EJB Development andSupport Services

EJB Development andSupport ServicesTopics to be Covered:• EJB Design• Bean/Container Interaction• Java Naming and Directory Interface

(JNDI)• Using Enterprise Beans• Server Side Services

EJB Development andSupport Services

EJB Design

Class and Interface Review

• javax.ejb package– Core of the EJB API

• Remote interface– Defines bean’s remote business methods

• Local interface– Defines bean’s local business methods

• Endpoint interface– Defines SOAP-accessible business methods

• Message interface– Defines methods for asynchronous messages

• Bean class– Implementation of business and lifecycle

methods

Remote Interface

• Defines business methods

import javax.ejb.Remote;

@Remotepublic interface CalculatorRemote {public int add(int x, int y);public int subtract(int x, int y);

}

Bean Class

• Actual implementation of business methods

import javax.ejb.*;@Statelesspublic class CalculatorBean

implements CalculatorRemote {

public int add(int x, int y) {return x + y;

}public int subtract(int x, int y) {

return x – y;}

}

Entity

• Java Persistence API

import javax.persistence.*;

@Entity@Table(name=“CABIN”)

public class Cabin {

private int id;private String name;private int deckLevel;

Primary Key

@Id@GeneratedValue@Column(name=“ID”)public int getId() { return id; }

public void setId(int pk) { this.id = pk; }

Remaining Fields

@Column(name=“NAME”)public String getName() { return name; }

public void setName(String str) { this.name = str; }

@Column(name=“DECK_LEVEL”)public int getDeckLevel() { return deckLevel; }

public void setDeckLevel(int level) { this.deckLevel =

level; }}

Primary Keys

• Pointer that locates an enterprise bean• Defined by the bean developer• Must map to one of the following types:

– Any Java primitive type (including wrappers)

– java.lang.String– Primary-key class composed of

primitives and/or Strings

Primary Key Class

• Composed of primitives and/or strings• Must be serializable• Must have a public no-arg constructor• Must implement the equals() and hashCode() methods

Deployment Descriptors

• Specifies how to apply primary services– security– transactions– naming

• Specifies persistence unit and associated database

• Describe runtime attributes of server-side component

EJB Packaging

• JAR Files used for packaging– Applets– Applications– JavaBeans– Web Application– Enterprise JavaBeans

•Bean classes•Component interfaces•Supporting Classes•Appropriate Deployment Descriptors

Example Deployment Descriptor

<?xml version="1.0"?><ejb-jar>

<enterprise-beans> <session> <ejb-name>ProcPayBean</ejb-name> <remote>com.relaxalot.ProcPayRemote</remote> <local>com.relaxalot.ProcPayLocal</local> <ejb-class>com.relaxalot.ProcPayBean</ejb-class>

<session-type>Stateless</session-type> </session></enterprise-beans>

</ejb-jar>

XML and/or Annotations

• Defaults make XML deployment descriptors optional– Default transaction property

REQUIRED– Default security semantics

UNCHECKED• Annotations provide further

information– Metadata placed directly in the bean

class file– Deployment descriptors can override

annotations

Example persistence.xml

<persistence><persistence-unit name=“titan”> <jta-data-source>java:/TitanDB</jta-data-source>

</persistence-unit></persistence>

EJB Development andSupport Services

Bean/Container Interaction

EJB Container Implementation

• Component interfaces allow external or co-located clients to interact with session bean class

• Component interfaces interact with instances of the session bean class

• Proxy Stub– Interacts with client, sends message

to EJB Container• EJB Object

– Implements remote interface– Wraps enterprise bean instance– Generated by the container

bean

remoteinterface

EJB object

EJB Architecture

EJB Container

remoteinterface

EJB objectproxy

Client

EJB Container

• Intermediary between bean and server• Interaction defined by SessionBean

interface, and JMS-MessageDrivenBean onMessage() method

• javax.ejb.EJBContext interface implemented by the container.

• Bean uses EJBContext interface to communicate with EJB environment

• JNDI namespace

EJB Development andSupport Services

Java Naming andDirectory Interface

(JNDI)

Naming and Directory Services

• Naming Service– Associates names with Objects– Provides facility to find an object

based on a name– Examples: DNS, File System

• Directory Object– Contains attributes– Like a record in a database

• Directory Service– Provides directory object operations

for manipulating attributes

JNDI Architecture

JNDI Application

FilesystemService Provider

Filesystem

LDAPService Provider

LDAP Directory

RMIService Provider

RMI Registry

JNDI API Benefits

• Standard Java Extension– javax.naming– javax.naming.directory

• Unified system for resource access• Insulates application from naming and

directory service protocols• Extensible• Composite or federated namespaces

Naming Concepts

• Binding– Association of a name with an object

• Context– Set of bindings

• Subcontext– Binding one context within another

usr

bin

tom

Context

Subcontext

Binding

Context & InitialContext

• javax.naming.Context interface– Collection of bindings– Operations apply only to bindings,

not to Context itself• javax.naming.InitialContext class

– Implements the Context interface– Starting point for exploring a

namespace– Requires an initial context factory

com.sun.jndi.fscontext.RefFSContextFactory

InitialContext Properties

• InitialContext constructor takes a set of properties

Properties props = new Properties();props.put(Context.INITIAL_CONTEXT_FACTORY,“com.sun.jndi.fscontext.RefFSContextFactory”);props.put(Context.PROVIDER_URL,”file:///”);Context initialContext = new

InitialContext(props);

