Android通过HTTP协议实现多线程上载

package cn.itcast.net.download;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;public class MulThreadDownload {	/**	 * @param args	 */	public static void main(String[] args) {		String path = "http://net.itcast.cn/QQWubiSetup.exe";		try {			new MulThreadDownload().download(path, 3);		} catch (Exception e) {			e.printStackTrace();		}	}	/**	 * 从路径中获取文件名称	 * @param path 下载路径	 * @return	 */	public static String getFilename(String path){		return path.substring(path.lastIndexOf('/')+1);	}	/**	 * 下载文件	 * @param path 下载路径	 * @param threadsize 线程数	 */	public void download(String path, int threadsize) throws Exception{		URL url = new URL(path);		HttpURLConnection conn = (HttpURLConnection)url.openConnection();		conn.setRequestMethod("GET");		conn.setConnectTimeout(5 * 1000);		int filelength = conn.getContentLength();//获取要下载的文件的长度		String filename = getFilename(path);//从路径中获取文件名称		File saveFile = new File(filename);		RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");		accessFile.setLength(filelength);//设置本地文件的长度和下载文件相同		accessFile.close();		//计算每条线程下载的数据长度		int block = filelength%threadsize==0? filelength/threadsize : filelength/threadsize+1;		for(int threadid=0 ; threadid < threadsize ; threadid++){			new DownloadThread(url, saveFile, block, threadid).start();		}	}		private final class DownloadThread extends Thread{		private URL url;		private File saveFile;		private int block;//每条线程下载的数据长度		private int threadid;//线程id		public DownloadThread(URL url, File saveFile, int block, int threadid) {			this.url = url;			this.saveFile = saveFile;			this.block = block;			this.threadid = threadid;		}		@Override		public void run() {			//计算开始位置公式：线程id*每条线程下载的数据长度= ？		    //计算结束位置公式：（线程id +1）*每条线程下载的数据长度-1 =?			int startposition = threadid * block;			int endposition = (threadid + 1 ) * block - 1;			try {				RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");				accessFile.seek(startposition);//设置从什么位置开始写入数据				HttpURLConnection conn = (HttpURLConnection)url.openConnection();				conn.setRequestMethod("GET");				conn.setConnectTimeout(5 * 1000);				conn.setRequestProperty("Range", "bytes="+ startposition+ "-"+ endposition);				InputStream inStream = conn.getInputStream();				byte[] buffer = new byte[1024];				int len = 0;				while( (len=inStream.read(buffer)) != -1 ){					accessFile.write(buffer, 0, len);				}				inStream.close();				accessFile.close();				System.out.println("线程id:"+ threadid+ "下载完成");			} catch (Exception e) {				e.printStackTrace();			}		}			}}