[JAVA] Implement REST API with Spring Boot and JPA (Infrastructure layer)

Implementing a simple Web REST API server with Spring Boot + MySQL --Qiita

Outline Implement the infrastructure layer according to the following design. Consider the architecture of Web API implemented by Spring Boot --Qiita

Create the following 3 classes.

├── infrastructure
│   ├── entity
│   │   └── UserEntity.java
│   └── repository
│       ├── UserJpaRepository.java
│       └── UserRepositoryImpl.java

UserEntity.java The class to which MySQL records are mapped. Define a method to convert bidirectionally with Domain Object (User.java).


package com.example.springapi.infrastructure.entity;

import com.example.springapi.domain.object.User;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

 *RDB record mapping class
@Table(name = "test_users")
public class UserEntity {
    @Column(name = "id")
    private String id;

    @Column(name = "value")
    private String value;

     *Create an instance from a domain object
     * @param user domain object
     * @return UserEntity
    public static UserEntity build(User user) {
        return UserEntity.builder()

     *Convert to domain object
     * @return domain object
    public User toDomainUser() {
        return User.builder()

* JPA annotation

@Entity This expresses the JPA Entity (mapped class). @Table Specify the table name. @id Specifies that it is a primary key. In the case of a compound key, the writing method changes. @Column Specify the column name of the table.

* Lombok annotation

@NoArgsConstructor Automatically create a constructor with no arguments. A constructor with no arguments is required due to the life cycle of JPA Entity. Not required if the configuration has a constructor with no arguments. (If there is no final field, etc. It is absolutely necessary if you use @Builder) @AllArgsConstructor Create a constructor that takes all fields as arguments. If NoArgsConstructor is specified, @Builder will not work unless this is also specified (@Builder automatically generates a constructor that takes all fields as arguments, but does not create a constructor for a class with xxxArgsConstructor. And it doesn't work.)

UserJpaRepository.java Interface required to use JPA implementation. Inherit JpaRepository and specify Entity class and primary key type. At runtime, the standard implementation provided by spring-data-jpa called SimpleJpaRepository is injected by the DI container, so there is no need to write an implementation class.


package com.example.springapi.infrastructure.repository;

import com.example.springapi.infrastructure.entity.UserEntity;
import org.springframework.data.jpa.repository.JpaRepository;

 *Interface for using JPA
public interface UserJpaRepository extends JpaRepository<UserEntity, String> {

UserRepositoryImpl.java Implementation class of UserRepository interface defined in domain layer. The actual processing is done by SimpleJpaRepository.


package com.example.springapi.infrastructure.repository;

import com.example.springapi.domain.object.User;
import com.example.springapi.domain.repository.UserRepository;
import com.example.springapi.infrastructure.entity.UserEntity;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import java.util.Optional;

 *Persistence implementation class
 *Convert domain object to Entity and wrap JPA
public class UserRepositoryImpl implements UserRepository {

    private final UserJpaRepository userJpaRepository;

     * {@inheritDoc}
    public Optional<User> findById(String id) {
        return this.userJpaRepository.findById(id)

     * {@inheritDoc}
    public User save(User user) {
        return this.userJpaRepository.save(UserEntity.build(user))

     * {@inheritDoc}
    public void deleteById(String id) {

@Repository Another name for @Compornent. With @Service.

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