【Spring Boot (JPA編)】DB接続設定からエンティティおよびリポジトリの作成、値の取得まで

• Spring Framework + JPA でDB 接続〜エンティティ作成〜値取得までの完全例
• 前提: Spring Boot + Maven + MySQL (XAMPP)
• 実装手順: application.properties で接続情報 → Entity → Repository (JpaRepository 継承) → Service / Controller
• Repository に findById / findAll など標準メソッドが自動提供される

CREATE DATABASE spring_db CHARACTER SET utf8 COLLATE utf8_bin;

GRANT ALL PRIVILEGES
ON spring_db.*
TO spring_user@localhost
IDENTIFIED BY 'spring_password';

CREATE TABLE `user`(
id bigint(20),
name VARCHAR(50) NOT NULL
);

ALTER TABLE `user` ADD PRIMARY KEY (`id`);

ALTER TABLE `user` MODIFY `id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=1;

INSERT INTO user (name)VALUES('tarou'),('jirou');

    org.springframework.boot
    spring-boot-starter-data-jpa


    mysql
    mysql-connector-java
    runtime

spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/spring_db
spring.datasource.username=spring_user
spring.datasource.password=spring_password
spring.jpa.database=MYSQL

spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl

package com.example.demo.entity;

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

@Entity
@Table(name="user")
public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column
    private long id;
    
    @Column(length=50, nullable = false)
    private String name;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package com.example.demo.repository;

import com.example.demo.entity.User;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository{
}

package com.example.demo.repository;

import com.example.demo.entity.User;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
 

@Repository
public interface UserRepository extends JpaRepository{

    @Query("SELECT c FROM User c WHERE c.id = :id")

    List findAllById(@Param("id") Integer id);

}

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.entity.User;
import com.example.demo.repository.UserRepository;

@SpringBootApplication
@RestController
public class DemoJpaMysqlApplication {
    
    @Autowired
    UserRepository userRepository;

    @RequestMapping("/")
    String hello() {
        Iterable users = userRepository.findAll();
        
        for (User user : (Iterable) users::iterator) {
            System.out.println(user.getName());
        }
        return "";
    }
    
    public static void main(String[] args) {
        SpringApplication.run(DemoJpaMysqlApplication.class, args);
    }

}

tarou
jirou