Android简单实现的多线程下载模块

class DownloadItem{
	// 文件的下载进度
	public float mPercent = 0;
	// 文件URL，需要是下载路径
	public URL mFileUrl;
	// 要下载文件的hash值，用于校验下载是否完整
	public String mHashValue;
	// 要下载的文件大小
	public long mFileLength;
	// 文件下载后的保存路径，需要是完整路径，包括文件名
	public String mLocalFilePath;
	public DownloadItem(URL url, String filePath,String hashValue) {
		this.mFileUrl = url;
		this.mLocalFilePath = filePath;
		this.mHashValue = hashValue;
	}
	public DownloadItem() {
	}
}

public class DownloadThread extends Thread {
	// 开始下载
	public final static int THREAD_BEGIN = 1;
	// 下载结束，图片正确
	public final static int THREAD_FINISHED_SUCC = 2;
	// 下载结束，图片错误
	public final static int THREAD_FINISHED_FAIL = 3;
	// 线程锁
	private static Lock sLock = new ReentrantLock();
	// 是否已经下载完成
	private static boolean sIsFinished = false;
	// 任务集合
	private static Queue<DownloadItem> needDownloadLists = new LinkedList<DownloadItem>();
	// 正在进行中的下载列表
	private static Queue<DownloadItem> downloadList = new LinkedList<DownloadItem>();
	public static final String LOG_TAG = "Download";
	//当前的下载线程已启动
	private boolean mIsStarted = false;
	//当前的下载线程下载的图片
	private DownloadItem mDownloadItem = null;
	
	public DownloadThread(DownloadItem tempDownloadItem) {
		mDownloadItem = tempDownloadItem;
	}

	public static void addToDownloadQueue(URL url, String filePath,String hashValue) {
		if(null == url || T.ckIsEmpty(filePath) || T.ckIsEmpty(hashValue)){
			Logger.w("url or filePath or hashValue is null");
			return ;
		}
		sLock.lock();
		try {
			DownloadItem tempDownloadThread = new DownloadItem(url,filePath,hashValue);
		    if(!needDownloadLists.contains(tempDownloadThread)){
		        needDownloadLists.add(tempDownloadThread);
		    }
		    DownloadThread.setFinished(false);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            sLock.unlock();
        }
		Message message = new Message();
		message.what = DownloadThread.THREAD_BEGIN;
		myHandler.sendMessage(message);
	}

	// 开始下载任务
	@Override
	public void run() {
		this.mIsStarted = true;
		BufferedInputStream bis = null;
		BufferedOutputStream bos = null;
		try {
			HttpURLConnection conn = (HttpURLConnection) this.mDownloadItem.mFileUrl
					.openConnection(); // 建立一个远程连接句柄，此时尚未真正连接
			conn.setConnectTimeout(5 * 1000); // 设置连接超时时间为5秒
			conn.setRequestMethod("GET"); // 设置请求方式为GET
			conn.setRequestProperty(
					"Accept",
					"image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
			conn.setRequestProperty("Charset", "UTF-8"); // 设置客户端编码
			conn.setRequestProperty(
					"User-Agent",
					"Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)"); // 设置用户代理
			conn.setRequestProperty("Connection", "Keep-Alive"); // 设置Connection的方式
			conn.connect(); // 和远程资源建立真正的连接，但尚无返回的数据流

