In this article, we will be talking about Server Push Technology that is actually part of the HTTP/2 spec.
The most important feature of Servlet 4.0, due to HTTP/2, is the implementation of the server push capability. The concept behind this technique is that if the client/browser requests a certain resource, the server assumes, in advance, that some other related resources may also be requested soon. Because of this assumption, it pushes them into the cache (called ‘cache push’) before they are actually needed. For example, it is very much likely that when a webpage is loaded, it may eventually request a CSS file or another image. The server proactively starts pushing the bytes of these assets simultaneously, without the need for the client to make an explicit request.