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Using the Latest Java Persistence API 2.0 Features
Arun Gupta, Java EE & GlassFish Guy
blogs.sun.com/arungupta, @arungupta
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
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
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
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
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
Collections of Basic Types

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




                                       7
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
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
Multiple Levels of Embedding

@Embeddable public class ContactInfo {
    @Embedded Address address;
    . . .
}


@Entity public class Employee {
    @Id int empId;
    String name;
    ContactInfo contactInfo;
    . . .
}




                                         10
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
Ordered Lists

@Entity public class CreditCard {
    @Id long cardNumber;
    @OneToOne Person cardHolder;
    . . .
    @OneToMany
    @OrderColumn
    List<CardTransaction> transactions;
}




                                          12
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
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
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
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
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
JPQL New Operators

INDEX
  For ordered Lists
KEY, VALUE, ENTRY
  For maps
CASE, COALESCE, NULLIF
  For case expressions, etc.
TYPE
  For restricted polymorphism



                                18
Ordered Lists

SELECT t
FROM CreditCard c JOIN c.transactions t
WHERE c.cardHolder.name = 'John Doe'
  AND INDEX(t) < 10




                                          19
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
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
Restricted Polymorphism

SELECT e
FROM Employee e
WHERE TYPE(e) IN :empTypes




                             22
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
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
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
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
Sample Database

            Card TX                       Supplier


                               Product
Customer   CreditCard
                               Supplier
             Phone

            Orders             Product



                        Book    DVD          CD

                                                     27
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
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
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
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
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
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
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
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
Standard Configuration Properties

• javax.persistence.jdbc.driver
• javax.persistence.jdbc.url
• javax.persistence.jdbc.user
• javax.persistence.jdbc.password
• ...




                                     36
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
<Insert Picture Here>




Using the Latest Java Persistence API 2.0 Features
Arun Gupta, Java EE & GlassFish Guy
blogs.sun.com/arungupta, @arungupta

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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