Implementing GraphQL Subscriptions in Spring Boot

GraphQL is increasingly being adopted for building APIs due to its flexibility and efficiency in data retrieval. One of its powerful features is subscriptions, which allows clients to receive real-time updates from the server. This is especially useful for applications that require constant data updates, such as chat applications or live data dashboards. In this post, we will explore how to implement GraphQL subscriptions in a Spring Boot application.

What are GraphQL Subscriptions?

Subscriptions in GraphQL provide a way to maintain an active connection between the client and server over WebSockets. When the data on the server changes, it sends updates to the clients that are subscribed to that data. This allows for real-time communication between the server and its clients.

Setting Up Your Spring Boot Application

Let’s start by creating a Spring Boot application that will utilize GraphQL subscriptions:

1. Create a New Spring Boot Project

Use Spring Initializr to create a new project and include the following dependencies:

• Spring Web
• Spring Data JPA
• Spring GraphQL
• WebSocket

2. Adding Dependencies

Add the necessary dependencies in your pom.xml file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-graphql</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-websocket</artifactId>
</dependency>

Creating a GraphQL Schema

Define your GraphQL schema by creating a schema.graphqls file in src/main/resources:

type Message {
    id: ID!
    content: String!
}

type Query {
    messages: [Message]
}

type Subscription {
    messageAdded: Message
}

Creating a Data Model

Create a simple Message entity class that will serve as the data model:

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Message {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String content;

    // Getters and Setters
}

Service for Managing Messages

Create a service to handle the business logic for messages:

import org.springframework.stereotype.Service;
import java.util.ArrayList;
import java.util.List;

@Service
public class MessageService {
    private List<Message> messages = new ArrayList<>();

    public List<Message> getMessages() {
        return messages;
    }

    public Message addMessage(String content) {
        Message message = new Message();
        message.setContent(content);
        messages.add(message);
        return message;
    }
}

Implementing the GraphQL Resolvers

Now create resolvers to handle queries and subscriptions:

import graphql.kickstart.tools.GraphQLQueryResolver;
import graphql.kickstart.tools.GraphQLSubscriptionResolver;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Sinks;

@Component
public class MessageResolver implements GraphQLQueryResolver, GraphQLSubscriptionResolver {
    @Autowired
    private MessageService messageService;

    private final Sinks.Many<Message> sink = Sinks.many().multicast().onBackpressureBuffer();

    public List<Message> messages() {
        return messageService.getMessages();
    }

    public Flux<Message> messageAdded() {
        return sink.asFlux();
    }

    public void addMessage(String content) {
        Message message = messageService.addMessage(content);
        sink.tryEmitNext(message);
    }
}

Running and Testing Your Application

Run your Spring Boot application and use a GraphQL client like Insomnia or Apollo Studio to test your subscriptions. First, you can check existing messages:

{ messages { id content } }

Then, create a subscription to listen for new messages:

subscription { messageAdded { id content } }

Conclusion

Integrating Spring Boot with GraphQL and supporting subscriptions allows you to build interactive and responsive applications that can send real-time updates to clients. This setup promotes a more dynamic and user-friendly application experience, paving the way for many engaging use cases.

For further insights into advanced features of Spring Boot and GraphQL, as well as event-driven solutions, check out the rich resources available at ITER Academy to elevate your development skills.

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