安卓笔记4--多线程断点续传

多线程断点续传无论在什么平台上都是极为重要的，这部分知识非常重要。老规矩，用一张图来介绍今天的内容。

图片看不清的话可以右键新窗口打开

直接看代码吧

public class MainActivity extends Activity {
	 String path = "http://192.168.15.77:8080/QQPlayer.exe";
	 int threadCount = 3;
	 int finishedThreadCount = 0;
	 int currentPbProgress;
	private ProgressBar pb;
	private TextView tv;
	
	Handler handler = new Handler(){
		public void handleMessage(android.os.Message msg) {
			tv.setText((long)pb.getProgress() * 100 / pb.getMax() + "%");
		}
	};
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		//进度条用于显示当前下载进度，下载的总字节数作为progress，目标文件的总大小作为max
		pb = (ProgressBar) findViewById(R.id.pb);
		tv = (TextView) findViewById(R.id.tv);
	}

	public void click(View v){
		Thread t = new Thread(){
			@Override
			public void run() {
				try {
					URL url = new URL(path);
					HttpURLConnection conn = (HttpURLConnection) url.openConnection();
					conn.setRequestMethod("GET");
					conn.setConnectTimeout(8000);
					conn.setReadTimeout(8000);
					
					if(conn.getResponseCode() == 200){
						//拿到要下载的文件的总长度
						int length = conn.getContentLength();
						
						//在本地生成一个临时文件，临时文件大小与目标文件大小一致
						File file= new File(Environment.getExternalStorageDirectory(), getFileName(path));
						RandomAccessFile raf = new RandomAccessFile(file, "rwd");
						raf.setLength(length);
						raf.close();
						
						//设置进度条的总进度为目标文件总长
						pb.setMax(length);
						
						//计算每条线程要下载的长度
						int size = length / threadCount;
						//计算每条线程的开始位置与结束位置
						for(int i = 0; i < threadCount; i++){
							int startIndex = i * size;
							int endIndex = (i + 1) * size - 1;
							if( i == threadCount - 1)
								endIndex = length - 1;
							
//							System.out.println("线程" + i + "的下载区间为：" + startIndex + "~" + endIndex);
							new DownLoadThread(startIndex, endIndex, i).start();
						}
						
					}
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		};
		t.start();
	}
	String getFileName(String path){
		int index = path.lastIndexOf("/");
		return path.substring(index + 1);
	}
	
	class DownLoadThread extends Thread{
		
		int startIndex;
		int endIndex;
		int threadId;
		
		
		public DownLoadThread(int startIndex, int endIndex, int threadId) {
			super();
			this.startIndex = startIndex;
			this.endIndex = endIndex;
			this.threadId = threadId;
		}

		@Override
		public void run() {
			//开启子线程下载目标文件
			try {
				File fileProgess = new File(Environment.getExternalStorageDirectory(), threadId + ".txt");
				int lastTotal = 0;
				//判断文本临时文件是否存在
				if(fileProgess.exists()){
					FileInputStream fis = new FileInputStream(fileProgess);
					BufferedReader br = new BufferedReader(new InputStreamReader(fis));
					//获取上一下载的进度
					lastTotal = Integer.parseInt(br.readLine());
					
					//改变下载的开始位置，已经下载过的数据，就不要再去请求了
					startIndex += lastTotal;
					fis.close();
					
					//把上一次下载的总进度写入进度条
					currentPbProgress += lastTotal;
					pb.setProgress(currentPbProgress);
					handler.sendEmptyMessage(0);
				}
				System.out.println("线程" + threadId + "的最终下载区间为：" + startIndex + "~" + endIndex);
				URL url = new URL(path);
				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
				conn.setRequestMethod("GET");
				conn.setConnectTimeout(8000);
				conn.setReadTimeout(8000);
				//定义请求的数据的范围
				conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
				
				if(conn.getResponseCode() == 206){
					//流里的数据只有startIndex到endIndex区间的数据，并不会包含目标文件所有数据
					InputStream is = conn.getInputStream();
					
					
					byte[] b = new byte[1024];
					int len;
					int total = lastTotal;
					File file= new File(Environment.getExternalStorageDirectory(), getFileName(path));
					RandomAccessFile raf = new RandomAccessFile(file, "rwd");
					//改变往raf中写入数据的开始位置
					raf.seek(startIndex);
					
					while((len = is.read(b)) != -1){
						total += len;
						System.out.println("线程" + threadId + "已下载的字节数为:" + total);
						raf.write(b, 0, len);
						
						//为了完成断点续传，while循环每次下载的进度，都写入一个文本临时文件中
						RandomAccessFile rafProgress = new RandomAccessFile(fileProgess, "rwd");
						rafProgress.write((total + "").getBytes());
						rafProgress.close();
						
						currentPbProgress += len;
						//所有线程每次下载len个长度的字节，都会写到进度条的总进度中
						pb.setProgress(currentPbProgress);
						handler.sendEmptyMessage(0);
					}
					System.out.println("线程" + threadId + "下载完毕---------------------");
					raf.close();
					
					finishedThreadCount++;

					//三个线程全部下载完毕，才去删除文本临时文件
					synchronized (path) {
						if(finishedThreadCount == 3){
							for (int i = 0; i < threadCount; i++) {
								File f = new File(Environment.getExternalStorageDirectory(), i + ".txt");
								if(f.exists())
									f.delete();
							}
							finishedThreadCount = 0;
						}
					}
				}
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}