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AJAX Push has always been an integral capability of the ICEfaces framework, but for the longest time it was not a primary consideration of the average technology evaluator. We always found this surprising, because the impact that push can have on a web application is far more profound than AJAX's primary claim to fame - eliminating the full page refresh. In recent months, however, we have seen a marked change in demand for push technology within the ICEfaces community, and we are now involved with a large number of projects where AJAX Push is front and center on the requirements list. So when people are evaluating their options for achieving web-based push, what makes them decide on ICEfaces?

Simply put - ICEfaces provides the most comprehensive open source solution in the industry for lightweight (plugin-free), push for web applications. Now, I will back up that statement with the supporting facts.

To begin with, while there are hundreds of open source AJAX libraries out there, only a small handful offer push capabilities - namely Dojo/Cometd, DWR/Reverse AJAX, and ICEfaces/AJAX Push. All three mechanisms are based on the same fundamental concept of HTTP protocol inversion - holding an open request from the browser, and responding to that request when something is available to be pushed. Normal and inverted HTTP connections are illustrated in the figure below.

So if all push mechanisms are based on this low-level protocol inversion, then how can they be fundamentally different from the developer's perspective? With ICEfaces we have strived to provide a natural extension to the JSF programming model in support of push style application development, and have sheltered the developer from the low-level mechanics for AJAX-based push. ICEfaces provides an application-level managed bean, the RenderHub, that orchestrates push events within the JSF lifecycle. Basically, you define groups of client sessions that need to receive the same push events, and register those render groups with the hub. Some trigger point in application logic can then request a render on a given render group, and the hub will make it all happen. The hub is responsible for executing the render phase for each session in the group, coalescing requests and maximizing throughput with multiple parallel render threads. Furthermore, the RenderHub architecture supports clustered deployments. This basic push architecture is illustrated below.