Building a GraphQL service with Spring for GraphQL

Spring for GraphQL provides support for Spring applications built on GraphQL Java.

This guide walks you through the process of creating a GraphQL service in Java using Spring for GraphQL.

What You Will Build

You will build a service that will accept GraphQL requests at http://localhost:8080/graphql.

What You Need

https://raw.githubusercontent.com/spring-guides/getting-started-macros/main/prereq_editor_jdk_buildtools.adoc

https://raw.githubusercontent.com/spring-guides/getting-started-macros/main/how_to_complete_this_guide.adoc

Starting with Spring Initializr

To manually initialize the project:

1. Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you.

2. Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java.

3. Choose Spring Boot 3.x.

4. Choose at least Java 17 (minimum requirement for Spring Boot 3.x).

5. Click Dependencies and select Spring for GraphQL and Spring Web.

6. Click Generate.

7. Download the resulting ZIP file, which is an archive of a GraphQL application that is configured with your choices.

Note	If your IDE has the Spring Initializr integration, you can complete this process from your IDE.

Note	You can also fork the project from GitHub and open it in your IDE or other editor.

A very short introduction to GraphQL

GraphQL is a query language to retrieve data from a server. It is an alternative to REST, SOAP, or gRPC.

In this tutorial, we will query the details for a specific book from an online store backend.

This is an example request you can send to a GraphQL server to retrieve book details:

query bookDetails {
  bookById(id: "book-1") {
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}

This GraphQL request says:

• perform a query for a book with id "book-1"

• for the book, return id, name, pageCount and author

• for the author, return firstName and lastName

The response is in JSON. For example:

{
  "bookById": {
    "id":"book-1",
    "name":"Effective Java",
    "pageCount":416,
    "author": {
      "firstName":"Joshua",
      "lastName":"Bloch"
    }
  }
}

An important feature of GraphQL is that it defines a schema language, and that it is statically typed. The server knows exactly what types of objects requests can query and what fields those objects contain. Furthermore, clients can introspect the server to ask for schema details.

Note	The word schema in this tutorial refers to a "GraphQL Schema", which is not related to other schemas like "JSON Schema" or "Database Schema".

The schema for the above query is:

type Query {
  bookById(id: ID): Book
}

type Book {
  id: ID
  name: String
  pageCount: Int
  author: Author
}

type Author {
  id: ID
  firstName: String
  lastName: String
}

This tutorial will focus on how to implement a GraphQL server with this schema in Java.

We’ve barely scratched the surface of what’s possible with GraphQL. Further information can be found on the official GraphQL page.

Our example API: getting book details

These are the main steps to create a server with Spring for GraphQL:

1. Define a GraphQL schema

2. Implement the logic to fetch the actual data for a query

Our example app will be a simple API to get details for a specific book. It is not intended to be a comprehensive API.

Schema

In your Spring for GraphQL application prepared earlier, create a directory src/main/resources/graphql.

Add a new file schema.graphqls to src/main/resources/graphql with the following content:

type Query {
  bookById(id: ID): Book
}

type Book {
  id: ID
  name: String
  pageCount: Int
  author: Author
}

type Author {
  id: ID
  firstName: String
  lastName: String
}

Every GraphQL schema has a top-level Query type, and the fields under it are the query operations exposed by the application. Here the schema defines one query called bookById that returns the details of a specific book.

It also defines the types Book with fields id, name, pageCount and author, and the type Author with fields firstName and lastName.

Note	The Domain Specific Language used above to describe a schema is called the Schema Definition Language or SDL. For more details, see the GraphQL documentation.

Source of the data

A key strength of GraphQL is that data can be sourced from anywhere. Data can come from a database, an external service, or a static in-memory list.

To simplify the tutorial, book and author data will come from static lists inside their respective classes.

Create the Book class

Add the following to Book.java. You choose where to save this file, it can be in the same directory as the class containing the @SpringBootApplication annotation.

import java.util.Arrays;
import java.util.List;

public record Book (String id, String name, int pageCount, String authorId) {

    private static List<Book> books = Arrays.asList(
            new Book("book-1", "Effective Java", 416, "author-1"),
            new Book("book-2", "Hitchhiker's Guide to the Galaxy", 208, "author-2"),
            new Book("book-3", "Down Under", 436, "author-3")
    );

    public static Book getById(String id) {
        return books.stream().filter(book -> book.id().equals(id)).findFirst().orElse(null);
    }
}

Create the Author class

Add the following to Author.java. Save it in the same directory as Book.java.

import java.util.Arrays;
import java.util.List;

public record Author (String id, String firstName, String lastName) {

    private static List<Author> authors = Arrays.asList(
            new Author("author-1", "Joshua", "Bloch"),
            new Author("author-2", "Douglas", "Adams"),
            new Author("author-3", "Bill", "Bryson")
    );

    public static Author getById(String id) {
        return authors.stream().filter(author -> author.id().equals(id)).findFirst().orElse(null);
    }
}

Adding code to fetch data

Spring for GraphQL provides an annotation-based programming model to declare handler methods to fetch the data for specific GraphQL fields.

