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Java EE: An Introduction

JPA, EJB, JSF

1Wednesday, January 27, 2010

Java EE Components

• Applets: GUI app’s executed in a web browser. They use theSwing API to provide powerful user interfaces.

• Applications: programs executed on a client. Typically GUIs or

batchprocessing programs that have access to all the facilities of the Java EE middle tier.

• Web applications: app’s executed in a web container and respondto HTTP requests from web clients.

• Made of servlets, servlet filters, web event listeners, JSP pages,and JSF. Servlets also support web service endpoints

• Enterprise Java Beans: containermanaged components forprocessing transactional business logic. They can be accessedlocally and remotely through RMI or HTTP for SOAP and

RESTful web services .2Wednesday, January 27, 2010

MVC Design Pattern

• The ModelView Controller MVC design pattern separates

the core business modelfunctionality from thepresentation and control logicthat uses this functionality.

• The separation allows multiple views to share the sameenterprise data model, whichmakes supporting multipleclients easier to implement,test, and maintain.

Source: Java BluePrints J2EE Patterns, MVC http://java.sun.com/blueprints/patterns/MVC-detailed.html


JEE app and the MVC architecture

• In a JEE application:

• The model business layer functionality represented by JavaBeans orEJBs

• The view the presentation layer functionality represented by JSFs the view

• The controller Servlet mediating between model and view

• Must accommodate input from various clients including HTTP requests from web clients, and…

• WML from wireless clients

• XML documents from suppliers

• Etc.




Model layer in a Web App

• Models the data and behavior behind the business process

• What it’s responsible for:

• Performing DB queries

• Calculating the business process

• Processing orders

• Encapsulation of data and behavior which are independentof presentation


View layer in a Web App

• Display information according to client types

• Display result of business logic Model

• Not concerned with how the information was obtained, orfrom where since that is the responsibility of Model


Controller in a Web App

• Serves as the logical connection between the user's

interaction and the business services on the back• Responsible for making decisions among multiple

presentations

• e.g. User's language, locale or access level dictates a di erentpresentation.

• A request enters the application through the control layer, which will decide how the request should be handled and what information should be returned


Web Applications

• A web application is a dynamic extension of a web or applicationserver. Types of web applications:

• Presentationoriented

• generates interactive web pages containing various types of markup language HTML, XHTML, XML, and so on and dynamic content in response to requests.

• Serviceoriented

• A serviceoriented web application implements the endpoint of a web service.

• In Java EE platform, web components provide the dynamicextension capabilities for a web server.

• Web components are either Java servlets, web pages, web serviceendpoints, or JSP pages




JPA

• Relational model i.e. RDBMS vs. Object Oriented model i.e. Java

• ObjectRelational Mapping ORM

• Java Persistence API JPA

• An API above JDBC

• Can access and manipulate relational data from Enterprise Java Beans EJBs , web components, and Java SE applications

• Includes an entity manager API to perform DBrelatedoperations like CRUD

• Includes JPQL, an objectoriented query language


JPA

• Objects vs. Entities

• Objects are instances that justlive in memory.

• Entities are objects that liveshortly in memory andpersistently in a database.

• JPA map objects to a database via metadata that can be suppliedusing annotations or in an XMLdescriptor

• Annotations: The code of theentity is directly annotated with allsorts of annotations described in

the javax.persistence package.

@Entity

public class Book {

@Id @GeneratedValue

private Long id;

@Column(nullable = false)

private String title;

private Float price;

@Column(length = 2000)

private String description;

private String isbn;

private Integer nbOfPage;

private Boolean illustrations;

// Constructors, getters, setters

}


JPA mapping


Enterprise Java Beans

• serverside components

• encapsulate business logic

• take care of transactions and security

• used in building business layers to sit on topof the persistence layer and as an entry pointfor presentationtier technologies like JavaServer Faces JSF .

• can be built by annotating a POJO that willbe deployed into a container




Types of EJBs

• Session beans and Messagedriven Beans MDBs

• Session Beans are used to encapsulate highlevel businesslogic and can be...

• Stateless: contains no conversational state between methods, andany instance can be used for any client

• Stateful: contains conversational state, which must be retainedacross methods for a single user

• Singleton: A single session bean is shared between clients andsupports concurrent access


EJB Example

@Stateless

public class BookEJB {

@PersistenceContext(unitName = "chapter06PU")

private EntityManager em;

public Book findBookById(Long id) {

return em.find(Book.class, id);

}

public Book createBook(Book book) {

em.persist(book);

return book;

}

}


Web pages and web servers

• Web servers

• Handles HTTP requests and sends a HTTP response typically

HTML page• Default HTTP port: 80

• Typical servers: Apache 47, MS 21

• Netcraft Web Server Survey December 2009

• “Web languages”

• HTML

• CSS

• JavaScript


JSF

• JSF applications arestandard webapplications thatintercept HTTP via the Faces servlet andproduce HTML




<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd

">

<html xmlns=""

http://www.w3.org/1999/xhtml"

xmlns:h="

"http://java.sun.com/jsf/html">

<h:head>

<title>Creates a new book</title>

</h:head>

<h:body>

<h1>Create a new book</h1>

<hr/>

<h:form>

<table border="0">

<tr><td><h:outputLabel value="ISBN : "/></td>

<td><h:inputText value="#{bookController.book.isbn}"/></td>

</tr>

<tr>

<td><h:outputLabel value="Title :"/></td>

<td><h:inputText value="#{bookController.book.title}"/></td>

</tr>

</table>

<h:commandButton value="Create a book"

action="#{bookController.doCreateBook}" styleClass="submit"/>

</h:form>

<hr/>

<i>APress - Beginning Java EE 6</i>

</h:body></html>


Packaging Java EE Web Apps

• A web application module contains:

• servlets, JSPs, JSF pages, and web services,

•as well as HTML and XHTML pages, Cascading Style Sheets CSS , JavaScripts, images, videos, and so on.

• All these artifacts are packaged in a jar file with a .war extension i.e., a war file, or Web Archive.

• WEB-INF/web.xml is the optional web deployment descriptor

• WEB-INF/ejb-jar.xml is the optional EJB Lite beansdeployment descriptor.

• WEB-INF/classes contains all the Java .class files

• WEB-INF/lib contains any dependent jar files.22Wednesday, January 27, 2010