学習22日目：メッセージボード作成の前準備。

// パスワードを入力しログイン
mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11555
Server version: 5.7.31 MySQL Community Server (GPL)

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Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

// message_boardアプリ用のデータベースを作成
mysql> CREATE DATABASE message_board DEFAULT CHARACTER SET utf8;
Query OK, 1 row affected (0.04 sec)

// データベースに接続するアカウントを登録
mysql> CREATE USER 'mesuser'@'localhost' IDENTIFIED BY '******';
Query OK, 0 rows affected (0.09 sec)

// さきほど登録したアカウントにINSERTやUPDATE等の実行ができる権限を付与
mysql> GRANT ALL PRIVILEGES ON message_board.* TO 'mesuser'@'localhost';
Query OK, 0 rows affected (0.01 sec)

package utils;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class DBUtil {
    private static final String PERSISTENCE_UNIT_NAME = "message_board";
    private static EntityManagerFactory emf;

    public static EntityManager createEntityManager() {
        return _getEntityManagerFactory().createEntityManager();
    }

    private static EntityManagerFactory _getEntityManagerFactory() {
        if (emf == null) {
            emf = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
        }

        return emf;
    }
}