range头加RandomAccessFile对象实现多线程文件下载 - 黑马程序员技术交流社区

package day04_tomcat;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;
public class Test {
public static void main(String[] args) throws IOException {
URL url=new URL("http://127.0.0.1:8080/day05_header/xiao.jpg");
speedThreadDownload(url, 3,"F:/3.jpg");
//download(url);
}
/**
*
* @param url 被请求下载的URL
* @param threadNum 用于下载的线程数
* @param path 文件保存位置
* @throws IOException
*/
private static void speedThreadDownload(URL url,int threadNum,final String path) throws IOException
{
int length=url.openConnection().getContentLength();
System.out.println("文件总字节数："+length);
final int baseNum=length/threadNum;
for(int i=1;i<=threadNum;i++){
final URLConnection con=url.openConnection();
String by="bytes="+baseNum*(i-1)+"-"+(i==threadNum?length:(baseNum*i-1));
//System.out.println(by);
con.setRequestProperty("range", by);
final int index=baseNum*(i-1);
new Thread(new Runnable() {
@Override
public void run() {
int len=0;
byte[] bytes=new byte[1024];
try (RandomAccessFile daf
= new RandomAccessFile(path, "rw");
InputStream in=con.getInputStream();){
daf.seek(index);
while((len=in.read(bytes))>0)
daf.write(bytes,0,len);
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}
}
}

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