Programmation des Applications Internet Internet Application Programming Hibernate These slides and

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Programmation des Applications Internet Internet
Application Programming HibernateThese slides
and case studies can be downloaded from
www.PauWare.com/MTI
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Hibernate

• Hibernate is the most popular persistence
  framework in the Java world (NHibernate in the
  .NET world)
• It is an open source product which can be
  downloaded from www.hibernate.org
• Hibernate Core is composed of the key libraries
  (.jar files)
• Hibernate EntityManager is the support for Java
  Persistence API (JPA)
• Hibernate is the default support for JPA in JBoss
  while TopLink is the default in GlassFish
• Hibernate eases the development of
  database-oriented applications (compared to JDBC
  for example)
• Hibernate promotes object-orientation
  (polymorphism, OO requests through HQL) and
  removes the direct non-evolutive codification of
  SQL inside the Java code (compared to JDBC)

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Case study (UML model)
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Case study (database schema)
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Case study (persistent object dependencies)
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Hibernate configuration

• The hibernate.cfg.xml file defines the main
  properties of the application. It is usually
  installed in the Java default package
• This file is loaded and interpreted through an
  instance of the org.hibernate.cfg.Configuration
  class
• The key notion behind Hibernate is the notions of
  session factory and session
• private org.hibernate.SessionFactory
  _session_factory new org.hibernate.cfg.Configura
  tion().configure().buildSessionFactory()
• private org.hibernate.Session getSession()
• return _session_factory.getCurrentSession()

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Example of a hibernate.cfg.xml file

• lt?xml version'1.0' encoding'utf-8'?gt
• lt!DOCTYPE hibernate-configuration PUBLIC
• "-//Hibernate/Hibernate Configuration DTD//EN"
• "http//hibernate.sourceforge.net/hibernate-config
  uration-3.0.dtd"gt
• lthibernate-configurationgt
• ltsession-factorygt
• ltproperty name"connection.driver_class"gtorg.apach
  e.derby.jdbc.ClientDriverlt/propertygt
• ltproperty name"connection.url"gtjdbcderby//local
  host1527/Prison_de_Nanteslt/propertygt
• ltproperty name"connection.username"gtbarbierlt/prop
  ertygt
• ltproperty name"connection.password"gtlena150496lt/p
  ropertygt
• ltproperty name"connection.pool_size"gt1lt/propertygt
  
• ltproperty name"dialect"gtorg.hibernate.dialect.Der
  byDialectlt/propertygt
• ltproperty name"show_sql"gttruelt/propertygt
• ltmapping resource"com/FranckBarbier/Java/_Prison_
  de_Nantes/Detenu.hbm.xml"/gt
• ltmapping resource"com/FranckBarbier/Java/_Prison_
  de_Nantes/Affaire.hbm.xml"/gt
• ltmapping resource"com/FranckBarbier/Java/_Prison_
  de_Nantes/Motif.hbm.xml"/gt
• ltmapping resource"com/FranckBarbier/Java/_Prison_
  de_Nantes/Incarceration.hbm.xml"/gt
• ltmapping resource"com/FranckBarbier/Java/_Prison_
  de_Nantes/Decision.hbm.xml"/gt
• lt/session-factorygt

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The notion of session

• Sessions are spaces in which objects get
  Hibernate-oriented states
• An object is included in a session as follows
• getSession().persist(_detenu)
• When attached (Persistent state), an object is
  synchronized with the database. All modifications
  on this object will lead to appropriate
  modifications in the database
• When flushed (or closed), all objects in a
  session lose their Persistent state to recover a
  Transient state.
• Sessions are manually or automatically associated
  with database transactions

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Session-oriented actions

• find (or get, or load) -gt it leads to the
  Persistent state and to a SELECT statement, for
  example
• return (Detenu) session.load(Detenu.class,
  primary_key)
• persist (or save) -gt it leads to an INSERT
  statement at flush/commit time
• merge (or update) -gt it leads to an UPDATE
  statement
• evict -gt it leads to the Detached state
• delete -gt it leads to a DELETE statement
• refresh -gt it leads to a SELECT statement

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Persistent objects

• A Hibernate persistent object (a.k.a. Plain Old
  Java Object or POJO) is a Java class whose
  instances are supposed to persist in a database
• A POJO is ruled by constraints constructor
  without arguments, normalized getter and setter
  methods for persistent attributes, no use of the
  final Java modifier for classes, methods and
  attributes
• A POJO implements the java.io.Serializable Java
  interface
• A class playing the role of primary composite key
  must also be subject to the above constraints

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Persistent object lifecycle

• Note the Transient state is realized through the
  value of the unsaved-value attribute

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Configuring persistent objects

