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 }