How it works...

A web application running under HTTP/1.0 sends a request to the server when it finds references for an image file, CSS file, and any other resources needed to render a web page.

With HTTP/2.0, you still can do this, but now, you can do this a lot better – the server can now push the resources beforehand, avoiding unnecessary new requests, decreasing the server load, and improving performance.

In this recipe, our resources are represented by the following code:

   meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
   link rel="stylesheet" type="text/css" href="resources/style.css">
   script src="resources/functions.js"></script>

The push happens at this part of our filter:

   HttpServletRequest httpReq = (HttpServletRequest)request;
   PushBuilder builder = httpReq.newPushBuilder();
        
   if (builder != null){
          builder
              .path("resources/javaee-logo.png")
              .path("resources/style.css")
              .path("resources/functions.js")
              .push(); 
          System.out.println("Resources pushed");
    }

So, when the browser needs those resources to render the web page, they are already available.