DownUtil.java

import java.io.*;
import java.net.*;

public class DownUtil{
	private String path;
	private String targetFile;
	private int threadNum;
	private DownThread[] threads;
	private int fileSize;

	public DownUtil(String path, String targetFile, int threadNum){
		this.path = path;
		this.targetFile = targetFile;
		this.threadNum = threadNum;
		threads = new DownThread[threadNum];
	} 

	public void download() throws Exception{
		URL url = new URL(path);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setConnectTimeout(5*1000);
		conn.setRequestMethod("GET");
		conn.setRequestProperty(
			"Accept",
			"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
					+ "application/x-shockwave-flash, application/xaml+xml, "
					+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
					+ "application/x-ms-application, application/vnd.ms-excel, "
					+ "application/vnd.ms-powerpoint, application/msword, */*");
		conn.setRequestProperty("Accept-Language", "zh-CN");
		conn.setRequestProperty("Charset", "UTF-8");
		conn.setRequestProperty("Connection", "Keep-Alive");

		fileSize = conn.getContentLength();
		conn.disconnect();
		int currentPartSize = fileSize / threadNum + 1;
		RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
		file.setLength(fileSize);
		file.close();
		for(int i=0; i<threadNum; i++){
			int startPos = i*currentPartSize;
			RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");
			currentPart.seek(startPos);
			threads[i] = new DownThread(startPos, currentPartSize, currentPart);
			threads[i].start();
		}
	}

	public double getCompleteRate(){
		int sumSize = 0;
		for(int i=0; i<threadNum; i++){
			sumSize += threads[i].length;
		}
		return sumSize*1.0/fileSize;
	}

	private class DownThread extends Thread{
		private int startPos;
		private int currentPartSize;
		private RandomAccessFile currentPart;
		public int length;
		public DownThread(int startPos, int currentPartSize, RandomAccessFile currentPart){
			this.startPos = startPos;
			this.currentPartSize = currentPartSize;
			this.currentPart = currentPart;
		}

		public void run(){
			try{
				URL url = new URL(path);
				HttpURLConnection conn = (HttpURLConnection) url.openConnection();
				conn.setConnectTimeout(5*1000);
				conn.setRequestMethod("GET");
				conn.setRequestProperty(
						"Accept",
						"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
								+ "application/x-shockwave-flash, application/xaml+xml, "
								+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
								+ "application/x-ms-application, application/vnd.ms-excel, "
								+ "application/vnd.ms-powerpoint, application/msword, */*");
				conn.setRequestProperty("Accept-Language", "zh-CN");
				conn.setRequestProperty("Charset", "UTF-8");
				conn.setRequestProperty("Connection", "Keep-Alive");

				InputStream inStream = conn.getInputStream();
				byte[] buffer = new byte[1024];
				inStream.skip(this.startPos);
				int hasRead = 0;
				while(length < currentPartSize
					&& (hasRead = inStream.read(buffer)) != -1){
					currentPart.write(buffer, 0, hasRead);
					length += hasRead;
				}
				currentPart.close( );
				inStream.close();
			}catch(Exception e){
				e.printStackTrace();
			}
		}
	}


}