Spring Data JPA 基础第二篇

主要调用工具类JpaUtils类

package cn.itcast.utils;

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

/**
 * 解决静态实体管理器工厂的浪费资源和耗时问题
 *     通过静态代码块的形式，当程序第一次访问此工具类时，创建一个公共的实体管理器工厂对象
 *
 * 第一次访问getEntityManager方法：经过静态代码块创建一个factory对象，再调用方法创建一个EntityManager对象
 * 第二次访问getEntityManager方法：直接通过一个已经创建好的factory对象，创建EntityManager对象
 */
public class JpaUtils {
    private  static EntityManagerFactory factory;
    static {
        //1.加载配置文件，创建entityManagerFactory
       factory = Persistence.createEntityManagerFactory("myJpa");
    }
    /**
     * 获取EntityManager对象
     */
    public  static EntityManager getEntityManager(){
       return factory.createEntityManager();
    }
}
主要在persistence.xml更改一下把之前的create插入改成update更新

<property name="hibernate.hbm2ddl.auto" value="create"/>

 主要的实体类

package cn.itcast.domain;

import javax.persistence.*;

/**
 * 客户实体类
 *     配置映射关系
 *        1、实体类和表的映射关系
 *        2、实体类中属性和表中字段的映射关系
 * @Entity：声明实体类
 * @Table:配置实体类和表的映射关系
 *       name:配置数据库标的名称
 * 2.实体类中属性和表中字段的映射光线
 */
@Entity
@Table(name = "cst_customer")
public class Customer {
    /**
     * @Id:声明主键配置
     * @GeneratedValue:配置主键的生成策略
     *       GenerationType.IDENTITY：自增 MySQL
     *                底层数据库必须支持自增长
     *       GenerationType.SEQUENCE:序列 oracle
     *                底层数据库必须支持序列
     *       GenerationType.TABLE:
     *             jpa提供的一种机制，通过一张数据库表的形式帮助我们完成自增长
     *       GenerationType.AUTO:
     *             有程序自动的帮助我们选择主键生成策略
     * @Column:配置属性和字段的映射关系
     *       name：数据库中字段的名称
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "cust_id")
    private  Long custId;//客户主键
    @Column(name = "cust_name")
    private  String custName;//客户名称
    @Column(name = "cust_source")
    private  String custSource;//客户来源
    @Column(name = "cust_industry")
    private  String custIndustry;//客户级别
    @Column(name = "cust_level")
    private  String custLevel;//客户所属行业
    @Column(name = "cust_address")
    private  String custAddress;//客户地址
    @Column(name = "cust_phone")
    private  String custPhone;//客户联系方式

    public Long getCustId() {
        return custId;
    }

    public void setCustId(Long custId) {
        this.custId = custId;
    }

    public String getCustName() {
        return custName;
    }

    public void setCustName(String custName) {
        this.custName = custName;
    }

    public String getCustSource() {
        return custSource;
    }

    public void setCustSource(String custSource) {
        this.custSource = custSource;
    }

    public String getCustIndustry() {
        return custIndustry;
    }

    public void setCustIndustry(String custIndustry) {
        this.custIndustry = custIndustry;
    }

    public String getCustLevel() {
        return custLevel;
    }

    public void setCustLevel(String custLevel) {
        this.custLevel = custLevel;
    }

    public String getCustAddress() {
        return custAddress;
    }

    public void setCustAddress(String custAddress) {
        this.custAddress = custAddress;
    }

    public String getCustPhone() {
        return custPhone;
    }

    public void setCustPhone(String custPhone) {
        this.custPhone = custPhone;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "custId=" + custId +
                ", custName='" + custName + '\'' +
                ", custSource='" + custSource + '\'' +
                ", custIndustry='" + custIndustry + '\'' +
                ", custLevel='" + custLevel + '\'' +
                ", custAddress='" + custAddress + '\'' +
                ", custPhone='" + custPhone + '\'' +
                '}';
    }
}
最后测试testFind类

/**
 * 根据id查询客户
 */
public  void testFind(){
    //1根据工具类获取entityManager
    EntityManager entityManager=JpaUtils.getEntityManager();
    //3.获取事务对象，开启事务
    EntityTransaction transaction=entityManager.getTransaction();//获取事务对象
    transaction.begin();//开启事务
    //3.增删改查--根据id查询客户
    Customer customer=entityManager.find(Customer.class,1l);
    System.out.print(customer);
    //5.提交事务（回滚事务）
    transaction.commit();
    //6.释放资源
    entityManager.close();
}