java http 分段上载_Java Web开发

java http 分段下载
大家好，我是java小白，最近研究了http分段下载，但是自己写的代码运行后下载的文件不能打开。文件数据大小和网上文件是一样的，所以我没有找到原因，在此求教，谢谢。
以下是我的函数，

Java code

public String upload(URL url) throws IOException{        String fileName = url.getFile();        InputStream in = null;        final long size = 1024*5;        if(fileName.equals("")){            throw new IOException("upload webfile \"" + fileName + "\" failed");        }        HttpURLConnection con = (HttpURLConnection) url.openConnection();        long total = con.getContentLength();        System.out.println("file size is "+total);        String newFileName = null;        con.disconnect();        if(total<=size){            con = (HttpURLConnection) url.openConnection();            con.connect();            in = con.getInputStream();                        return upload(fileName, in);                    }else {                                    long part = total%size != 0 ? total/size+1 : total/size;            long len;            byte[] b = null;            for(int i = 0; i< part;i++){                len = i!=part-1 ? size : total%size;                b = new byte[IoUtils.safeLongToInt(len)];                //con.setConnectTimeout(30000);                con.setReadTimeout(30000);                 //设置传输位置                 con.setRequestProperty("RANGE","bytes=" + i*size + "-" + (i*size+len-1)    + "/" + total);                 //设置请求信息                con.setRequestProperty("GET","/large/774fca33gw1dozmkrsu6ej.jpg HTTP/1.1");                //设置接受信息                con.setRequestProperty("[code=Java]Accept

","image/gif,image/x-xbitmap,application/msword,*/*");
//设置连接信息
con.setRequestProperty("Connection","Keep-Alive");
//con.setRequestProperty("RANGE","bytes " + i*size + "-" + (i*size+len-1) + "/" + total);
// 获得输入流
con.connect();
in = con.getInputStream();
DataInputStream dis = new DataInputStream(in);

RandomAccessFile oSavedFile = new RandomAccessFile("C:/bbb.jpg","rw");
//FileOutputStreamWrite fout = new FileOutputStream(oSavedFile);
long nPos = i*size;
// 定位文件指针到 nPos 位置
oSavedFile.seek(nPos);

// 从输入流中读入字节流，然后写到文件中
dis.read(b,0,IoUtils.safeLongToInt(len));
oSavedFile.write(b);
con.disconnect();

}
in.close();
return newFileName;
}
}[/code]

------解决方案--------------------------------------------------------
这里有误
// 从输入流中读入字节流，然后写到文件中
dis.read(b,0,IoUtils.safeLongToInt(len));

并不是每次你让他读多少他就正好读多少数据进来，所以要在这里做个循环，一直读完。

Java code

        int wlen = 0;        while (wlen < len) {            int read = bis.read(b, 0, len);            wlen += read;            oSavedFile.write(b, 0, read);        }