Maven 入門 | データベースの利用 | JPA を使用するプログラム

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
    xmlns="http://xmlns.jcp.org/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
        http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
 
    <persistence-unit name="sample-persistance" transaction-type="RESOURCE_LOCAL">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>com.devkuma.MyEntity</class>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:db" />
            <property name="javax.persistence.jdbc.user" value="sa" />
            <property name="eclipselink.ddl-generation" value="drop-and-create-tables" />
            <property name="eclipselink.ddl-generation.output-mode" value="database" />
        </properties>
    </persistence-unit>
</persistence>

package com.devkuma;
 
import java.util.Date;
import java.util.Calendar;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
 
@Entity
public class MyEntity {
    @Id
    @GeneratedValue
    private Integer id;
 
    private String name;
    private String message;
    private Date date = Calendar.getInstance().getTime();
 
    public MyEntity(){
        super();
    }
 
    public MyEntity(String name, String msg){
        super();
        this.name = name;
        this.message = msg;
    }
 
    public Integer getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getMessage() {
        return message;
    }
    public void setMessage(String msg) {
        this.message = msg;
    }
    public Date getDate() {
        return date;
    }
 
    @Override
    public String toString() {
        return "{\n\tid: " + id + ",\n\tname: " + name + ",\n\tmessage: "
             + message+ ",\n\tdate: " + date + "\n}";
    }
 
}

package com.devkuma;
 
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
 
public class App {
    private static EntityManagerFactory factory
        = Persistence.createEntityManagerFactory("sample-persistance");
 
    public static void main( String[] args ){
        EntityManager manager = factory.createEntityManager();
        try {
            manager.getTransaction().begin();
            manager.persist(new MyEntity("sungjin", "This is sample message!"));
            manager.persist(new MyEntity("wonsuk", "안녕하세요!"));
            manager.persist(new MyEntity("byeongho", "이것을 테스트입니다."));
            manager.getTransaction().commit();
 
            Query query = manager.createQuery("select i from MyEntity i");
            List<MyEntity> list = query.getResultList();
            int count = 0;
            for (MyEntity p : list) {
                System.out.print("No," + ++count + " ");
                System.out.println(p);
            }
            System.out.println(" -- total: " + list.size() + " data.");
        } finally {
            manager.close();
        }
    }
}