Beginning EJB 3 Application Development

Beginning EJB 3 Application Development

Beginning EJB 3Application Development

Raghu R KodaliConsulting Product Manager, & Evangelist

Oracle Fusion MiddlewareOracle USA

Author – Beginning EJB 3 Application Development (Apress)

Agenda

• An Introduction to EJB• Java Persistence API (JPA)• Session beans and Interceptors• Message-Driven Beans• Web Services• Performance

The case for EJB: A brief history

• Around 1996, EJB was conceived to unify enterprise technologies such as RMI and JTA into a standard server-side component framework

• Its mission: To define, deploy, and execute business components in a distributed, multi-user, secure environment


• As EJB evolved, it added new features and jettisoned others

• EJB 3 provides a far simplified model over its precursors

• Incorporates ideas and technology unabashedly from TopLink, Hibernate, Spring, and JDO

• Leverages JDK 1.5 features (annotations, generics)• Meta data can be specified with annotations

• XML is optional


• JSR 220: Enterprise JavaBeansTM 3.0• Java Persistence API (JPA Entities)• EJB Core Contracts and Requirements (Session Beans and MDBs)• EJB 3.0 Simplified API

EJB 3 Goals

• Simplify Development• EJB = Plain Java Object (POJO)• Use metadata annotations• Reduce number of artifacts• Attract broad range of developers• Container injection

• Standardize persistence API• O-R Mapping similar to Oracle TopLink, Hibernate• Utilize metadata annotations• EntityManager API for CRUD Operations

Configuration by Exception

• Minimize configuration• Use generally accepted defaults• Only configure that what is different from the defaults• Results in less code

• Caveat: much behavior is not evident just by looking at the code!

Agenda


Java Persistence API (JPA) Goals

• Simplify programming model • Lightweight POJO’s• Remove unnecessary artifacts

• Improve modelling capabilities• Inheritance and polymorphism• O/R mapping

• Extend query capabilities and language

Along The Way

• Persistence API expanded • Evolved into Java Persistence API (JPA) usable both inside and

outside Java EE Containers• Merger of expertise from Hibernate, TopLink, JDO, EJB vendors and

individuals• Pluggability

• Notion of a Persistence Provider invoked by the Container• Can mix EJB Containers and third-party Persistence Providers

POJO Entities

• Concrete classes (no longer abstract)• No required interfaces

• No required business interfaces• No required callback/life cycle interfaces

• Use new() to create instances• Direct field access or getter/setter methods

• Can contain logic (e.g. for validation, etc.)• Use Collection interfaces for relationships• Can be local or moved around

• Can be moved to any tier

Example: JPA Entity

@Entity public class Customer { private Long id;private String name;private HashSet orders = new HashSet();

@Id (generate=SEQUENCE, generator="SEQ_GEN")@SequenceGenerator(name="SEQ_GEN",

sequenceName="CUST_SEQ",allocationSize=1)

@Column(name = "ID", primaryKey = true)public Long getId() {return id;}

protected void setId (Long id) {this.id = id;}...

}

Object/Relational Mapping

• Specified as annotations or XML• Logical and physical mapping views

• Logical—object model (e.g. @OneToMany)• Physical—DB tables and columns (e.g. @Table)

• Support for basic, serialized objects and LOBs• Unary, n-ary relationship mappings• Rules for defaulting of DB table

and column names• Access to object state using fields or properties• Multiple tables, composite relationship keys

Mapping Annotations

• Direct • @Basic• @Lob• @EmbeddedId

• Relationship• @OneToOne• @ManyToOne• @ManyToMany• @JoinColumn• @JoinTable• @Embedded

• @Transient – attribute not persistent

O-R Mapping

• Sensible default mapping strategies• Use annotations to overwrite defaults

• Collection interfaces used for relationships• @OneToOne, @OneToMany, @ManyToOne,

etc.• Ability to map one or more persistent object to a

table• Embeddable

• Support for typical inheritance strategies• Single table per class hierarchy, per class, etc.

Mapping XML

• Mapping meta data may also be declared in XML, in the orm.xml file

• Meta data may be defined in both places, even for the same element

• When conflicting meta data is detected, the XML always overrides

• Allows late-bound mapping changes, for instance, without affecting the entity class itself

• The <xml-mapping-metadata-complete> tag allows assembler to declare that all mapping is contained in the orm.xml file – a deploy-time optimization

EntityManager

• An EntityManager is tied to a <persistence-unit>• Create new POJOs using their constructors (new)• EntityManager serves as untyped “home”

• Query and manipulate persistent state of entities• Injected into clients using @PersistenceContext

annotation• Provides lifecycle operations

• persist()• remove()• merge()

• Factory for Query objects

Operations on Entities

• EntityManager API—To control lifecycle of entities and create queries• persist()- Insert the identity of an entity into the db• remove()- Delete the persistent identity of the entity from the db• refresh()- Reload the entity state from the db• merge()- Synchronize the state of detached entity with the pc• find()- Execute a simple PK query• createQuery()- Create query instance using dynamic JPA QL• createNamedQuery()- Create query instance for a predefined

query• createNativeQuery()-Create query instance for an SQL query• contains()- Determine if entity is managed by pc• flush()- Force synchronization of pc to database

