How do you implement subscriptions in GraphQL with Spring Boot?

Table of Contents

• Introduction
• Setting Up GraphQL Subscriptions in Spring Boot
  • 1. Add Dependencies for Spring Boot and GraphQL
  • 2. Configure WebSocket for Subscriptions
    • Example WebSocket Configuration
  • 3. Define a GraphQL Subscription
    • Example Subscription Definition
  • 4. Create a Subscription Resolver
    • Example Subscription Resolver
  • 5. Implementing a Publisher (Optional)
    • Example Publisher Class
  • 6. Client-side WebSocket Configuration
• Conclusion

Introduction

GraphQL subscriptions allow clients to receive real-time updates when data changes, enabling features like live notifications, chat applications, or real-time dashboards. In a Spring Boot application, implementing subscriptions involves configuring WebSockets for communication and using Spring GraphQL to handle subscription logic. This guide walks you through the steps needed to set up GraphQL subscriptions in Spring Boot, enabling real-time data updates for your application.

Setting Up GraphQL Subscriptions in Spring Boot

1. Add Dependencies for Spring Boot and GraphQL

To implement GraphQL subscriptions in Spring Boot, you need the following dependencies:

• spring-boot-starter-websocket for WebSocket support.
• spring-boot-starter-graphql for GraphQL integration.
• spring-boot-starter-data-graphql for GraphQL data handling.

Add the dependencies to your pom.xml:

This setup ensures that WebSockets and GraphQL integration are properly configured in your Spring Boot application.

2. Configure WebSocket for Subscriptions

GraphQL subscriptions use WebSockets to establish a persistent connection between the client and the server. In Spring Boot, WebSockets can be enabled by configuring a @Configuration class to define WebSocket endpoints.

Example WebSocket Configuration

Here:

• The WebSocket connection is made to /graphql.
• The message broker will handle the subscriptions via the /topic prefix.
• SockJS fallback is enabled to ensure compatibility with clients that may not support WebSockets.

3. Define a GraphQL Subscription

GraphQL subscriptions are defined like queries or mutations but are meant to emit data updates over time. To implement a subscription in Spring Boot, you'll need to create a subscription resolver that will handle subscription logic.

Example Subscription Definition

In your GraphQL schema file (schema.graphqls), define the subscription as follows:

This subscription returns a String when a new message is received.

4. Create a Subscription Resolver

Now, implement a subscription resolver that will publish messages to the subscribed clients. You can use the GraphQLSubscriptionResolver interface to define how the subscription is handled.

Example Subscription Resolver

In this example, the messageReceived method returns a Mono<String>, which is a reactive stream that sends updates to the client.

• Mono.just("...") is used here to simulate sending a message, but in a real-world scenario, it could be triggered by events like database changes or other system events.

5. Implementing a Publisher (Optional)

If you need to emit events in response to some external actions (such as a new chat message or a data change), you can implement a publisher to push messages to subscribed clients.

Example Publisher Class

Here, Sinks.many().replay().all() is used to create a publisher that replays all emitted values to new subscribers. You can use this MessagePublisher to push new data to the subscribers whenever an event occurs.

6. Client-side WebSocket Configuration

On the client side, you can use libraries like Apollo Client or a WebSocket client to listen for updates to the subscription. Here's an example using Apollo Client:

This client listens for updates to the messageReceived subscription and logs the message when it arrives.

Conclusion

Implementing GraphQL subscriptions in Spring Boot allows your application to push real-time data to clients. By integrating WebSockets with Spring GraphQL, you can easily set up a subscription model that delivers live updates. This is especially useful for applications requiring real-time data like chat apps, live notifications, or dynamic dashboards. With WebSocket configuration, subscription resolvers, and proper client integration, you can efficiently manage and implement real-time data streams in your Spring Boot GraphQL application.