多线程下载：1.发送请求，获取下载文件的长度2.通过RandomAccessFile file=new RandomAccessFile(file,"rwd")对象，创建一个于要下载文件同样大小的文件3.定义一个线程的数据，计算每条线程的下载量，long block=filesize%threadsize==0?filesize/threadsize:filesize/threadsize+14.定义一个内部类实现thread，作为下载的实现，把线程的id,和每条线程要下载的数量传递给这个类5.计算要下载的开始位置，和结束位置，start=id*block; end=(id+1)*block-1;6.设置分段请求，HttpGet get.setHread("Range","bytes="+start+"-"+end);7.分段请求的数据返回的状态码是206,之后获取通过RandomAccessFile对象的一个seek(start);方法，获取内容进行写入即可

public void download(View v) {		new Thread(new Runnable() {			public void run() {				try {					HttpClient client = new DefaultHttpClient();					HttpGet head = new HttpGet("http://10.0.2.2:8080/FoodService/a.mp4");					HttpResponse rsponse = client.execute(head);					if (rsponse.getStatusLine().getStatusCode() == 200) {						long length = rsponse.getEntity().getContentLength();						RandomAccessFile accessFile = new RandomAccessFile(new File(Environment.getExternalStorageDirectory(), "b.mp4"),"rwd");						accessFile.setLength(length);						int size = 3;						//根据线程的数量计算一个文件分为多少块						long block = length % size == 0 ? length / size: length / size + 1;						for (int i = 0; i < size; i++) {							new downLoadImage(i, block).start();						}					}				} catch (Exception e) {					e.printStackTrace();				}			}		}).start();private class downLoadImage extends Thread {		int threadid;//线程id		long block;//下载的量		long start;//开始下载位置		long end;//结束的下载位置		public downLoadImage(int i, long block) {			this.threadid = i;			this.block = block;			//计算每个线程的下载量			start=threadid*block;			end=(threadid+1)*block-1;		}		public void run() {			try {				RandomAccessFile accessFile = new RandomAccessFile(new File(Environment.getExternalStorageDirectory(), "b.mp4"), "rwd");				accessFile.seek(start);								HttpClient client=new DefaultHttpClient();				HttpGet request=new HttpGet("http://10.0.2.2:8080/FoodService/a.mp4");				request.setHeader("Range","bytes="+start+"-"+end);				HttpResponse response = client.execute(request);				if(response.getStatusLine().getStatusCode()==206){					InputStream inputStream = response.getEntity().getContent();					int len=0;					byte[] buffer=new byte[1024];					while((len=inputStream.read(buffer))!=-1){						accessFile.write(buffer, 0, len);					}					inputStream.close();					Log.i("MainActivity", threadid+"线程");				}			} catch (Exception e) {				e.printStackTrace();			}		}	}