Kotlin + Spring + Groovy Templates CRUD Example

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

Following technologies stack being used:
  • Spring Boot 2.5.5
  • Spring MVC 5.3.10
  • Gradle
  • Kotlin
  • Groovy templates 2.5.5
  • 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-groovy-templates")
   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.kotlinspringbootcrudexample.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.kotlinspringbootcrudexample.repository

import com.knf.dev.demo.kotlinspringbootcrudexample.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.kotlinspringbootcrudexample.service

import com.knf.dev.demo.kotlinspringbootcrudexample.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringbootcrudexample.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.kotlinspringbootcrudexample.controller

import com.knf.dev.demo.kotlinspringbootcrudexample.model.User
import org.springframework.beans.factory.annotation.Autowired
import com.knf.dev.demo.kotlinspringbootcrudexample.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("create", true)
        model.addAttribute("actionUrl", "/create")
        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("create", false)
        model.addAttribute(
            "actionUrl",
            "/update/" + if (user == null) 0 else user.id
        )
        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 Groovy templates

home.tpl

yieldUnescaped '<!DOCTYPE html>'
html(lang: 'en') {
    head {
        meta('http-equiv': '"Content-Type" content="text/html; ' +
                'charset=utf-8"')
        title("Groovy example")
        link(rel: "stylesheet", type: "text/css",
        href: "https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css")

    }
    body {

        div(class: 'container') {
            h2("User CRUD operation with Groovy Template")
            div {
                nobr {
                    a(class: 'btn btn-primary', href: "/create", "Add User")
                }
            }
            br()
            br()
            div {
                table(class: 'table') {
                    tr {
                        th("Id")
                        th("First Name")
                        th("Last Name")
                        th("Email")
                        th("")
                        th("")
                    }
                    users.each { user ->
                        tr {
                            td("$user.id")
                            td("$user.first_name")
                            td("$user.last_name")
                            td("$user.email")
                            td {
                                a(class: 'btn btn-warning',
                                        href: "/update/$user.id", "Edit")
                            }
                            td {
                                a(class: 'btn btn-danger',
                                        href: "/delete/$user.id", "Delete")
                            }
                        }
                    }
                }
            }

        }
    }
}

create-update.tpl

yieldUnescaped '<!DOCTYPE html>'
html(lang: 'en') {
    head {
        meta('http-equiv': '"Content-Type" content="text/html; ' +
                'charset=utf-8"')
        title("Groovy example")
        link(rel: "stylesheet", type: "text/css",
        href: "https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css")
    }
    body {
        div(class: 'container') {
            if (create) {
                h1("Create a User:")
            } else {
                h1("Edit User")
            }
            a(class: 'btn btn-primary', href: "/", "Back to User List")
            br()
            br()
            form(id: "editForm", action: "$actionUrl", method: "POST") {
                table(class: 'table') {
                    if (!create) {
                        tr {
                            td("Id")
                            td(":")
                            td(user.id ?: '')
                        }
                    }
                    tr {
                        td("First Name")
                        td(":")
                        td {
                            input(name: 'first_name', type: 'text',
                                    value: user.last_name ?: '')
                        }
                    }
                    tr {
                        td("Last Name")
                        td(":")
                        td {
                            input(name: 'last_name', type: 'text',
                                    value: user.last_name ?: '')
                        }
                    }
                    tr {
                        td("Email")
                        td(":")
                        td {
                            input(name: 'email', type: 'text',
                                    value: user.email ?: '')
                        }
                    }
                }
                br()
                if (create) {
                    input(class: 'btn btn-success', type: 'submit',
                            value: 'Create')
                } else {
                    input(class: 'btn btn-success', type: 'submit',
                            value: 'Update')
                }
            }
        }
    }
}

Spring Boot Main Class

package com.knf.dev.demo.kotlinspringbootcrudexample

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

@SpringBootApplication
class KotlinspringbootcrudexampleApplication

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

Run

Start Spring Boot: gradle bootRun.

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

Create User:

List all Users:

Update User:

Download the source code: 

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