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.*;@Entitypublic 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.csdn.net/wu560130911/article/details/8299422