JPA开发

1. 什么是JPA

1. JPA(Java Persistence API)是Sun官方提出的Java持久化规范。它为Java开发人员提供了一种对象/关系映射工具来管理Java应用中的关系数据。他的出现主要是为了简化现有的持久化开发工作和整合ORM技术，结束现在Hibernate、TopLink、JDO等ORM框架各自为营的局面。值得注意的是，JPA是在充分吸收了现有Hibernate、TopLink、JDO等ORM框架的基础上发展而来的，具有易于使用、伸缩性强等优点。从目前的开发社区的反应上看，JPA受到了极大的支持和赞扬，其中就包括了Spring与EJB3.0的开发团队。着眼未来几年的技术走向，JPA作为ORM领域标准化整合者的目标应该不难实现。

2. JPA的总体思想和现有Hibernate、TopLink、JDO等ORM框架大体一致，总的来说，JPA包括以下3方面的技术：

2.1 ORM映射元数据

JPA支持XML和JDK5.0注释(注解)两种元数据的形式，元数据描述对象和表之间的映射关系，框架据此将实体对象持久化到数据库表中。

2.2 Java持久化API

用来操作实体对象，执行CRUD操作，框架在后台替我们完成所有的事情，开发者可以从繁琐的JDBC和SQL代码中解脱出来。

2.3 查询语言

这是持久化操作中很重要的一个方面，通过面向对象而非面向数据库的查询语言查询数据，避免程序的SQL语句紧密耦合。

提示：JPA不是一种新的ORM框架，他的出现只是用于规范现有的ORM技术，它不能取代现有的Hibernate、TopLink等ORM框架。相反，在采用JPA开发时，我们仍将使用这些ORM框架，只是此时开发出来的应用不再依赖于某个持久化提供商。应用可以在不修改代码的情况下在任何JPA环境下运行，真正做到低耦合，可扩展的程序设计。

2. 开发JPA依赖的jar文件

Hibernate核心包(8个文件)

hibernate-distribution-3.3.1.GA

hibernate3.jar lib\bytecode\cglib\hibernate-cglib-repack-2.1_3.jar lib\required\*.jar

Hibernate注解包(3个文件)：hibernate-annotations-3.4.0.GA

hibernate-annotations.jar lib\ejb3-persistence.jar、hibernate-commons-annotations.jar

Hibernate针对JPA的实现包(3个文件):hibernate-entitymanager-3.4.0.GA

hibernate-entitymanager.jar lib\test\log4j.jar、slf4j-log4j12.jar

3.JPA的配置文件

JPA规范要求在类路径的META-INF目录下放置persistence.xml, 文件的名称是固定的，配置模板如下：

<persistence 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_1_0.xsd"    version="1.0">    <persistence-unit name="itcast" transaction-type=”RESOURCE-LOCAL”>       <properties>          <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>          <property name=”hibernate.connection.driver_class” value=”org.gjt.mm.mysql.Driver” />          <property name=”hibernate.connection.username” value=”root” />          <property name=”hibernate.connection.password” value=”root” />          <property name=”hibernate.connection.url”  value=”jdbc:mysql://localhost:3306/itcast?useUnicode=true&amp;characterEncoding=UTF-8”/>          <property name=”hibernate.max_fetch-depth” value=”3” />          <property name="hibernate.hbm2ddl.auto" value="update"/>       </properties>    </persistence-unit> </persistence>

4. JPA实例

建立一个名为JPA的java project, 在src目录下新建META-INF文件夹，并把persistence.xml文件放入其中

建立实体bean

package cn.itcast.bean; import javax.persistence.Entity; import javax.persistentce.GeneratedValue; import javax.persistentce.GeneratedType; import javax.persistentce.Id;   @Entity @Table(name=”xxx”) public class Person { private Integer id; private String name; private Date birthday; //1887-12-10 private Gender gerder = Gender.MAN; private String info;  //存放大文本数据 private Byte[] file;   //大数据(大于1M)延迟加载 private String imagepath;  //不希望该字段映射到数据库   public Person(String name) {     this.name = name; }   @Id @GeneratedValue public Integer getId() {         return id; } public void setId(Integer id) {     this.id = id; } @Column(length=10,nullable=false,name=”personName”) public String getName() {     return name; } public void setName(String name) {     this.name = name; } @Temporal(TemporalType.DATE) public Date getBirthday() {     return birthday; } public void setBirthday(Date birthday) {     this.birthday = birthday; } @Enumerated(EnumType.STRING) @Column(length=5,nullable=false) public Gender getGender() {     return gender; } public vod setGender(Gender gender) {     this.gender = gender; } @Lob public String getInfo {     return info; } public void setInfo(String info) {     this.info = info; } @Lob @Basic(fetch=FetchType.LAZY) public Byte[] getFile() {     return file; } public void setFile(Byte[] file) {     this.file = file; } @Transient publc String getImagepath() {     return imagepath; } public void setImagepath(String imagepath) {     this.imagepath = imagepath; } }

