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Apache OpenJPA Examples - Simple
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package hellojpa;

import java.util.List;

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import jakarta.persistence.Query;


/**
 * A very simple, stand-alone program that stores a new entity in the
 * database and then performs a query to retrieve it.
 */
public class Main {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
        // Create a new EntityManagerFactory using the System properties.
        // The "hellojpa" name will be used to configure based on the
        // corresponding name in the META-INF/persistence.xml file
        EntityManagerFactory factory = Persistence.
            createEntityManagerFactory("hellojpa", System.getProperties());

        // Create a new EntityManager from the EntityManagerFactory. The
        // EntityManager is the main object in the persistence API, and is
        // used to create, delete, and query objects, as well as access
        // the current transaction
        EntityManager em = factory.createEntityManager();

        // Begin a new local transaction so that we can persist a new entity
        em.getTransaction().begin();

        // Create and persist a new Message entity
        em.persist(new Message("Hello Persistence!"));

        // Commit the transaction, which will cause the entity to
        // be stored in the database
        em.getTransaction().commit();

        // It is always good practice to close the EntityManager so that
        // resources are conserved.
        em.close();

        // Create a fresh, new EntityManager
        EntityManager em2 = factory.createEntityManager();

        // Perform a simple query for all the Message entities
        Query q = em2.createQuery("select m from Message m");

        // Go through each of the entities and print out each of their
        // messages, as well as the date on which it was created
        for (Message m : (List) q.getResultList()) {
            System.out.println(m.getMessage()
                + " (created on: " + m.getCreated() + ")");
        }

        // Again, it is always good to clean up after ourselves
        em2.close();
        factory.close();
    }
}