Kotlin + Spring Boot + FreeMarker + JPA - CRUD example

Hello everyone, Today we will learn how to develop a Spring Boot CRUD web application, using Kotlin, Spring Boot, FreeMarker template, H2DB, and JPA.


Following technologies stack being used:
  • Spring Boot 2.5.5
  • Spring MVC 5.3.10
  • Gradle
  • Kotlin
  • FreeMarker 2.3.31
  • H2DB 
  • Bootstrap

Project Structure:


Project Dependency(build.gradle.kts)

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

plugins {
   id("org.springframework.boot") version "2.5.5"
   id("io.spring.dependency-management") version "1.0.11.RELEASE"
   kotlin("jvm") version "1.5.31"
   kotlin("plugin.spring") version "1.5.31"
   kotlin("plugin.jpa") version "1.5.31"
}

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-data-jpa")
   implementation("org.springframework.boot:spring-boot-starter-freemarker")
   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")
   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()
}

Configure the Entity class

package com.knf.dev.demo.kotlinspringjpafreemarkercrud.model

import javax.persistence.*

@Entity
@Table(name = "user")
class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: Long? = null

    @Column(name = "first_name")
    var firstName: String? = null

    @Column(name = "last_name")
    var lastName: String? = null

    @Column(name = "email", nullable = false, length = 200)
    var email: String? = null

    constructor() : super() {}
    constructor(firstName: String?, lastName: String?, email: String?) : super() {
        this.firstName = firstName
        this.lastName = lastName
        this.email = email
    }

    override fun toString(): String {
        return ("User [id=" + id + ", firstName=" + firstName + ", lastName="
                + lastName + ", email=" + email + "]")
    }
}

Create CRUD Repository

package com.knf.dev.demo.kotlinspringjpafreemarkercrud.repository

import com.knf.dev.demo.kotlinspringjpafreemarkercrud.model.User
import org.springframework.data.repository.CrudRepository
import org.springframework.stereotype.Repository

@Repository
interface UserRepository : CrudRepository<User?, Long?>

Create the Service class

package com.knf.dev.demo.kotlinspringjpafreemarkercrud.service

import com.knf.dev.demo.kotlinspringjpafreemarkercrud.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringjpafreemarkercrud.repository.UserRepository
import org.springframework.stereotype.Service
import java.util.ArrayList
import kotlin.Throws
import javax.persistence.EntityNotFoundException

@Service
class UserService {
    @Autowired
    var repository: UserRepository? = null
    val allusers: List<User?>
        get() {
            val result = repository!!.findAll() as List<User?>
            return if (result.size > 0) {
                result
            } else {
                ArrayList()
            }
        }

    @Throws(EntityNotFoundException::class)
    fun getUserById(id: Long): User {
        val user = repository!!.findById(id)
        return if (user.isPresent) {
            user.get()
        } else {
            throw EntityNotFoundException("No user record exist for given id")
        }
    }

    fun createOrUpdateUser(entity: User): User {
        var entity = entity
        return if (entity.id == null) {
            entity = repository!!.save(entity)
            entity
        } else {
            val user = repository!!.findById(
                entity.id!!
            )
            if (user.isPresent) {
                var newEntity = user.get()
                newEntity.email = entity.email
                newEntity.firstName = entity.firstName
                newEntity.lastName = entity.lastName
                newEntity = repository!!.save(newEntity)
                newEntity
            } else {
                entity = repository!!.save(entity)
                entity
            }
        }
    }

    @Throws(EntityNotFoundException::class)
    fun deleteUserById(id: Long) {
        val user = repository!!.findById(id)
        if (user.isPresent) {
            repository!!.deleteById(id)
        } else {
            throw EntityNotFoundException("No user record exist for given id")
        }
    }
}

Create the Web Controller class

package com.knf.dev.demo.kotlinspringjpafreemarkercrud.controller

import com.knf.dev.demo.kotlinspringjpafreemarkercrud.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringjpafreemarkercrud.service.UserService
import org.springframework.stereotype.Controller
import org.springframework.ui.Model
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.PostMapping
import org.springframework.web.bind.annotation.ModelAttribute
import org.springframework.web.bind.annotation.PathVariable
import kotlin.Throws
import javax.persistence.EntityNotFoundException

