Using the latest Java Persistence API 2 Features - Tech Days 2010 India
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This document provides an overview of new features in Java Persistence API (JPA) 2.0, including more flexible object/relational mapping capabilities like collections of basic types and embeddables with relationships. It describes the Criteria API, expanded query language, pessimistic locking support, and standardization of configuration options in JPA 2.0.
Using the latest Java Persistence API 2 Features - Tech Days 2010 India
- 1. <Insert Picture Here> Using the Latest Java Persistence API 2.0 Features Arun Gupta, Java EE & GlassFish Guy blogs.sun.com/arungupta, @arungupta
- 2. Java Persistence API Object/Relational Mapping for Java Developers • The standard API for object/relational persistence for Java SE and Java EE applications • Automatic mapping from Java object domain model to relational database • Mapping is explicit, not “magic” • Uses annotations and/or XML • Many useful defaults • Lots of hooks and options for customization • SQL-like query language (JPQL) • Applied to domain model • Supports both static and dynamic queries 2
- 3. Background • JPA 1.0 • Introduced as part of Java EE 5; also available standalone • Part of the EJB 3.0 simplification effort • Based on experience with existing technology: • TopLink, Hibernate, JDO • Covered all the essentials++ 3
- 4. JPA 2.0 (JSR 317) • JPA 2.0 • Part of Java EE 6 and/or available standalone • Adds more sophisticated mapping and modeling options • Expanded query language • Adds Criteria API, together with Metamodel API • Support for Validation • EclipseLink is reference implementation • Integrated in GlassFish 4
- 5. Object/Relational Mapping Essentials • Entities • Basic types • Strings, integers, floats, decimals, … • Embeddable classes • E.g., Address • Relationships • One-to-one, one-to-many/many-to-one, many-to-many • Collections modeled with java.util Collection, Set, List, or Map • Customized via metadata: @JoinColumn, @JoinTable, etc. • Inheritance • Single table, joined subclass, table per class (optional) 5
- 6. Object/Relational Mapping New in JPA 2.0 • Element collections • Collections of strings, integers, floats, decimals, … • Collections of embeddable classes • Embeddable classes • Nested embeddables; embeddables with relationships • Persistently ordered lists • Improved Map support • More relationship mapping options • Unidirectional one-many foreign key mappings • Join table mappings for one-one, one-many/many-one 6
- 7. Collections of Basic Types @Entity public class Person { @Id protected String ssn; protected String name; protected Date birthDate; . . . @ElementCollection protected Set<String> nickNames; } 7
- 8. Collections of Basic Types @Entity public class Person { @Id protected String ssn; protected String name; protected Date birthDate; . . . @ElementCollection @CollectionTable(name=”ALIAS”) protected Set<String> nickNames; } 8
- 9. Collection of Embeddable Types @Embeddable public class Address { String street; String city; String state; . . . } @Entity public class RichPerson extends Person { . . . @ElementCollection protected Set<Address> vacationHomes; . . . } 9
- 10. Multiple Levels of Embedding @Embeddable public class ContactInfo { @Embedded Address address; . . . } @Entity public class Employee { @Id int empId; String name; ContactInfo contactInfo; . . . } 10
- 11. Embeddables with Relationships @Embeddable public class ContactInfo { @Embedded Address address; @OneToMany Set<Phone> phones; . . . } @Entity public class Employee { @Id int empId; String name; ContactInfo contactInfo; . . . } 11
- 12. Ordered Lists @Entity public class CreditCard { @Id long cardNumber; @OneToOne Person cardHolder; . . . @OneToMany @OrderColumn List<CardTransaction> transactions; } 12
- 13. Maps @Entity public class VideoStore { @Id Integer storeId; Address location; . . . @ElementCollection Map<Movie, Integer> inventory; } @Entity public class Movie { @Id String title; @String director; . . . } 13
- 14. Automatic Orphan Deletion For entities logically “owned” by “parent” @Entity public class Order { @Id int orderId; . . . @OneToMany(cascade=PERSIST, orphanRemoval=true) Set<Item> lineItems; . . . } 14
- 15. Key Interfaces • EntityManagerFactory • Used to create entity managers • One entity manager factory per persistence unit • EntityManager • Used to manage persistence context • Entities read/written from database • Operations: persist, remove, find, refresh, createQuery,… • Query, TypedQuery • Used for query configuration, parameter binding, query execution 15
- 16. Java Persistence Query Language • String-based SQL-like query language • SELECT, FROM, WHERE, GROUP BY, ORDER BY,… • Queries written over Java domain model • Entities, state, relationships • Supports navigation using dot-notation • Mapped into SQL by the provider • Supports static and dynamic use SELECT AVG (p.price) FROM Order o JOIN o.products p WHERE o.customer.address.zip = ‘94301’ 16
- 17. Java Persistence Query Language New in JPA 2.0 • Support for all new modeling and mapping features • Operators and functions in select list • Case, coalesce, nullif expressions • Restricted polymorphism • Collection-valued parameters for IN-expressions 17
- 18. JPQL New Operators INDEX For ordered Lists KEY, VALUE, ENTRY For maps CASE, COALESCE, NULLIF For case expressions, etc. TYPE For restricted polymorphism 18
- 19. Ordered Lists SELECT t FROM CreditCard c JOIN c.transactions t WHERE c.cardHolder.name = 'John Doe' AND INDEX(t) < 10 19
- 20. Maps // Inventory is Map<Movie, Integer> SELECT v.location.street, KEY(i).title, VALUE(i), FROM VideoStore v JOIN v.inventory i WHERE KEY(i).director LIKE '%Hitchcock%' AND VALUE(i) > 0 20
