Kotlin + Quarkus + MyBatis - Build REST CRUD API example

Hello everyone. Today we will learn how to develop REST-style CRUD APIs with Kotlin, Quarkus, MyBatis, and H2 Database. You can download the source code from our Github repository.

Quarkus is a Java framework designed to run within containers. Fixating on expeditious start-up times and low memory utilization makes it more felicitous to run within container orchestration platforms like Kubernetes.Quarkus supports many industry-standard libraries such as Hibernate, Kubernetes, RESTEasy,  Eclipse MicroProfile, and more...

MyBatis is an open-source persistence framework that simplifies the implementation of database access in Java applications. It provides support for custom SQL, stored procedures, and different types of mapping relations. Simply put, it's an alternative to JDBC and Hibernate.

After completing this tutorial what we will build? 

We will build REST API  CRUD features: 
  1. GET - Fetch all User       :     /api/v1/users
  2. GET - Get User by ID     :     /api/v1/users/{id} 
  3. POST - Create User         :     /api/v1/users 
  4. PUT - Edit User Details   :     /api/v1/users/
  5. DELETE - Delete User    :     /api/v1/users/{id}

Technologies used:

  • Quarkus 2.2.3.Final
  • MyBatis 0.0.9
  • Kotlin
  • Gradle
  • H2DB

 

Project Directory:



Gradle Build(build.gradle.kts):
import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
java
id("io.quarkus")
kotlin("jvm") version "1.5.31"
}

repositories {
mavenCentral()
mavenLocal()
}

val quarkusPlatformGroupId: String by project
val quarkusPlatformArtifactId: String by project
val quarkusPlatformVersion: String by project

dependencies {
implementation(enforcedPlatform(
"${quarkusPlatformGroupId}:${quarkusPlatformArtifactId}:${quarkusPlatformVersion}"))
implementation("io.quarkus:quarkus-arc")
implementation("io.quarkus:quarkus-resteasy-jsonb")
implementation("io.quarkiverse.mybatis:quarkus-mybatis:0.0.9")
implementation("io.quarkus:quarkus-jdbc-h2")
testImplementation("io.quarkus:quarkus-junit5")
testImplementation("io.rest-assured:rest-assured")
implementation(kotlin("stdlib-jdk8"))
}

group = "com.knf.dev.demo"
version = "1.0.0-SNAPSHOT"

java {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}

tasks.withType<JavaCompile> {
options.encoding = "UTF-8"
options.compilerArgs.add("-parameters")
}
val compileKotlin: KotlinCompile by tasks
compileKotlin.kotlinOptions {
jvmTarget = "11"
}
val compileTestKotlin: KotlinCompile by tasks
compileTestKotlin.kotlinOptions {
jvmTarget = "11"
}


Database Setup [schema.sql]:

We will create a table called users with a few simple columns. We can initialize a schema by creating a schema.sql file in the resources.
create table users
(
id integer not null,
firstName varchar(255) not null,
lastName varchar(255) not null,
emailId varchar(255) not null,
primary key(id)
);


application.properties:

quarkus.datasource.db-kind = h2
quarkus.datasource.username = sa
# quarkus.datasource.password =
quarkus.datasource.jdbc.url = jdbc:h2:mem:test
quarkus.mybatis.initial-sql=schema.sql


Create User Model [User.kt]:
package com.knf.dev.demo.model

class User {
var id: Long = 0
var firstName: String? = null
var lastName: String? = null
var emailId: String? = null

constructor() {}
constructor(id: Long, firstName: String?,
lastName: String?, emailId: String?) : super() {
this.id = id
this.firstName = firstName
this.lastName = lastName
this.emailId = emailId
}
}


Create User Repository [UserRepository.kt]:
package com.knf.dev.demo.repository

import com.knf.dev.demo.model.User
import org.apache.ibatis.annotations.*


@Mapper
interface UserRepository {
@Select("select * from users")
fun findAll(): List<User?>?

@Select("SELECT * FROM users WHERE id = #{id}")
fun findById(id: Long): User?

@Delete("DELETE FROM users WHERE id = #{id}")
fun deleteById(id: Long): Int

@Insert(
"INSERT INTO users(id, firstName, lastName,emailId) " +
" VALUES (#{id}, #{firstName}, #{lastName}, #{emailId})"
)
fun insert(user: User?): Int

@Update(
"Update users set firstName=#{firstName}, " +
" lastName=#{lastName}, emailId=#{emailId} where id=#{id}"
)
fun update(user: User?): Int
}


UserController.kt:
package com.knf.dev.demo.controller

import com.knf.dev.demo.model.User
import com.knf.dev.demo.repository.UserRepository
import javax.inject.Inject
import javax.ws.rs.*
import javax.ws.rs.core.MediaType


@Path("/api/users")
class UserController {
@Inject
var userRepository: UserRepository? = null

@GET
@Produces(MediaType.APPLICATION_JSON)
fun getUsers(): kotlin.collections.List<User?>? {
return userRepository!!.findAll()
}

@GET
@Path("/{id}")
@Produces(MediaType.APPLICATION_JSON)
fun getUser(@PathParam("id") id: Long?): User? {
return userRepository!!.findById(id!!)
}

@PUT
@Consumes(MediaType.APPLICATION_JSON)
fun updateUser(user: User?) {
userRepository!!.update(user)
}

@POST
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
fun addUser(user: User?) {
userRepository!!.insert(user)
}

@DELETE
@Path("/{id}")
fun deleteUser(@PathParam("id") id: Long?) {
userRepository!!.deleteById(id!!)
}
}


Verify REST APIs

Build application jar file: gradle build


Start application: java -jar quarkus-run.jar

1. Add User

2. Get Single User

3. Fetch All Users

4. Update User

5. Delete User




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