1. J2EE-Tutorial
Developing a J2EE-Application with JBoss
Übung SAVES, Sommersemester 2006
Holger Klus
Sebastian Herold
Technische Universität Kaiserslautern
Fachbereich Informatik
AG Softwarearchitektur

2. Overview
Application Scenario „Drink Account Manager“
Current situation
Goals of „Drink Account Manager“
J2EE-Introduction
Short Overview
Container-Concept
Entity Beans
Session Beans
Servlets/JSP‘s
Packaging and Deployment
XDoclet

3. Application Scenario „Drink Account Manager“
Current situation Wasser Cola (0,5 Apfelschorle …
A printed list with available drinks (0,7 Liter) Liter) (0,7 Liter)
and possible consumers is provided
in our kitchen
Sebastian
Every person makes a bar in the Herold
corresponding field if he removes a
drink Holger Klus
Additionally a price list is available
Every 4-5 weeks a bill is sent to the …
consumers by E-Mail
Goals of „Drink Account Manager“
Making bars via Touch-Screen in the Getränk Preis
kitchen Wasser (0,7 Liter) 0,40 €
Automatic generation of bills and the
corresponding E-Mail Cola (0,5 Liter) 0,75 €
But first: Implementing basic
functionality like Apfelschorle (0,7 Liter) 0,70 €
- Show/Add/Edit/Delete
- Consumers …
- Drinks
- Removals
- Prices
- Bills

4. Application Scenario „Drink Account Manager“
Implementation of this scenario using two different
approaches
Fat-Client-Approach
- Client is a Java application using Hibernate for Object-Relational
mapping
- All data will be stored in a MySQL-Database
Ultra-Thin-Client-Approach (using J2EE)
- Client accesses the application through a web interface
- Web-pages are generated on server-side and will then be sent to
the client
- The application runs in an application server including
- Business logic and
- Persistence functionality
- Also: dynamic generation of required web-pages
- Data will also be stored in a MySQL-Database

5. Relational DB-Schema
tblBill
pk_id fk_consumer dateOfIssue expirationDate balanced
tblConsumer
pk_id firstName lastName email
tblRemoval
pk_id fk_consumer fk_bill fk_drink amount dateOfRemoval
tblDrink tblPrice
pk_id name capacity pk_id fk_drink amount validFrom validUntil

6. J2EE - Short Overview
J2EE ≡ “Java 2 Platform Enterprise Edition”
The newest version is called “Java Platform, Enterprise Edition (Java EE)”
Provides a programming platform for developing and running
distributed, and
multi-tier architecture
Java applications
J2EE is based on software components executable in an application
server
There are specific runtime environments for specific components
- Containers
Allows developers to create an enterprise application that is portable
between platforms
„Write once, run anywhere, and reuse everywhere“
Possible, because J2EE is standardized

7. J2EE – Short Overview
One of the most important concepts in J2EE are
Containers
Provide an environment in which the components can be
executed in a controlled and managed way
They provide services that the components can use either in a
programmatic or a declarative way
Allows declarative transaction management (only possible in the
EJB-container)
Different types of Containers
Application Container
Applet Container
EJB-Container
- Entity Beans, Session Beans, Message-driven Beans
Web-Container
- Servlets, JSPs

8. J2EE – Container-Concept

9. J2EE – Enterprise Java Beans (EJB)
Three types of EJBs (all executed in the EJB-Container)
Entity Beans
- Provide an object-oriented view to the underlying persistent data
- Container- vs. Bean Managed Persistence
- Synchronous access using RMI-IIOP
Session Beans
- Modelling business processes
- Stateless vs. Stateful Session Beans
- They are conversational and perform specific actions
- Synchronous access using RMI-IIOP
Message-driven Beans
- Similar to Session Beans but provide asynchronous access using
JMS

10. J2EE – Bean-Usage
Beans are registered in a JNDI-repository
Lookup by name
Access Beans through interfaces
Remote Interface
- Interface to the application-specific services of the bean
- setName()
- getName()
- getDrinkList()
Home Interface
- Interface for managing bean instances
- create()
- findAll()
- findByPrimaryKey()
Each type available in local and remote version (since EJB 2.0)

