Build REST CRUD API's with Kotlin, Spring, and MongoDB

In this article, we will show you how to develop a  REST-style web service with Kotlin, Spring Boot, MongoDB.
A quick overview of Kotlin, Spring Boot, and MongoDB  

Kotlin:

It’s a modern programming language targeting the Java platform. Kotlin is concise, safe, pragmatic, and fixated on interoperability with Java code. It can be used virtually everywhere Java is utilized today: for server-side development, Android apps, and much more. Kotlin works great with all subsisting Java libraries and frameworks and runs with the same level of performance as Java. 

MongoDB:

MongoDB is a document database built on a scale-out architecture that has to propagate with developers of all kinds who are building scalable applications utilizing agile methodologies.
MongoDB was built for people who are building internet and business applications who need to evolve expeditiously and scale elegantly. If you are doing that, you should consider MongoDB.

Companies and development teams of all sizes use MongoDB because:
  • The document data model is a potent way to store and retrieve data that sanctions developers to move expeditiously.
  • MongoDB’s horizontal, scale-out architecture can fortify astronomically immense volumes of both data and traffic.
  • MongoDB has a great utilizer experience for developers who can install MongoDB and commence inscribing code immediately. 

Spring Boot:

Spring boot to develop REST web services and microservices. Spring Boot has taken the Spring framework to the next level. It has drastically reduced the configuration and setup time required for spring projects. We can set up a project with almost zero configuration and start building the things that actually matter to your application. 

Technologies used :

  • Spring Boot 2.3.7.RELEASE
  • Spring  5.2.12.RELEASE
  • Kotlin 2.11.3
  • MongoDB
  • Maven 3
  • Java 8

After completing this tutorial what we will build? 

We will build REST API  CRUD features: 

  1. GET - Fetch all Employee       :     /api/v1/employees
  2. GET - Get Employee by ID     :     /api/v1/employees/{id} 
  3. POST - Create Employee         :     /api/v1/employees 
  4. PUT - Edit Employee Details   :     /api/v1/employees/{id} 
  5. DELETE - Delete Employee    :     /api/v1/employees/{id} 

Project Directory:



Maven[pom.xml]:

Maven is a powerful project management tool that is based on POM (project object model). It is used for project build, dependency and documentation. 
<?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-parent</artifactId>
<version>2.3.7.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.knf.dev</groupId>
<artifactId>springboot_kotlin_crud</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>springboot_kotlin_crud</name>
<description>Demo project for Spring Boot</description>

<properties>
<java.version>1.8</java.version>
<kotlin.version>1.3.72</kotlin.version>
</properties>

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.module</groupId>
<artifactId>jackson-module-kotlin</artifactId>
</dependency>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-reflect</artifactId>
</dependency>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib-jdk8</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>

<build>
<sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
<testSourceDirectory>
${project.basedir}/src/test/kotlin
</testSourceDirectory>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<configuration>
<args>
<arg>-Xjsr305=strict</arg>
</args>
<compilerPlugins>
<plugin>spring</plugin>
</compilerPlugins>
</configuration>
<dependencies>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-allopen</artifactId>
<version>${kotlin.version}</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
</project>

Creating the Document:

The employee model here is the POJO, We use the annotation @Document to set the collection name that will be used by the model. If the collection doesn’t exist, MongoDB will create it.
package com.knf.dev.model

import org.bson.types.ObjectId
import org.springframework.data.annotation.Id
import org.springframework.data.mongodb.core.mapping.Document
import org.springframework.web.bind.annotation.CrossOrigin

@Document(collection = "employees")
data class Employee(
@Id
var id: String? = ObjectId().toHexString(),
val firstName: String,
val lastName: String,
val emailId: String
)


Creating the Repository:

The API implementation happens in the repository. It acts as a link between the model and the database and has all the methods for CRUD operations.
package com.knf.dev.repository

import com.knf.dev.model.Employee
import org.springframework.data.mongodb.repository.MongoRepository
import org.springframework.stereotype.Repository

@Repository
interface EmployeeRepository : MongoRepository<Employee, String>


Creating the Rest Controller:

Rest Controller annotation is mainly used for building restful web services using Spring MVC. The class annotated with @RestController is called Rest Controller. The class annotated with @RestController annotation returns JSON response in all the methods.
package com.knf.dev.controller

import com.knf.dev.model.Employee
import com.knf.dev.repository.EmployeeRepository
import org.springframework.http.HttpStatus
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.*
import java.util.*

@RestController
@RequestMapping("/api/v1/")
class EmployeeController(private val employeeRepository: EmployeeRepository) {

@GetMapping("/employees")
fun getAllEmployees(): List<Employee> =
employeeRepository.findAll()

@PostMapping("/employees")
fun createNewEmployee(@RequestBody employee: Employee): Employee =
employeeRepository.save(employee)

@GetMapping("/employees/{id}")
fun getEmployeeById(@PathVariable(value = "id") employeeId: String):
ResponseEntity<Employee> {
return employeeRepository.findById(employeeId).map { emp ->
ResponseEntity.ok(emp)
}.orElse(ResponseEntity.notFound().build())
}

@PutMapping("/employees/{id}")
fun updateEmployeeById(@PathVariable(value = "id") employeeId: String,
@RequestBody newEmployee: Employee):
ResponseEntity<Employee> {

return employeeRepository.findById(employeeId).map { existingEmployee ->
val updatedEmployee: Employee = existingEmployee
.copy(firstName = newEmployee.firstName, lastName =
newEmployee.lastName, emailId = newEmployee.emailId)
ResponseEntity.ok().body(employeeRepository.save(updatedEmployee))
}.orElse(ResponseEntity.notFound().build())

}

@DeleteMapping("/employees/{id}")
fun deleteEmployeeById(@PathVariable(value = "id") employeeId: String):
ResponseEntity<Void> {
return employeeRepository.findById(employeeId).map { emp ->
employeeRepository.delete(emp)
ResponseEntity<Void>(HttpStatus.OK)
}.orElse(ResponseEntity.notFound().build())

}
}


Spring Boot Main Class:

Create the main class SpringbootKotlinCrudApplication.kt in the root package com.knf.dev.
package com.knf.dev

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

@SpringBootApplication
class SpringbootKotlinCrudApplication

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


Run:

Github repository download link is provided at the end of this tutorial

Local Setup:

Step 1: Download or clone the source code to a local machine.

Spring Boot 

Step 2: mvn clean install

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


Testing API's using Postman

Create an Employee:

Fetch All Employee:

Update Employee:

Delete Employee By Id:

Get Employee By Id:


More Kotlin practice:

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