distributed object-oriented programming (3) – enterprise javabeans snu idb lab. taewhi lee may...

Distributed Object-Oriented Programming(3) – Enterprise JavaBeans

SNU iDB Lab.Taewhi Lee

May 14th, 2007

Review – Distributed Programming

Paradigm Shift

Socket

RPC

CORBA RMI

CORBA Component

Model

OOP CBD Object – limited reusability Component – independent service Several components are plugged

in to a component architecture

systemStructured Programming

OOP SP – Complexity of system modeling Difficulty in code change/extension OOP – Natural object modeling Reusability by inheritance Flexibility by polymorphism

Distributed Component Model

Distributed Object Model

Basic Inter-Process Communication

Distributed Structural Model

Web Services

Service-Oriented Architecture

Distributed Computing SOA DC – client/server are tightly coupled SOA – everything is decoupled

EJB

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

Java EE [1/5]

Jave EE History

1995 1998 1998 2004~

Java J2SE J2EE Java SEJava EE

Object-oriented

Platform-independe

nt

Garbage collection

For Stand-alone

applications

Java 1.2 +Libraries(e.g. GUI,

DB, networkin

g)

Since Java 1.5

For Distributed enterprise application

s

J2SE +Libraries

(e.g. Security,

Transaction)

Java EE [2/5]

What is Jave EE? Java EE (Java Platform, Enterprise Edition)

The industry standard for developing enterprise applications Portable, robust, scalable and secure server-side Java applications

Provides web services, component model, management, and communication APIs

Java EE goals Highly available – to meet the needs of today’s global business

environment Secure – to protect the privacy of users and the integrity of

enterprise data Reliable and scalable – to insure that business transactions are

accurately and promptly processed

Java EE [3/5]

Jave EE & EJBJava EE

WebServices

Technologies

WebApplication

Technologies

Management& Security

Technologies

EnterpriseApplication

Technologies

Java EE [4/5]

Jave EE Technologies Web Services Technologies

Implementing Enterprise Web Services Java API for XML-Based Web Services (JAX-WS) 2.0 Java API for XML-Based RPC (JAX-RPC) 1.1 Java Architecture for XML Binding (JAXB) 2.0 SOAP with Attachments API for Java (SAAJ) Streaming API for XML Web Service Metadata for the Java Platform

Web Application Technologies Java Servlet 2.5 JavaServer Faces 1.2 JavaServer Pages 2.1 JavaServer Pages Standard Tag Library

Java EE [5/5]

Jave EE Technologies (cont’d) Enterprise Application Technologies

Enterprise JavaBeans 3.0 J2EE Connector Architecture 1.5 Common Annotations for the Java Platform Java Message Service API The Java Database Connectivity API (JDBC) Java Persistence API Java Transaction API (JTA) JavaBeans Activation Framework (JAF) 1.1 JavaMail

Management and Security Technologies J2EE Application Deployment J2EE Management Java Authorization Contract for Containers

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

EJB Overview [1/11]

What are Enterprise JavaBeans? Enterprise JavaBeans (EJB)

A standard-based component model APIs to implement business logics

EJB design goals Common services

Multithreading Transaction management Resource management (e.g., connection pooling) Persistence management Security services

Distribution and scalability “Throw money at it” solution

EJB Overview [2/11]

EJB Architecture

EJB architecture Specifies the responsibilities and interactions

among EJB entities

EJB ServerEJB Server

EJB ContainerClients

Enterprise

Bean

Enterprise

Bean

EJB Client



Enterprise

Bean

Enterprise

Bean

EJB Client

EJB Overview [3/11]

EJB Server

EJB server Provides a run-time environment Provides system services and manages

resources Process and thread management System resources management Database connection pooling and caching Management API



Enterprise

Bean

Enterprise

Bean

EJB Client

EJB Overview [4/11]

EJB Container EJB container

Provides a run-time environment for an enterprise bean

Likely provided by server vendor Hosts the EJBs and provides services to EJBs

Naming Life cycle management Persistence (state management) Transaction Management Security



Enterprise

Bean

Enterprise

Bean

EJB Client

EJB Overview [5/11]

