In Lacture CSS-441 Advanced Programming using JAVA EE

1. In LactureCSS-441Advanced Programming using JAVA EE Topic : JPA Kaster Nurmukan

2. Agenda • Overview of JPA • EntityManager

3. Agenda O/R Mapping Primary entity annotations EntityManager Entity Relationships Practice

4. O/R Mapping Database Table POJO Java Persistence API Forward Engineering Reverse Engineering

5. Hibernate and JPA • Java Persistence API (JPA) • Annotations for object-relational mapping • Data access API • An object-oriented query language JPQL • Hibernate • The most popular Java ORM library • An implementation of JPA

6. Hibernate Usage • Hibernate without JPA • API: SessionFactory, Session, Query, Transaction • More features • Hibernate with JPA • API: EntityManagerFactory, EntityManager, Query, Transaction • Better portability • Behaviors are better defined and documented

7. A Hibernate Example • Java classes • Employee.java • JPA configuration file • persistence.xml • Code to access the persistent objects • EmployeeTest.java • (Optional) Logging configuration files • log4j.properties

8. Java Classes • Plain Java classes (POJOs); however, it is recommended that • Each persistent class has an identity field • Each persistent class implements the Serializable interface • Each persistent field has a pair of getter and setter, which don’t have to be public

9. Primary Entity Annotations • @Entity. Mark class as an entity • @Id. Define primary key • @EmbeddedId. Define composite key • @Table(name=“TABLE_NAME”). Define table name for entity class. • @Column. Define column property. • @Transient. Ignored by persistence framework. • @GeneratedValue,@SequenceGenerator. Autopopulate column with sequence generator.

10. EntityManager • Maintains a cache of instances within a transactional context (persistence context) • We can acquire EntityManager instance using : • Dependency Injection • EntityManagerFactory • JNDI Lookup • Operations : persist(), merge(), remove(), find(), createNamedQuery(), createQuery() • Persistence unit is declared in persistence.xml

11. Entity Relationships @OneToOne. One to One is represented by a single-value entity reference at one or both ends of the relationship @OneToMany. This annotation is added to a Collection relationship field. @ManyToOne. Indicating that is an entity is part of a Collection @ManyToMany. This annotation is assigned to a Collection relationship field to indicate the target entity also has a Collection of thesource entity type. Lazy vs Eager Binding Cascade (ALL, PERSIST, MERGE, REMOVE, REFRESH)

12. javax.persistence.EntityManager Replaces much of the EJB 2.x “Home” functionality Handles O/R Mapping of Entities to the database Provides APIs inserting objects into database getting objects from database synchronizing objects with database querying database Provides caching Coordinates with transactional services (JTA) Tightly integrated with Java EE and EJB, but not limited to that environment v110912 Java Persistence: EntityManager 12

13. javax.persistence.EntityManager Replaces much of the EJB 2.x “Home” functionality Handles O/R Mapping of Entities to the database Provides APIs inserting objects into database getting objects from database synchronizing objects with database querying database Provides caching Coordinates with transactional services (JTA) Tightly integrated with Java EE and EJB, but not limited to that environment v110912 Java Persistence: EntityManager 13

14. Entities (formerly and sometimes still called Entity Beans) are now Plain Old Java Objects (POJOs) nothing special happens when calling new Author author = new Author(); are not persistent until associated with an EntityManager em.persist(author); v110912 Java Persistence: EntityManager 14

15. Example Author POJO Entity Warning: Using GeneratedValue without specifying a specific strategy should only be used when you have no intention of controlling how the provider manages primary keys for this object type. This would be rare. @javax.persistence.Entity public class Author { private long id; private long version=0; private String firstName; private String lastName; private String subject; private Date publishDate; public Author() {} public Author(long id) { this.id = id; } @Id @GeneratedValue public long getId() { return id;} private void setId(long id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } ... } v110912 Java Persistence: EntityManager 15

16. Creating Entity in Database Author author = new Author(); //primary key will be gen author.setFirstName("dr"); author.setLastName("seuss"); author.setSubject("children"); author.setPublishDate(new Date()); log_.info("creating author:" + author); em.persist(author); log_.info("created author:" + author); //output -creating author:id=0, fn=dr, ln=seuss, subject=children, pdate=Fri Sep 15 11:54:15 EDT 2006 -created author:id=50, fn=dr, ln=seuss, subject=children, pdate=Fri Sep 15 11:54:15 EDT 2006 v110912 Java Persistence: EntityManager 16

17. Managed and Unmanaged Entities Unmanaged state (detached) instance not associated with an EntityManager state changes are not tracked can be serialized to client and returned to be synchronized with database nothing equivalent to this state in EJB 2.1 entity beans Managed state (attached) instance associated with an EntityManager state changes are tracked within a Persistence Context EJB 2.1 entity beans were always managed client interfaced with data through a proxy or state transferred through a Data Transfer Object v110912 Java Persistence: EntityManager 17

