5. Enterprise JavaBeans 5.3 Entity Beans. Entity Beans

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Michael Gibbs
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1 Entity Beans Vue objet d une base de données (exemples: client, compte, ) en général, une ligne d une table relationnelle (SGBD-R) ou un objet persistant (SGBD- OO) sont persistant (long-lived) la gestion de la persistance peut être faite par le bean (bean managed persistence) ou déléguée à son conteneur (container managed persistence) acceptent les accès multiples effectués par plusieurs clients gestion de la concurrence différents niveaux d isolation peuvent participer à des transactions survivent aux pannes d un serveur EJB les pannes sont transparentes aux clients Le client peut soit créer un nouveau Entity Bean ou trouver un Bean existant La "Home interface" fournit des méthodes de recherche ("finder methods") findbyprimarykey clé unique dans un home Méthodes de recherche spécifiques à l'application

2 Entity Bean: Structure

3 Entity Bean: Structure

4 * Order Bean 1 Key: Order ID Customer ID Product ID * 1 Customer Key: Customer ID 1 Product Key: Product ID 1 Invoice Entity Beans and Database Tables Order Bean Table Order ID Customer ID Product ID Invoice Table Invoice ID Order ID Key: Invoice ID Order ID Customer Table Customer ID Orders 2 1 Address...

5 Entity Bean: créer un objet

6 Entity Bean: Retrouver un objet

7 Entity Bean: Recherche d'objets

8 Entity Bean: Efficacité?

9 Entity Bean: Réservoir (Pool)

10 Cycle de vie des instances

11 Cycle de vie vu du client

12 Cycle de vie vu du client

13 Persistence Two kinds Bean Managed: Programmatic Container Managed: Declarative Bean Managed Bean provider must write routines to access the data store Declares instance variables to contain the persistent data Finder method implementation written by Bean provider Container invokes these routines at an appropriate times in lifecycle More common when underlying data store is an application

14 Persistence (2) Container Managed Allows Bean to be logically independent of data source e.g.: same code for relational database, IMS database, etc. Container generates code to access the data store Deployer maps the fields of the Bean to the columns of the database Bean provider describes Bean s fields and relationships to other Beans in deployment descriptor Container may use lazy access methods and caching Finder methods are described in the deployment descriptor Description is in EJB QL Implementation is generated when Bean is deployed Virtual fields are used in the Bean to contain the persistent data Access is via getxxx/setxxx methods. Relationship between Beans Similar to foreign keys in relational databases (one to one, many to one, one to many, many to many) Allows container to ensure referential integrity e.g.: setting a Bean in field for a one to one relationship will automically remove the Bean from a prior relationship

15 Deployment Descriptor Captures declarative information Well-formed XML Contains Structural information Name of Bean, class, interfaces, Bean type, persistence type, container managed fields,... Not all combinations of structural information make sense Application assembly information Security roles, method permissions, transaction attributes, etc.

16 Deployment Descriptor Example <!DOCTYPE ejb-jar PUBLIC "-/Sun Microsystems, Inc.//DTD EnterpriseJavaBeans 2.0//EN" " <ejb-jar> <enterprise-beans> <entity> <ejb-name>cabinejb</ejb-name> <home>com.titan.cabinhomeremote</home> <remote>com.titan.cabinremote</remote> <local-home>com.titan.cabinhomeremote</local-home> <local>com.titan.cabinremote</local> <ejb-class>com.titan.cabinbean</ejb-class> <persistence-type>container</persistence-type> <prim-key-class>java.lang.integer</prim-key-class> <reentrant>false</reentrant> </entity> </enterprise-beans> </ejb-jar>

17 EJB QL A query language Similar to a subset of SQL Used in the deployment descriptor to describe the behavior of finder (and other) methods for Beans with Container Managed Persistence <query> <query-method> <method-name>findbyname</method-name> <method-params> <method-param>java.lang.string<method-param> <method-params> </query-method> <ejb-ql> SELECT OBJECT(c) FROM Cruise WHERE c.name =?1 </ejb-ql> </query>

NetBeans IDE Field Guide

NetBeans IDE Field Guide Copyright 2005 Sun Microsystems, Inc. All rights reserved. Table of Contents Extending Web Applications with Business Logic: Introducing EJB Components...1 EJB Project type Wizards...2