HttpURLConnection实现断点下载

package cn.demo;

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

public class BreakDown {
public static void main(String[] args) throws Exception {
String fileName = "video.avi";
String path = "http://localhost:6666/day22_cos/up/"+fileName;
String savePath = "d:/a/"+fileName;
File file = new File(savePath);
long size = file.length();
System.err.println(file.length());

URL url = new URL(path);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("GET");
//设置下载区间
con.setRequestProperty("range","bytes="+size+"-");
con.connect();
int code = con.getResponseCode();//只要断点下载，返回的已经不是200，206
System.err.println(code);
if(code==206){
InputStream in= con.getInputStream();
int serverSize = con.getContentLength();
System.err.println("服务器返回的长度:"+serverSize);
System.err.println("这次从哪开开始写:"+size);
//必须要使用
RandomAccessFile out = new RandomAccessFile(file,"rw");
out.seek(size);

byte[] b = new byte[1024];
int len = -1;
while((len=in.read(b))!=-1){
out.write(b,0,len);
}
out.close();
}
}
}