You're reading from Java EE 8 Cookbook Build reliable applications with the most robust and mature technology for enterprise development

Product type Paperback

Published in Apr 2018

Publisher Packt

ISBN-13 9781788293037

Length 382 pages

Edition 1st Edition

Languages

Java

Tools

Java EE

Concepts

Application Development

Authors (2):

Edson Yanaga

Elder Moraes

View More author details

Running your first Servlet 4.0 code

Servlet 4.0 is one the of biggest APIs of Java EE 8. Since the very beginning of the Java EE platform (the old J2EE), the Servlet specification has always played a key role.

The coolest additions of this version are surely HTTP/2.0 and Server Push. Both of them bring performance improvements to your application.

This recipe will use Server Push to do one of the most basic tasks in a web page—loading an image.

Getting ready

Let's add the dependencies that we need:

<dependency>
    <groupId>javax</groupId>
    <artifactId>javaee-api</artifactId>
    <version>8.0</version>
    <scope>provided</scope>
</dependency>

How to do it...

We will create a servlet:

@WebServlet(name = "ServerPush", urlPatterns = {"/ServerPush"})
public class ServerPush extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, 
    HttpServletResponse 
    response) throws ServletException, IOException {

        PushBuilder pb = request.newPushBuilder();
        if (pb != null) {
            pb.path("images/javaee-logo.png")
              .addHeader("content-type", "image/png")
              .push();
        }

        try (PrintWriter writer = response.getWriter();) {
            StringBuilder html = new StringBuilder();
            html.append("<html>");
            html.append("<center>");
            html.append("<img src='images/javaee-logo.png'><br>");
            html.append("<h2>Image pushed by ServerPush</h2>");
            html.append("</center>");
            html.append("</html>");
            writer.write(html.toString());
        }
    }
}

To try it, run the project in a Java EE 8 server and open this URL:

https://localhost:8080/ch01-servlet/ServerPush

How it works...

We use the PushBuilder object to send an image to the client before it is requested by the img src tag. In other words, the browser doesn't need to do another request (what it usually does with img src) to have an image available for rendering.

It might seem as if it doesn't make too much difference for a single image, but it would with dozens, hundreds, or thousands of images. Less traffic for your client and from your server. Better performance for all!

There's more...

If you are using JSF, you can get the benefits from Server Push for free! You don't even need to rewrite a single line of your code, as JSF relies on the Server Push specification.

Just make sure that you run it under the HTTPS protocol, as HTTP/2.0 only works under it.