Implementing server-side push notifications in Java applications with GlassFish and Server-Sent Events (SSE)

17 Sep 2023

In today’s fast-paced world, real-time updates and notifications are becoming increasingly important in web applications. One way to achieve this is through server-side push notifications. In this article, we will explore how you can implement server-side push notifications in a Java web application using GlassFish and Server-Sent Events (SSE).

What are Server-Sent Events (SSE)?

Server-Sent Events (SSE) is a web standard that allows the server to send real-time updates to the client over a single long-lived HTTP connection. Unlike other real-time communication mechanisms such as WebSockets, SSE is a unidirectional communication channel where the server can push updates to the client.

Setting up a GlassFish server

To get started, you will first need to set up a GlassFish server. GlassFish is an open-source application server that is easy to use and supports the latest Java technologies. You can download GlassFish from the official website and follow the installation instructions.

Once you have GlassFish installed, start the server by running the following command:

asadmin start-domain

Creating a Java web application

Next, let’s create a Java web application that will serve as the backend for our push notifications. You can use your favorite IDE to create a new Maven-based Java web application or follow these simple steps:

Create a new directory for your project and navigate to it.
Run the following command to create a new Maven-based Java web application:

mvn archetype:generate -DgroupId=com.example -DartifactId=my-webapp -DarchetypeArtifactId=maven-archetype-webapp -DinteractiveMode=false

Open the pom.xml file and add the GlassFish dependency:

<dependencies>
    <dependency>
        <groupId>org.glassfish.main.extras</groupId>
        <artifactId>glassfish-embedded-all</artifactId>
        <version>3.1.2.2</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

Create a new Java class called PushNotificationServlet that extends javax.servlet.http.HttpServlet:

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class PushNotificationServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/event-stream");
        response.setCharacterEncoding("UTF-8");

        // TODO: Implement SSE logic here
    }
}

Implement the SSE logic in the doGet method. This is where you will push notifications to the client. For example:

import java.io.IOException;
import java.io.PrintWriter;

public class PushNotificationServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/event-stream");
        response.setCharacterEncoding("UTF-8");

        PrintWriter writer = response.getWriter();
        writer.write("data: New notification\n\n"); // Push a notification to the client

        writer.flush();
        writer.close();
    }
}

Deploying to GlassFish

Now that we have our Java web application ready, let’s deploy it to GlassFish:

Build the web application by running the following command in the project directory:

mvn clean package

Deploy the web application to GlassFish using the following command:

asadmin deploy target/my-webapp.war

Verify that the web application is deployed by accessing the following URL in your browser:

http://localhost:8080/my-webapp/

Testing the server-side push notifications

To test the server-side push notifications, you can use a simple HTML page that listens to SSE updates:

<!DOCTYPE html>
<html>
<head>
    <title>Server-Sent Events Example</title>
</head>
<body>
    <script>
        var eventSource = new EventSource('/my-webapp/push-notifications');

        eventSource.onmessage = function (event) {
            console.log('Received notification: ' + event.data);
        };
    </script>
</body>
</html>

Open this HTML page in your browser and you should see a message in the browser’s console whenever a new notification is pushed from the server.

Conclusion

In this article, we have learned how to implement server-side push notifications in Java web applications using GlassFish and Server-Sent Events (SSE). With SSE, you can easily push real-time updates from the server to the client, allowing you to create more interactive and dynamic web applications.