枚举类

package cn.itcast.bean; public enum Gender {     MAM,WOMEN }

 

测试代码

package junit.test;   public class PersonTest {   @Test public void save() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务     em.persist(new Persion(“传智博客”));   //new状态     em.getTransaction().commit();     em.close();     factory.close(); } @Test public void getPerson() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     Person person = em.find(Person.class,1);     System.out.println(person.getName());     em.close();     factory.close(); } @Test public void getPerson() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     Person person = em.getReference(Person.class,1);     System.out.println(person.getName());     em.close();     factory.close(); }   @Test public void updatePerson() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务     Person person = em.find(Person.class,1);  //托管状态     person.setName (“老张”);  //处于托管状态，对person的修改可以同步到数据库     //em.clear();  //把实体管理器的所有实体变成游离状态     em.getTransaction().commit();     em.close();     factory.close(); } @Test public void updatePerson2() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务     em.clear();  //把实体管理器的所有实体变成游离状态     person.setName (“老黎”);  //处于托管状态，对person的修改可以同步到数据库     em.merge(person);     em.getTransaction().commit();     em.close();     factory.close(); } @Test public void delete() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务     Person person = em.find(Person.class,1);     em.remove(person);     em.getTransaction().commit();     em.close();     factory.close(); } @Test public void query() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();         Query query = em.createQuery(“select o from Person o where o.id=?1”);         query.setParameter(1,2);         List<Person> persons = query.getResultList();         for(Person person:persons)             System.out.println(person.getName());     em.close();     factory.close(); } @Test public void deletequery() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();         Query query = em.createQuery(“delete from Person o where o.id=?1”);         query.setParameter(1,2);         query.executeUpdate();     em.getTransaction().commit();     em.close();     factory.close(); }   @Test public void queryupdate() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务     Query query = em.createQuery(“update Person o set o.name=:name where o.id=:id”);     query.setParameter(“name”,”xxx”);     query.setParameter(“id”,3);     query.executeUpdate();     em.getTransaction().commit();     em.close();     factory.close(); } }

5. JPA中的一对多双向关联与级联操作

多的一方为关系维护端，关系维护端负责外键记录的更新，关系被维护端是没有权利更新外键记录

package cn.itcast.bean; import javax.persistence.Entity; @Entity public class OrderItem { private Integer id; private String productName; private Float sellPrice = 0f; private Order order;   @Id @GeneratedValue public Integer getId() {     return id; } public setId(Integer id) {     this.id = id; } @Column(length=40,nullable=false) public String getProductName() {     return productName; } public void setProductName(String productName) {     this.productName = productName; } @Column(nullable=false) public Float getSellPrice() {     return sellPrice; } public void setSellPrice (Float sellPrice) {     this. sellPrice = sellPrice } @ManyToOne(cascade={ascadeType.MERGE, CascadeType.REFERSH},optional=false) @JoinColumn(name=”order_id”) public Order getOrder() { //默认立即加载     return order; } public void setOrder(Order order) {    this.order = order; } }

Order实体

@Entity @Table(name=”orders”) public class Order { private String orderid; private Float amount = 0f; private Set<OrderItem> items = new HashSet<OrderItem>();   @Id @Column(length=12) public String getOrderid() {     return ordered; } public void setOrderid(String ordered) {     this.orderid = ordered; } @Column(nullable=false) public Float getAmount() {     return amount; } public void setAmount(Float amount) {     this.amount = amount; } @OneToMany(cascade={CascadeType.REFRESH,CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REMOVE},fetch=FetchType.LAZY，mappedBy=”order”) public Set<OrderItem> getItems() {  //默认延迟加载     return items; } public void setItems(Set<OrderItem> items) {     this.items = items; }

保存操作

public class OneToManyTest {  @Test public void save() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务       Order order = new Order();     order.setAmout(34f);     order.setOrderid(“999”);     OrderItem orderItem1 = new OrderItem();     orderItem1.setProductName(“足球”);     orderItem1.setSellPrice(90f);     OrderItem orderItem2 = new OrderItem();     orderItem1.setProductName(“瑜伽球”);     orderItem1.setSellPrice(30f);     order.addOrderItem(orderItem1);     order.addOrderItem(orderItem2);       em.persist(order);     em.getTransaction().commit();     em.close();     factory.close(); } }

6. JPA中一对一双向关联

Peron实体

@Entity public class Person { private Integer id; private String name; private IDCard idcard; public Person(){} public Public(String name) { this.name = name } @Id @GeneratedValue public Integer getId() {     return id; } public void setId(Integer id) {     this.id = id; } public String getName() {     return name; } pubic void setName() {     this.name = name; } @OneToOne(optional=false,cascade=CascadeType.ALL) @JoinColumn(name=”idcard_id”) public IDCard getIdcard() {     return idcard; } public void setIdcard(IDCard idcard) {     this.idcard = idcard; } }

 

