week8多线程

下面的程序可以下载多个网页文件(download方法已写好），请将它改成多线程进行下载，如果可能， 显示计算全部下载完成程序所用的时间（提示：new Date().getTime()可以得到当前时间的毫秒数）。

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

class Downloader
{
    public static void main(String[] args)
        throws Exception
    {
        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 idx=0; idx
            try{
                System.out.println( urls[idx] );
                download( urls[idx], files[idx]);
            }catch(Exception ex){
                ex.printStackTrace();
            }
        }
    }
    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);
            }
        }
    }
}

代码:

package week8;

import java.net.URL;
import java.io.*;
 
public class Downloader extends Thread{
	
	String file;
	URL url;
	
	public Downloader(URL url, String file){
		this.url=url;
		this.file=file;
	}
	

	public void run(){
		java.io.InputStream input = null ;
		java.io.OutputStream output = null ;
		try{
			input =  url.openStream();
	        output = new FileOutputStream(file);
	        byte[] data = new byte[1024];
            int length;
            try {
				while((length=input.read(data))!=-1){
						output.write(data,0,length);
				} 
			}catch (IOException e1) {
				e1.printStackTrace();
			}
	    }catch(IOException e1){
	    	e1.printStackTrace();
	    }

	}


public static void main(String[] args) throws Exception  {
		        
	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",
        };
	
        	Thread t1=new Thread(new Downloader(urls[0],files[0]));
    		t1.start();
    		
    		Thread t2=new Thread(new Downloader(urls[1],files[1]));
    		t2.start();
    		
    		Thread t3=new Thread(new Downloader(urls[2],files[2]));
    		t3.start();
    		
    		Thread t4=new Thread(new Downloader(urls[3],files[3]));
    		t4.start();

	
	}
}

运行之后，在文件对应保存目录增加了4个htm文件