Presentation made at JavaONE, Hyderabad, on 10th May 2011. Slides are a slightly modified version of what's presented by Linda D. at JavaONE, SF, in 2010.

1. <Insert Picture Here>
JavaTM Persistence API 2.0: An Overview
Sanjeeb Sahoo
Sr. Staff Engineer, Sun, an Oracle Company

2. The following/preceding is intended to outline
our general product direction. It is intended for
information purposes only, and may not be
incorporated into any contract. It is not a
commitment to deliver any material, code, or
functionality, and should not be relied upon in
making purchasing decisions.
The development, release, and timing of any
features or functionality described for Oracle’s
products remains at the sole discretion of
Oracle.
2

3. JavaTM Persistence API: Brief History
• Java Persistence 1.0
– Standardized object/relational mapping for Java
applications
– Available as part Java EE 5 Platform or standalone
– Covered most of the essential features
• Java Persistence 2.0
– More and better increased application portability
– Released in December 2009
– Available as part of Java EE 6 Platform or standalone
– Reference Implementation is EclipseLink
– Available as part of GlassFish v3
3

4. 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
4

5. Packaging
• Java SE (Standalone Java Application)
– Jar file with entities, application classes and META-
INF/persistence.xml
• Java EE
– War file
• WEB-INF/classes/META-INF/persistence.xml
• WEB-INF/lib/entities.jar (with META-INF/persistence.xml)
– EJB jar
• EJBs and entities and META-INF/persistence.xml
– EAR file
• lib/entities.jar with META-INF/persistence.xml
5

6. Bootstrapping
• Java SE (Standalone Java Application)
– Persistence.createEntityManagerFactory
• Java EE
– @PersistenceContext EntityManager em;
– @PersistenceUnit EntityManagerFactory emf;
6

7. JavaTM Persistence 2.0:
New Features
• Expanded modeling capabilities
• Additional O/R mapping options
• Additions to Java Persistence query language
• Metamodel API
• Criteria API
• Pessimistic locking
• Standardization of many configuration options
• Support for validation
7

8. 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)
8

9. JavaTM Persistence 2.0:
Expanded modeling and mapping
• Collections of basic types
• Collections of embeddables
• Richer support for embeddable classes
– Multiple levels of embedding
– Embeddable classes with relationships
• Persistently ordered lists
• Improved map support
– Joins with additional columns
– Ternary relationships
• Orphan deletion
9

10. JavaTM Persistence 2.0:
Expanded modeling and mapping
• Derived identities
– Improved modeling for overlapping primary and foreign
keys
• Combinations of access types
• Expanded relationship mapping options
– Unidirectional one-many foreign key mappings
– One-one, many-one/one-many join table mappings
10

11. Collections of Basic Types and Embeddables
• Collections of strings, integers, etc.
• Collections of embeddables (e.g., Address, Detail)
• Specified by @ElementCollection
• Stored in “collection table”
• Customize mappings with:
– @CollectionTable
– @Column (for basic types)
– @AttributeOverride, @AssociationOverride (for
embeddables)
11

12. Collections of Basic Types
@Entity
public class Person {
@Id protected String ssn;
protected String name;
protected Date birthDate;
...
@ElementCollection
protected Set<String> nickNames;
...
}
12

13. Collections of Basic Types
PERSON
SSN NAME BIRTHDATE
PERSON_NICKNAMES
PERSON_SSN NICKNAMES
13

14. Collections of Embeddable Types
@Entity public class Landlord {
@Id String taxId;
String name;
@ElementCollection
@CollectionTable(name=“rentals”)
Set<Address> properties;
...
}
@Embeddable public class Address {
String street;
String city;
String state;
...
}
14

15. Collections of Embeddable Types
LANDLORD
TAXID NAME …
RENTALS
LANDLORD_TAXID STREET CITY STATE …
15

16. Multiple Levels of Embedding
@Entity public class Employee {
@Id int empId;
String name;
ContactInfo contactInfo;
. . .
}
@Embeddable public class ContactInfo {
@Embedded Address address;
. . .
}
16

17. Embeddables with Relationships
@Entity public class Employee {
@Id int empId;
String name;
ContactInfo contactInfo;
. . .
}
@Embeddable public class ContactInfo {
@Embedded Address address;
@OneToMany Set<Phone> phones;
. . .
}
17

18. Persistently Ordered Lists
• Order is maintained in database by provider
– Uses additional (integral) ordering column
• Specified with @OrderColumn
• Provides alternative to @OrderBy
18

19. Persistently Ordered Lists
@Entity public class CreditCard {
@Id String cardNumber;
@ManyToOne Customer customer;
...
@OneToMany(mappedBy=“creditCard”)
@OrderColumn(name=“TXORDER”)
List<CardTransaction> transactionHistory;
...
}
@Entity public class CardTransaction {
@Id @GeneratedValue Long id;
@ManyToOne @JoinColumn(name=“CARDID”)
CreditCard creditCard;
@Temporal(DATE) Date txDate;
...
}
19