Enterprise Bean

Enterprise Bean A specialized component for the real business

logic Consists of several classes and interfaces Distributed over a network

Server vendors provide tools that automatically generate distribution, transaction and security behavior



Enterprise

Bean

Enterprise

Bean

EJB Client

EJB Overview [6/11]

EJB Client

Client access is controlled by the container in which the enterprise bean is deployed

Clients locates an enterprise bean through Java Naming and Directory Interface (JNDI)

RMI is the standard method for accessing a bean over a network



Enterprise

Bean

Enterprise

Bean

EJB Client

EJB Overview [7/11]

Pros and Cons of EJB Pros

Component modularization Reusability ↑ , maintenance cost ↓

Component portability “Write Once, Run Anywhere” (WORA)

Development simplification A number of tricky middleware services are automatically

managed Programmers can concentrate on writing business logic

Development speed ↑ , code quality ↑

Cons Need to buy EJB container Implementation according to EJB specification

EJB Overview [8/11]

RMI vs. EJB

RMI EJB

Business object type Distributed objectDistributed component

Basic communication protocol

RMI RMI

Business method declaration

Remote interface Remote interface

Business method implementation

Remote class Bean class

How to implement business method

Remote class directly implements remote

interfaceDelegation

Business object construction,

destruction, findNo Home interface

Middleware services(transaction, security…)

No Yes

EJB Overview [9/11]

Code example: HelloWorld in RMI

Remote interface

Remote class

public interface Hello extends Remote { public String sayHello(String name) throws RemoteException;}

public class HelloImpl extends UnicastRemoteObject implements Hello { public HelloImpl() throws RemoteException { } public String sayHello(String name) throws RemoteException { return “Hello, ” + name; }}

EJB Overview [10/11]

Code example: HelloWorld in EJB

Home interface

Remote interface

public interface HelloHome extends EJBHome { public Hello create() throws RemoteException, CreateException;}

public interface Hello extends EJBObject { public String sayHello(String name) throws RemoteException;}

EJB Overview [11/11]

Code example: HelloWorld in EJB (cont’d)

Bean classpublic class HelloBean implements SessionBean { SessionContext ctx; // EJB container contract methods public void ejbCreate() { } public void ejbRemove() { } public void ejbActivate() { } public void ejbPassivate() { } public void setSessionContext(SessionContext ctx) { this.ctx = ctx; } // business method public String sayHello(String name) { return “Hello, ” + name; }}

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

Enterprise Bean [1/7]

Types of Enterprise Beans

Session bean Implements some business logic Business process component

e.g., order, payment in an online shopping mall

Entity bean Object-oriented view of entities stored in

persistent storage Normally, each instance represents a row in a RDB

table

e.g., product information, user information


Types of Enterprise Beans

Stateful session bean Maintains a state The state is relevant only for a single client

Cannot be seen by other clients Expires after a certain timeout

e.g., shopping cart


Stateful Session Bean

Stateless session bean No state

Can have fields, but they are not unique to any client

Since the container knows the bean has no state, it can: Use a single bean instance (while each client thinks it has

its own copy) Destroy/re-instantiate on the fly Redirect requests to different instances (load balancing)

e.g., currency conversion


Stateless Session Bean

CMP(Container-Managed Persistence) entity bean Container is responsible for saving the persistent

state

DB-related classes are auto-generated

You specify the container-managed attributes

Persistence is independent of the data source The mapping can be applied to other DBs very portable

Container can manage caching, locking strategies

Can only be used with data sources supported by JDBC


CMP Entity Bean

BMP(Bean-Managed Persistence) entity bean The bean writer must provide code for

storing/restoring persistent state

Less portable

Can exploit any persistence framework Not limited to databases

Manual tuning can result in performance benefits At the price of portability and hard work


BMP Entity Bean

Deployment Process to plug-in enterprise beans to EJB

container

Jar packaging + plug-in

Class files are auto-generated

Deployment Descriptor XML file

Additional information to run enterprise beanse.g., transaction type, security information

Makes it possible to use enterprise beans which are developed by other developers


Deployment Descriptor

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

Choice of the bean type Session bean? Entity bean?

Session bean – Stateful? Stateless?

Entity bean – CMP? BMP?