11. J2EE – Entity Beans
An Entity Bean is a Java class with some additional
features/attributes
They can be made persistent in an relational database
- Bean-Managed persistence (BMP)
- The programmer has to implement several callback methods like
ejbCreate, ejbRemove, …
- Container-Managed persistence (CMP)
- Only a mapping to the relational DB has to be provided by the
programmer, the rest will be managed by the container
- Three descriptors involved
- mysql-ds.xml (located in jboss-4.0.4RC1serverdefaultdeploy)
- jbosscmp-jdbc.xml
- ejb-jar.xml
- Mapping of relations between beans is also done in these descriptors
Naming convention
- setProperty()
- getProperty()

12. EJB-QL (EJB Query Language)
Defines queries for the finder and select methods of an entity bean
with container-managed persistence
The scope of an EJB-QL query spans the abstract schemas of
related entity beans that are packaged in the same EJB jar-file.
They are defined in the deployment descriptor of the entity bean
(ejb-jar.xml).
SELECT OBJECT(a) FROM Drink AS a
SELECT DISTINCT OBJECT(p)
FROM Drink d
WHERE d.name = ?1 AND d.capacity = ?2

13. J2EE – Session Beans
Used for realizing superior business logic
Often their methods correspond to use cases and use
services of one or many Entity Beans
E.g. Methods which provides appropriate data for the
presentation layer
Session Beans encapsulate Entity Beans
Session Beans represent a classical facade
Entity Bean
Client Session Bean Entity Bean Entity Bean
Entity Bean
EJB-Container

14. J2EE – Value Objects / Data Access Objects (DAO)
Value objects/DAOs are simple POJOs (plain old java
objects)
Are used to exchange application-specific data
Example: DrinkListEntry
Simple POJOs can be generated automatically
Important:
Value Objects have to be serializable

15. J2EE - Servlets
Special Java classes located on the server
Appropriate for the implementation of web-based user interfaces
Dynamic generation of web content instead of returning static content
The client invokes a servlet using an HTTP request
The web container forwards the request to the servlet.
The servlet processes it and generates the content dynamically.
The web container then transmits the response back to the web server and
finally to the client.
Servlets can access components running in the EJB container (-> Session
Beans)
But: html-code is generated using println-statements
PrintWriter out = resp.getWriter();
out.println("<html><head><title>");
…
Disadvantages
Html mixed with Java
Recompilation required after changes in the source code

16. J2EE - JSPs
Special html-pages located on the server
They can be developed like html-pages but can also include Java-code
Naturally appropriate for the implementation of web-based user interfaces
Not particular well suited to perform processing logic
JSPs are transformed into Servlets at runtime
No Recompilation required after changes of the layout
Some important jsp-Tags
<% … %>
- Here you can insert Java code, so called “Scriptlets”
<%@ … %>
- Among others you can insert an import-statement with libraries to be included
- Content of this tag is called “Directive”
<jsp:forward>
- Can be used to redirect the request to another jsp-page
Important
jsp-tags, names, parameters, … are case-sensitive

17. J2EE – Packaging and Deployment
Packaging
All components and deployment descriptors have to be packaged in a
specific way
.ear
- .war
- *.jsp
- WEB-INF
- jboss-web.xml
- web.xml
- .jar
- META-INF
- ejb-jar.xml
- jboss.xml
- jbosscmp-jdbc.xml
- META-INF
- application.xml

18. J2EE – Deployment and Packaging
Deployment
Step of transferring the J2EE-Application to the application
server
Only the .ear-file has to be deployed
Doing all that stuff manually would take a lot of time!
Therefore XDoclet has been developed in order to automate
these tasks like
- Generating required interfaces
- Generating deployment descriptors
- …

19. XDoclet
Open Source code generation engine
Enables Attribute-Oriented Programming for Java
Adding meta data to the java source
XDoclet parses the source files and generates artifacts
such as XML descriptors and/or source code from it
Currently XDoclet can only be used as part of the build
process utilizing Jakarta Ant
Details look at
http://xdoclet.sourceforge.net/xdoclet/index.html

20. XDoclet – Main Idea
XDoclet-Tags
Java-Files XDoclet-build.xml
ant
.java web.xml jboss.xml ejb-jar.xml …

21. Advantages/Disadvantages of J2EE
Advantages
J2EE provides a complete architecture for developing
- Distributed systems including object persistence, session tracking,
transaction management, …
Separation of technical and application-specific code
- Deployment descriptors
- Container Managed Persistence
Disadvantages
Very complex technology
- Even simple examples require many interfaces, bean classes, deployment
descriptors, …
Many errors occur only at runtime (several steps required until the
application is running)
- Compilation
- Packaging
- Deployment
- Running the application