上传图片，不成功啊？没反应

URL httpUrl=new URL(url);
   HttpURLConnection conn=(HttpURLConnection)httpUrl.openConnection();
   conn.setRequestMethod("POST");
   conn.setDoOutput(true);
   conn.setDoInput(true);//请求属性
   conn.setRequestProperty("Content-Type","multipart/form-data;boundary="+boundary);
   DataOutputStream out=new DataOutputStream(conn.getOutputStream());
   out.writeBytes(prefix+boundary+end);
   out.writeBytes("Content-Disposition:form-data;"+"name=\"upload\";filename=\""+"Sky.jpg"+"\""+end);
   out.writeBytes(end);//回车换行符
   FileInputStream fileInputStream=new FileInputStream(new File(fileName));
   byte[] b=new byte[1024*4];
   int len;
   while((len=fileInputStream.read(b))!=-1){
    out.write(b,0,len);
   }
   out.writeBytes(end);
   out.writeBytes(prefix+boundary+prefix+end);//最后結束行
   out.flush();