Build REST CRUD APIs with Kotlin, Spring Boot and MyBatis

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

What is MyBatis?

MyBatis is a persistence framework with support for custom SQL, stored procedures and advanced mappings. MyBatis eliminates almost all of the JDBC code and manual setting of parameters and retrieval of results. MyBatis can use simple XML or Annotations for configuration and map primitives, Map interfaces and Java POJOs (Plain Old Java Objects) to database records.

Some of the features of MyBatis:
  • In memory object filtering
  • Fortifies clustering and simultaneous access by other applications without loss of transaction integrity
  • Query Caching - Built-in support
  • Fortifies disconnected operations
  • Support for Remoting. Distributed Objects.

Technologies used :

  • Spring Boot 2.5.4
  • Spring  5.3.9
  • MyBatis 
  • Kotlin
  • Gradle

After completing this tutorial what we will build? 

We will build REST API  CRUD features: 

Project Directory



Gradle Build(build.gradle.kts)

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
   id("org.springframework.boot") version "2.5.4"
   id("io.spring.dependency-management") version "1.0.11.RELEASE"
   kotlin("jvm") version "1.5.21"
   kotlin("plugin.spring") version "1.5.21"
}

group = "com.knf.dev.demo"
version = "0.0.1-SNAPSHOT"
java.sourceCompatibility = JavaVersion.VERSION_11

repositories {
   mavenCentral()
}

dependencies {
   implementation("org.springframework.boot:spring-boot-starter-web")
   implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
   implementation("org.jetbrains.kotlin:kotlin-reflect")
   implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
   implementation("org.mybatis.spring.boot:mybatis-spring-boot-starter:2.2.0")
   runtimeOnly("com.h2database:h2")
   testImplementation("org.springframework.boot:spring-boot-starter-test")
}

tasks.withType<KotlinCompile> {
   kotlinOptions {
      freeCompilerArgs = listOf("-Xjsr305=strict")
      jvmTarget = "11"
   }
}

tasks.withType<Test> {
   useJUnitPlatform()
}


Database Setup

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)
);


Create User Model

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 MyBatis Repository

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
}


Global Exception Handling

UserIdNotFoundException

package com.knf.dev.demo.exception

import java.lang.RuntimeException

class UserIdNotFoundException : RuntimeException("User Id Not Found")



UserIdAlreadyExistException

package com.knf.dev.demo.exception

import java.lang.RuntimeException

class UserIdAlreadyExistException : RuntimeException("User Id Already Exist")



GlobalExceptionHandler

package com.knf.dev.demo.exception

import org.springframework.web.bind.annotation.ControllerAdvice
import com.knf.dev.demo.exception.UserIdNotFoundException
import org.springframework.web.context.request.WebRequest
import org.springframework.http.ResponseEntity
import java.time.LocalDateTime
import org.springframework.http.HttpStatus
import com.knf.dev.demo.exception.UserIdAlreadyExistException
import org.springframework.web.bind.annotation.ExceptionHandler
import java.lang.Exception

@ControllerAdvice
class GlobalExceptionHandler {
    @ExceptionHandler(UserIdNotFoundException::class)
    fun globalExceptionHandler(ex: Exception, request: WebRequest?): 
            ResponseEntity<CustomErrorResponse> {
        val errors = CustomErrorResponse()
        errors.timestamp = LocalDateTime.now()
        errors.error = ex.message
        errors.status = HttpStatus.NOT_FOUND.value()
        return ResponseEntity<CustomErrorResponse>(errors, HttpStatus.NOT_FOUND)
    }

    @ExceptionHandler(UserIdAlreadyExistException::class)
    fun globalExceptionHandler2(ex: Exception, request: WebRequest?): 
            ResponseEntity<CustomErrorResponse> {
        val errors = CustomErrorResponse()
        errors.timestamp = LocalDateTime.now()
        errors.error = ex.message
        errors.status = HttpStatus.INTERNAL_SERVER_ERROR.value()
        return ResponseEntity<CustomErrorResponse>(errors, 
            HttpStatus.INTERNAL_SERVER_ERROR)
    }
}


CustomErrorResponse

package com.knf.dev.demo.exception

import com.fasterxml.jackson.annotation.JsonFormat
import java.time.LocalDateTime

class CustomErrorResponse {
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd hh:mm:ss")
    var timestamp: LocalDateTime? = null
    var status = 0
    var error: String? = null
}



Create User Rest Controller

package com.knf.dev.demo.controller

import org.springframework.web.bind.annotation.RestController
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.repository.UserRepository
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.PostMapping
import org.springframework.web.bind.annotation.RequestBody
import com.knf.dev.demo.exception.UserIdAlreadyExistException
import org.springframework.web.bind.annotation.PathVariable
import org.springframework.http.ResponseEntity
import com.knf.dev.demo.exception.UserIdNotFoundException
import com.knf.dev.demo.model.User
import org.springframework.web.bind.annotation.PutMapping
import org.springframework.web.bind.annotation.DeleteMapping
import java.util.HashMap

