week8多线程

版权声明： https://blog.csdn.net/lyw_321/article/details/79981323

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）。

1. import java.net.URL;
2. import java.io.*;
3.  
4. class Downloader 
5. {
6.     public static void main(String[] args)
7.         throws Exception
8.     {
9.         final URL[] urls = {
10.             new URL("http://www.pku.edu.cn"),
11.             new URL("http://www.baidu.com"),
12.             new URL("http://www.sina.com.cn"),
13.             new URL("http://www.dstang.com")
14.         };
15.         final String[] files = {
16.             "pku.htm", 
17.             "baidu.htm",
18.             "sina.htm", 
19.             "study.htm",
20.         };
21.  
22.         for(int idx=0; idx<urls.length; idx++){
23.             try{
24.                 System.out.println( urls[idx] );
25.                 download( urls[idx], files[idx]);
26.             }catch(Exception ex){
27.                 ex.printStackTrace();
28.             }
29.         }
30.     }
31.     static void download( URL url, String file)
32.         throws IOException
33.     {
34.         try(InputStream input = url.openStream();
35.             OutputStream output = new FileOutputStream(file))
36.         {
37.             byte[] data = new byte[1024];
38.             int length;
39.             while((length=input.read(data))!=-1){
40.                 output.write(data,0,length);
41.             }
42.         }
43.     }
44. }

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