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One of the most important new features of Jakarta Servlet 4 is its HTTP/2.0 support. It brings another cool and reliable feature – Server Push.
This recipe will show you how to use Server Push in a filter and push the resources needed in every request that we want.
First, we need to add the required dependencies:
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-api</artifactId>
<version>8.0</version>
<scope>provided</scope>
</dependency>
To complete this recipe, please perform the following steps:
@WebServlet(name = "UserServlet", urlPatterns = {"/UserServlet"})
public class UserServlet extends HttpServlet {
protected void doRequest(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
request.getRequestDispatcher("/user.jsp").forward(request, response);
System.out.println("Redirected to user.jsp");
}
@Override
protected void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doRequest(request, response);
}
@Override
protected void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doRequest(request, response);
}
}
@WebServlet(name = "ProfileServlet", urlPatterns = {"/ProfileServlet"})
public class ProfileServlet extends HttpServlet {
protected void doRequest(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
request.getRequestDispatcher("/profile.jsp").
forward(request, response);
System.out.println("Redirected to profile.jsp");
}
@Override
protected void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doRequest(request, response);
}
@Override
protected void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doRequest(request, response);
}
}
@WebFilter(filterName = "PushFilter", urlPatterns = {"/*"})
public class PushFilter implements Filter {
@Override
public void doFilter(ServletRequest request,
ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
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");
}
chain.doFilter(request, response);
}
}
<body>
<a href="UserServlet">User</a>
<br/>
<a href="ProfileServlet">Profile</a>
</body>
<head>
<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>
<title>User Push</title>
</head>
<body>
<h1>User styled</h1>
<img src="resources/javaee-logo.png">
<br />
<button onclick="message()">Message</button>
<br />
<a href="javascript:window.history.back();">Back</a>
</body>
<head>
<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>
<title>User Push</title>
</head>
<body>
<h1>Profile styled</h1>
<img src="resources/javaee-logo.png">
<br />
<button onclick="message()">Message</button>
<br />
<a href="javascript:window.history.back();">Back</a>
</body>
When you run the preceding code, make sure to use the HTTPS port as it only works under this protocol; for example, https://localhost:4848/ch02-serverpush-1.0.
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.
Note that your browser needs to support the Server Push feature; otherwise, your page will work as usual. So, make sure you check that PushBuilder is null before using it and ensure all users will have the working application.
JSF 2.3 is built on top of the Server Push feature, so if you just migrate your JSF application to a Jakarta EE 8-compatible server, you get its performance boost for free!
Finally, Server Push only works under a Secure Sockets Layer (SSL) protocol, so pay attention to it.
You can view the full source code for this recipe at https://github.com/eldermoraes/javaee8-cookbook/tree/master/chapter02/ch02-serverpush.
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