			this.mDownloadItem.mFileLength = conn.getContentLength();
			byte[] buffer = new byte[4096]; // 下载的缓冲池为4KB
			bis = new BufferedInputStream(conn.getInputStream()); 
			File tempPic = new File(this.mDownloadItem.mLocalFilePath+"_temp");
			// 后续可以修改这部分内容，即可实现断点续传
			if (tempPic.exists()) {
				delFileByPath(this.mDownloadItem.mLocalFilePath+"_temp");
			}
			bos = new BufferedOutputStream(new FileOutputStream(tempPic));
			long downloadLength = 0;// 当前已下载的文件大小
			int bufferLength = 0;
			MessageDigest md5 = MessageDigest.getInstance("MD5");
			String picMd5 = "";
			while ((bufferLength = bis.read(buffer)) != -1) {
				bos.write(buffer, 0, bufferLength);
				md5.update(buffer, 0, bufferLength);
				bos.flush();
				// 计算当前下载进度
				downloadLength += bufferLength;
				this.mDownloadItem.mPercent = downloadLength / this.mDownloadItem.mFileLength;
			}
			byte[] bs = md5.digest();
			picMd5 = HexUtil.bytes2HexStr(bs).toLowerCase(Locale.CHINA);
			//下载完成，对比md5
			Message msg = new Message();
			msg.obj = this.mDownloadItem;
			if(picMd5.equalsIgnoreCase(this.mDownloadItem.mHashValue)){
				File localFile = new File(this.mDownloadItem.mLocalFilePath);
				if (localFile.exists()) {
					delFileByPath(this.mDownloadItem.mLocalFilePath);
				}
				boolean flag = tempPic.renameTo(localFile);
				if(flag){
					msg.what = THREAD_FINISHED_SUCC;
					Logger.d("rename pic succ："+this.mDownloadItem.mLocalFilePath);
				}else{
					msg.what = THREAD_FINISHED_FAIL;
					Logger.d("rename pic failed："+this.mDownloadItem.mLocalFilePath);
				}
			}else{
				msg.what = THREAD_FINISHED_FAIL;
				Logger.w("picMd5:"+picMd5+";hashValue:"+this.mDownloadItem.mHashValue);
				delFileByPath(this.mDownloadItem.mLocalFilePath);
			}
			// 发送下载完毕的消息
			DownloadThread.myHandler.sendMessage(msg);
		} catch (Exception e) {
			e.printStackTrace();
			// 这里处理下载失败（建议发送下载失败的消息）
		} finally {
			try {
				if (bis != null) {
					bis.close();
				}
				if (bos != null) {
					bos.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	
	private static boolean isFinished() {
		return sIsFinished;
	}
	
	private static void setFinished(boolean isFinished) {
		sIsFinished = isFinished;
	}

	private boolean isStarted() {
		return mIsStarted;
	}

	public static void delFileByPath(String filePath){
		if(T.ckIsEmpty(filePath)){
			return ;
		}
		File tempPicFile = new File(filePath);
		if(null != tempPicFile){
			tempPicFile.delete();
		}
	}

	private static Handler myHandler = new Handler() {

		@Override
		public void handleMessage(Message msg) {
			Message message = new Message();
			DownloadItem tempDownloadItem = new DownloadItem();
			switch (msg.what) {
			case DownloadThread.THREAD_BEGIN:
				sLock.lock();
				if (!needDownloadLists.isEmpty()) {
					do{
						tempDownloadItem = needDownloadLists.poll();
						if(!downloadList.contains(tempDownloadItem)){
							DownloadThread tempDownloadThread = new DownloadThread(tempDownloadItem);
							if (!tempDownloadThread.isStarted()) {
								tempDownloadThread.start();
							}
							downloadList.add(tempDownloadItem);
						}
					}while(!downloadList.contains(tempDownloadItem));
					
				} else {
					if(!downloadList.isEmpty()){
						//没有新的要下载图片了
						Logger.d("no new task");
					}else{
						// 下载已经完成了
						if(DownloadThread.isFinished()){
							//下载结束不重复通知
							Logger.d("all task finished have been notified");
						}else{
							DownloadThread.setFinished(true);
							Logger.d("all task finished");
						}
					}
				}
				sLock.unlock();
				break;
			case DownloadThread.THREAD_FINISHED_SUCC:
				sLock.lock();
				tempDownloadItem = (DownloadItem) msg.obj;
				if(downloadList.contains(tempDownloadItem)){
					//移除
					downloadList.remove(tempDownloadItem);
				}
				message.what = DownloadThread.THREAD_BEGIN;
				sendMessage(message);
				sLock.unlock();
				break;
			case DownloadThread.THREAD_FINISHED_FAIL:
				sLock.lock();
				tempDownloadItem = (DownloadItem) msg.obj;
				if(downloadList.contains(tempDownloadItem)){
					//移除
					downloadList.remove(tempDownloadItem);
				}
				message.what = DownloadThread.THREAD_BEGIN;
				sendMessage(message);
				sLock.unlock();
				break;
			}
		}

	};
	// 具体的功能测试和调用方法
	public static void main(String[] args)
    {
		//TODO 找个MSDK的日志
		addToDownloadQueue(null, null, null);
		addToDownloadQueue(null, null, null);
		addToDownloadQueue(null, null, null);
		addToDownloadQueue(null, null, null);
        
    }
}