I followed this blog to configure my instance of glassfish to enable gzip compression for HTTP traffic. Here is my version of the configuration:
<property name="compression" value="on"/> <property name="compressableMimeType" value="text/html,text/xml,text/plain,image/gif,image/jpeg,image/png,text/css,text/javascript,application/json"/>
After restarted the sever, I noticed that not all files were compressed. Some css files were compressed while some other css files didn’t. I wonder why?
Dave's Blogs 
I think you should ask this question on users @ glassfish.dev.java.net or webtier @ glassfish.dev.java.net
Maybe cause you don’t put the parameter
minCompressionSize
Take a look:
http://docs.sun.com/app/docs/doc/820-4338/abhco?a=view