downpartfile.java

用多线程下载URL定位的文件,主要供学习java多线程的人和HTTP协议的人参考

import java.io.*;
import java.net.*;
/*
 * DownPartFile.java
 *
 * Created on 2006年12月10日, 下午7:52
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

/**
 *
 * @author Administrator
 */
public class DownPartFile{
    URL url=null;
    HttpURLConnection hURL;
    String httpURLString;
    BufferedInputStream bufferIn;
    RandomAccessFile file;
    String fileName;
    int fileLength;
    /** Creates a new instance of DownPartFile */
    public DownPartFile(String url,String FilePart) {
        httpURLString=url;
        fileName=FilePart;
       
    }
    //下载
    public void down(){
        int length=0;
        try {
            if((fileLength=getSize())!=-1){
                System.out.println("文件长度为："+fileLength);                
            }            
            url=new URL(httpURLString);
            hURL=(HttpURLConnection) url.openConnection(); 
            //hURL.setRequestProperty("User-Agent","NetFox");
            String sProperty="bytes="+0+"-";
            hURL.setRequestProperty("RANGE",sProperty);
            bufferIn=new BufferedInputStream(hURL.getInputStream());
            //file=new FileOutputStream(fileName);
            int size;
            byte[] buf=new byte[1024];
            while((size=bufferIn.read(buf))!=-1){
                System.out.println(size);
                file.write(buf,0,size);  
                length+=size;                
            }  
            System.out.println("共写入："+length);
            file.close();            
            bufferIn.close();
            hURL.disconnect();                      
        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        }
          catch (IOException ex) {
                ex.printStackTrace();
        }       
    }
    //下载指定的段
    public void getPartFile(long startPos,long endPos){
        int partLength=(int)(endPos-startPos);
        System.out.println("文件段长度："+partLength);
        int length=0;
            try {
                url=new URL(httpURLString);
                hURL=(HttpURLConnection) url.openConnection();
                String sProperty="bytes="+startPos+"-";
                System.out.println("文件开始下载位置："+sProperty);
                hURL.setRequestProperty("RANGE",sProperty);
                BufferedInputStream bIn=new BufferedInputStream(hURL.getInputStream());
                byte[] buf=new byte[1024];
                int len;
                file=new RandomAccessFile(fileName,"rw"); 
                file.seek(startPos);
                while((len=bIn.read(buf))!=-1){ 
                    if(len>partLength-length){
                        len=partLength-length;
                    }
                    file.write(buf,0,len); 
                    System.out.println(len);                   
                    length+=len;
                    if(length>=partLength){
                        file.close();
                        break;
                    }                  
                }
                  System.out.println("下载文件长度："+length);
            } catch (IOException ex) {
                ex.printStackTrace();
            }                           
    }
    public int getSize(){
        int fileLength=-1;
        try {
            url=new URL(httpURLString);
            hURL=(HttpURLConnection) url.openConnection(); 
            int code=hURL.getResponseCode();
            if(code==-1){
                System.out.println("不是有效的状态码！");    
                return -1;
            }
            if(code==400){
                System.out.println("发生错误！");   
                return -1;
            }
            if(code==200){
                System.out.println("正确接收信息！");
            }
            String sHeader;
            for(int i=1;;i++){
                //查找标识文件长度的文件头，获取文件长度
                sHeader=hURL.getHeaderFieldKey(i);
                if(sHeader!=null){
                    if(sHeader.equals("Content-Length")){
                        fileLength=
                                Integer.parseInt(hURL.getHeaderField(sHeader));
                        break;
                    }
                } else
                    break;
            }
           
        } catch (IOException ex) {
            ex.printStackTrace();
        }
         return fileLength;
    }

    public static void main(String[] args) {
        String urlString=new String("http://www.zhouyunhai.com/book/whomovedmycheese.exe");
        String filePart=new String("H:\\2.exe");
        DownPartFile downFile=new DownPartFile(urlString,filePart);
        //downFile.down();
        long startPos=0;
        long endPos=10000000;
        downFile.getPartFile(startPos,endPos);        
    }
}