Android实现异步处理 -- HTTP请求为例
package com.chenjun.utils;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.BlockingQueue;import java.util.concurrent.ThreadFactory;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;/** * 线程池辅助类，整个应用程序就只有一个线程池去管理线程。 * 可以设置核心线程数、最大线程数、额外线程空状态生存时间，阻塞队列长度来优化线程池。 * 下面的数据都是参考Android的AsynTask里的数据。 * @author zet * */public class ThreadPoolUtils { private ThreadPoolUtils(){ } //线程池核心线程数 private static int CORE_POOL_SIZE = 5; //线程池最大线程数 private static int MAX_POOL_SIZE = 100; //额外线程空状态生存时间 private static int KEEP_ALIVE_TIME = 10000; //阻塞队列。当核心线程都被占用，且阻塞队列已满的情况下，才会开启额外线程。 private static BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>( 10); //线程工厂 private static ThreadFactory threadFactory = new ThreadFactory() { private final AtomicInteger integer = new AtomicInteger(); @Override public Thread newThread(Runnable r) { return new Thread(r, "myThreadPool thread:" + integer.getAndIncrement()); } }; //线程池 private static ThreadPoolExecutor threadPool; static { threadPool = new ThreadPoolExecutor(CORE_POOL_SIZE, MAX_POOL_SIZE, KEEP_ALIVE_TIME, TimeUnit.SECONDS, workQueue, threadFactory); } /** * 从线程池中抽取线程，执行指定的Runnable对象 * @param runnable */ public static void execute(Runnable runnable){ threadPool.execute(runnable); }}?
? ?有了线程池之后，我们就只要编写自己的Runnable（或者是Callable）去实现业务，然后交给线程池让它分配线程并完成业务。
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? ?这里的业务以Android的HTTP下载为例。
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? ?对于Android的HTTP服务，我们的整个应用程序也只需要一个HttpClient对象，可以生成一个线程安全的HttpClient，这个HttpClient可以为我们多个HttpGet、HttpPost提供服务。具体代码如下，这里直接拷贝了《精通Android 3》里的源码：
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package com.chenjun.network.http;import org.apache.http.HttpVersion;import org.apache.http.client.HttpClient;import org.apache.http.conn.ClientConnectionManager;import org.apache.http.conn.params.ConnManagerParams;import org.apache.http.conn.scheme.PlainSocketFactory;import org.apache.http.conn.scheme.Scheme;import org.apache.http.conn.scheme.SchemeRegistry;import org.apache.http.conn.ssl.SSLSocketFactory;import org.apache.http.impl.client.DefaultHttpClient;import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;import org.apache.http.params.BasicHttpParams;import org.apache.http.params.HttpConnectionParams;import org.apache.http.params.HttpParams;import org.apache.http.params.HttpProtocolParams;import org.apache.http.protocol.HTTP;/** * 辅助类，为整个应用程序提供唯一的一个HttpClient对象。 * 这个对象有一些初始化的属性连接属性，这些属性可以被HttpGet、HttpPost的属性覆盖 * @author zet * */public class HttpClientHelper { private static HttpClient httpClient; private HttpClientHelper(){ } public static synchronized HttpClient getHttpClient(){ if(null == httpClient){ //初始化工作 HttpParams params = new BasicHttpParams(); HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1); HttpProtocolParams.setContentCharset(params, HTTP.DEFAULT_CONTENT_CHARSET); HttpProtocolParams.setUseExpectContinue(params, true); //设置连接管理器的超时 ConnManagerParams.setTimeout(params, 1000); //设置连接超时 HttpConnectionParams.setConnectionTimeout(params, 5000); //设置Socket超时 HttpConnectionParams.setSoTimeout(params, 10000); SchemeRegistry schReg = new SchemeRegistry(); schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80)); schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 80)); ClientConnectionManager conManager = new ThreadSafeClientConnManager(params, schReg); httpClient = new DefaultHttpClient(conManager, params); } return httpClient; }}?
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? ?这个HttpClient有一些初始化配置的属性，如果HttpGet和HttpPost没有设定特定的属性，那么生成的HttpGet和HttpPost会沿用HttpClient的初始化属性。但是我们可以根据不同的情况，为HttpGet和HttpPost设置属性，这些属性将覆盖掉HttpClient的初始化属性，这样，我们得到的HttpGet和HttpPost就有特定的属性了。
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? ?具备以上的一些内容，我们就可以在自己的Activity里去实现一个Runnable和Handler即可。在Runnable里完成我们的业务逻辑，并适时的发送Message给Handler来更新UI，在Handler里处理Message并和UI交互。实例代码：
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package com.chenjun.httpdemo;import org.apache.http.HttpResponse;import org.apache.http.client.methods.HttpGet;import org.apache.http.params.BasicHttpParams;import org.apache.http.params.HttpConnectionParams;import org.apache.http.params.HttpParams;import org.apache.http.util.EntityUtils;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Toast;import com.chenjun.asynctask.DownloadImageTask;import com.chenjun.network.http.HttpClientHelper;import com.chenjun.utils.ThreadPoolUtils;public class HttpDemoActivity extends Activity { private static final int START_DOWNLOAD_MESSAGE = 0x01; private static final int FINISH_DOWNLOAD_MESSAGE = 0x02; private static final int ERROR_DOWNLOAD_MESSAGE = 0x03; private Handler myHandler; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); myHandler = new MyHandler(); ThreadPoolUtils.execute(new MyRunnable()); } private class MyRunnable implements Runnable{ @Override public void run() { HttpGet httpGet = new HttpGet("http://www.sina.com.cn"); //为这个HttpGet设置一些特定的属性，别的属性沿用HttpClient HttpParams params = new BasicHttpParams(); HttpConnectionParams.setConnectionTimeout(params, 60000); httpGet.setParams(params); myHandler.sendEmptyMessage(START_DOWNLOAD_MESSAGE); try { HttpResponse httpResponse = HttpClientHelper.getHttpClient().execute(httpGet);; byte[] bytes = EntityUtils.toByteArray(httpResponse.getEntity()); //在大多数情况下，这个下载下来的是XML或者Json。应该解析完组装成对象再放置到Message中。 //这里简单起见，直接变成字符串打印了 String result = new String(bytes); Message msg = myHandler.obtainMessage(); msg.what = FINISH_DOWNLOAD_MESSAGE; msg.obj = result; myHandler.sendMessage(msg); } catch (Exception ex){ ex.printStackTrace(); myHandler.sendEmptyMessage(ERROR_DOWNLOAD_MESSAGE); } } } private class MyHandler extends Handler{ @Override public void dispatchMessage(Message msg) { switch(msg.what){ case START_DOWNLOAD_MESSAGE: Toast.makeText(HttpDemoActivity.this, "开始下载", Toast.LENGTH_SHORT).show(); break; case FINISH_DOWNLOAD_MESSAGE: Toast.makeText(HttpDemoActivity.this, "下载成功", Toast.LENGTH_SHORT).show(); //简单起见，直接输出了。 System.out.println(msg.obj); break; case ERROR_DOWNLOAD_MESSAGE: Toast.makeText(HttpDemoActivity.this, "下载失败", Toast.LENGTH_SHORT).show(); break; default: System.out.println("nothing to do"); break; } } }}?
? 总结：个人有点不习惯用AsynTask，更倾向于这种写法。也许Google开发的AsynTask有更为深远的意义，但是我暂时还没领会到，所以就暂时沿用自己的这种写法了。