用java 實現 http檔案下載

import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownLoad {
 
    public void down(){
     
     
     String path1 = "http://localhost:8080/wallpaper/aa/aa.txt";
     String path2 = "D:/aa.txt";
     
     File file2 = new File(path2);
     
     try{
      System.out.println("下載");
      URL file1 = new URL(path1);
      HttpURLConnection httpConnection = (HttpURLConnection)file1.openConnection();
      httpConnection.disconnect();

      //設定User-Agent
      httpConnection.setRequestProperty("User-Agent","NetFox");
      //設定斷點續傳的開始位置
      httpConnection.setRequestProperty("RANGE", "bytes="+5+"-");
      //獲得輸入資料流
      InputStream input = httpConnection.getInputStream();

         int filesize1 = (int) file2.length();
         
      byte[] buff = new byte[1024];
      int t = 0;
      RandomAccessFile randomFile = new RandomAccessFile(file2, "rw");  
       // 檔案長度，位元組數  
            long fileLength = randomFile.length();  
           
            int nPos = 5; 
             randomFile.seek(nPos);  
          while(-1 != (t = input.read(buff, 0, buff.length))){
                    randomFile.write(buff, 0,t);
                    randomFile.close();  

          }
        System.out.println("檔案下載完畢！");  
          
     }catch(Exception e){
      e.printStackTrace();
      
     }
     
    }
   
    public static void main(String[] args) {
  DownLoad d = new DownLoad();
  d.down();
 }
}