Add the following to BookController.java. You choose where to save this file, it can be in the same directory as the class containing the @SpringBootApplication annotation.

import org.springframework.graphql.data.method.annotation.Argument;
import org.springframework.graphql.data.method.annotation.QueryMapping;
import org.springframework.graphql.data.method.annotation.SchemaMapping;
import org.springframework.stereotype.Controller;

@Controller
public class BookController {
    @QueryMapping
    public Book bookById(@Argument String id) {
        return Book.getById(id);
    }

    @SchemaMapping
    public Author author(Book book) {
        return Author.getById(book.authorId());
    }
}

The @QueryMapping annotation binds this method to a query, a field under the Query type. The query field is then determined from the method name, bookById. The query field could also be declared on the annotation.

Note	Spring for GraphQL uses RuntimeWiring.Builder that registers each such controller method as a GraphQL Java graphql.schema.DataFetcher that provides the logic to fetch the data for a query or for any schema field. The Spring Boot starter for GraphQL has auto-config that automates this registration.

In the GraphQL Java engine, DataFetchingEnvironment provides access to a map of field-specific argument values. Use the @Argument annotation to have an argument bound to a target object and injected into the handler method. By default, the method parameter name is used to look up the argument. The argument name can be specified in the annotation.

The @SchemaMapping annotation maps a handler method to a field in the GraphQL schema and declares it to be the DataFetcher for that field. The field name defaults to the method name, and the type name defaults to the simple class name of the source/parent object injected into the method. In this example, the field defaults to author and the type defaults to Book. The type and field can be specified in the annotation.

For more, see the documentation for the Spring for GraphQL annotated controller feature.

That’s all the code we need!

Let’s run our first query.

Running our first query

Enable the GraphiQL Playground

GraphiQL is a useful visual interface for writing and executing queries, and much more. Enable GraphiQL by adding this config to the application.properties file.

spring.graphql.graphiql.enabled=true

Boot the application

Start your Spring application.

Navigate to http://localhost:8080/graphiql or your custom URL.

Run the query

Type in the query and click the play button at the top of the window.

query bookDetails {
  bookById(id: "book-1") {
    id
    name
    pageCount
    author {
      id
      firstName
      lastName
    }
  }
}

You should see a response like this.

Congratulations, you have built a GraphQL service and executed your first query! With the help of Spring for GraphQL, you were able to achieve this with only a few lines of code.

Testing

Spring for GraphQL provides helpers for GraphQL testing in the spring-graphql-test artifact. We have already included this artifact as part of the project generated by Spring Initializr.

Thoroughly testing a GraphQL service requires tests with different scopes. In this tutorial, we will write a @GraphQlTest slice test, which focuses on a single controller. There are other helpers to assist with full end-to-end integration tests and focused server side tests. For the full details, see the Spring for GraphQL Testing documentation and Auto-configured Spring for GraphQL tests in the Spring Boot documentation.

Let’s write a controller slice test that verifies the same bookDetails query requested in the GraphiQL playground a few moments ago.

Add the following to a test file BookControllerTest.java. Save this file in a location within the test folder.

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.graphql.GraphQlTest;
import org.springframework.graphql.test.tester.GraphQlTester;

@GraphQlTest(BookController.class)
public class BookControllerTest {

    @Autowired
    private GraphQlTester graphQlTester;

    @Test
    void shouldGetFirstBook() {
        this.graphQlTester
                .document("""
                    query bookDetails {
                      bookById(id: "book-1") {
                        id
                        name
                        pageCount
                        author {
                          id
                          firstName
                          lastName
                        }
                      }
                    }
                """)
                .execute()
                .path("bookById")
                .matchesJson("""
                    {
                        "id": "book-1",
                        "name": "Effective Java",
                        "pageCount": 416,
                        "author": {
                          "firstName": "Joshua",
                          "lastName": "Bloch"
                        }
                    }
                """);
    }
}

Run the test and verify that the result is identical to the GraphQL query manually requested in the GraphiQL playground.

The @GraphQlTest annotation is useful for writing controller slice tests, which are focused on a single controller. @GraphQlTest auto-configures the Spring for GraphQL infrastructure, without any transport nor server being involved. Automatic configuration enables us to write tests faster by skipping boilerplate code. As this is a focused slice test, only a limited number of beans are scanned including @Controller and RuntimeWiringConfigurer. For the list of scanned beans, see the documentation.

GraphQlTester is a contract that declares a common workflow for testing GraphQL requests, independent of transport. In our test, we provide a document (our query text) with document, then execute the request, then select a part of the response to verify with path. Finally, we verify that the JSON at this path matches the expected result.

Congratulations! In this tutorial you built a GraphQL service, ran your first query, and wrote your first GraphQL test!

Further reading

Sample source code

The source code for this tutorial can be found on GitHub.

Documentation

Read the Spring for GraphQL documentation.

GraphQL Java is the GraphQL engine powering Spring for GraphQL. Read the GraphQL Java documentation.

More Spring for GraphQL examples

See more samples in the 1.0.x branch, which will soon be moved into a separate repository.

Stack Overflow questions

You can raise questions on Stack Overflow with the spring-graphql tag.

Want to write a new guide or contribute to an existing one? Check out our contribution guidelines.

All guides are released with an ASLv2 license for the code, and an Attribution, NoDerivatives creative commons license for the writing.