@RestController
@RequestMapping("/api/v1")
class UserController {
    @Autowired
    private val userRepository: UserRepository? = null

    // get all users
    @get:GetMapping("/users")
    val allUsers: List<User?>?
        get() = userRepository!!.findAll()

    // create user rest API
    @PostMapping("/users")
    fun createUser(@RequestBody user: User): User? {
        return if (userRepository!!.findById(user.id) == null) {
            val id = userRepository.insert(user)
            userRepository.findById(user.id)
        } else {
            throw UserIdAlreadyExistException()
        }
    }

    // get user by id rest api
    @GetMapping("/users/{id}")
    fun getUserById(@PathVariable id: Long?): ResponseEntity<User> {
        val user = userRepository!!.findById(id!!) ?: throw UserIdNotFoundException()
        return ResponseEntity.ok(user)
    }

    // update user rest api
    @PutMapping("/users/{id}")
    fun updateUser(
        @PathVariable id: Long?,
        @RequestBody userDetails: User
    ): ResponseEntity<User> {
        if (userRepository!!.update(
                User(
                    id!!, userDetails.firstName,
                    userDetails.lastName, userDetails.emailId
                )
            ) == 0
        ) {
            throw UserIdNotFoundException()
        }
        return ResponseEntity.ok(userRepository.findById(id))
    }

    // delete user rest api
    @DeleteMapping("/users/{id}")
    fun deleteUser(@PathVariable id: Long?): ResponseEntity<Map<String, Boolean>> {
        userRepository!!.deleteById(id!!)
        val response: MutableMap<String, Boolean> = HashMap()
        response["deleted"] = java.lang.Boolean.TRUE
        return ResponseEntity.ok(response)
    }
}


Spring Boot Main Driver

package com.knf.dev.demo

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class KotlinSpringbootMybatisCrudExampleApplication

fun main(args: Array<String>) {
   runApplication<KotlinSpringbootMybatisCrudExampleApplication>(*args)
}


Local Setup and Run the application

Step1: Download or clone the source code from GitHub to a local machine - Click here


Step 2: mvn clean install


Step 3: Run the Spring Boot application - mvn spring-boot:run


Testing APIs using Postman

Create a User:

Fetch all the users:

Get user by id:

Update User:

Delete User:




Popular posts from this blog

Learn Java 8 streams with an example - print odd/even numbers from Array and List

Example 1: Java 8 program to print odd numbers from a List   import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; /*Java 8 Program to find Odd Numbers from a List*/ public class DriverClass { public static void main( String [] args) { List < Integer > numbers = Arrays. asList( 1 , 4 , 8 , 40 , 11 , 22 , 33 , 99 ); List < Integer > oddNumbers = numbers.stream(). filter(o -> o % 2 != 0 ). collect(Collectors.toList()); System.out.println(oddNumbers); } } 1. Initialize List using Arrays.asList() method. Java's built-in Arrays.asList() method converts an array into a list. This method takes an array as an argument and returns a List object. 2.  Java List interface provides stream() method which returns a sequential Stream with list of Integer as its source. 3. The Java stream filter(...
Read more

Java Stream API - How to convert List of objects to another List of objects using Java streams?

Image
In this section, we will show you how to convert a List of objects to another List of objects in Java using the Java streams map(). The ‘map’ method maps each element to its corresponding result. Java Stream API   The Java Stream API provides a functional programming approach over the object oriented capabilities of Java. It is used for processing collections of objects. The Stream in Java can be defined as a sequence of elements from a source List, Set or Array. Most of the stream operations return a Stream. This avails engender a chain of stream operations(stream pipe-lining). The streams withal support the aggregate or terminal operations on the elements. for example, finding the sum or maximum element or finding the average etc...Stream operations can either be executed sequentially or parallel. when performed parallelly, it is called a parallel stream.   Stream map() Method   The Java 8 Stream map() is an intermediate operation. It converts Stream<obj1> to Str...
Read more

Registration and Login with Spring Boot + Spring Security + Thymeleaf

Image
In this section, we will learn how to create user registration and login using Spring boot, Spring security, Thymeleaf, JPA, and H2DB. The GitHub repository link is provided at the end of this tutorial. You can download the source code. Technologies used: Spring Boot 2.5.5  Spring Data JPA  Spring Security  Thymeleaf  Maven 3+  Java 17  H2 Database   User Interface User Registration Authentication Failed Authentication success Sign out Final Project Structure: Complete pom.xml: <? 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 https://maven.apache.org/xsd/maven-4.0.0.xsd" > < modelVersion >4.0.0</ modelVersion > < parent > < groupId >org.springframework.boot</ groupId > < artifactId >spring-boot-starter-pare...
Read more

