There are countless articles related to web performance. The most comprehensive one is performed by researchers from Yahoo. They have identified a number of best practices for making web pages fast. You can find the details here.
Also, they created a tool called YSlow: YSlow which analyzes web pages and tells you why they're slow based on the rules for high performance web sites. YSlow is a Firefox add-on integrated with the popular Firebug web development tool.
The aim of wro4j project is to help application developed on java platform to address a couple of those problems described by Yahoo research. More, exactly it is about "Minimize HTTP Requests" and "Gzip Components".
