多线程下载文件

package mutiDownload;

import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * 多线程下载文件
 * @author Administrator
 *
 */
public class Demo {


	public final static int threadcount=3;
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub

		//获取服务器上的文件长度，在本地创建一个和服务器上的文件一样大的临时文件
		String pathString="http://192.168.1.84:8091/androidServer/test.mkv";
		URL url=new URL(pathString);
		HttpURLConnection connection=(HttpURLConnection) url.openConnection();
		connection.setConnectTimeout(5000);
		connection.setRequestMethod("GET");
		int code=connection.getResponseCode();
		if(code==200){	//请求成功
			int length=connection.getContentLength();
			System.out.println("文件长度:"+length);
			RandomAccessFile ref=new RandomAccessFile("test.mkv","rwd");
			//指定创建的临时文件的长度
			ref.setLength(length);
			ref.close();

			int blocksize=length/threadcount;
			for(int threadId=1;threadId<=threadcount;threadId++){
				int startIndex=(threadId-1)*blocksize;	//线程开始位置
				int endIndex=threadId*blocksize-1;
				if(threadId==threadcount){
					endIndex=length;
				}
				System.out.println("线程"+threadId+"下载---"+startIndex+"-->"+endIndex);
				new Downhread(threadId, startIndex, endIndex, pathString).start();;

			}
		}else{
			System.out.println("服务器错误");
		}

	}

	/**
	 * 下载文件子线程
	 * @author Administrator
	 *
	 */
	public static class Downhread  extends Thread {
		private int threadId;
		private int startIndex;
		private int endIndex;
		private String path;



		/**
		 * 
		 * @param threadId	线程id
		 * @param startIndex	线程下载的开始位置
		 * @param endIndex
		 * @param path	下载文件在服务器上的位置
		 */
		public Downhread(int threadId, int startIndex, int endIndex, String path) {
			super();
			this.threadId = threadId;
			this.startIndex = startIndex;
			this.endIndex = endIndex;
			this.path = path;
		}


		@Override
		public void run() {
			// TODO Auto-generated method stub
			//super.run();
			try {
				URL url=new URL(path);
				HttpURLConnection connection=(HttpURLConnection) url.openConnection();
				connection.setConnectTimeout(5000);
				connection.setRequestMethod("GET");
				connection.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
				int code=connection.getResponseCode();
				System.out.println("code:"+code);
//				if(code==200){	//请求成功
//					
//				}
				InputStream is=connection.getInputStream();
				RandomAccessFile raf=new RandomAccessFile("test.mkv","rwd");
				//写文件的时候指定从哪个位置开始写
				raf.seek(startIndex);

				int len=0;
				byte [] buffer=new byte[1024];
				while((len=is.read(buffer))!=-1){
					raf.write(buffer, 0, len);

				}
				is.close();
				raf.close();
				System.out.println("线程:"+threadId+"下载完毕了...");

			} catch (MalformedURLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

}