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 Spring Data JPA.

The Groovy markup template engine provides an innovative templating system based on the builder syntax.
 
It offers various key features: 
  • hierarchical (builder) syntax to generate XML-like contents (in particular, HTML5) 
  • compilation of templates to bytecode for fast rendering
  • internationalization 
  • layout mechanism for sharing structural patterns 
  • optional type checking
and more! 

The 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 User Entity

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 User Service

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

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 Driver

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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