- 21. Case Expressions UPDATE Employee e SET e.salary = CASE e.rating WHEN 1 THEN e.salary * 1.05 WHEN 2 THEN e.salary * 1.02 ELSE e.salary * 0.95 END 21
- 22. Restricted Polymorphism SELECT e FROM Employee e WHERE TYPE(e) IN :empTypes 22
- 23. Criteria API New in JPA 2.0 • Object-based API for building queries • Designed to mirror JPQL semantics • Strongly typed • Based on type-safe metamodel of persistent classes and relationships • Heavy use of Java generics • Supports object-based or string-based navigation • Query construction at development time or runtime 23
- 24. Criteria API: Core Interfaces • CriteriaBuilder • Used to construct criteria queries, selections, predicates, orderings • CriteriaQuery • Used to add / replace/ browse query elements • from, select, where, orderBy, groupBy, having,… methods • Root • Query roots • Join, ListJoin, MapJoin, … • Joins from a root or existing join • Path • Navigation from a root, join, or path • Subquery 24
- 25. How to Build a Criteria Query EntityManager em = …; CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<ResultType> cquery = cb.createQuery(ResultType.class); Root<MyEntity> e = cquery.from(MyEntity.class); Join<MyEntity, RelatedEntity> j = e.join(…); … cquery.select(…) .where(…) .orderBy(…) .groupBy(…); TypedQuery<ResultType> tq = em.createQuery(cquery); List<ResultType> result = tq.getResultList(); 25
- 26. Validation New in JPA 2.0 • Leverages work of Bean Validation (JSR 303) • Automatic validation upon lifecycle events • PrePersist • PreUpdate • PreRemove • Validation-mode element in “persistence.xml” • AUTO, CALLBACK, NONE • Standardization of many configuration options 26
- 27. Sample Database Card TX Supplier Product Customer CreditCard Supplier Phone Orders Product Book DVD CD 27
- 28. Metamodel • Abstract “schema-level” view of managed classes • Entities, mapped superclasses, embeddables • Accessed dynamically • EntityManagerFactory.getMetamodel() • EntityManager.getMetamodel() • And/or materialized as static metamodel classes • Used to create strongly-typed criteria queries • Spec defines canonical format 28
- 29. Generating Static Metamodel javac -processor org.eclipse.persistence.internal.jpa.modelgen.CanonicalM odelProcessor -sourcepath src -d src -classpath /ace2_apps/eclipselink/jlib/eclipselink.jar:.:/ace2_apps /eclipselink/jlib/JPA/javax.persistence_2.0.0.v200911271 158.jar -proc:only -Aeclipselink.persistencexml=src/META- INF/persistence.xml src/demo/*.java Note: Creating the metadata factory … Note: Building metadata class for round element: demo.Item . . . http://weblogs.java.net/blog/lancea/archive/2009/12/15/generating-jpa-20-static-metamodel-classes-using-eclipselink-20-and-n 29
- 30. Entity Class package com.example; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Embedded; import javax.persistence.OneToMany; import java.util.Set; @Entity public class Customer { @Id int custId; @Embedded Address address; @OneToMany Set<Order> orders; … } 30
- 31. Metamodel Class package com.example; import javax.annotation.Generated; import javax.persistence.metamodel.SetAttribute; import javax.persistence.metamodel.SingularAttribute; import javax.persistence.metamodel.StaticMetamodel; @Generated(“EclipseLink JPA 2.0 Canonical Model Generation”) @StaticMetamodel(Customer.class) public class Customer_ { public static volatile SingularAttribute<Customer,Integer> custId; public static volatile SingularAttribute<Customer,Address> address; public static volatile SetAttribute<Customer,Order> orders; … } 31
- 32. Concurrency • Java Persistence assumes optimistic concurrency • Short-term read locks • Long-term write locks • Provider can defer writing to database to transaction commit • Application can flush to database on demand • Optimistic “locking” done via version attributes • Integral or timestamp attributes, managed by provider • Provider validates version when writing to database • Explicit lock() calls available to validate read data 32
- 33. Pessimistic Locking New in JPA 2.0 • Java Persistence assumes optimistic concurrency • Normal pessimistic locking • Persistent state of entity • Relationships, Element collections • Grab database locks upfront • JPA spec defines semantics, not mechanism • Provider can lock more (not less) • Lock modes • PESSIMISTIC_READ – grab shared lock • PESSIMISTIC_WRITE – grab exclusive lock • PESSIMISTIC_FORCE_INCREMENT – update version 33
- 34. Locking APIs • EntityManager methods: lock, find, refresh • Query / TypedQuery methods: setLockMode, setHint • NamedQuery annotation: lockMode element • javax.persistence.lock.scope property • javax.persistence.lock.timeout hint • PessimisticLockException (if transaction rolls back) • LockTimeoutException (if only statement rolls back) 34
- 35. Caching Configuration New in JPA 2.0 • EntityManager persistence context corresponds to “first level” cache • Entities managed by persistence provider • Entities read from database • Entities to be written to database • Most implementations also use second-level caches • Not always transparent to application • JPA 2.0 standardizes basic second-level cache options 35
- 36. Standard Configuration Properties • javax.persistence.jdbc.driver • javax.persistence.jdbc.url • javax.persistence.jdbc.user • javax.persistence.jdbc.password • ... 36
- 37. Summary of JPA 2.0 New Features • More flexible modeling capabilities • Expanded O/R mapping functionality • Additions to Java Persistence query language • Criteria API • Metamodel API • Pessimistic locking • Support for validation • Standardization of many configuration options 37
- 38. <Insert Picture Here> Using the Latest Java Persistence API 2.0 Features Arun Gupta, Java EE & GlassFish Guy blogs.sun.com/arungupta, @arungupta