Code writing Home interface

Remote interface

Bean class

Primary key class (entity bean only)

Deployment descriptor

EJB Programming [1/25]

EJB Programming

Template

Example

public interface <BeanName>Home extends javax.ejb.EJBHome { public <BeanName> create(<rmiParams>) throws [<otherException>, …]

javax.ejb.CreateException, java.rmi.RemoteException;}

public interface CartHome extends EJBHome { public Cart create(String customerName, String account) throws BadAccountException, CreateException, RemoteException;}

EJB Programming [2/25] Stateful Session Bean (1/6) Code Example: Shopping Cart – Home Interface

Template

Example

public interface <BeanName> extends javax.ejb.EJBObject { public <rmiReturnType> <businessMethod> (<rmiParams>) throws

[<otherException>, …], java.rmi.RemoteException;}

public interface Cart extends EJBObject { public void addItem(int item) throws RemoteException; public void purchase() throws RemoteException;}

EJB Programming [3/25] Stateful Session Bean (2/6) Code Example: Shopping Cart – Remote Interface

Templatepublic class <BeanName>Bean implements javax.ejb.SessionBean { public <rmiReturnType> <businessMethod> (<rmiParams>) throws

[<otherException>, …], java.rmi.RemoteException { { /* implementation */ } // … other business methods

// EJB container contract methods public void ejbCreate (<rmiParams>) … { /* implementation */ } private SessionContext _context; public void setSessionContext(SessionContext ctx) { _context = ctx; } public void ejbRemove() { /* implementation */ } public void ejbActivate() { } public void ejbPassivate() { } }

EJB Programming [4/25] Stateful Session Bean (3/6) Code Example: Shopping Cart – Bean Class

Examplepublic class CartBean implements SessionBean { private SessionContext _context; private String customerName, account; // to maintain state information

public void setSessionContext(SessionContext ctx) { _context = ctx; } public void ejbCreate (String customerName, String account) { this.customerName = customerName; this.account = account; } public void ejbRemove() { } public void ejbActivate() { /* implementation for activation */ } public void ejbPassivate() { /* implementation for de-activation */ }

public void addItem(int item) { /* implementation */ } public void purchase() { /* implementation */ } }

EJB Programming [5/25] Stateful Session Bean (4/6) Code Example: Shopping Cart – Bean Class (cont’d)

<session id=“Cart"><ejb-name>Cart</ejb-name><home>demo.j2ee. CartHome</home><remote>demo.j2ee. Cart</remote><ejb-class>demo.j2ee.CartBean</ejb-class><session-type>Stateful</session-type><transaction-type>Container</transaction-type>

</session>

EJB Programming [6/25] Stateful Session Bean (5/6) Deployment Descriptor – Shopping Cart

Context initialContext = new InitialContext();

// Get the reference of the home object using JNDI CartHome cartHome = (CartHome)PortableRemoteObject.narrow(

initialContext.lookup(“java:comp/env/ejb/cart”), CartHome.class);

// Create EJB objectCart cart = cartHome.create(“John”, “7506”);

cart.addItem(96); // business method callcart.purchase();

EJB Programming [7/25] Stateful Session Bean (6/6) Code Example: Shopping Cart – Client code

Template

Example

EJB Programming [8/25] Stateless Session Bean (1/5) Code Example: Currency Converter – Home Interface

public interface <BeanName>Home extends javax.ejb.EJBHome { public <BeanName> create() throws javax.ejb.CreateException,

java.rmi.RemoteException;}

public interface CurrencyConverterHome extends EJBHome { public CurrencyConverter create() throws CreateException,

RemoteException;}

Template

Example

public interface <BeanName> extends javax.ejb.EJBObject { public <rmiReturnType> <businessMethod> (<rmiParams>) throws

[<otherException>, …], java.rmi.RemoteException;}

public interface CurrencyConverter extends EJBObject { public double convertUsdToWon(double usd) throws RemoteException;}

EJB Programming [9/25] Stateless Session Bean (2/5) Code Example: Currency Converter – Remote Interface

Templatepublic class <BeanName>Bean implements javax.ejb.SessionBean { public <rmiReturnType> <businessMethod> (<rmiParams>) throws

[<otherException>, …], java.rmi.RemoteException { { /* implementation */ } // … other business methods

