java版android Handler机制模型

使用示例

import com.handler.Handler;import com.handler.Looper;import com.handler.Message;public class Main {public static void main(String[] args) {new Main().start();}private void start(){Looper.prepare();onCreate();//死循环，阻塞式Looper.loop();//下面 的代码通常不会执行System.out.println("exit........");throw new RuntimeException("Main thread loop unexpectedly exited");}private void onCreate() {//////////////////////////////////////////////////////////////// 下面的操作相当于运行在android的UI线程中 //////////////////////////////////////////////////////////////////////final Thread thread = Thread.currentThread();System.out.println("main thread=" + thread);Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {//若thread == Thread.currentThread()，则证明已经运行在主线程中了System.out.println("current thread is main thread? " + (thread == Thread.currentThread()));System.out.println(msg);System.out.println();}};// 测试1       主线程创建handler，子线程使用该handler发送消息 new Thread() {public void run() {try {//模拟耗时操作Thread.sleep(1000 * 2);} catch (InterruptedException e) {}Message message = new Message();message.obj = "new Thread" + Thread.currentThread();message.what = (int) System.currentTimeMillis();//在子线程中发送消息 handler.sendMessage(message);try {Thread.sleep(1000 * 2);} catch (InterruptedException e) {}message = new Message();message.obj = "hanler...waht==1" ;message.what = 1;//在子线程中发送消息 handler.sendMessage(message);message = new Message();message.obj = "hanler...waht==2" ;message.what = 2;//在子线程中发送消息 handler.sendMessage(message);message = new Message();message.obj = "hanler...waht==3" ;message.what = 3;//在子线程中发送消息 handler.sendMessage(message);};}.start();// 测试2 在thread内部创建handler，结果会抛出异常new Thread() {public void run() {try {sleep(1000 * 3);} catch (InterruptedException e) {}/* * 在线程内部使用默认构造函数创建handler会抛出异常。 * android中也可以在子线程中创建Handler，但要在初始化时传入Looper， * Looper.getMainLooper()获取到的就是主线程的Looper，所以可以这样创建 *  * new Handler(Looper.getMainLooper()){@Overridepublic void handleMessage(Message msg) {//运行在主线程中}}; */Handler h = new Handler() {public void handleMessage(Message msg) {System.out.println("haneler msg...." + msg);};};Message message = new Message();message.obj = "handler in new Thread";message.what = (int) System.currentTimeMillis();//在子线程中发送消息 h.sendMessage(message);};}.start();//////////////////////////////////////////////////////////////// 上面的操作相当于运行在android的UI线程中 //////////////////////////////////////////////////////////////////////}}

运行结果：

main thread=Thread[main,5,main]current thread is main thread? truewhat=18175614 obj=new ThreadThread[Thread-0,5,main]Exception in thread "Thread-1" java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()at com.handler.Handler.<init>(Handler.java:14)at Main$3$1.<init>(Main.java:103)at Main$3.run(Main.java:103)current thread is main thread? truewhat=1 obj=hanler...waht==1current thread is main thread? truewhat=2 obj=hanler...waht==2current thread is main thread? truewhat=3 obj=hanler...waht==3

/////////////////////////////////////////java版android Handler机制模型////////////////////////////////////////////////////

package com.handler;public class Handler {private MessageQueue messageQueue;public Handler() {Looper looper=Looper.myLooper();if (looper==null) { throw new RuntimeException(                "Can't create handler inside thread that has not called Looper.prepare()");       }this.messageQueue=looper.messageQueue;}public void sendMessage(Message msg) {//Looper循环中发现message后，调用message.targer就得到了当前handler，使用taget.handleMessage//就把消息转发给了发送message时的handler的handleMessage函数msg.target=this;messageQueue.enqueueMessage(msg);}public void handleMessage(Message msg) {    }}

package com.handler;public class Looper {private static final ThreadLocal<Looper> threadLocal=new ThreadLocal<>();/** * 存储Message的队列，阻塞式，没有消息则一直等待 */final MessageQueue messageQueue;private Looper() {messageQueue=new MessageQueue();}/**为该线程创建Looper， * 若该线程已经有Looper了则不需要再次调用prepare */public  static void prepare() {if (threadLocal.get() != null) {            throw new RuntimeException("Only one Looper may be created per thread");        }threadLocal.set(new Looper() );}public static void loop() {Looper looper=myLooper();if (looper == null) {            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");        }MessageQueue messageQueue=looper.messageQueue;for(;;){Message message=messageQueue.next();message.target.handleMessage(message);}}/** * 获取当先线程的Looper * @return */public static Looper myLooper() {return threadLocal.get();}}

package com.handler;import java.util.concurrent.BlockingQueue;import java.util.concurrent.LinkedBlockingQueue;public class MessageQueue {private BlockingQueue<Message>blockingQueue=new LinkedBlockingQueue<>();/** * 阻塞式，没有消息则一直等待 * @return */public Message next() {try {return blockingQueue.take();} catch (InterruptedException e) {throw new RuntimeException();}}/** * 插入到消息队列尾部 * @param message */void enqueueMessage(Message message) {try {blockingQueue.put(message);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

package com.handler;import java.util.HashMap;import java.util.Map;/** * ThreadLocal简单实现 * @author Young * * @param <T> */public class ThreadLocal<T> {private Map<Thread,T>map;public ThreadLocal() {map=new HashMap<>();}public void set(T obj) {map.put(Thread.currentThread(),obj);}public T get() {return map.get(Thread.currentThread());}}

package com.handler;public class Message {Handler target;public Object obj;public int what;@Overridepublic String toString() {return  "what="+what+" obj="+obj.toString();}}

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