HTTPUrlConnection error (Can't open OutputStream after reading from an inputStream)

Question

I am new to Java and am running into the above mentioned error while using HTTPURLConnection to send multiple post requests on Android. I have written an HTTPTransport class in which I would like to have sendMessage and recvMessage methods.

public class HTTPTransport
{
   private HttpURLConnection connection;

   public HTTPTransport()
   {
      URL url = new URL("http://test.com");

      connection = (HttpURLConnection) url.openConnection(); 
      connection.setRequestMethod("POST"); 
      connection.setDoInput(true); 
      connection.setDoOutput(true); 
      connection.setRequestProperty("Content-Type", "application/octet-stream");
      connection.setRequestProperty("Accept-Encoding", "gzip");
      connection.setRequestProperty("Connection", "Keep-Alive");
   }

   public void sendMessage(byte[] msgBuffer, long size)
   {
      try
      {
         DataOutputStream dos = new DataOutputStream(connection.getOutputStream());
         dos.write(msgBuffer, 0, (int)size); 
         dos.flush();
         dos.close();

         dos.close();
      }
      catch( IOException e )
      {
         // This exception gets triggered with the message mentioned in the title.
         Log.e(TAG, "IOException: " + e.toString());
      }
   }
   public byte[] recvMessage()
   {

      int readBufLen = 1024;

      byte[] buffer = new byte[readBufLen];

      int len = 0;
      FileOutputStream fos = new FileOutputStream(new File("/sdcard/output.raw"));

      DataInputStream dis = new DataInputStream(connection.getInputStream());
      while((len = dis.read(buffer, 0, readBufLen)) > 0) 
      {
         Log.d(TAG, "Len of recd bytes " + len + ", Byte 0 = " + buffer[0]);
         //Save response to a file
         fos.write(buffer, 0, len);
      }

      fos.close();
      dis.close();
      return RecdMessage;      
   }
}

I am able to send the first message successfully using sendMessage and recvMessage. When I try to send the second one, I see this error: IOException: java.net.ProtocolException: can't open OutputStream after reading from an inputStream

Please let me know how I can write this class.

Thanks!

Answer 1

You need to use a new HttpURLConnection per request. The TCP connection itself will be pooled behind the scenes. Don't try to do that yourself.

Answer 2

Your implementation of HTTPUrlConnection does not allow you to reuse the connection in this manner . I believe you'll have to use an HttpConnectionManager to make use of Keep-Alive in the manner you want.