JPA

1、JPA

JPA（Java持久性API）是存储业务实体关联的实体的来源。它显示了如何定义一个面向普通Java对象（POJO）作为一个实体，以及如何管理关系实体。

2、安装JPA

（1）创建一个新的JPA项目，首先选择File->New->JPA Project。

（2）输入项目名称JPA01，选择Target runtime jre7如下。

（3）点击下载库（如果没有库）中的用户库部分，在下载库对话框中选择EclipseLink库的最新版本，点击下一步。然后接受许可条款，单击Finish。下载后，选择用户库部分中的下载库，然后单击Finish完成操作。

3、简单实例

（1）目录结构

（2）persistence.xml

1. <?xml version="1.0" encoding="UTF-8"?>

2. <persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">

3. <persistence-unit name="JPA01" transaction-type="RESOURCE_LOCAL">

4. <class>cn.hwd.jpa.entity.Employee</class>

5. <properties>

6. <property name="javax.persistence.jdbc.url"

7. value="jdbc:mysql://localhost:3306/hwd"/>

8. <property name="javax.persistence.jdbc.user" value="root"/>

9. <property name="javax.persistence.jdbc.password" value="mysql"/>

10. <property name="javax.persistence.jdbc.driver"

11. value="com.mysql.jdbc.Driver"/>

12. <property name="eclipselink.logging.level" value="FINE"/>

13. <property name="eclipselink.ddl-generation"

14. value="create-tables"/>

15. </properties>

16. </persistence-unit>

17. </persistence>

（3）Employee.java

1. package cn.hwd.jpa.entity;

2.  

3. import javax.persistence.Entity;

4. import javax.persistence.GeneratedValue;

5. import javax.persistence.GenerationType;

6. import javax.persistence.Id;

7. import javax.persistence.Table;

8.  

9. @Entity

10. @Table

11. public class Employee {

12.  

13. @Id

14. @GeneratedValue(strategy= GenerationType.AUTO)

15. private int id;

16. private String name;

17. private double salary;

18. public int getId() {

19. return id;

20. }

21. public void setId(int id) {

22. this.id = id;

23. }

24. public String getName() {

25. return name;

26. }

27. public void setName(String name) {

28. this.name = name;

29. }

30. public double getSalary() {

31. return salary;

32. }

33. public void setSalary(double salary) {

34. this.salary = salary;

35. }

36. public Employee() {

37. super();

38. // TODO Auto-generated constructor stub

39. }

40. public Employee(int id, String name, double salary) {

41. super();

42. this.id = id;

43. this.name = name;

44. this.salary = salary;

45. }

46. @Override

47. public String toString() {

48. return "Employee [id=" + id + ", name=" + name + ", salary=" + salary

49. + "]";

50. }

51. }

（4）EmployeeServiceTest.java

1. package cn.hwd.jpa.test;

2.  

3. import javax.persistence.EntityManager;

4. import javax.persistence.EntityManagerFactory;

5. import javax.persistence.Persistence;

6.  

7. import org.junit.Test;

8.  

9. import cn.hwd.jpa.entity.Employee;

10.  

11. public class EmployeeServiceTest {

12.  

13. @Test

14. public void createEmployee() {

15. EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("JPA01");

16. EntityManager entitymanager = emfactory.createEntityManager();

17. entitymanager.getTransaction().begin();

18.  

19. Employee employee = new Employee();

20. employee.setId(1);

21. employee.setName("Jerry");

22. employee.setSalary(6999);

23. entitymanager.persist(employee);

24. entitymanager.getTransaction().commit();

25.  

26. entitymanager.close();

27. emfactory.close();

28. }

29.  

30. @Test

31. public void deleteEmployee() {

32. EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("JPA01");

33. EntityManager entitymanager = emfactory.createEntityManager();

34. entitymanager.getTransaction().begin();

35.  

36. Employee employee=entitymanager.find(Employee.class, 1);

37. entitymanager.remove(employee);

38. entitymanager.getTransaction().commit();

39.  

40. entitymanager.close();

41. emfactory.close();

42. }

43.  

44. @Test

45. public void findEmployee() {

46. EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("JPA01");

47. EntityManager entitymanager = emfactory.createEntityManager();

48.  

49. Employee employee=entitymanager.find(Employee.class, 1);

50. System.out.println(employee);

51. }

52.  

53. @Test

54. public void updateEmployee() {

55. EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("JPA01");

56. EntityManager entitymanager = emfactory.createEntityManager();

57. entitymanager.getTransaction().begin();

58.  

59. Employee employee=entitymanager.find(Employee.class, 1);

60. //before update

61. System.out.println(employee);

62. employee.setSalary(7200);

63. entitymanager.getTransaction().commit();

64. //after update

65. System.out.println(employee);

66.  

67. entitymanager.close();

68. emfactory.close();

69. }

70.  
71.