Looking Up Objects

• lookup() method• Specify the name of the child• Type of returned object determined by

service provider• Container with children should

implement javax.naming.Context

Object obj = initialContext.lookup(name);

Listing Objects

• list() method• Returns a list of names of an object’s

children as an instance of javax.naming.NamingEnumeration

• NamingEnumeration contains a collection of javax.naming.NameClassPair objects

• Browsing is a combination of list() and lookup() calls

NamingEnumberation kids = initialContext.list(name);

Binding Objects

• bind() method• Creates a Binding object• Use rebind() if name already exists• Use unbind() to remove a binding

File newfile = File(“c:\temp\

newfile”);tempContext.bind(“newfile”, newfile);

JNDI and JDBC

• JDBC 2.0 DataSource– Provides Database connections– Information to create connections are

stored as properties– Registered with a directory service

Context ctx = new InitialContext();DataSource ds = (DataSource)

ctx.lookup(“jdbc/EmployeeDB”);Connection con = ds.getConnection();con.close();

JNDI and EJB

• JNDI used to locate a specific EJB Home

Context ctx = new InitialContext();Object ref = ctx.lookup(“TravelAgntBean”);TravelAgntRemote dao = (TravelAgntRemote)

PortableRemoteObject.narrow(ref,

TravelAgntRemote.class);dao.makeReservation();

JNDI Environment Naming Context

• Part of Bean-Container Contract• Common naming context

– java:comp/env• Declare resources using XML

deployment descriptor or Annotation– EJBs– JDBC DataSource– Java Message Service– Environment Properties

Context ctx = new InitialContext();

ENC Example (Deployment Descriptor) – Describing the Resource

<resource-ref>

<description>DataSource for Relaxalot Database</description>

<res-ref-name>theDataSource</res-ref-name><res-type>javax.sql.DataSource</res-type><res-auth>Container</res-auth>

<mapped-name>java:/DefaultDS</mapped-name><injection-target>

<injection-target-class>edu.weber.ProcessPaymentBean

</injection-target-class><injection-target-name>dataSource</injection-target-name>

<injection-target></resource-ref>

ENC Example (Annotation) – Describing the Resource

public class ProcessPaymentBean implements ProcessPaymentRemote

{...

@Resource(mappedName=“java:/DefaultDS”)DataSource dataSource

ENC Example – Use the Resource

public class ProcessPaymentBean implements ProcessPayment Remote

{...private boolean process(){Connection con = dataSource.getConnection();...con.close();

}

EJB Development andSupport Services

Using Enterpise Beans

Entities• Model data and behavior

– Provide interface to data– Business rules that directly affect data– Relationships with other entities

// Use javax.persistence.PersistenceContext// annotation to get access to entities// using an EntityManager service that// references a persistence unit

@PersistenceContext(unitName=“titan”)private EntityManager manager;

...public void createCabin(Cabin cabin) {

manager.persist(cabin);}

Session Beans• Model processes and tasks

– Functions of the business•Inappropriate for client application or entity beans

• Provide business logic• Control workflow// Lookup session beanTravelAgent tAgent = (TravelAgent)...

// Create a reservation tAgent.setCustomer(customer);tAgent.setRoomID(roomID);tAgent.setHotelID(hotelID);

Ticket ticket = tAgent.bookReserve(creditCard,

price);

Session Beans• Stateful

– Maintain conversational state•State kept in memory•Dedicated to a single client

• Stateless– No conversational state

•Method calls are independent– Provide higher performance

•A few stateless beans can service many clients

EJB Development andSupport Services

Server Side Services

Resource Management• Instance Pooling

– Clients do not directly access EJB’s– Number of instances can be efficiently

managed and minimized– Reuse existing beans for different

client requests• Activation Mechanism

– Used for stateful session beans– Passivation

•Serialize bean’s state to storage – Activation

•Restore a stateful bean instance’s state

Concurrency

• Multiple clients accessing the same bean at the same time

• Not supported by session beans• Entities represent shared data

– Java Persistence spec: persistence container protects shared data by making a copy of the entity bean on a per-transaction basis

– Defense against stale reads or simultaneous updates is vendor specific

– EJB prohibits synchronized keyword– EJB prohibits beans from creating

threads

Transactions

• Set of tasks executed together– Atomic

•Reservation and Payment must both be successful

• Manage automatically– Declare transactional attribute

• Manage explicitly– Use javax.transaction.UserTransaction object

Persistence

• Applies to Entities– Java Persistence specification

•Plain Old Java objects (POJO)•Can be created outside the scope of the EJB container

•Attached/Detached•Entity Manager

– Object-to-relational persistence•Map entity state to relational database tables and columns

Distributed Object Interoperability

• Location Transparency– CORBA IIOP– Support mandated in EJB 3.0

•RMI/IIOP•SOAP via JAX-RPC API•Programming model used by Java EJB

Client– Other protocols and clients can be

supported by servers•CORBA clients written in C++, Smalltalk,

Ada using EJB-to-CORBA mapping•SOAP clients written in Visual Basic.NET,

C#, Perl using EJB-to-SOAP mapping

Asynchronous Enterprise Messaging

• Message-driven Beans (MDBs)• Route messages from JMS clients to

JMS-MDB• Reliable delivery

– Attempt redelivery on failure• Persisted messages• Transactional• EJBs can send messages

EJB Development andSupport ServicesTopics to be Covered:• EJB Design• Bean/Container Interaction• Java Naming and Directory Interface

(JNDI)• Using Enterprise Beans• Server Side Services