OPENJPA使用JPA规范

最近学习JPA,但在我们中国学习的资源还是比较少，尤其是最新的一些技术，下面我将讲讲我搭建的JPA规范的项目。

首先，创建一个项目（web或java项目都可以）,然后在myeclipse里增加jpa的架包。

选择OpenJPA2.0

然后编写persistence.xml文件

我的文件是：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0">
	<persistence-unit name="wms">
		<provider>org.apache.openjpa.persistence.PersistenceProviderImpl
		</provider>
		<class>com.wms.jpa.model.User</class>
		<class>com.wms.jpa.model.Message</class>
		<properties>
			<property name="openjpa.ConnectionDriverName" value="com.mysql.jdbc.Driver" />
			<property name="openjpa.ConnectionURL" value="jdbc:mysql://localhost/jpawms0004?userUnicode=true&characterEncoding=UTF-8&createDatabaseIfNotExist=true&autoReconnect=true" />
			<property name="openjpa.ConnectionUserName" value="root" />
			<property name="openjpa.ConnectionPassword" value="2011_2015" />
			<!-- <property name="openjpa.Multithreaded" value="true" />
			<property name="openjpa.DynamicEnhancementAgent" value="false" />
			<property name="openjpa.RuntimeUnenhancedClasses" value="unsupported" />
			<property name="openjpa.ConnectionFactoryProperties" value="PrintParameters=true" />
			<property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema(ForeignKeys=True)" /> -->
		</properties>
	</persistence-unit>

</persistence>

具体的配置可以去官网查看文档。

然后写一个实体类，每写一个实体类都要在persistence.xml里增加class.

package com.wms.jpa.model;

import java.util.*;
import javax.persistence.*;

@Entity
public class Message {
    @Id
    private long id = System.currentTimeMillis();

    @Basic
    private String message;

    @Basic
    private Date created = new Date();

    public Message() {
    }

    public Message(String msg) {
        message = msg;
    }

    public void setId(long val) {
        id = val;
    }

    public long getId() {
        return id;
    }

    public void setMessage(String msg) {
        message = msg;
    }

    public String getMessage() {
        return message;
    }

    public void setCreated(Date date) {
        created = date;
    }

    public Date getCreated() {
        return created;
    }
}

编写测试文件：

/*
 * 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 com.wms.jpa.test;

import java.util.List;

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

import com.wms.jpa.model.Message;


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

    @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("wms", 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<Message>) 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();
    }
}

然后可以看到如下的运行结果：

最后提醒下要导入必要的数据库驱动。

转载请注明出处http://blog.youkuaiyun.com/wu560130911/article/details/8299422