Android图片异步加载类

关键字：缓存池，加载队列

/**
 * Title:图片异步加载类
 * Description:
 * Copyright:Copyright(c) 2012
 * Company:
 * 
 * @author tom_liang
 */
package com.zouba.dd.ui.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.Serializable;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

public class DandanAsynchImageLoader {
	public static boolean isStop = false;				//是否停止异步加载图片线程
	private static Object locker = new Object();		//同步锁
	private static Thread loadThread = null;			//异步加载线程对象
	private static Map<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();	//所有图片缓存
	private static List<AsynchImage> taskQueue = new ArrayList<AsynchImage>();	//异步加载任务的队列
	//消息处理器
	private static final Handler handler = new Handler() {
		public void handleMessage(Message message) {
			//当前任务加载到图片后，执行回调
			Bundle bundle = message.getData();
			AsynchImage asynchImage = (AsynchImage)bundle.getSerializable("handled_task");
			asynchImage.getCallback().imageLoaded((Drawable) message.obj,asynchImage.getImgURL());
		}
	};

	static {
		DandanAsynchImageLoader.loadThread = new Thread() {
			public void run() {
				while (!DandanAsynchImageLoader.isStop) {
					synchronized (locker) {
						if (taskQueue.size() == 0) {
							try {
								locker.wait();
							} catch (InterruptedException e) {
								
								e.printStackTrace();
							}
						}
						AsynchImage temptask = taskQueue.remove(0);
						Drawable drawable = loadImageFromUrl(temptask.getImgURL());
						imageCache.put(temptask.getImgURL(),new SoftReference<Drawable>(drawable));
						Message message = handler.obtainMessage(0,drawable);
						Bundle bundle = new Bundle();
						bundle.putSerializable("handled_task", temptask);
						message.setData(bundle);
						handler.sendMessage(message);
						locker.notifyAll();
					}
				}
			}
		};
		//启动异步线程（网络事件线程）
		DandanAsynchImageLoader.loadThread.start();
	}

	/**
	 *     异步加载图片的静态方法，首先检查缓存里面是否有之前加载好的图片
	 *     有的话直接返回；没有，加入到异步任务队列进行加载
	 * @param imageUrl		网络替片的URL
	 * @param imageCallback	回调接口
	 * @return 返回异步图片的Drawable对象
	 */
	public static Drawable loadDrawable(final String imageUrl,final ImageCallback imageCallback) {
		if (imageCache.containsKey(imageUrl)) {
			SoftReference<Drawable> softReference = imageCache.get(imageUrl);
			Drawable drawable = softReference.get();
			if (drawable != null) {
				return drawable;
			}
		}
		new Thread(){
			public void run(){
				synchronized (locker) {
					if( !taskQueue.contains(imageUrl) ){
						taskQueue.add(new AsynchImage(imageUrl, imageCallback));
					}
					locker.notifyAll();
				}
			}
		}.start();

		return null;
	}

	/**
	 *     网络图片加载的回调接口
	 * @author zouba
	 *
	 */
	public interface ImageCallback {
		public void imageLoaded(Drawable imageDrawable, String imageUrl);
	}

	/**
	 *     描述：真实的网络图片加载方法
	 * @param url	网络图片的地址
	 * @return 返回网络图片的Drawable对象
	 */
	private static Drawable loadImageFromUrl(String url) {
		URL m;
		InputStream i = null;
		try {
			m = new URL(url);
			i = (InputStream) m.getContent();
		} catch (MalformedURLException e1) {
			e1.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		Drawable d = Drawable.createFromStream(i, "src");
		return d;
	}
	
	/*************************************************************************************
	 * 异步加载图片的Java Bean，对异步图片信息的简单封装
	 *************************************************************************************/
	static class AsynchImage implements Serializable{
		private static final long serialVersionUID = 1L;
		private String imgURL;
		private ImageCallback callback;

		public AsynchImage(String imgURL, ImageCallback callback) {
			this.imgURL = imgURL;
			this.callback = callback;
		}

		public String getImgURL() {
			return imgURL;
		}

		public void setImgURL(String imgURL) {
			this.imgURL = imgURL;
		}

		public ImageCallback getCallback() {
			return callback;
		}

		public void setCallback(ImageCallback callback) {
			this.callback = callback;
		}
	}
}