• The mapping between database elements (tables)
  and persistent objects are described in XML
  files, for instance Detenu.hbm.xml
• Persistent fields are associated with table
  columns, for instance
• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE hibernate-mapping PUBLIC
  "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  "http//hibernate.sourceforge.net/hibernate-mappin
  g-3.0.dtd"gt
• lthibernate-mappinggt
• ltclass name"com.FranckBarbier.Java._Prison_de_Nan
  tes.Detenu" table"DETENU"gt
• ltproperty column"PRENOM" name"_prenom"
  type"string"/gt
• ltproperty column"NOM" name"_nom"
  type"string"/gt
• ltproperty column"DATE_NAISSANCE"
  name"_date_naissance" type"date"/gt
• ltproperty column"LIEU_NAISSANCE"
  name"_lieu_naissance" type"string"/gt

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Mapping several tables in a persistent object

• Example incorporating the DETENU and
  INCARCERATION tables into the Detenu POJO
• ltjoin optional"false" table"INCARCERATION"gt
• ltkey column"N_ECROU"/gt
• ltproperty column"DATE_INCARCERATION"
  name"_date_incarceration" type"date"/gt
• lt/joingt
• The mark optional"true" is based on the fact
  that one may have "missing" rows in the
  INCARCERATION table

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Setting up business identifiers

• Hibernate does not support so well business
  primary keys. However, one may have
• lthibernate-mappinggt
• ltclass name"com.FranckBarbier.Java._Prison_de_Nan
  tes.Detenu" table"DETENU"gt
• ltid column"N_ECROU" name"_n_ecrou"gt
• ltgenerator class"assigned"/gt
• lt/idgt

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Overriding equals and hashCode

• public class Detenu implements java.io.Serializabl
  e
• private String _n_ecrou
• public String get_n_ecrou()
• return _n_ecrou
• public void set_n_ecrou(String n_ecrou)
• _n_ecrou n_ecrou
• // other persistent fields here
• _at_Override
• public boolean equals(Object object)
• if (!(object instanceof Detenu))
• return false
• Detenu other (Detenu) object
• if (_n_ecrou ! other._n_ecrou (_n_ecrou
  null !_n_ecrou.equals(other._n_ecrou)))
• return false
• return true

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Setting up composite identifiers

• Hibernate does not also support so well composite
  (business) primary keys, for instance
• lthibernate-mappinggt
• ltclass name"com.FranckBarbier.Java._Prison_de_Nan
  tes.Affaire" table"AFFAIRE"gt
• ltcomposite-id class"com.FranckBarbier.Java._Priso
  n_de_Nantes.AffairePK" name"_primary_key"gt
• ltkey-property column"N_AFFAIRE"
  name"_n_affaire" type"string"/gt
• ltkey-property column"NOM_JURIDICTION"
  name"_nom_juridiction" type"string"/gt
• lt/composite-idgt
• As shown here, composite primary keys require
  dedicated classes, e.g., AffairePK

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Setting up technical (surrogate) identifiers

• Example
• lthibernate-mappinggt
• ltclass name"com.FranckBarbier.Java._Prison_de_Nan
  tes.Detenu" table"DETENU"gt
• ltid column"ID_DETENU" name"_id_detenu"gt
• ltgenerator class"native"/gt
• lt/idgt

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DBMS-oriented identifier generation

• Example
• lthibernate-mappinggt
• ltclass name"com.FranckBarbier.Java._Prison_de_Nan
  tes.Detenu" table"DETENU"gt
• ltid column"ID_DETENU" name"_id_detenu"gt
• ltgenerator class"sequence"gt
• ltparam name"sequence"gtmy_generatorlt/paramgt
• lt/generatorgt
• lt/idgt
• Creating sequences in Oracle CREATE SEQUENCE
  my_generator

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Other modes for managing identifiers

• Example
• ltid column"ID_DETENU" name"_id_detenu"
  type"Long" unsaved-value"null"gt
• ltgenerator class"increment"/gt
• lt/idgt
• Note the unsaved-value attribute is set to
  undefined when identifiers are assigned by users
  (business primary keys)
• Other modes uuid.hex or uuid.string (uses IP
  addresses to compute identifiers), foreign

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One-to-one associations

• An incarceration is concerned with one and only
  one prisoner (and vice-versa)
• ltone-to-one name"_detenu" constrained"false"/gt
• constrained"true" is used when there is a
  foreign key between the two tables
• The foreign key of the Incarceration persistent
  object may be constrained by that of the Detenu
  persistent object
• ltid column"N_ECROU" name"_n_ecrou"gt
• ltgenerator class"foreign"gt
• ltparam name"property"gt_detenult/paramgt
• lt/generatorgt
• lt/idgt