IDCard实体

public class IDCard { private Integer id; private String cardno; private Persion person; public IDCard (){} public IDCard (String cardno) { this.cardno = cardno; }   @Id @GeneratedValue public Integer getId() {     return id; } pubic void setId(Integer id) {     this.id = id; } @Column(length=18,nullable=false) public String getCardno() {     return name; } public void setName(String name) {     this.name = name; } @OneToOne(mappedBy=”idcard”,cascade={CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REFRESH},optional=”false”) public Person getPerson() {     return person; } pubic void setPerson(Person person) {     this.person = person; } }

保存操作

public class OneToManyTest {  @Test public void save() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();   //开始事务         Person person = new Person(“老张”);     IDCard idcard = new IDCard(“11111”);       em.persist(person);     em.getTransaction().commit();     em.close();     factory.close(); } }

7. JPA中多对多双向关联

public class Student { private Integer id; private String name; private Set<Teacher> teachers= new HashSet<Teacher>(); public Student() {} public Student(String name) { this name = name; } @Id @GeneratedValue public Integer getId() {…} public void setId(Integer id) {…} @Column(length=10,nullable=false) public String getName() {…} public void setId(String name){…} @ManyToMany(cascade=CascadeType.REFRESH) @JoinTable(name=”student_teacher”,inverseJoinColumns=@JoinColumn(name=”teacher_id”),joinColumns=@JoinColumn(name=”student_id”)) public Set<Teacher> getTeacher() {…} public void setTeacher(Set<Teacher> teacher) {…} }

Teacher实体

@Entity public class Teacher private Integer id; private String name; private Set<Student> student = new HashSet< Student >(); public Teacher() {} public Teacher(String name) { this.name = name; } @Id @GeneratedValue public Integer getId() {…} public void setId(Integer id) {…} public String getName() {…} public void setId(String name){…} @ManyToMany(cascade=CascadeType.REFRESH,mappendBy=”teachers”) public Set< Student> get Student () {…} public void setTeacher(Set<Student> student) {…} }

保存操作

public class ManyToManyTest {  @Test public void save() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();     em.persist(new Student(“小张”);     em.persist(new Teacher(“李勇”);     em.getTransaction().commit();     factory.close(); } //建立学生跟老师的关系 @Test public void buildTS() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();     Student student = em.find(Student.class,1);     student.addTeacher(em.getReference(Teacher.class,1));     em.getTransaction().commit();     em.close():     factory.close();     factory.close(); } //解除学生跟老师的关系 @Test public void deleteTS() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();     Student student = em.find(Student.class,1);     student.removeTeacher(em.getReference(Teacher.class,1));     em.getTransaction().commit();     em.close()     factory.close();     factory.close(); } //删除老师 @Test public void deleteTeacher() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();     Student student = em.find(Student.class,1);     student.removeTeacher(em.getReference(Teacher.class,1));     em.remove(teacher);     em.getTransaction().commit();     em.close()     factory.close();     factory.close(); } //删除学生 @Test public void deleteStudent() {     EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);     EntityManager em = factory.createEntityManager();     em.getTransaction().begin();     Student student = em.getReference(Student.class,1);         em.remove(student);     em.getTransaction().commit();     em.close()     factory.close();     factory.close(); }   }

8. 联合主键

@Embeddable public class AirLinePK implements Serializable { private String startCity; private String endCity;   @Column(length=3) public String getStartCity() {     return startCity; } public void setStartCity(String startCity) {     this.startCity = startCity; } @Column(length=3) public String getEndCity() {     return endCity; } public void setEndCity(String endCity) {     this. endCity = endCity; }   public int hashCode() {     final int prime = 31;     int result = 1;     result = prime * result + ((endCity ==null)?0:endCity.hashCode());     result = prime * result + ((startCity == null)?0:startCity.hashCode());     return result; } public boolean equals(Object obj) {     if(this == obj) return true;     if(obj == null) return false;     if(getClass() != obj.getClass()) return false;     final AirLinePK other = (AirLinePK) obj;     if(endCity == null) {         if(other.endCity != null) return false;      }else if(!endCity.equals(other.endCity)) {          return false;      }      if(startCity == null) {         if(other. startCity != null) return false;      }else if(!estartCity.equals(other. startCity)) {          return false;      }     return true; } }

AirLine实体

@Entity public class AirLine { private AirLinePK id; private String name; public AirLine() {} public AirLine(AirLinePK id) {    this.id = id; } public AirLine(String startCity,String endCity,String name) {     this.id = new AirLinePk(startCity,endCity);     this.name = name; } @EmbeddedId public AirLinePK getId() {     return id; } public void setId(AirLinePK id) {     this.id = id; } @Column(length=20) public String getName() {     return name; } public void setName(String name) {     this.name = name; } }

单元测试

@Test public void save() {

EntityManagerFactory factory = Persistence.createEntityManagerFactory(“itcast”);

    EntityManager em = factory.createEntityManager();

    em.getTransaction().begin();

    em.persist(new AirLine(“PEK”,”SHA’,”北京飞上海”));

    em.getTransaction().commit();

    em.close()

    factory.close();

    factory.close();

 

}