Java, Spring Boot Mini Project - Library Management System - Download

Image
Hello everyone, Hope you are doing well. Here, we provide a Library Management System mini-project for beginners, it's free for download. Maybe you can build more on top of this project and create your own product, that's all about you. The source code download link is provided at the end of this post. 1. Benefit of this project You could cover the following technologies and features by learning and debugging this mini project. Java 17 Java Stream Java Lamda Expressions Java Records Functional programming Object-oriented programming var Keyword in Java Generics in Java Java Switch Spring boot 2.6.4 Spring Security Thymeleaf template engine OpenCSV Spring Data JPA Server Side Pagination H2 Database  Bootstrap HTML CSS and more... 2. Objective Of Spring Boot On Library Management System The main objective of this project is to manage the details of the books, author, category, and publisher. Only Admin/Librarian will manage all these activities. Also, they can export the data in ...
Read more

ReactJS, Spring Boot JWT Authentication Example

Image
In this tutorial, we’ll create a user registration & login example using ReactJS, Spring Boot, Spring Security, and JWT authentication. You could download the source code from our Github repository, the download link is provided at the end of this tutorial. Technologies used Backend Technologies: Java 17 Spring Boot 2.7.0 Spring Security Spring Data JPA JWT H2 Database Frontend Technologies: React 17.0.1 Axios 0.27.2 Redux 4.0.5 Bootstrap 4.5.2 ReactJS - SpringBoot - JWT - Flow Backend Project Directory: Frontend Project Directory: Following is the screenshot of our application - User Registration: User Signin: Profile View: Access Resource: We will build two projects:  1. Backend:   spring-boot-security-jwt 2. Frontend: react-redux-jwt Project 1: spring-boot-security-jwt Pom.xml <?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"...
Read more

Top 5 Java ORM tools - 2024

Image
  The term ORM refers to object-relational mapping, which uses objects to adapt programming languages to database systems while allowing them to function with SQL and object-oriented programming ideas. Any kind of database management system that can accomplish object mapping to the table in the virtual system is suitable for the implementation of ORM. Java has a wide variety of ORM tools, some of which are mentioned below: 1. Hibernate Hibernate is a lightweight, open-source, non-invasive Java ORM (Object-Relational Mapping) framework that allows developers to create objects that function independently of database software and create persistence logic in any Java or JavaEE application. It offers an abstraction layer, so developers don't have to bother about implementations; Hibernate handles these tasks internally, such as connecting to databases and creating queries to carry out CRUD operations, among other things. Persistence logic development is done with it. Persistence logic r...
Read more

Java - Blowfish Encryption and decryption Example

Image
Blowfish is an encryption method developed by Bruce Schneier in 1993 as an alternative to the DES encryption method. It is significantly faster than DES and provides good encryption speed, although no effective cryptanalysis technique has been found to date. It is one of the first secure block ciphers that is not protected by any patents and is therefore freely available for anyone to use. This is a symmetric block cipher algorithm. Block size: 64 bits Key size: variable size from 32 to 448 bits number of subsections: 18 [P-array] number of rounds: 16 number of substitution blocks: 4 [each with 512 records of 32 bits each] develop  Example 1: Encryption and decryption using Blowfish import java.io.UnsupportedEncodingException; import java.nio.charset.Charset; import java.security.InvalidKeyException; import java.security.NoSuchAlgorithmException; import java.util.Base64; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.IllegalBlockSiz...
Read more

Spring boot video streaming example-HTML5

Image
Hello everyone, Today we will learn how to stream MP4 video using Spring Boot and Spring Web Flux.  The Source code download link is provided at the end of this post. New, Quarkus Practice User Interface   Project Structure: G radle(build.gradle) plugins { id 'org.springframework.boot' version '2.5.4' id 'io.spring.dependency-management' version '1.0.11.RELEASE' id 'java' } group = 'com.knf.demo' version = '0.0.1-SNAPSHOT' sourceCompatibility = '11' repositories { mavenCentral() } dependencies { implementation 'org.springframework.boot:spring-boot-starter-webflux' testImplementation 'org.springframework.boot:spring-boot-starter-test' testImplementation 'io.projectreactor:reactor-test' } test { useJUnitPlatform() } Service (VideoStreamingService.java) package  com.knf.demo.service ; import org.springframework.beans.factory.annotation. Autowired ; import org.springframework...
Read more

Google Cloud Storage + Spring Boot - File Upload, Download, and Delete

Image
In this section, we will learn  how to  create a simple spring boot application to perform different file operations such as upload, download, list, and delete files from the Google Cloud Storage. 1.  A little bit of Background Google Cloud Storage Cloud Storage is a managed service for storing unstructured data. Store any amount of data and retrieve it as often as you like. More Info - click here! Spring Boot Spring Boot makes it easy to create stand-alone, production-grade Spring-based Applications that you can "just run".  More Info - click here! 2. Create a GCP Project First, Sign into the Google console at  https://console.cloud.google.com . You can create a new project by first selecting the project dropdown in the top left and selecting " New Project ". Next, specify your GCP  Project name  and  Project ID . Then  Click on the " CREATE " button. Copy " Project ID " and keep it for future purposes. 3. Create a Google Cloud Storage bucke...
Read more