GraphQL + Kotlin & Spring Boot - Part 1

Summary

Welcome back to your humble dev.to blog! In this post I will try to give you the tools to set up a simple graphql with spring boot project. As a small disclaimer the folder structure and design patterns are not to be followed in a real application.

Prerequisites

You need to set up your local environment.
To do this we have already created a step by step guide in here.
You can check that you have installed Kotlin and JDK by typing this in your terminal:

$ kotlin -version
## output: Kotlin version 1.3.61-release-180 (JRE 13.0.2+8)
$ javac -version
## output: javac 13.0.2
$ gradle -version

Spring Boot Initializr

You can go to Spring Boot Initializr page and select the next.

• Project: Gradle Project
• Language: Kotlin
• Spring Boot: 2.2.5
• Group: com.grekz
• Artifact: graphqlDemo
• Dependencies: Spring Web, Spring Boot DevTools

And click in the Generate button.

Add dependencies

We need to add some dependencies necessary to have our GraphQL up and running.

// file build.gradle.kts
dependencies {
    implementation ("com.graphql-java:graphql-spring-boot-starter:5.0.2")
    implementation ("com.graphql-java:graphiql-spring-boot-starter:5.0.2")
    implementation ("com.graphql-java:voyager-spring-boot-starter:5.0.2")
    implementation ("com.graphql-java:graphql-java-tools:5.2.4")
    // ... rest of dependencies
}

Here we just added graphql, GraphiQL (A graphical interactive in-browser GraphQL IDE), Voyager (Represents your GraphQL API as an interactive graph) and utilities classes to help you with your GraphQL integrations.

Update application configuration

After updating the dependencies, we need to have a file that contains the configurations to tell our application how to behave.
You need to create a file named application.yml in your folder ./src/main/resources

# file application.yml
graphql:
  servlet:
    mapping: /graphql
    enabled: true
    corsEnabled: true
graphiql:
  mapping: /graphiql
  endpoint: /graphql
  enabled: true
  pageTitle: GraphiQL
  cdn:
    enabled: false
    version: 0.11.11

Create a data class

Now we are going to create a data class named Book, that will contain two attributes.

package com.grekz.graphqlDemo

data class Book( val id: String, val name: String )
// file: ./src/main/kotlin/com/grekz/graphqlDemo/Book.kt

Create a GraphQL query resolver

package com.grekz.graphqlDemo

import org.springframework.stereotype.Component
import com.coxautodev.graphql.tools.GraphQLQueryResolver

@Component
class BookResolver() : GraphQLQueryResolver {
    // this method name needs to be same and in the schema
    fun books(): List<Book> {
        val book1 = Book("1", "name1")
        val book2 = Book("2", "name2")
        return listOf(book1, book2)
    }
}
// file: ./src/main/kotlin/com/grekz/graphqlDemo/BookResolver.kt

Defining your schema

In GraphQL you need to specify the types and how data can be queried or mutated.
You can put the next in the file: ./src/main/resources/models.graphqls

type Query {
  books: [Book]
}

type Book {
  id: String!
  name: String!
}

Run the project!

This is all you need to have your graphql application running.
To do this you need to type the command:

$ gradle bootRun

After starting your server you can go to:
http://localhost:8080/graphiql?query=query%7B%0A%20%20books%7B%0A%20%20%20%20id%0A%20%20%7D%0A%7D

And hit the play button on the top to see the results.
Another cool thing you just did is to install Voyager. To see it running you can check: http://localhost:8080/voyager

Now that you have graphql up and running the sky is the limit!

Follow up

If you want another example on another thing you can do with GraphQL you can check this Auth0 post.