SpringMVC在上传文件的时候提示The current request is not a multipart request，如何破？

String uploadUrl = actionUrl;  
    String end = "\r\n";  
    String twoHyphens = "--";  
    String boundary = "******";  
    try  
    {  
      URL url = new URL(uploadUrl);  
      HttpURLConnection httpURLConnection = (HttpURLConnection) url  
          .openConnection();  
      httpURLConnection.setDoInput(true);  
      httpURLConnection.setDoOutput(true);  
      httpURLConnection.setUseCaches(false);  
      httpURLConnection.setRequestMethod("POST");  
      httpURLConnection.setRequestProperty("Connection", "Keep-Alive");  
      httpURLConnection.setRequestProperty("Charset", "UTF-8");  
      httpURLConnection.setRequestProperty("Content-Type",  
          "multipart/form-data;boundary=" + boundary);  
  
      DataOutputStream dos = new DataOutputStream(httpURLConnection.getOutputStream());  
      dos.writeBytes(twoHyphens + boundary + end);  
      dos.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\""  
              + srcPath.substring(srcPath.lastIndexOf("/") + 1)  
              + "\"" + end);  
      dos.writeBytes(end);