20. OrderColumn
CREDITCARD
CARDNUMBER …
CARDTRANSACTION
CARDID ID TXDATE … TXORDER
20

21. @OrderBy Alternative
@Entity public class CreditCard {
@Id String cardNumber;
@ManyToOne Customer customer;
...
@OneToMany(mappedBy=“creditCard”)
@OrderColumn(name=“TXORDER”) @OrderBy(“txDate”)
List<CardTransaction> transactionHistory;
...
}
@Entity public class CardTransaction {
@Id @GeneratedValue Long id;
@ManyToOne @JoinColumn(name=“CARDID”)
CreditCard creditCard;
@Temporal(DATE) Date txDate;
...
}
21

22. Generalized Maps
• Map key can be
– Basic type
– Embeddable
– Entity
• Map value can be
– Basic type
– Embeddable
– Entity
• Support for legacy join tables with additional
columns
• Support for ternary relationships
22

23. Generalized Maps
• Map collection is specified with
– @ElementCollection, @OneToMany, @ManyToMany
– Annotation is determined by map value
• Customize mapping with:
– @CollectionTable (for element collection)
– @JoinTable (for relationship)
– @MapKeyColumn (for basic map key)
– @MapKeyJoinColumn(s) (for entity key)
– @AttributeOverride(s) using “key.” or “value.” syntax
(for embeddables)
23

24. Generalized Maps
@Entity
public class VideoStore {
@Id Integer storeId;
Address location;
@ElementCollection
@CollectionTable(
joinColumn=@JoinColumn(name=“VIDEO_STOREID”))
Map<Movie, Integer> inventory;
...
}
@Entity
public class Movie {
@Id String title;
String director;
...
}
24

25. Generalized Maps
VIDEOSTORE
STOREID NAME STREET CITY STATE …
MOVIE
TITLE DIRECTOR …
VIDEOSTORE_INVENTORY
VIDEO_STOREID INVENTORY_KEY INVENTORY
25

26. Automatic Orphan Deletion
• Deletion of related entities when removed from
relationship
– For entities logically “owned” by “parent”
– For one-to-one and one-to-many relationships
• Specified with orphanRemoval element
– cascade=REMOVE is redundant
26

27. Orphan Deletion
@Entity
public class Order {
@Id int orderId;
...
@OneToMany(cascade=PERSIST, orphanRemoval=true)
Set<Item> items;
}
27

28. Java Persistence Query Language:
New Functionality
• Support for all new modeling and mapping
features
• Operators and functions in select list
• Case, coalesce, nullif expressions
• Restricted polymorphism
• Collection-valued input parameters
• Date / time / timestamp literals
28

29. New Operators
• INDEX
– For ordered lists
• KEY, VALUE, ENTRY
– For maps
• CASE, COALESCE, NULLIF
– For case expressions and the like
• TYPE
– For entity type expressions / restricted polymorphism
29

30. Restricted Polymorphism,
Collection-valued Input Parameters
SELECT e
FROM Employee e
WHERE TYPE(e) IN (PartTime, Contractor)
SELECT e
FROM Employee e
WHERE TYPE(e) IN :empTypes
30

31. Criteria API
• Object-based API for building queries
• Designed to mirror JPQL semantics
• Strongly typed
– Based on type-safe metamodel of persistence unit
– Heavy use of Java generics
– Typing carries through to query execution as well
• Supports object-based or strong-based navigation
31

32. Criteria API: Core Interfaces
• CriteriaQuery
– Represents a query definition object
– Used to add / replace / browse constituent query elements
– select, from, where, orderBy, groupBy, having,… methods
• CriteriaBuilder
– Factory for CriteriaQuery objects
– Obtained from EntityManager or EntityManagerFactory
– Used to create selections, expressions, restrictions,
orderings…
• Root
– Query root
32

33. Criteria API: Core Interfaces
• Join, ListJoin, MapJoin,…
– Joins from a root or existing join
• Path
– Navigation from a root, join, path
• Subquery
• Parameter
• TypedQuery
– Executable query object
– Extends Query interface
• Tuple
– Multiple-valued result type
33

34. The World’s Simplest Query
SELECT c
FROM Customer c
CriteriaBuilder cb = ...;
CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);
Root<Customer> c = cq.from(Customer.class);
cq.select(c);
34

35. Joins and Navigation
SELECT c
FROM Customer c join c.orders o
CriteriaBuilder cb = ...;
CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);
Root<Customer> c = cq.from(Customer.class);
Join<Customer, Order> o = customer.join(“orders”);
cq.select(c);
35

36. Joins and Navigation: What’s the Problem?
SELECT c
FROM Customer c join c.orders o
CriteriaBuilder cb = ...;
CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);
Root<Customer> c = cq.from(Customer.class);
Join<Customer, Order> o = customer.join(“wombats”);
cq.select(c);
36