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Many-to-many associations

• Example (Detenu.hbm.xml file)
• ltbag name"_toutes" table"DETENU_AFFAIRE"gt
• ltkey column"N_ECROU"/gt
• ltmany-to-many class"com.FranckBarbier.Java._Priso
  n_de_Nantes.Affaire"gt
• ltcolumn name"N_AFFAIRE"/gt
• ltcolumn name"NOM_JURIDICTION"/gt
• lt/many-to-manygt
• lt/baggt
• An extract from the Detenu class is as follows
• private java.util.CollectionltAffairegt _toutes
• public java.util.CollectionltAffairegt get_toutes()
  
• return _toutes
• public void set_toutes(java.util.CollectionltAffair
  egt toutes)
• _toutes toutes

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Bidirectionality

• Example (Affaire.hbm.xml file)
• ltset inverse"true" name"_participants"
  table"DETENU_AFFAIRE"gt
• ltkeygt
• ltcolumn name"N_AFFAIRE"/gt
• ltcolumn name"NOM_JURIDICTION"/gt
• lt/keygt
• ltmany-to-many class"com.FranckBarbier.Java._Priso
  n_de_Nantes.Detenu" column"N_ECROU"/gt
• lt/setgt
• An extract from the Affaire class is as follows
• private java.util.CollectionltDetenugt
  _participants
• public java.util.CollectionltDetenugt
  get_participants()
• return _participants
• public void set_participants(java.util.Collectionlt
  Detenugt participants)
• _participants participants

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Bidirectionality consistency

• The inverse"true" mark in Affaire.hbm.xml forces
  Hibernate to maintain the DETENU_AFFAIRE table
  from the Detenu persistent object
• As a result, the following code is required
  (Affaire class)
• public void addTo_participants(Detenu detenu)
• get_participants().add(detenu)
• detenu.get_toutes().add(this)
• public void removeFrom_participants(Detenu
  detenu)
• get_participants().remove(detenu)
• detenu.get_toutes().remove(this)

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One-to-many associations

• Example (Detenu.hbm.xml file)
• ltlist name"_condamnation" table"CONDAMNATION"
  lazy"false"gt
• ltkey column"N_ECROU"/gt
• ltlist-index column"N_TYPE_DECISION"/gt
• ltone-to-many class"com.FranckBarbier.Java._Prison
  _de_Nantes.Condamnation"/gt
• lt/listgt
• An extract from the Detenu class is as follows
• private java.util.CollectionltCondamnationgt
  _condamnation
• public java.util.CollectionltCondamnationgt
  get_condamnation()
• return _condamnation
• public void set_condamnation(java.util.Collectionlt
  Condamnationgt condamnation)
• _condamnation condamnation

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Many-to-one associations

• Example (Incarceration.hbm.xml file)
• ltmany-to-one column"N_MOTIF" name"_motif"
  not-null"true"/gt
• ltmany-to-one name"_principale" not-null"true"gt
• ltcolumn name"N_AFFAIRE"/gt
• ltcolumn name"NOM_JURIDICTION"/gt
• lt/many-to-onegt
• The not-null"true" mark forces Hibernate to
  respect the 1.. multiplicity compared to the
  0.. multiplicity

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Lazy loading (1/2)

• Given a persistent object, a question is about
  the access to its linked (also persistent)
  objects. For instance, given d an instance of
  Detenu, one may want to access to its criminal
  cases
• java.util.CollectionltAffairegt all
  d.get_toutes()
• An extract of the mapping file is as follows
• ltset name"_toutes" table"DETENU_AFFAIRE"
  lazy"true" fetch"select"gt lt!--default values--gt
• ltkey column"N_ECROU"/gt
• ltmany-to-many class"com.FranckBarbier.Java._Priso
  n_de_Nantes.Affaire"gt
• ltcolumn name"N_AFFAIRE"/gt
• ltcolumn name"NOM_JURIDICTION"/gt
• lt/many-to-manygt
• lt/setgt

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Lazy loading (2/2)

• By default, dependent objects are not loaded
  (when an object is itself loaded, d below) and
  thus becomes persistent. As a result, Hibernate
  executes a deferred SELECT request when one
  accesses the criminal cases of a prisoner
• java.util.CollectionltAffairegt all
  d.get_toutes()
• The way by which lazy loading may be inhibited,
  relies on the lazy and/or fetch parameter as
  follows
• ltset name"_toutes" table"DETENU_AFFAIRE"
  lazy"false"
• ltkey column"N_ECROU"/gt
• ltmany-to-many class"com.FranckBarbier.Java._Priso
  n_de_Nantes.Affaire"gt
• ltcolumn name"N_AFFAIRE"/gt
• ltcolumn name"NOM_JURIDICTION"/gt
• lt/many-to-manygt
• lt/setgt
• Note fetch"join" (left outer join) prevails on
  lazy

