Java实现多线程下载

  1 package cn.test.DownLoad;
  2 
  3 import java.io.File;
  4 import java.io.InputStream;
  5 import java.io.RandomAccessFile;
  6 import java.net.HttpURLConnection;
  7 import java.net.URL;
  8 
  9 public class MultiPart {
 10     public void down() throws Exception
 11     {
 12         //1、声明URL
 13         String fileName="a.rar";
 14         String path="http://localhost:8080/day23_MultiThreadDownLoad/file/"+fileName;
 15         URL url=new URL(path);
 16         //2、返回连接对象
 17         HttpURLConnection conn=(HttpURLConnection) url.openConnection();
 18         //3、设置请求类型
 19         conn.setRequestMethod("GET");
 20         //4、设置允许接收消息
 21         conn.setDoInput(true);
 22         //5、连接
 23         conn.connect();
 24         //6、状态码
 25         int code=conn.getResponseCode();
 26         if(code==200)
 27         {
 28             int sum=conn.getContentLength();//总长度
 29             String downFile="d:\\"+fileName;
 30             //7、创建一个相同大小的空文件
 31             RandomAccessFile file=new RandomAccessFile(new File(downFile), "rw");
 32             file.setLength(sum);
 33             file.close();
 34             //8、声明线程数量
 35             int threadCount=3;
 36             //9、声明每个线程的下载量
 37             int threadSize=sum/threadCount+((sum%threadCount==0)?0:1);
 38             for(int i=0;i<threadCount;i++)
 39             {
 40                 int start=i*threadSize;
 41                 int end=start+threadSize-1;
 42                 System.out.println("线程： "+i+" : "+start+" : "+end);
 43                 //10、启动线程
 44                 new myThread(start,end,downFile,url).start();
 45             }        
 46         }
 47         //11、关闭连接
 48         conn.disconnect();
 49     }
 50     
 51     public static void main(String[] args) {
 52         try {
 53             new MultiPart().down();
 54         } catch (Exception e) {
 55             e.printStackTrace();
 56         }
 57         System.out.println("OK");
 58     }
 59 }
 60 
 61 class myThread extends Thread
 62 {
 63     private int start;
 64     private int end;
 65     private String downFile;
 66     private URL url;    
 67     public myThread(int start, int end, String downFile, URL url) {
 68         this.start = start;
 69         this.end = end;
 70         this.downFile = downFile;
 71         this.url = url;
 72     }
 73 
 74     public void run() {
 75         try {
 76             HttpURLConnection conn=(HttpURLConnection) url.openConnection();
 77             conn.setRequestMethod("GET");
 78             conn.setDoInput(true);
 79             //设置从哪里下载。断点
 80             conn.setRequestProperty("range", "bytes="+start+"-"+end);
 81             conn.connect();
 82             int code=conn.getResponseCode();
 83             if(code==206)
 84             {
 85                 int size=conn.getContentLength();
 86                 InputStream in=conn.getInputStream();
 87                 //写同一文件
 88                 RandomAccessFile file=new RandomAccessFile(new File(downFile), "rw");
 89                 //设置从文件的哪里开始写
 90                 file.seek(start);
 91                 byte[] b=new byte[1024];
 92                 int len=-1;
 93                 while((len=in.read(b))!=-1)
 94                 {
 95                     file.write(b, 0, len);
 96                 }
 97                 file.close();
 98             }
 99             conn.disconnect();            
100             
101         } catch (Exception e) {
102             e.printStackTrace();
103         }        
104     }    
105 }