// EJB container contract methods public void ejbCreate() … { /* implementation */ } private SessionContext _context; public void setSessionContext(SessionContext ctx) { _context = ctx; } public void ejbRemove() { /* implementation */ } public void ejbActivate() { } public void ejbPassivate() { } }

EJB Programming [10/25] Stateless Session Bean (3/5) Code Example: Currency Converter – Bean Class

Examplepublic class CurrencyConverterBean implements SessionObject { private SessionContext _context; private static final double WON_PER_USD = 950;

public void setSessionContext(SessionContext ctx) { _context = ctx; } public void ejbCreate () { } public void ejbRemove() { } public void ejbActivate() { } public void ejbPassivate() { }

public double convertUsdToNis(double usd) { return usd * WON_PER_USD; }}

EJB Programming [11/25] Stateless Session Bean (4/5) Code Example: Currency Converter – Bean Class (cont’d)

<session id="CurrencyConverter"><ejb-name>CurrencyConverter</ejb-name><home>demo.CurrencyConverterHome</home><remote>demo.CurrencyConverter</remote><ejb-class>demo.CurrencyConverterBean</ejb-

class><session-type>Stateless</session-type><transaction-type>Container</transaction-type>

</session>

EJB Programming [12/25] Stateless Session Bean (5/5) Deployment Descriptor – Currency Converter


Session Bean Lifecycle

Template

EJB Programming [14/25] CMP Entity Bean (1/6) Code Example: Product – Home Interfacepublic interface <BeanName>Home extends javax.ejb.EJBHome { public <BeanName> create(<rmiParams>) throws [<otherException>, …]

javax.ejb.CreateException, java.rmi.RemoteException; public <BeanName> findByPrimaryKey(<PrimaryKey>) throws [<otherException>, …] javax.ejb.CreateException, java.rmi.RemoteException; public Collection findXXX(<rmiParams>) throws [<otherException>, …] javax.ejb.CreateException, java.rmi.RemoteException;}

Example

EJB Programming [15/25] CMP Entity Bean (2/6) Code Example: Product – Home Interface

public interface ProductHome extends EJBHome { public Product create(String productId, String description, double price) throws CreateException, RemoteException; public Product findByPrimaryKey(String productId) throws

RemoteException, FinderException; public Collection findByPriceRange(double low, double high) throws

RemoteException, FinderException;}

Example

EJB Programming [16/25] CMP Entity Bean (3/6) Code Example: Product – Remote Interface

public interface Product extends EJBObject { public void setPrice(double price) throws RemoteException; public double getPrice() throws RemoteException; public String getDescription() throws RemoteException;}

Example

EJB Programming [17/25] CMP Entity Bean (4/6) Code Example: Product – Bean Class

public class ProductBean implements EntityBean { public String productId, description; public double price;

private EntityContext context;

public ejbCreate(String productId, String description, double price) throws CreateException { if (productId == null) throw new CreateException(“productId required.”); this.productId = productId; this.description = description; this.price = price; return null; }

Example (cont’d)

EJB Programming [18/25] CMP Entity Bean (5/6) Code Example: Product – Bean Class (cont’d)

public void setPrice(double price) { this.price = price; } public double getPrice() { return price; } public String getDescription() { return description; }

public void setEntityContext(EntityContext ctx) { this.context = ctx; } public void ejbActivate() { productId = (String)context.getPrimaryKey(); } public void ejbPassivate() { productId = null; description = null; }

public void ejbRemove() { } public void ejbLoad() { } public void ejbStore() { } public void unsetEntityContext() { } public void ejbPostCreate(String productId, String description, double price) { }}

<entity id="Account"> <persistence-type>Container</persistence-type> <ejb-name>Product</ejb-name> <home>demo.ProductHome</home> <remote>demo.Product</remote> <ejb-class>demo.ProductBean</ejb-class> <prim-key-class>java.lang.String</prim-key-class> <abstract-schema-name>Product</abstract-schema-name> <cmp-field><field-name>productId</field-name></cmp-field> <cmp-field><field-name>description</field-name></cmp-field> <cmp-field><field-name>price</field-name></cmp-field> <primkey-field>productId</primkey-field> <query> <query-method> <method-name>findByPriceRange</method-name> </query-method>