EntityManager API example

@PersistenceContext public EntityManager em;...public void addLoan(String provider, long term,

String loan_type, double interest_rate)

{Loans loan = new Loans();loan.setProvider(provider);loan.setTerm(term);loan.setLoanType(loan_type);loan.setInterestRate(interest_rate);em.persist(loan);

}

• Utilize JPQL (Java Persistence Query Language), Expressions, SQL• SQL allows for direct SQL over database schema

• Successor to EJBQL• Defined dynamically or stored within an Entity

public List findByName (String name) {return em.createQuery ("SELECT c FROM Customer c").getResultList();

}

JPQL: Query API

Named Queries

@NamedQuery(name=“Employee.findAll", query="select o from Employee o where

o.name = :name")

• Define parameterized queries• Replaces finder methods in EJB 2.x• Executed by EntityManager to return collection or

single-value result• Dynamic (runtime) queries also supported

META-INF/persistence.xml

• The presence of a META-INF/persistence.xml file in a .jar is required for the entities in that .jar file to be recognized

• A persistence.xml file defines one or more <persistence-unit> elements

• A <persistence-unit> in a persistence.xml file may explicitly specify the entities that it includes/excludes in the .jar

• If no entities explicitly included/excluded, all entities found in the .jar are part of the <persistence-unit>

Example persistence.xml file

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_1_0.xsd" version="1.0"><persistence-unit name="default"

transaction-type="RESOURCE_LOCAL"><provider>

oracle.toplink.essentials.PersistenceProvider</provider><class>inventory.model.Inventory</class><class>inventory.model.Order</class><class>inventory.model.Item</class><properties><!–- platform-specific properties go here -->

</properties></persistence-unit>

</persistence>

JPA Deployment

• JPA persistence unit is defined by the presence of a META-INF/persistence.xml file

• When deployed, a group of colocated JPA entities, together with supporting @MappedSuperclass and other classes, is known as a persistence unit

• A persistence unit may be deployed as:• Standalone .jar file• Bundled with an EJB .jar file• Bundled with a WAR (web archive) file

Java SE vs. Java EE

• Entities can run inside or outside a Java EE container

• Java SE clients obtain an application managed EntityManager from an EntityManagerFactory

• Java SE clients can get entities through a Session bean in Java EE container, manipulate entities on client, and merge the changes

D E M O N S T R A T I O N

JPA

Agenda


EJB 3 Session bean

public interface Calculator {int add (int a, int b) int subtract (int a, int b)

}

@Statelesspublic class CalculatorBean implements Calculator {

public int add (int a, int b) {return a + b;}public int subtract (int a, int b) {return a – b;}

}

Dependency Injection

• Eliminates use of JNDI complexities• Results in fewer lines of code• Yields more concise code• Can be overridden with XML elements in deployment

descriptors

Session Beans and Injection

@Stateful(name="WhatDriverEJB")public class WhatDriverEJBBean implements WhatDriverEJB,

WhatDriverEJBLocal {

@Resource(name="jdbc/OracleDS") public DataSource mylocalscott;…public void foo() {

try {System.out.println("getting a new connection from

the pool");conn= mylocalscott.getConnection();

}…

Interceptors

• Methods and classes that are called before invoking the methods they intercept

• Only available for session beans (stateless and stateful) and MessageDriven beans

• Provide more granular control of bean method invocation flow

• Useful to implement custom transaction and security

• AOP model: aggregates behavior without interfering with the method being aggregated

• Like @EntityListener classes, a single interceptor class can serve multiple session beans or MDBs

Interceptors

@Stateless(name="BasicEJB")@Interceptors({LogMyTest.class, GenericInfo.class})public class BasicEJBBean implements BasicEJB, BasicEJBLocal

{public BasicEJBBean() {

System.out.println("BasicEJBBean.BasicEJBBean");}

… @AroundInvokepublic Object thatSIt(InvocationContext ctx) throws

Exception {System.out.println("BasicEJBBean.thatSIt I HOPE YOU

LIKE MY INTERCEPTOR DEMO");return ctx.proceed();

}

Stateful Session Beans and Callback Interceptor Methods

@Stateful(name="WhatDriverEJB")public class WhatDriverEJBBean implements WhatDriverEJB,

WhatDriverEJBLocal{…@PostConstructpublic void itIsAnInit() {System.out.println("PostConstruct WDEB.itIsAnInit");try {System.out.println("getting a new connection from the

pool");conn = mylocalscott.getConnection();

}…

Stateful Session Bean and Callback Interceptor Methods

@PrePassivatepublic void goPassivate() {… @PostActivatepublic void goActivate() {…@Removepublic void iMDone() {

System.out.println("WhatDriverEJBBean.iMDone");}


Session bean

EJB 3 Deployment

• EJB 3 modules no longer require ejb-jar.xml file• Presence of 1 or more classes annotated @Stateless,

