Can I compress HTTP Requests using GZIP?

Question

I am communicating to a Tomcat Server using a Java ME application on my mobile device.
I was wondering if I could compress my requests/responses using Gzip to reduce the number of bytes sent over the network.

Answer 1

Modern phones have so much CPU power and the network is relatively slow so compression makes perfect sense. It's quite easy to do also.

On the J2ME side, you do something like this (assuming you use HttpConnection),

  hc.setRequestProperty("Accept-Encoding", "gzip, deflate");
  if (hc.getResponseCode() == HttpConnection.HTTP_OK) {
      InputStream in = hc.openInputStream();
      if ("gzip".equals(hc.getEncoding())) 
         in = new GZIPInputStream(in);
  ...

We use GZIPInputStream from tinyline but I am sure there are others,

http://www.tinyline.com/utils/index.html

On the server side, it's all built-in. Just add following attributes to the Connector in server.xml on Tomcat,

<Connector 
compression="on"
compressionMinSize="2048"
compressableMimeType="text/html,application/json"
... />

Answer 2

You can compress the content of an HTTP request or response, but not the headers. See section 3.6 of the HTTP 1.1 spec, and the later section that describes the Content-Encoding header.

EDIT: The flip side of this is that there is no guarantee that an HTTP server side will accept any particular compression format. And depending on the quality of the server-side implementation of HTTP, it might not even recognize that the request content has been compressed. So you don't want to do this unless you know that the server-side supports compressed request content.

Answer 3

Since you are using Tomcat, consider the possibility of putting an instance of Apache HTTP Server in front of the Tomcat server.

This can be done using the mod_jk module for Apache HTTP Server. Once you have done that, you can use mod_gzip/mod_deflate in Apache.

Of course, your client should have the ability to handle the compressed responses, for this to work. If you force your client to work with compressed responses, the client will end up displaying gibberish, since it would have been (usually) expecting plain text responses. You will find the definite indicator of the client's capability to handle compressed responses, in the client's Accept-Encoding headers.

This can be done programatically, using a servlet or a servlet filter that writes to a ZipOutputStream or GZipOutputStream, if you want to avoid the introduction of the Apache HTTP Server in the network. You will find some pointers on how to do this at the OReilly OnJava.com site.

Answer 4

On the server side, you can enable it as described here, but the mobile application will need a library that can decompress gzip, such as this one. Might be a bit of work to get it working though...