<ejb-ql>select object(o) from Product owhere o.price >= ?1 and o.price <= ?2</ejb-ql>

</query></entity>

EJB Programming [19/25] CMP Entity Bean (6/6) Deployment Descriptor – Product

Example

EJB Programming [20/25] BMP Entity Bean (1/5) Code Example: Product – Bean Class

…// Not to locate the record, but to verify that the record existspublic String ejbFindByPrimaryKey(String primaryKey) throws FinderException { boolean result; try { result = selectByPrimaryKey(primaryKey) } catch (Exception e) { } if (result) return primaryKey; else throw new ObjectNotFoundException(“Row for ” + primaryKey + “ not found”);}…

Example


…public boolean selectByPrimaryKey(String primaryKey) throws SQLException { String selectStmt = “select productId ” + “from product where productId = ?”; PreparedStatement prepStmt = _conn.prepareStatement(selectStmt); prepStmt.setString(1, primaryKey);

ResultSet rs = prepStmt.executeQuery(); boolean result = rs.next(); prepStmt.close(); return result;}…

Example


public void ejbLoad() { try { loadRow(); } catch (Exception e) { }}Private void loadRow() throws SQLException { String selectStmt = “select description, price ” + “from product where productId = ?”; PreparedStatement prepStmt = _conn.prepareStatement(selectStmt); prepStmt.setString(1, this.productId); ResultSet rs = prepStmt.executeQuery(); if (rs.next()) { this.description = rs.getString(1); this.price = rs.getDouble(2); } else throw new NoSuchEntityException(“Row for ” + productId + “not found”);}

Example


public Collection ejbFindByPriceRange(double low, double high) throws FinderException { try { result = selectByPriceRange(low, high); } catch (Exception e) { } if (result.isEmpty()) throw new ObjectNotFoundException(“No rows found”); else return result;}

Example


public Collection selectByPriceRange(double low, double high) throws SQLException { String selectStmt = “select productId from product ” + “where price >= low and price <= high”; PreparedStatement prepStmt = _conn.prepareStatement(selectStmt); prepStmt.setDouble(1, low); prepStmt.setDouble(2, high); ResultSet rs = prepStmt.executeQuery(); ArrayList a = new ArrayList(); while (rs.next()) { String productId = rs.getString(1); a.add(productId); } prepStmt.close(); return a;}


Entity Bean Lifecycle

Does not exist

Ready

Pooled

newInstance()setEntityContext()

unset-EntityContext()

ejbRemove() orejbPassivate()

ejbCreate()or ejbActivate()

ejbLoad()business method

ejbStore()

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

EJB 2.1 technology very powerful, but too complex Too many classes, interfaces Boilerplate javax.ejb interface methods Clumsy programming model Deployment descriptors

EJB 3.0 Goals Make EJB easier to learn and use Improve developer productivity Attract broader range of developers

Changes in EJB 3.0 [1/3]

Motivation

Simplification of the EJB APIs Removal of need for EJBHome and EJBObject Removal of JNDI APIs from developer and client

view Removal of need for deployment descriptors

Use advantages of Java language metadata Metadata designed so that the most common

cases are easiest to express Defaults available for expected cases

More work is done by container, less by developer

Changes in EJB 3.0 [2/3]

EJB 3.0 Approach

Example

Enterprise Bean [3/3] Stateful Session Bean (1/4) Code Example: Shopping Cart – Bean Class

@stateful public class CartBean implements Cart{ public int addItem(int item) { … } public void purchase() { … } … @PreDestroy remove() { … }}

public interface Cart { public int addItem(int item); public void purchase();}

No Home interface Deployment descriptor

annotations

Outline

Java EE

EJB Overview

Enterprise Beans

EJB Programming

Changes in EJB 3.0

References

References

EJB 프로그래밍 입문http://www.javastudy.co.kr/docs/lec_ejb/ejb/sunny_ejb1.pdf

Jboss – open source

http://labs.jboss.com/

http://sourceforge.net/projects/jboss (download)

distributed object-oriented programming (3) – enterprise javabeans snu idb lab. taewhi lee may...

Documents

java ee java platform

java architecture

java saajstreaming api

networkingsince java

referencesjava ee

processedjava ee

transactionjava ee

attachments api