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Cascading actions

• Insertions, deletions may be cascaded from a
  persistent object to its dependent objects
• ltbag name"_decision" table"DECISION"
  cascade"all"gt
• ltkey column"N_ECROU"/gt
• ltone-to-many class"com.FranckBarbier.Java._Prison
  _de_Nantes.Decision"/gt
• lt/baggt
• Values save-update, persist, merge, delete, lock,
  evict and replicate are for one-to-one,
  many-to-one tags (outside collections)
• Values for collections are save-update, persist,
  merge, delete, delete-orphan, lock, evict,
  replicate and all-delete-orphan

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Inheritance

• Hibernate supports three main modes for managing
  inheritance relationships (and thus
  polymorphism)
• A column in the table corresponding to the root
  class plays the role of discriminator. There are
  no tables for the subclasses
• Subclasses have corresponding tables and a
  foreign key on their ancestor table
• No need of a table exists for the root class

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Inheritance, no tables for subclasses

• Example (Decision.hbm.xml)
• ltdiscriminator column"N_TYPE_DECISION"
  type"string" insert"false"/gt
• ltsubclass name"com.FranckBarbier.Java._Prison_de_
  Nantes.Condamnation" discriminator-value"1"gt
• ltproperty name"_duree" column"DUREE"
  type"integer"/gt
• lt/subclassgt
• ltsubclass name"com.FranckBarbier.Java._Prison_de_
  Nantes.Reduction_peine" discriminator-value"2"gt
• ltproperty name"_duree" column"DUREE"
  type"integer"/gt
• lt/subclassgt
• ltsubclass name"com.FranckBarbier.Java._Prison_de_
  Nantes.Liberation_definitive" discriminator-value
  "3"gt
• ltproperty name"_date_liberation" column
  "DATE_LIBERATION" type"date"/gt
• lt/subclassgt
• Disadvantages some data in the DECISION table
  are with null values for specialized attributes,
  e.g., _duree

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Inheritance, tables for all classes

• ltjoined-subclass name"com.FranckBarbier.Java._Pri
  son_de_Nantes.Condamnation" table"CONDAMNATION"gt
• ltkeygt
• ltcolumn name"N_TYPE_DECISION"/gt
• ltcolumn name"N_ECROU"/gt
• ltcolumn name"DATE_DECISION"/gt
• lt/keygt
• ltproperty name"_duree" column"DUREE"
  type"integer"/gt
• lt/joined-subclassgt
• ltjoined-subclass name"com.FranckBarbier.Java._Pri
  son_de_Nantes.Reduction_peine" table"Reduction_pe
  ine"gt
• ltkeygt
• ltcolumn name"N_TYPE_DECISION"/gt
• ltcolumn name"N_ECROU"/gt
• ltcolumn name"DATE_DECISION"/gt
• lt/keygt
• ltproperty name"_duree" column"DUREE"
  type"integer"/gt
• lt/joined-subclassgt
• ltjoined-subclass name"com.FranckBarbier.Java._Pri
  son_de_Nantes.Liberation_definitive"
  table"Liberation_definitive"gt
• ltkeygt
• ltcolumn name"N_TYPE_DECISION"/gt

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No table need for the root class

• ltunion-subclass name"com.FranckBarbier.Java._Pris
  on_de_Nantes.Condamnation" table"CONDAMNATION"gt
• ltproperty column"DUREE" name"_duree"
  type"integer"/gt
• lt/union-subclassgt
• ltunion-subclass name"com.FranckBarbier.Java._Pris
  on_de_Nantes.Reduction_peine" table"REDUCTION_PEI
  NE"gt
• ltproperty column"DUREE" name"_duree"
  type"integer"/gt
• lt/union-subclassgt
• ltunion-subclass name"com.FranckBarbier.Java._Pris
  on_de_Nantes.Liberation_definitive"
  table"LIBERATION_DEFINITIVE"gt
• ltproperty column"DATE_LIBERATION"
  name"_date_liberation" type"date"/gt
• lt/union-subclassgt

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Sessions and transactions

• Hibernate supports a home-made transaction
  management mode
• org.hibernate.Session session
  _session_factory.openSession()
• org.hibernate.Transaction utx
  session.beginTransaction()
• utx.commit() // or utx.rollback()
• JTA-oriented transactions
• private javax.transaction.UserTransaction _utx
• org.hibernate.Session session
  session_factory.getCurrentSession()
• _utx.begin()
• _utx.commit() // or _utx.rollback()

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Working with JTA

• ltproperty name"hibernate.transaction.manager_look
  up_class"gtorg.hibernate.transaction.SunONETransact
  ionManagerLookuplt/propertygt lt!--GlassFish
  support--gt
• ltproperty name"hibernate.transaction.factory_clas
  s"gtorg.hibernate.transaction.JTATransactionFactory
  lt/propertygt
• ltproperty name"hibernate.current_session_context_
  class"gtjtalt/propertygt