Spring with Kotorin --8 Repository layer

Overview / Description

Spring with Kotorin --7 Service has been modified to avoid concentrating responsibilities on a single module. The reason is to avoid becoming a ** Fat Controller ** with low maintainability, extensibility, and readability. For that purpose, we separated the application logic from the Controller layer and provided a ** Service ** layer.

This makes it possible to separate the functional areas to be focused on in the Controller layer and the Service layer.

Now consider the newly created responsibilities of the Service layer.

The role of the Service layer is to handle business logic other than accepting requests. In other words, as it is, the persistence processing of the result of business logic will also be performed in this Sevice layer.

By the way, if you think about data persistence, if you are aware of the target area to be persisted in the Service layer, It is necessary to design according to the type of target area.

In addition, the dependency on the type of external area becomes stronger, and the range of influence becomes larger when making changes. For example, taking a database as an example, changing from Oracle DB to MySQL requires a design that is aware of the dialect differences.

Considering the role of the service layer, ** business logic processing **, it is easier to design and maintainability if the result can be processed transparently without being aware of the persistence destination.

A ** Repository ** layer is provided as a mechanism to separate the persistence process from this Service layer.

Assumptions / Environment

Runtime version

• Kotlin : 1.3.11
• SpringBoot : 2.1.1.RELEASE

Spring Dependencies

• Web
• Actuator
• JDBC
• JPA

Development environment

• OS : Mac
• IDE : IntelliJ IDEA
• Build : Gradle
• DB : H2 Database

When setting up the Repository layer, this time we will target the database as a persistence area. Also, for the sake of brevity, we will use the H2 database as the database type and run it in embedded mode.

Procedure / Explanation

Dependency Add the following Dependency to build.gradle for database access.

• org.springframework.boot:spring-boot-starter-jdbc
• org.springframework.boot:spring-boot-starter-data-jpa

Also, add the following Dependency to use H2 Database.

• com.h2database:h2

Database definition

Add the following definitions for the H2 database to application.yml.

spring:
  datasource:
    tomcat:
      test-on-borrow: true
      validation-interval: 30000
      validation-query: SELECT 1
      remove-abandoned: true
      remove-abandoned-timeout: 10000
      log-abandoned: true
      log-validation-errors: true
      max-age: 1800000
      max-active: 50
      max-idle: 10
    driver-class-name: org.h2.Driver
    url: jdbc:h2:mem:app;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=TRUE
    username: guest
    password: guest
  h2:
    console:
      enabled: true
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

Repository layer

The following interface definition was made to provide a layer for persistence processing.

interface MessageRepository : CrudRepository<Message, String>

Makes you work with entities that persist data through this interface.

Service layer

From the Service layer, the entity is operated via the injected Repository layer instance.

@Autowired
lateinit var repository: MessageRepository

fun getMessages() : Iterable<MessageDTO> = repository.findAll().map { it -> MessageDTO(it) }

fun insertMessage(messageDto: MessageDTO) = MessageDTO(
        repository.save(Message(
                                title = messageDto.title,
                                message = messageDto.message
        ))
)

Summary / Looking back

You can see that the code has become much simpler than before the separation by designing the roles as Controller / Service / Repository separately. By designing in this way, it is possible to prevent the module from becoming bloated, spaghetti coded, and reduced in scalability.

This source

• shinyay/spring-just-rest-kotlin/tree/first-repository-layer