@Controller
class UserController {
    @Autowired
    private val userService: UserService? = null
    @GetMapping("/")
    fun getAllUserView(model: Model): String {
        val users = userService!!.allusers
        model.addAttribute("users", users)
        return "home"
    }

    @GetMapping("/create")
    fun createUserView(model: Model): String {
        val user = User()
        model.addAttribute("user", user)
        model.addAttribute("isUpdate", false)
        return "create-update"
    }

    @PostMapping("/update/{id}")
    fun createUser(
        @ModelAttribute("user") user: User,
        @PathVariable("id") id: Long?
    ): String {
        user.id = id
        userService!!.createOrUpdateUser(user)
        return "redirect:/"
    }

    @GetMapping("/update/{id}")
    @Throws(EntityNotFoundException::class)
    fun updateUser(
        model: Model,
        @PathVariable("id") id: Long?
    ): String {
        val user = userService!!.getUserById(id!!)
        model.addAttribute("user", user)
        model.addAttribute("isUpdate", true)
        return "create-update"
    }

    @PostMapping("/create")
    fun createUser(@ModelAttribute("user") user: User?): String {
        userService!!.createOrUpdateUser(user!!)
        return "redirect:/"
    }

    @GetMapping("/delete/{id}")
    @Throws(EntityNotFoundException::class)
    fun deleteUser(@PathVariable("id") id: Long?): String {
        userService!!.deleteUserById(id!!)
        return "redirect:/"
    }
}

Creating FreeMarker templates

home.ftlh

<!doctype html>
<head>
    <title>Freemarker Example</title>
    <meta charset="utf-8">
    <meta content="width=device-width, initial-scale=1" name="viewport">
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"
          rel="stylesheet">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js">
    </script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js">
    </script>
</head>
<body>
<div class="container">
            <h2>User CRUD operation with Freemarker Template</h2>
     <a href="/create" class="btn btn-primary" role="button">Create New User</a>
    <table class="table">
        <thead >
        <tr>
            <th scope="col">Id</th>
            <th scope="col">First Name</th>
            <th scope="col">Last Name</th>
            <th scope="col">Email</th>
            <th scope="col"></th>
            <th scope="col"></th>
        </tr>
        </thead>
        <tbody>
        <#list users as user>
        <tr>
            <th scope="row">${user.id}</th>
            <td>${user.firstName}</td>
            <td>${user.lastName}</td>
            <td>${user.email}</td>
            <td><a href="/update/${user.id}" class="btn btn-warning" role="button">
                     Update</a></td>
            <td><a href="/delete/${user.id}" class="btn btn-danger" role="button">
                     Delete</a></td>
        </tr>
        </#list>
        </tbody>
    </table>
</div>
</body>
</html>

create-update.ftlh

<!doctype html>
<head>
    <title>Freemarker Example</title>
    <meta charset="utf-8">
    <meta content="width=device-width, initial-scale=1" name="viewport">
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"
          rel="stylesheet">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js">
    </script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js">
    </script>
</head>
<body>
<div class="container">
            <h2>
                <#if !isUpdate>Create</#if>
            <#if isUpdate>Update</#if>
        User
        </h2>
<div>
    <form action="<#if isUpdate>/update/${user.id}</#if><#if !isUpdate>/create</#if>"
          method="post" name="user">
        <table class="table">
            <tbody>
            <thead>
            <tr>
                <th>Field</th>
                <th>Value</th>
            </tr>
            </thead>
            <tbody>
            <#if isUpdate>
            <tr>
                <th>ID</th>
                <td>
                    <div name="id">${user.id}</div>
                </td>
            </tr>
            </#if>
            <tr>
                <th>First Name</th>
                <td><input name="firstName" type="text"
                           value="<#if user.firstName??>${user.firstName}</#if>"/>
                                                    </td>
            </tr>
            <tr>
                <th>Last Name</th>
                <td><input name="lastName" type="text"
                           value="<#if user.lastName??>${user.lastName}</#if>"/></td>
            </tr>
            <tr>
                <th>Email</th>
                <td><input name="email" type="text"
                           value="<#if user.email??>${user.email}</#if>"/></td>
            </tr>
            </tbody>
        </table>
        <button class="btn btn-primary" type="submit">Save</button>
    </form>
</div>
</div>
</body>
</html>

Spring Boot Main Class

package com.knf.dev.demo.kotlinspringjpafreemarkercrud

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

@SpringBootApplication
class KotlinspringjpafreemarkercrudApplication

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

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