java實現多線程下載網絡文件

package com.zkq.dowload;

import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class MulThreadDownload {
	public static void main(String[] args) throws Exception{
		//網絡文件地址
		String path="http://192.168.1.186:8080/web/setup_8.8.0.2001b.exe";
		new MulThreadDownload().download(path,3);
	}
	/**
	 * 下載
	 * @param path	網絡文件地址
	 * @param threadsize	線程數
	 * @throws Exception
	 */
	private void download(String path,int threadsize) throws Exception {
		URL url=new URL(path);
		HttpURLConnection conn=(HttpURLConnection)url.openConnection();
		conn.setConnectTimeout(5000);
		conn.setRequestMethod("GET");
		if(conn.getResponseCode()==200){
			int length=conn.getContentLength();//獲取網絡文件的長度
			String filename=getFileName(path);
			//可以在這裏設置文件的保存路徑 如："d:/data/"+filename
			File file=new File(filename);
			RandomAccessFile accessFile=new RandomAccessFile(file, "rwd");
			accessFile.setLength(length);
			accessFile.close();
			//計算每條線程下載的數據量
			int block=length%threadsize==0 ? length/threadsize : length/threadsize + 1;
			for (int threadid = 0; threadid < threadsize; threadid++) {
				//啓動線程
				new DownloadThread(threadid,block,url,file).start();
			}
		}else{
			System.out.println("下載失敗");
		}
	}
	/**
	 * 獲取文件名稱
	 * @param path
	 * @return
	 */
	private String getFileName(String path) {
		return path.substring(path.lastIndexOf("/")+1);
	}
	
	private class DownloadThread extends Thread{
		private int threadid;
		private int block;
		private URL url;
		private File file;
		public DownloadThread(int threadid, int block, URL url, File file) {
			this.threadid = threadid;
			this.block = block;
			this.url = url;
			this.file = file;
		}
		public void run() {
			int start=threadid * block;//計算該線程從網絡文件 什麼爲是開始下載
			int end=(threadid+1) * block - 1;//計算下載到網絡文件的什麼位置結束
			try {
				RandomAccessFile accessFile=new RandomAccessFile(file, "rwd");
				accessFile.seek(start);//設置文件指針的位置
				HttpURLConnection conn=(HttpURLConnection)url.openConnection();
				conn.setConnectTimeout(5000);
				conn.setRequestMethod("GET");
				conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
				if(conn.getResponseCode()==206){
					InputStream inStream=conn.getInputStream();
					byte[] buffer=new byte[1024];
					int len=0;
					//文件保存到了項目根目錄
					while((len=inStream.read(buffer))!=-1){
						accessFile.write(buffer,0,len);
					}
					accessFile.close();
					inStream.close();
				}
				System.out.println("第"+(threadid+1)+"條線程下載完成");
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		
	}
}