Master GraphQL with Spring Boot 3: Full-Stack API Guide

Overview

GraphQL is both a query language for APIs and a runtime that provides a clear, type‑based description of your data, allowing clients to request exactly the fields they need without over‑fetching. It enables fetching multiple related resources in a single request and evolves easily over time.

Environment Configuration

Use Spring Boot 3.0.9 with the following Maven dependencies:

<code>&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
  &lt;artifactId&gt;spring-boot-starter-data-jpa&lt;/artifactId&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
  &lt;artifactId&gt;spring-boot-starter-graphql&lt;/artifactId&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
  &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
  &lt;groupId&gt;com.mysql&lt;/groupId&gt;
  &lt;artifactId&gt;mysql-connector-j&lt;/artifactId&gt;
  &lt;scope&gt;runtime&lt;/scope&gt;
&lt;/dependency&gt;</code>

Application properties (application.yml) should configure the datasource, JPA, and GraphQL endpoint:

<code>spring:
  datasource:
    driverClassName: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/testjpa?serverTimezone=GMT%2B8&nullCatalogMeansCurrent=true&useSSL=false
    username: root
    password: xxxxxx
    type: com.zaxxer.hikari.HikariDataSource
    hikari:
      minimumIdle: 10
      maximumPoolSize: 200
      autoCommit: true
      idleTimeout: 30000
      poolName: MasterDatabookHikariCP
      maxLifetime: 1800000
      connectionTimeout: 30000
      connectionTestQuery: SELECT 1
  jpa:
    generateDdl: false
    hibernate:
      ddlAuto: update
    openInView: true
    show-sql: true
  graphql:
    path: /graphql
    graphiql:
      enabled: true
      path: /graphiql
    cors:
      allow-credentials: true
      allowed-headers: '*'
      allowed-methods: '*'
    schema:
      locations:
        - classpath*:graphql/**/
      file-extensions:
        - .graphqls
        - .gqls
      printer:
        enabled: true</code>

Enabling spring.graphql.graphql.enabled=true provides a UI for testing queries.

Entity Definitions

Define JPA entities for Book and Author :

<code>@Entity
@Table(name = "t_book")
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Integer pageCount;
    @Transient
    private List<Author> author = new ArrayList<>();
}

@Entity
@Table(name = "t_author")
public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String firstName;
    private String lastName;
    // foreign key to Book
    private Long bid;
}</code>

Repository Definitions

<code>public interface BookRepository extends JpaRepository<Book, Long>, JpaSpecificationExecutor<Book> {}

public interface AuthorRepository extends JpaRepository<Author, Long>, JpaSpecificationExecutor<Author> {
    List<Author> findByBid(Long bid);
}</code>

Service Definition

<code>@Service
public class BookService {
    @Resource
    private BookRepository bookRepository;
    @Resource
    private AuthorRepository authorRepository;

    public Book queryBook(Long id) {
        Book book = bookRepository.findById(id).orElse(null);
        List<Author> authors = authorRepository.findByBid(id);
        book.setAuthor(authors);
        return book;
    }
}</code>

GraphQL Schema

<code>schema {
  query: BookQuery
}

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

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

type Author {
  id: ID
  firstName: String
  lastName: String
}</code>

Controller

<code>@Controller
public class BookController {
    @Resource
    private BookService bookService;
    @Resource
    private AuthorRepository authorRepository;

    @SchemaMapping(typeName = "BookQuery", field = "bookById")
    public Book bookById(@Argument Long id) {
        return bookService.queryBook(id);
    }
}</code>

Testing the API

Access the GraphQL endpoint (default http://localhost:8080/graphql ) and send queries such as:

Only the requested fields are returned, e.g., querying just book information or selecting specific fields.

Clients fully control which fields to retrieve, making the API flexible and efficient.