使用JPA + Eclipselink操作PostgreSQL数据库

首先确保您已经安装了PostgreSQL。您可以参考我这篇文章PostgreSQL扫盲教程。

使用Eclipse创建一个新的JPA project：

Platform选择EclipseLink，作为JPA的provider之一。

在Eclipse里自动生成的project如下图所示：

用下列xml的内容覆盖自动生成的xml：

<?xml version="1.0" encoding="UTF-8"?> <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"> <persistence-unit name="jerryjpa" transaction-type="RESOURCE_LOCAL"> <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> <class>jpatest.Person</class> <properties> <property name="eclipselink.ddl-generation" value="create-tables" /> <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/postgres"/> <property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver"/> <property name="javax.persistence.jdbc.user" value="postgres"/> <property name="javax.persistence.jdbc.password" value="test_password"/> </properties> </persistence-unit> </persistence> 

新建一个Java class:

 package jpatest; import javax.persistence.Basic; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.NamedQuery; import javax.persistence.Table; @Entity @Table(name = "T_PERSON") @NamedQuery(name = "AllPersons", query = "select p from Person p") public class Person { @Id @GeneratedValue private long id; @Basic private String firstName; @Basic private String lastName; public long getId() { return id; } public void setId(long newId) { this.id = newId; } public String getFirstName() { return this.firstName; } public void setFirstName(String newFirstName) { this.firstName = newFirstName; } public String getLastName() { return this.lastName; } public void setLastName(String newLastName) { this.lastName = newLastName; } }

现在可以写测试程序了：

package jpatest; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.EntityTransaction; import javax.persistence.Persistence; public class Test { public static void main(String[] args) { String persistenceUnitName = "jerryjpa"; EntityManagerFactory factory = Persistence.createEntityManagerFactory(persistenceUnitName); EntityManager entityManager = factory.createEntityManager(); EntityTransaction transaction = entityManager.getTransaction(); transaction.begin(); Person user = new Person(); user.setFirstName("Jerry_SAP"); user.setLastName("Wang"); entityManager.persist(user); transaction.commit(); entityManager.close(); factory.close(); System.out.println("done"); } }

成功执行后，在PostgreSQL的Admin UI上能看到测试Java程序里用JPA插入数据库的记录：

本文完整的源代码和所需的库文件可以在我的github上找到。

• eclipselink-2.5.1.jar
• javax.persistence-2.1.0.jar
• postgresql-42.1.1.jar

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