自定义Handler机制

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Handler机制大致结构

notion image
对应关系
  1. 每个Thread对应一个Looper
  1. 每个Looper对应一个MessageQueue
  1. 每个MessageQueue对应N个Message
  1. 每个Message对应一个Handler

实现要求

目标:先在主线程执行一些操作,然后发起一个异步任务,再在主线程继续做其它操作,当异步任务完成后,再回调通知主线程做一些操作
要求:不使用任何Android系统的API
其实用Future也可以实现这点,但是,future的get操作是阻塞的,这意味着当你在主线程去获取异步任务的结果时,会阻塞主线程,这显然不是我们希望的!
好了,如果你有更好的实现方式,欢迎交流!这里我先上自己的测试类,让大家看看效果,然后再来分析具体的实现思路

测试代码

package senior.thread_concurrent.handler;


import base.util.LogUtil;

/**
 * 模拟子线程请求网络
 * <p>
 * Created by yutianran on 16/7/4.
 */
public class TestClient {

  private senior.thread_concurrent.handler.MyHandler mainHandler;

  public static void main(String[] args) {
      new TestClient().test();
  }

  private void test() {
      //初始化主线程Looper
      MyLooper.prepare();
      mainHandler = new senior.thread_concurrent.handler.MyHandler(new senior.thread_concurrent.handler.MyHandler.CallBack() {
          @Override
          public void handleMessage(senior.thread_concurrent.handler.MyMessage msg) {
              // 刷新界面
              String obj = (String) msg.obj;
              LogUtil.print("刷新界面:" + obj);
          }
      });
      //发起网络请求
      LogUtil.print("在主线程发起一个网络请求");
      NetThread netThread = new NetThread("http://baidu.com");
      netThread.start();
      LogUtil.print("在主线程继续其它操作");

      //开始消息循环
      MyLooper.loop();
  }


  //网络线程类
  private class NetThread extends Thread {
      private String url;

      public NetThread(String url) {
          this.url = url;
      }

      @Override
      public void run() {
          String body = getWebData(url);
          senior.thread_concurrent.handler.MyMessage msg = new senior.thread_concurrent.handler.MyMessage();
          msg.obj = body;
          mainHandler.sendMessage(msg);
      }
  }

  //执行网络请求
  private String getWebData(String url) {
      LogUtil.print("执行请求网络:" + url);
      try {
          Thread.sleep(3000);
      } catch (InterruptedException e) {
          e.printStackTrace();
      }
      String body = "这是" + url + "的响应值";
      LogUtil.print("请求网络成功:" + body);
      return body;
  }
}
输出日志
这里写图片描述-1.png

自定义消息处理器-Handler

思路分析
  1. 首先我们仿照Android的Handler,给我们的自定义Handler定义了:阻塞队列、处理消息的回调、分发和发送消息的方法
  1. 然后在创建Handler时,我们获取了当前线程的Looper和MessageQueue
  1. 最后,当我们发送消息的时候,将消息添加进之前得到的MessageQueue
package senior.thread_concurrent.handler;

/**
 * 消息处理器
 * <p>
 * Created by yutianran on 16/7/4.
 */
public class MyHandler {

  private MyMessageQueue queue;// 用于进行线程间通信的阻塞队列
  private CallBack callBack; // 处理消息的回调

  public MyHandler(CallBack callBack) {
      MyLooper looper = MyLooper.myLooper();
      if (looper == null) {
          throw new RuntimeException("在新开的线程中。创建MyHandler对象需要先调用MyLooper.prepare()方法。");
      }
      queue = looper.queue;
      this.callBack = callBack;
  }

  //消息接收的回调
  public interface CallBack {
      void handleMessage(MyMessage msg);
  }

  //发送消息
  public void sendMessage(MyMessage msg) {
      msg.target = this;
      queue.enqueueMessage(msg);
  }

  //派发消息
  public void dispatchMessage(MyMessage msg) {
      callBack.handleMessage(msg);
  }

}

自定义消息循环器-Looper

思路分析
  1. 在Looper中,我们用一个ThreadLocal存储当前Looper的相关数据
  1. 定义了一个消息队列,用来管理消息
  1. 在prepare()时,用ThreadLocal存储Looper的数据;在myLooper时,读取ThreadLocal存储的Looper数据
  1. 在loop()时,用一个死循环来不断的接受和分发消息
package senior.thread_concurrent.handler;

/**
 * 消息循环器
 * <p>
 * Created by yutianran on 16/7/4.
 */
public class MyLooper {

  private static ThreadLocal<MyLooper> threadLocal = new ThreadLocal<>();
  private static MyLooper myLooper;
  public MyMessageQueue queue;//一个线程对应一个阻塞队列

  private MyLooper() {
      queue = new MyMessageQueue();
  }

  //获取当前线程相对应的Looper对象
  public static MyLooper myLooper() {
      return threadLocal.get();//当未调用prepare()方法时。ThreadLocal.get()方法返回的为null;
  }

  //为本线程准备对应的MyLooper对象
  public static void prepare() {
      if (threadLocal.get() != null) {
          throw new RuntimeException( "Only one MyLooper may be created per thread");
      }
      threadLocal.set(new MyLooper());
  }

  //这里启动消息循环
  public static void loop() {
      while (true) {
          myLooper = myLooper();
          MyMessageQueue mQueue = myLooper.queue;
          senior.thread_concurrent.handler.MyMessage msg = mQueue.next();// take()方法是个阻塞方法。线程运行到此会阻塞住。以准备接收发过来的消息
          msg.target.dispatchMessage(msg);
      }
  }
}

自定义消息实体和消息队列-MessageQueue

下面的消息队列就没什么好说的了,主要就是一个入队和出队的方法
package senior.thread_concurrent.handler;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * 消息队列
 * <p>
 * Created by yutianran on 16/7/4.
 */
public class MyMessageQueue {

  private BlockingQueue<MyMessage> queue;
  private boolean quit = false;

  public MyMessageQueue() {
      queue = new LinkedBlockingQueue<>();
      queue.clear();
  }

  //入队
  public boolean enqueueMessage(MyMessage msg) {
      if (msg.target == null) {
          throw new RuntimeException("消息必须有一个消息处理者");
      }
      try {
          queue.put(msg);
      } catch (InterruptedException e) {
          e.printStackTrace();
      }
      return true;
  }

  //出队
  public MyMessage next() {
      MyMessage msg = null;
      if (quit) {
          return null;
      }
      try {
          msg = queue.take();
      } catch (InterruptedException e) {
          e.printStackTrace();
      }
      return msg;
  }

  //销毁
  public synchronized void quit() {
      quit = true;
  }
}
用到的消息实体如下:
package senior.thread_concurrent.handler;

/**
 * 消息实体
 * <p>
 * Created by yutianran on 16/7/4.
 */
public class MyMessage {
  public int msg1;
  public int msg2;
  public int what;
  public Object obj;
  public MyHandler target;
  public Runnable runnable;
}
这里的LogUtil其实也与Android无关:
package base.util;

/**
 * Created by yutianran on 16/7/4.
 */
public class LogUtil {

  public static void print(String msg) {
      System.out.println("Thread:" + Thread.currentThread().getName() + "\t" + System.currentTimeMillis() + "\t" + msg);
  }

}
好了,我的自定义消息传递机制搞定!

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