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

class ThreadDownload 
{
	public static void main(String[] args)
		throws IOException
	{
		final URL[] urls = {
			new URL("http://www.pku.edu.cn"),
			new URL("http://www.baidu.com"),
			new URL("http://www.sina.com.cn"),
			new URL("http://www.dstang.com")
		};
		final String[] files = {
			"pku.htm", 
			"baidu.htm",
			"sina.htm", 
			"study.htm",
		};

		for(int i=0; i<urls.length; i++){
			final int idx = i;
			new Thread( ()-> {
				try{
					System.out.println( urls[idx] );
					download( urls[idx], files[idx]);
				}catch(Exception ex){
					ex.printStackTrace();
				}
			}).start();
		}
	}
	static void download( URL url, String file)
		throws IOException
	{
		try(InputStream input = url.openStream();
			OutputStream output = new FileOutputStream(file))
		{
			byte[] data = new byte[1024];
			int length;
			while((length=input.read(data))!=-1){
				output.write(data,0,length);
			}
		}
	}
}