37. Metamodel
• Abstract, “schema-level” view of managed
classes of persistence unit
– Entities, mapped superclasses, embeddables, and their
attributes and relationships
• Accessible at runtime
– EntityManagerFactory.getMetamodel()
– EntityManager.getMetamodel()
• Useful for frameworks
• Provides foundation for type-safe queries
• Can be materialized as static metamodel classes
– Use javac + annotation processor
37

38. Type-safe Navigation
SELECT c
FROM Customer c join c.orders o
CriteriaBuilder cb = ...;
CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);
Root<Customer> c = cq.from(Customer.class);
Join<Customer, Order> o = customer.join(Customer_.orders);
cq.select(c);
38

39. Optimistic Locking
• Assumes read-committed isolation, deferred
writes
– Short term read-locks
– Long term write-locks
• Layered on top of @Version use
– Verify version for updated entities before transaction
commit
• Lock Modes
– OPTIMISTIC (READ)
– OPTIMISTIC_FORCE_INCREMENT (WRITE)
• “READ” lock => verify version for clean data
• “WRITE” lock => update version for clean data
39

40. Pessimistic Locking
• Grab database locks upfront
• Lock Modes
– PESSIMISTIC_READ
– PESSIMISTIC_WRITE
– PESSIMISTIC_FORCE_INCREMENT
• Normal (default) pessimistic locking
– Persistent state of entity (except element collections)
– Relationships where entity holds foreign key
• Extended pessimistic locking
– Uses javax.persistence.lock.scope property (EXTENDED)
– Element collections and relationships in join tables
– Phantoms are possible
40

41. Pessimistic Locking
@Stateless public class HRBean {
...
@PersistenceContext EntityManager em;
...
public void giveRaises(int deptId) {
Department dept =
em.find(Department.class, deptId,
LockModeType.PESSIMISTIC_READ);
if (dept.getBudget() > 100000) {
Query q = em.createQuery(
“SELECT emp ” +
“FROM Employee emp ” +
“WHERE emp.dept.id = ” + deptId);
q.setLockMode(LockModeType.PESSIMISTIC_WRITE);
List = q.getResultList();
// update employee salaries selectively...
}
}
}
41

42. 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)
42

43. Second Level Cache APIs
• APIs and control options added for portability
• Cache interface methods: evict, evictAll, contains
• @Cacheable + shared-cache-mode XML element
– ALL, NONE, ENABLE_SELECTIVE, DISABLE_SELECTIVE
• Properties for find, refresh, setProperty methods
– javax.persistence.cache.retrieveMode property
• USE, BYPASS
– javax.persistence.cache.storeMode property
• USE, BYPASS, REFRESH
43

44. Validation
• Leverages work of Bean Validation JSR (JSR 303)
• Automatic validation upon lifecycle events
– PrePersist
– PreUpdate
– PreRemove
• persistence.xml validation-mode element
– AUTO
– CALLBACK
– NONE
44

45. Validation
@Entity public class Employee {
@Id Integer empId;
@NotNull String name;
Float salary;
@Max(15) Integer vacationDays;
@Valid Address worksite;
...
}
@Embeddable public class Address {
@Size(max=30) String street;
@Size(max=20) String city;
@Size(min=2,max=2) String state;
@Zipcode String zipcode;
...
}
45

46. Standard Configuration Properties
• javax.persistence.jdbc.driver
• javax.persistence.jdbc.url
• javax.persistence.jdbc.user
• javax.persistence.jdbc.password
• ...
46

47. JPA 2.1 Candidate Features
http://jcp.org/en/jsr/detail?id=338
NEW

Multi-tenancy

Support for stored procedures, vendor function

Update and Delete Criteria queries, JPQL ↔
Criteria

Query by Example

Support for schema generation

UUID generator type

Persistence Context synchronization control

Dynamic definition of PU

Additional event listeners
47

48. Summary
• Expanded modeling capabilities
• Additional O/R mapping options
• Additions to Java Persistence query language
• Metamodel API
• Criteria API
• Pessimistic locking
• Standardization of many configuration options
• Support for validation
• Improved portability
48

49. Resources
• Java Persistence 2.0 Specification
http://jcp.org/en/jsr/detail?id=317
• Reference Implementation is EclipseLink
http://www.eclipse.org/eclipselink
• Available as part of Java EE 6 with GlassFish
http://glassfish.org
• Book: Pro JPA 2 (Keith & Schincariol)
49

50. The following/preceding is intended to outline
our general product direction. It is intended for
information purposes only, and may not be
incorporated into any contract. It is not a
commitment to deliver any material, code, or
functionality, and should not be relied upon in
making purchasing decisions.
The development, release, and timing of any
features or functionality described for Oracle’s
products remains at the sole discretion of
Oracle.
50