Kotlin + Spring Boot + Mustache + JPA - CRUD example

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


Following technologies stack being used:
  • Spring Boot 2.5.5
  • Spring MVC 5.3.10
  • Gradle
  • Kotlin
  • Mustache 1.15
  • 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-mustache")
   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.kotlinspringjpamustachecrud.model

import javax.persistence.*

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

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

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

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

Create CRUD Repository

package com.knf.dev.demo.kotlinspringjpamustachecrud.repository

import com.knf.dev.demo.kotlinspringjpamustachecrud.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.kotlinspringjpamustachecrud.service

import com.knf.dev.demo.kotlinspringjpamustachecrud.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringjpamustachecrud.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.first_name = entity.first_name
                newEntity.last_name = entity.last_name
                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.kotlinspringjpamustachecrud.controller

import com.knf.dev.demo.kotlinspringjpamustachecrud.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringjpamustachecrud.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 Mustache templates

home.mustache

<!doctype html>
<head>
    <title>Mustache 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 Mustache 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>
        {{#users}}
        <tr>
            <th scope="row">{{id}}</th>
            <td>{{first_name}}</td>
            <td>{{last_name}}</td>
            <td>{{email}}</td>
            <td><a href="/update/{{id}}" class="btn btn-warning" role="button">
                Update</a></td>
            <td><a href="/delete/{{id}}" class="btn btn-danger" role="button">
                Delete</a></td>
        </tr>
        {{/users}}
        </tbody>
    </table>
</div>
</body>
</html>

create-update.mustache

<!doctype html>
<head>
    <title>Mustache 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">
    <h1>{{^isUpdate}}Create{{/isUpdate}}
        {{#isUpdate}}Update{{/isUpdate}}User</h1>
    <div>
        <form action="{{#isUpdate}}/update/{{user.id}}
        {{/isUpdate}}{{^isUpdate}}/create{{/isUpdate}}"
              name="user" method="post">
            <table class="table">
                <tbody>
                <thead>
                <tr>
                    <th>Field</th>
                    <th>Value</th>
                </tr>
                </thead>
                <tbody>
                {{#isUpdate}}
                <tr>
                    <td>ID</td>
                    <td><div name="id">{{user.id}}</div></td>
                </tr>
                {{/isUpdate}}
                {{#user}}
                <tr>
                    <th>First Name</th>
                    <td><input type="text" name="first_name"
                         value="{{#first_name}}{{first_name}}{{/first_name}}" /></td>
                </tr>
                <tr>
                    <th>Last Name</th>
                    <td><input type="text" name="last_name"
                           value="{{#last_name}}{{last_name}}{{/last_name}}" /></td>
                </tr>
                <tr>
                    <th>Email</th>
                    <td><input type="text" name="email"
                               value="{{#email}}{{email}}{{/email}}" /></td>
                </tr>
                {{/user}}
                </tbody>
            </table>
            <button type="submit" class="btn btn-primary">Save</button>
        </form>
    </div>
</div>
</body>
</html>

Spring Boot Main Class

package com.knf.dev.demo.kotlinspringjpamustachecrud

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

@SpringBootApplication
class KotlinspringjpamustachecrudApplication

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

Run

Start Spring Boot: gradle bootRun.

Access the URL in  the browser: http://localhost:8080/

Create User:

List all Users:

Update User:

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