多线程下载辅助类实现

如需转载，必须注明转自： http://blog.csdn.net/xiazdong/article/details/7738298

使用声明：

类名：MultiThreadDownloadUtil

API：

(1)download(String path,int count);

path：文件URL；

count：线程数量；

 

package org.xiazdong.multidownload.util;



import java.io.File;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;





public class MultiThreadDownloadUtil{

	private static int filesize;

	private static int block;

	private static String filename;

	private static int downloadsize;

	private class MyThread extends Thread{

		private int i;			//线程ID

		private String path;	//下载文件的URL



		public MyThread(int i, String path) {

			this.i = i;

			this.path = path;

			downloadsize = 0;

		}

		@Override

		public void run() {

			try{

				System.out.println("线程"+(i+1)+"开始下载");

				//1.打开文件，并定位位置

				RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");

				raf.seek(i*block);			//定位到此线程要负责下载的位置

				int start = i*block;

				int end = (i+1)*block-1;

				//2.连接服务器

				URL url = new URL(path);

				HttpURLConnection conn = (HttpURLConnection)url.openConnection();

				conn.setRequestMethod("GET");

				conn.setRequestProperty("range", "bytes="+start+"-"+end);	//发出请求头

				

				if(conn.getResponseCode()==206){		//注意：分段下载的返回码为206，而不是200

					InputStream in = conn.getInputStream();

					int length = 0;

					byte[]data = new byte[1024];

					while((length=in.read(data))!=-1){

						raf.write(data,0,length);		//写入本地文件

					}

				}

				//显示下载进度

				downloadsize += (end-start);

				System.out.println("已下载"+downloadsize/1024.0+"k,共"+filesize/1024.0+"k");

				//3.关闭文件

				raf.close();

				System.out.println("线程"+(i+1)+"结束下载...");

			}

			catch(Exception e){

				e.printStackTrace();

			}

		}

	}

	/**

	 * 下载文件

	 * @param path			URL

	 * @param threadcount   线程数

	 * @throws Exception

	 */

	public static void download(String path,int threadcount) throws Exception{

		filename = path.substring(path.lastIndexOf('/')+1);

		filesize = getFileSize(path);

		block = getBlockSize(filesize,threadcount);

		createLocalRandomFile(filesize);

		MultiThreadDownloadUtil mdu = new MultiThreadDownloadUtil();

		for(int i=0;i<threadcount;i++){

			mdu.new MyThread(i,path).start();

		}

	}

	/**

	 * 创建一个本地文件，并设置文件的大小

	 * @param filesize

	 * @throws Exception

	 */

	private static void createLocalRandomFile(int filesize) throws Exception {

		RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");

		raf.setLength(filesize);

		raf.close();

	}

	/**

	 * 根据文件总大小和线程数求出每个线程要下载的数据量

	 * @param filesize

	 * @param threadcount

	 * @return

	 */

	private static int getBlockSize(int filesize, int threadcount) {

		return filesize%threadcount==0?filesize/threadcount:(filesize/threadcount+1);

	}

	/**

	 * 求出文件总大小

	 * @param path

	 * @return

	 * @throws Exception

	 */

	private static int getFileSize(String path) throws Exception{

		URL url = new URL(path);

		HttpURLConnection conn = (HttpURLConnection)url.openConnection();

		conn.setRequestMethod("GET");

		if(conn.getResponseCode()==200){

			return conn.getContentLength();

		}

		else{

			return 0;

		}

	}

}

 

 

测试类：

package org.xiazdong.download;



import org.xiazdong.multidownload.util.MultiThreadDownloadUtil;





public class MultiThreadDownloader {



	public static void main(String[] args) throws Exception {

		int threadCount = 3;	//指定线程数量

		String path = "http://dlc2.pconline.com.cn/filedown_61761_6694063/drivethelife2010_pconline_setup.exe";	//指定下载文件路径

		MultiThreadDownloadUtil.download(path, threadCount);

	}

}

将此文件下载到工程目录后，运行可用；