Android 网络学习之使用多线程下载，支持断点续传

public void downloade(View v)
    {
    	Thread thread = new Thread()
    	{
    		//服务器地址
    		String path = "http://192.168.1.123:8080/Wireshark.exe";
    		@Override
    		public void run() {
    			try {
					URL url = new URL(path);
					HttpURLConnection conn = (HttpURLConnection) url.openConnection();
					conn.setRequestMethod("GET");
					conn.setReadTimeout(5000);
					conn.setReadTimeout(5000);
					
					if(conn.getResponseCode() == 200)
					{
						//获取数据的总大小
						int length = conn.getContentLength();
						//每个线程的大小
						int size = length / threadCount;
						
						for(int i = 0; i < threadCount; i++)
						{
							int startIndex = i * size;
							int endIndex = (i + 1)*size - 1;
							//最后一个线程的结束地址为文件总大小-1
							if(i == threadCount - 1)
							{
								endIndex = length - 1;
							}
							
							System.out.println("线程" + i + "的下载区间为：" + startIndex + "---" + endIndex);
						}
						
					}
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
    		}
    	};
    	
    	thread.start();
    }

System.out.println("线程" + i + "的下载区间为：" + startIndex + "---" + endIndex);
							//开启threadCount去下载数据
							new downloadThread(startIndex, endIndex, i).start();

class downloadThread extends Thread{
    	int startIndex;//开始位置
    	int endIndex;//结束位置
    	int threadId;//线程Id
    	
    	//构造方法
		public downloadThread(int startIndex, int endIndex, int threadId) {
			super();
			this.startIndex = startIndex;
			this.endIndex = endIndex;
			this.threadId = threadId;
		}
		
		@Override
		public void run() {
			//这次需要请求要下载的数据了
			URL url;
			try {
				url = new URL(path);
				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
				conn.setRequestMethod("GET");
				conn.setReadTimeout(5000);
				conn.setReadTimeout(5000);
				//设置本次HTTP请求数据的区间
				conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
				//请求部分数据，返回码为206
				if(conn.getResponseCode() == 206)
				{
					//此时取到的流里的数据只有上面给定区间的大小
					InputStream is = conn.getInputStream();
					byte[] b = new byte[1024];
					int len = 0;
					int total = 0;
					
					//再次打开临时文件
					File file = new File(Environment.getExternalStorageDirectory(), filename);
					RandomAccessFile raf = new RandomAccessFile(file, "rwd");
					//把文件的写入位置指定到startindex
					raf.seek(startIndex);
					
					while((len = is.read(b)) != -1)
					{
						raf.write(b, 0, len);
						total += len;
						System.out.println("线程" + threadId + "下载了" + total);
					}
					
					System.out.println("线程" + threadId + "---------------下载完毕-------------------");
					raf.close();
				}
				
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
    }

//获取数据的总大小
						int length = conn.getContentLength();
						
						//设置进度条的最大值
						pBar.setMax(length);
						
						//每个线程的大小
						int size = length / threadCount;

						raf.write(b, 0, len);
						total += len;
						System.out.println("线程" + threadId + "下载了" + total);
						
						//设置当前进度，是3个线程的总和
						currProgress += len;
						pBar.setProgress(currProgress);

	Handler handler = new Handler()
	{
		public void handleMessage(android.os.Message msg) 
		{
			//显示下载比例，转为为long型，int的时候有时候不够大
			tView.setText((long)pBar.getProgress() * 100 / pBar.getMax() + "%");
		};
	};

			File bakFile = new File(Environment.getExternalStorageDirectory(), threadId + ".txt");
			try {
				//判断文件是否存在
				if(bakFile.exists())
				{
					FileInputStream fis = new FileInputStream(bakFile);
					BufferedReader bReader = new BufferedReader(new InputStreamReader(fis));
					//从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
					int lastProgress = Integer.parseInt(bReader.readLine());
					startIndex += lastProgress;
					
					//把上次下载的进度显示至进度条
					currProgress += lastProgress;
					pBar.setProgress(currProgress);
					
					//发送消息，让主线程刷新文本进度
					handler.sendEmptyMessage(1);
					fis.close();
				}

					while((len = is.read(b)) != -1)
					{
						raf.write(b, 0, len);
						total += len;
						System.out.println("线程" + threadId + "下载了" + total);
						
						//设置当前进度，是3个线程的总和
						currProgress += len;
						pBar.setProgress(currProgress);
						//通过发送消息，更新文本。而进度条不需要通过发消息刷新UI，因为进度条本身就是在别的任务中使用的
						handler.sendEmptyMessage(1);
						
						//将当前的下载进度保存到配置文件中
						RandomAccessFile bakRaFile = new RandomAccessFile(bakFile, "rwd");
						bakRaFile.write((total + "").getBytes());
						bakRaFile.close();
					}