18. Persistence Context A set of attached entity instances managed by an EntityManager All entities become detached once closed Two types Transaction-scoped Persistence Contexts begin/end at transaction boundaries only made available through container managed persistence contexts Extended Persistence Contexts live beyond any single transaction allow longer-lived interactions with database without lengthy transactions tying up database resources v110912 Java Persistence: EntityManager 18

19. Persistence Context Examples Transaction-scoped (inside server container) @PersistenceContext(unitName=”jpaDemo”)EntityManager em; @TransactionAttribute(REQUIRED) public void update(long authorId, String type) { Author author = em.find(Author.class, authorId); author.setType(type); } Extended (inside or outside server container) EntityManager em = Persistence. createEntityManagerFactory(“jpaDemo”).createEntityManager(); tx.begin(); //tx 1 begins Author author = em.find(Author.class, authorId); tx.commit(); //tx 1 ends, but author remains managed ... tx.begin(); //tx 2 begins author.setType(type); tx.commit(); //tx 2 ends, and author is still managed until close 19

20. Persistence Unit A set of classes that are mapped to the database defined in META-INF/persistence.xml must have an identity “” is a valid identity Classes may be named in persistence.xml file may be automatically scanned for in the classpath orm.xml optionally provided to augment, provide, or replace class persistence metadata (more on orm.xml in Core ORM topic) 20

21. Example Component Layout META-INF/ +---persistence.xml ejava + ---examples +---… +---DAOException.class +---AuthorDAO.class +---jpa | +---JPAAuthorDAO.class | +---JPADAOBase.class +--domain +---Author.class v110912 Java Persistence: EntityManager 21

22. Example persistence.xml <?xml version="1.0" encoding="UTF-8"?> <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="jpaDemo"> <jta-data-source>java:/ejavaDS</jta-data-source> <properties> <property name="hibernate.hbm2ddl.auto" value="create"/> <property name="hibernate.show_sql" value="true"/ </properties> </persistence-unit> </persistence> referenced by name • global JNDI name by which provider references resource (will be used when deployed within server) • may use properties element in Java SE environments that lack JNDI • vendor-specific way to configure persistence provider 22

23. Another Example persistence.xml <?xml version="1.0" encoding="UTF-8"?> <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="jpaDemo"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <properties> <property name="hibernate.cache.provider_class" value="net.sf.ehcache.hibernate.Provider"/> <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/> <property name="hibernate.connection.url" value="jdbc:hsqldb:hsql://localhost:9001"/> <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/> <property name="hibernate.connection.password" value=""/> <property name="hibernate.connection.username" value="sa"/> <property name="hibernate.show_sql" value="false"/> <property name="hibernate.hbm2ddl.auto" value="create"/> </properties> </persistence-unit> </persistence v110912 Java Persistence: EntityManager 23

24. persistence.xml elements name – identity to reference Persistence Unit provider – fully qualified name of javax.persistence.PersistenceProvider not needed if provider found in classpath acceptable mapping-file – resource path to optional mapping file can be used to specify <class>es or specify/override @Annotation details jta-data-source vendor-specific reference to data source using JTA transactions non-jta-data-source vendor-specific reference to data source using RESOURCE_LOCAL transactions jar-file optional/additional jar file to scan for classes class specifies entity classes not automatically scanned by provider exclude-unlisted-classes if set, provider will not automatically scan archive for entity classes properties may be used to provide vendor-specific properties to configure persistence providers 24

25. Java SE Steps Startup Get EntityManagerFactory Runtime Create EntityManager Start Transaction Interact with Entity Manager Commit Transaction Close EntityManager Shutdown Close EntityManagerFactory 25

26. updating entities Updates to managed entities automatically get propagated to database according to flush policy public Author update(Author author) { Author dbAuthor = em.find(Author.class,author.getId()); dbAuthor.setFirstName(author.getFirstName()); dbAuthor.setLastName(author.getLastName()); dbAuthor.setSubject(author.getSubject()); dbAuthor.setPublishDate(author.getPublishDate()); return dbAuthor; } Note that if author passed in was already managed... the changes have already been queued the dbAuthor returned from the find() will be the same object as author the sets are unnecessarily changing the values of the Author to their current values 26

27. (optional!)Potential Utiltity Class package ejava.examples.dao.jpa; import java.util.HashMap; import java.util.Map; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; public class JPAUtil { private static final Map<String, EntityManagerFactory> factories = new HashMap<String, EntityManagerFactory>(); public static EntityManagerFactory getEntityManagerFactory(String puName) { EntityManagerFactory emf = factories.get(puName); if (emf == null) { synchronized(factories) { emf = factories.get(puName); if (emf == null) { emf = Persistence.createEntityManagerFactory(puName); factories.put(puName, emf); } } } return emf; } public static void close() { synchronized(factories) { for(String puName : factories.keySet()) { factories.get(puName).close(); } factories.clear(); } } } v110912 Java Persistence: EntityManager 27

28. Reference • http://www.oracle.com IndicThreads.com Java Meet June 2006

29. Q&A