GraphQL API with Java: Step-by-Step Tutorial for Beginners

Introduction: Why GraphQL and Java Are a Powerful Combination

Modern API development requires flexibility and efficiency. REST API, despite its popularity, often faces the problem of over-fetching or under-fetching. GraphQL solves these problems by allowing the client to request only the data it needs.

Java, in turn, remains one of the most reliable languages for enterprise development. The combination of GraphQL and Java through the Spring Boot framework provides a powerful tool for creating scalable and performant APIs. In this step-by-step tutorial, we will create a simple GraphQL API from scratch.

This material will be useful for Java developers who want to master a modern approach to building APIs. We will cover key concepts, write code, and test our implementation.

1. Project Setup and Dependencies

The first step is to create a basic Spring Boot project. We will use Maven for dependency management. Make sure you have JDK 17+ and Maven 3.8+ installed.

Create a pom.xml file with the following content:

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0         http://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>

    <parent>        <groupId>org.springframework.boot</groupId>        <artifactId>spring-boot-starter-parent</artifactId>        <version>3.2.0</version>    </parent>

    <groupId>com.example</groupId>    <artifactId>graphql-java-tutorial</artifactId>    <version>1.0.0</version>

    <properties>        <java.version>17</java.version>    </properties>

    <dependencies>        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-web</artifactId>        </dependency>        <dependency>            <groupId>com.graphql-java</groupId>            <artifactId>graphql-spring-boot-starter</artifactId>            <version>5.0.2</version>        </dependency>        <dependency>            <groupId>com.graphql-java</groupId>            <artifactId>graphql-java-tools</artifactId>            <version>5.2.4</version>        </dependency>    </dependencies></project>

After setting up the pom.xml, create the main application class:

package com.example.graphqldemo;

import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplicationpublic class GraphqlDemoApplication {    public static void main(String[] args) {        SpringApplication.run(GraphqlDemoApplication.class, args);    }}

Now the project structure is ready. Let's move on to defining the data.

2. Defining the Data Model and GraphQL Schema

The GraphQL Schema is the contract between the client and the server. We will start by creating a simple Book model.

2.1 Java Model Class

package com.example.graphqldemo.model;

public class Book {    private String id;    private String title;    private String author;    private int pages;

    public Book(String id, String title, String author, int pages) {        this.id = id;        this.title = title;        this.author = author;        this.pages = pages;    }

    // Getters and Setters    public String getId