1.创建一个JPA工程

首先，创建一个JPA工程（若不知道JPA创建或出现at least one user library must be selected等错误，请参考http://blog.csdn.net/baidu_37107022/article/details/76554393）

jar包说明

2.创建实体类

有关实体类中相关注解的说明

* @Table 标注类对应的表* 若表名和类型相同时，省略@Table,比如类Users 和表 users;* 若不相同时，必须有@Table，并设置name,为该类对应的表名。@Table(name="users")* * @Entity 标注实体* * @Id 标注id* * @Transient 标注该属性不做与表的映射(原因：可能表中没有该属性对应的字段)* 有该注解，在执行sql语句时，就不会出现该属性，否则会有，若表中没有该字段则会报错* * @Basic 默认所有属性都有该注解(主键需要单独使用@Id)，所以可以省略* 该注解可以放在属性上，也可以放在对应的getter方法上。* 注意：要么统一将@Basic放在属性上，要么统一放在对应的getter方法上。（一般都放在属性上，可读性比较好）* * @Column 类中属性名和表中对应字段名不相同时，会使用该注解，指明在类中对应的字段* @Column(name="对应的表中字段名")

构建实体类Users

import javax.persistence.Basic; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.Transient; /*** @Table 标注类对应的表* 若表名和类型相同时，省略@Table,比如类Users 和表 users;* 若不相同时，必须有@Table，并设置name,为该类对应的表名。@Table(name="users")* * @Entity 标注实体* * @Id 标注id* * @Transient 标注该属性不做与表的映射(原因：可能表中没有该属性对应的字段)* 有该注解，在执行sql语句时，就不会出现该属性，否则会有，若表中没有该字段则会报错* * @Basic 默认所有属性都有该注解(主键需要单独使用@Id)，所以可以省略* 该注解可以放在属性上，也可以放在对应的getter方法上。* 注意：要么统一将@Basic放在属性上，要么统一放在对应的getter方法上。（一般都放在属性上，可读性比较好）* * @Column 类中属性名和表中对应字段名不相同时，会使用该注解，指明在类中对应的字段* @Column(name="对应的表中字段名")**/ @Table(name="users") @Entity public class Users {//标注id@Idprivate String uid;@Basic@Column(name="uname")private String uname;@Basicprivate int age;@Transientprivate String remark;//备注public String getRemark() {return remark;}public void setRemark(String remark) {this.remark = remark;}public String getUid() {return uid;}public void setUid(String uid) {this.uid = uid;}public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Users [uid=" + uid + ", uname=" + uname + ", age=" + age + "]";}public Users(String uid, String uname, int age) {super();this.uid = uid;this.uname = uname;this.age = age;}public Users() {super();// TODO Auto-generated constructor stub}}

3.JPA的配置文件persistence.xml的配置

<?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="JPA" transaction-type="RESOURCE_LOCAL"><!-- 配置jpa ORM产品 --><provider>org.hibernate.jpa.HibernatePersistenceProvider</provider><!-- 添加对应的持久化类 --><class>com.java.bean.Users</class><properties><!-- jpa中连接数据库 --><property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" /><property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpa" /><property name="javax.persistence.jdbc.user" value="root" /><property name="javax.persistence.jdbc.password" value="123"></property><!-- jpa中配置hibernate基本属性 --><property name="hibernate.show_sql" value="true" /><property name="hibernate.format_sql" value="true" /></properties></persistence-unit> </persistence>

4.测试增删改查CRUD

import java.util.HashMap; import java.util.Map;import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.EntityTransaction; import javax.persistence.Persistence;import com.java.utils.JPAUtils;import junit.framework.TestCase;public class TestUsers extends TestCase {// 插入数据 persist 相当于hibernate save方法public void testInsert() {// 1.获得FactoryEntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA");// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启uiwuEntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users = new Users("1", "小明", 18);manager.persist(users);// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}/*** 创建EntityManagerFactory的第二种方式 可以将如下配置放在创建factory是进行配置，使用map* <property name="hibernate.show_sql" value="true" /> <property name=* "hibernate.format_sql" value="true" />* * 当配置文件中和创建factory时有同一配置时，会按照创建的factory中的设置执行*/public void testInsert2() {// 1.获得FactoryMap properties = new HashMap<String, Object>();properties.put("hibernate.format_sql", "false");EntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA", properties);// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启uiwuEntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users = new Users("2", "小明2", 18);manager.persist(users);// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}// 根据id查询 find 相当于hibernate get方法public void testFind() {// 1.获得FactoryEntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA");// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启事务EntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users = manager.find(Users.class, "1");System.out.println(users);// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}// 根据id查询 getReference 相当于hibernate load方法// find和getReference的区别----与hibernate中get和load的区别一样---懒加载--id没有对应值时报异常public void testGet() {// 1.获得FactoryEntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA");// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启事务EntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users=manager.getReference(Users.class, "1"); System.out.println(users);// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}// 修改数据public void testUpdate() {// 1.获得FactoryEntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA");// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启事务EntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users=manager.find(Users.class, "1"); users.setUname("哈哈哈1");// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}// 删除数据 remove 相当于hibernate delete方法// remove方法只能移除执久化对象，不能删除游离对象public void testRemove() {// 1.获得FactoryEntityManagerFactory factory = Persistence.createEntityManagerFactory("JPA");// 2.获取ManagerEntityManager manager = factory.createEntityManager();// 3.获得事务，并开启事务EntityTransaction transaction = manager.getTransaction();transaction.begin();// 4.执行sqlUsers users=manager.find(Users.class, "2"); manager.remove(users);// 5.提交事务，关闭资源transaction.commit();manager.close();factory.close();}}

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