多线程下载

最新推荐文章于 2025-05-13 18:10:57 发布

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最新推荐文章于 2025-05-13 18:10:57 发布

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分类专栏： android基础学习

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本文介绍了一个用于图片下载的辅助类DownloadAssist的实现细节。该类通过管理下载任务队列和利用多线程来实现图片资源的有效下载。此外，还提供了网络连接检查、任务优先级设置等功能。

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public class DownloadAssist {
	
	public static final int IMAGE_DOWNLOADED_FINISHED = 0xFF000001;
	
	private static final int MAX_TASK_NUM = 8;
	
	private ArrayList<DownLoadMsg> mMsgQueue = null;
	private Object mLock = new Object();
	private final static int MAX_MSG_QUEUE_COUNT = 200;
	private ImageLoader mImageLoader = null;
	private Handler mHandler = null;
	private DownLoadTask[] mDownLoadTasks = null;
	private Context mApplication = null;
	
	public DownloadAssist(Context context, String type, Handler handler){
		mApplication = context;
		mHandler = handler;
		mImageLoader = new ImageLoader(context, type);
		mMsgQueue = new ArrayList<DownLoadMsg>();
		mDownLoadTasks = new DownLoadTask[MAX_TASK_NUM];
		startDownLoadTask();
	}
	
	public boolean isOnline() {
		ConnectivityManager cmAll = (ConnectivityManager) mApplication.getSystemService(Context.CONNECTIVITY_SERVICE);
		NetworkInfo mActiveNetworkInfo = cmAll.getActiveNetworkInfo();
		if (mActiveNetworkInfo != null && mActiveNetworkInfo.isConnected()) {
			return true;
		}
		return false;
	}
	
	private void startDownLoadTask(){
		stopDownLoadTask();
		for(int i = 0; i < mDownLoadTasks.length; i++){
			mDownLoadTasks[i] = new DownLoadTask();
			try{
				mDownLoadTasks[i].start();
			}catch(Exception e){
				
			}
		}
	}
	
	private void stopDownLoadTask(){
		for(int i = 0; i < mDownLoadTasks.length; i++){
			if(mDownLoadTasks[i] != null){
				try{
					mDownLoadTasks[i].mEnableRunning = false;
				}catch(Exception e){
					
				}
			}
		}
	}
	
	public void destroyInstance(){
		clearMsgQueue();
		stopDownLoadTask();	
		
	}
	
	public void removeTaskByCategoryId(int categoryId){
		synchronized(mLock){	
			for(int i = 0; i < mMsgQueue.size(); i++){
				DownLoadMsg msg = mMsgQueue.get(i);
				if(msg.mCategoryId == categoryId){
					mMsgQueue.remove(i);
					i--;
				}
			}
			
			
		}
	}
	
	public void downLoad(int categoryId, int medidId, String url){
		downLoadImage(categoryId, medidId, url, false);
	}
	
	public void downLoad(int categoryId, int medidId, String url, boolean bFront){
		DownLoadMsg msg = getDownLoadMsg(categoryId, medidId, url);
		if(msg != null){
			pushMsg(msg, bFront);
		}
	}
	
	private void notifyDownloadFinished(int categoryId, int mediaId, Bitmap bitmap){
		if(mHandler != null){
			Message msg = new Message();
			msg.what = IMAGE_DOWNLOADED_FINISHED;
			msg.arg1 = categoryId;
			msg.arg2 = mediaId;
			msg.obj = bitmap;
			mHandler.sendMessage(msg);
		}
	}
	
	private void pushMsg(DownLoadMsg msg, boolean bFront){
		synchronized(mLock){
			while(mMsgQueue.size() >= MAX_MSG_QUEUE_COUNT){
				mMsgQueue.remove(MAX_MSG_QUEUE_COUNT - 1);
			}
			
			for(int i = 0; i < mMsgQueue.size(); i++){
				if((msg.mMediaId == mMsgQueue.get(i).mMediaId) &&
						(msg.mCategoryId == mMsgQueue.get(i).mCategoryId)){
					mMsgQueue.remove(i);
					i--;
				}
			}
			
			if(bFront){
				mMsgQueue.add(0, msg);
			}else{
				mMsgQueue.add(mMsgQueue.size(), msg);
			}
			
		}
	}
	
	private void pushMsg(DownLoadMsg msg){
		pushMsg(msg, false);
	}
	
	private DownLoadMsg popMsg(){
		synchronized(mLock){	
			if(mMsgQueue.size() > 0){
				DownLoadMsg msg = mMsgQueue.get(0);
				mMsgQueue.remove(0);
				return msg;
			}
			
			return null;
		}
	}
	
	private void clearMsgQueue(){
		synchronized(mLock){
			mMsgQueue.clear();
		}
	}
	
	private DownLoadMsg getDownLoadMsg(int categoryId, int mediaId, String url){
		if(url == null){
			return null;
		}
		
		DownLoadMsg msg = new DownLoadMsg();
		msg.mCategoryId = categoryId;
		msg.mMediaId = mediaId;
		msg.mUrl = url;
		return msg;
	}
	
	private class DownLoadMsg{
		protected int mCategoryId;
		protected int mMediaId;
		protected String mUrl = null;
		protected int mRepeatDownLoadCount = 0;
	}
	
	private class DownLoadTask extends Thread{
		protected volatile boolean mEnableRunning = true;
		private boolean mBSuccess = true;
		@Override
		public void run(){
			while(true){
				if(mEnableRunning == false){
					break;
				}
				
				mBSuccess = true;
				
				DownLoadMsg msg = popMsg();
				if(msg != null){										
					try{
						if((msg.mUrl != null) && (msg.mUrl.isEmpty() == false)){
							Bitmap bitmap = mImageLoader.getBitmap(msg.mUrl);
							notifyDownloadFinished(msg.mCategoryId, msg.mMediaId, bitmap);
							if(bitmap == null){
								mBSuccess = false;
								
							}
						}
					}catch(Exception e){
						mBSuccess = false;
					}
				}
				
				try {
					if(mBSuccess == false){
						if(msg.mRepeatDownLoadCount < 5){
							msg.mRepeatDownLoadCount++;
							pushMsg(msg, true);
						}else{
							notifyDownloadFinished(msg.mCategoryId, msg.mMediaId, null);
						}
					}
					sleep(300);
					
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}
	}
}