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：

    
        org.eclipse.persistence.jpa.PersistenceProvider
        jpatest.Person
        
            
                     
              
              
             
        
    

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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