
 /**
  * 
  * 
  * 给出消息发送完成的标识.
  * 
  *
  */
 public void sendFinish() {
  sendFinish = true;
 }
 /**
  * 
  * 
  * 资源释放.
  * 
  *
  */
 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;
  }
 }
 /**
  * 
  * 
  * 往队列发送消息.
  * 
  *
  * @param text
  */
 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();
 }

}