@Stateful, or @MessageDriven is sufficient for the Java EE server to recognize an EJB module

• EJB module packaged into a .jar file• May bundle a JPA persistence unit inside the EJB .jar

file, or reference it as a deployed library

EJB deployment descriptor

• Meta data may also be declared in XML, in the ejb-jar.xml file

• Meta data may be defined in both places, even for the same element

• When conflicting meta data is detected, the XML always overrides

• Allows late-bound mapping changes, for instance, without affecting the entity class itself

• The <metadata-complete> tag allows assembler to declare that all mapping is contained in the ejb-jar.xml file – a deploy-time optimization

Example ejb-jar.xml

<?xml version="1.0" encoding="windows-1252" ?><ejb-jar xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/javaeehttp://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd"

xmlns="http://java.sun.com/xml/ns/javaee" version="3.0"><enterprise-beans><session id="SessionEJB">

<ejb-name>SessionEJB</ejb-name><mapped-name>ejb/SessionEJB</mapped-name><ejb-class>org.acme.ejb.SessionEJB</ejb-class><session-type>Stateless</session-type><transaction-type>Container</transaction-type>

</session></enterprise-beans><assembly-descriptor/>

</ejb-jar>

Agenda


What is a Message-Driven Bean?

• Asynchronous message consumer• Processes messages delivered via JMS• Operates on either:

• JMS queue (point-to-point model)• JMS topic (publish-subscribe model)

• Leverages enterprise services in the EJB container (security, transactions, resources, concurrency, etc.)

MessageDriven Beans

…@MessageDriven(activationConfig =

{@ActivationConfigProperty(propertyName="connectionFactoryJndiName",propertyValue="jms/QueueConnectionFactory"),@ActivationConfigProperty(propertyName="destinationName", propertyValue="jms/demoQueue"),@ActivationConfigProperty(propertyName="destinationType", propertyValue="javax.jms.Queue")})

public class MessageDrivenEJB30Bean implements MessageListener{public void onMessage(Message message) {

… }

EJB 3 as Web Service

• Annotate business interface• Deploys to Java EE container(s) as a Web Service• Session bean class may also identify its @WebService

endpoing interface

EJB 3 as Web Service

package buslogic;

import java.rmi.RemoteException;import java.rmi.Remote;import javax.jws.WebMethod;import javax.jws.WebService;

@WebServicepublic interface CustomerFacade{

@WebMethodpublic Integer getCreditRating(String ssn);

}


EJB 3 Web Service

Agenda

• An Introduction to EJB• Java Persistence API (JPA)• Session beans and Interceptors• Message-Driven Beans• Web Services• Ease-of-Development & Performance

Compare # of Files

02468

1012141618

# of Java Files # of XML Files

EJB 2.1EJB 3.0

Compare # of Lines of Code

0100200300400500600700800900

1000

# of lines (Java) # of lines (XML)

EJB 2.1EJB 3.0

Conclusion(s)

• Big thumbs up on ease of use • POJO architecture is the right way to go, as it has

been proven by frameworks like TopLink, Hibernate etc…

• EntityManager API big plus• Ease of use to develop CRUD operations• Query with @NamedQuery/@NamedQueries annotations

• Testability outside container is big plus

Data Transfer Object - Results

Aggregate Average Response TimeData Transfer Object

0

500

1000

1500

2000

2500

15 U

sers

25 U

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50 U

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100 U

sers

150 U

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200 U

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250 U

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Mill

isec

onds

EJB 2.1 - DTO OnEJB 2.1 - DTO OffEJB 3.0

Data Transfer Object - Results

Total Transactional RateData Transfer Object

0

50

100

150

200

250

300

15 U

sers

25 U

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50 U

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100 U

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150 U

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Req

uest

s pe

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EJB 2.1 - DTO OnEJB 2.1 - DTO OffEJB 3.0

Data Transfer Object - Conclusions

• The average difference between EJB 2.1 DTO On and EJB 3 is within the margin of error (4%)• EJB 3 behaves better under higher load

• DTO Off is about 25% less performant because every invoke to an accessor is a transaction by itself

Session Façade - Results

Aggregate Average Response TimeSession Facade

0200400600800

10001200140016001800

15 Users 25 Users 50 Users 75 Users 100Users

Mill

isec

onds

EJB 2.1EJB 3.0

Session Façade - Results

Total Transactional RateSession Facade

020406080

100120140160180

15 Users 25 Users 50 Users 75 Users 100Users

Req

uest

s pe

r Sec

ond

EJB 2.1EJB 3.0

Session Façade - Conclusions

• The difference is roughly double on both, response time and throughput• The difference increases under higher load

• EJB 2.1 System throughput is pretty much at peak for all user loads• EJB 3 shows a more typical throughput curve

Q U E S T I O N S

A N S W E R S&

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Beginning EJB 3 Application DevelopmentRaghu KodaliConsulting Product Manager & SOA Evangelist –Oracle Fusion MiddlewareAuthor – Beginning EJB 3 Application Development

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Beginning EJB 3 Application Development