断点续传

package com.log4e.union;

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

import org.junit.Test;

public class Download {
	
	/**
	 * 
	 * @param sURL  文件地址
	 * @param nPos  文件指针位置
	 * @param savePath  下载保存路径
	 * @throws IOException
	 */
	
	boolean stop = false;
	public  void down(String sURL,long  nPos,String savePath) throws IOException{
		URL url = new URL(sURL);
		HttpURLConnection httpConnection = (HttpURLConnection) url
				.openConnection();
		httpConnection.setConnectTimeout(5000000);
		httpConnection.setRequestProperty("User-Agent", "NetFox");
		String sProperty = "bytes=" + nPos + "-";
		// nStartPos 字节开始传,前面的字节不用传了
		httpConnection.setRequestProperty("RANGE", sProperty);
		Utility.log(sProperty);
		InputStream input = httpConnection.getInputStream();
		byte[] b = new byte[1024*10];
		//"rw" 读写方式打开文件
		RandomAccessFile oSaveFile = new RandomAccessFile(savePath, "rw");
		//seek()方法来访问记录,并进行读写
		oSaveFile.seek(nPos);
		int result = -1;
		System.out.println("下载中....");
		while((result = input.read(b))!=-1){
			oSaveFile.write(b, 0, result);
		}
		System.out.println("下载完成....");

		httpConnection.disconnect();
	}
	
	//获得文件长度
	public  long getFileSizeByUrl(String url) throws Exception{
		URL u = new URL(url);
		HttpURLConnection httpURLConnection = (HttpURLConnection) u.openConnection();
		long length =  httpURLConnection.getContentLength();
		httpURLConnection.disconnect();
		return length;
	}

	//
	@Test
	public  void testDownLoad(){
		String url = "http://ww4.sinaimg.cn/bmiddle/769c42dcjw1dojdmycmu9g.gif";
		String savePath = "F:\\download";
		String fileName = url.substring(url.lastIndexOf("/"));
		File file = new File(savePath + fileName);
		try {
			long serverFileLength = getFileSizeByUrl(url);
			System.out.println("serverFileLength : "+serverFileLength );
			if (file.exists()) {
				if(file.length()<serverFileLength){
					down(url, file.length(), file.getPath());
				}
			}else{
				 file.createNewFile();
				 if(file.length()<serverFileLength){
					 down(url, file.length(), file.getPath());
				 }
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	
	
	
	
}