J2ee Tutorial

J2EE-Tutorial Developing a J2EE-Application with JBoss

Übung SAVES, Sommersemester 2006 Holger Klus Sebastian Herold Technische Universität Kaiserslautern Fachbereich Informatik AG Softwarearchitektur

Overview ƒ Application Scenario „Drink Account Manager“ ƒ Current situation ƒ Goals of „Drink Account Manager“

ƒ J2EE-Introduction ƒ ƒ ƒ ƒ ƒ ƒ ƒ

Short Overview Container-Concept Entity Beans Session Beans Servlets/JSP‘s Packaging and Deployment XDoclet

Application Scenario „Drink Account Manager“ ƒ

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Current situation

ƒ A printed list with available drinks and possible consumers is provided in our kitchen ƒ Every person makes a bar in the corresponding field if he removes a drink ƒ Additionally a price list is available ƒ Every 4-5 weeks a bill is sent to the consumers by E-Mail

Goals of „Drink Account Manager“

ƒ Making bars via Touch-Screen in the kitchen ƒ Automatic generation of bills and the corresponding E-Mail ƒ But first: Implementing basic functionality like - Show/Add/Edit/Delete -

Consumers Drinks Removals Prices Bills

Wasser (0,7 Liter)

Cola (0,5 Liter)

Apfelschorle (0,7 Liter)

Sebastian Herold Holger Klus

…

Getränk

Preis

Wasser (0,7 Liter)

0,40 €

Cola (0,5 Liter)

0,75 €

Apfelschorle (0,7 Liter)

0,70 €

…

…

Application Scenario „Drink Account Manager“ ƒ Implementation of this scenario using two different approaches ƒ Fat-Client-Approach - Client is a Java application using Hibernate for Object-Relational mapping - All data will be stored in a MySQL-Database

ƒ 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

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

J2EE - Short Overview ƒ J2EE ≡ “Java 2 Platform Enterprise Edition” ƒ The newest version is called “Java Platform, Enterprise Edition (Java EE)”

ƒ Provides a programming platform for developing and running ƒ distributed, and ƒ multi-tier architecture ƒ Java applications

ƒ J2EE is based on software components executable in an application server ƒ There are specific runtime environments for specific components - Containers

ƒ Allows developers to create an enterprise application that is portable between platforms ƒ „Write once, run anywhere, and reuse everywhere“ ƒ Possible, because J2EE is standardized

J2EE – Short Overview ƒ One of the most important concepts in J2EE are Containers

ƒ Provide an environment in which the components can be executed in a controlled and managed way ƒ They provide services that the components can use either in a programmatic or a declarative way ƒ Allows declarative transaction management (only possible in the EJB-container)

ƒ Different types of Containers ƒ Application Container ƒ Applet Container ƒ EJB-Container

- Entity Beans, Session Beans, Message-driven Beans

ƒ Web-Container

- Servlets, JSPs

J2EE – Container-Concept

J2EE – Enterprise Java Beans (EJB) ƒ Three types of EJBs (all executed in the EJB-Container) ƒ Entity Beans - Provide an object-oriented view to the underlying persistent data - Container- vs. Bean Managed Persistence - Synchronous access using RMI-IIOP

ƒ Session Beans -

Modelling business processes Stateless vs. Stateful Session Beans They are conversational and perform specific actions Synchronous access using RMI-IIOP

ƒ Message-driven Beans - Similar to Session Beans but provide asynchronous access using JMS

J2EE – Bean-Usage ƒ Beans are registered in a JNDI-repository ƒ Lookup by name

ƒ Access Beans through interfaces ƒ Remote Interface - Interface to the application-specific services of the bean - setName() - getName() - getDrinkList()

ƒ Home Interface - Interface for managing bean instances - create() - findAll() - findByPrimaryKey()

ƒ Each type available in local and remote version (since EJB 2.0)

J2EE – Entity Beans ƒ An Entity Bean is a Java class with some additional features/attributes ƒ 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-4.0.4RC1\server\default\deploy) - jbosscmp-jdbc.xml - ejb-jar.xml - Mapping of relations between beans is also done in these descriptors

ƒ Naming convention - setProperty() - getProperty()

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

J2EE – Session Beans ƒ Used for realizing superior business logic ƒ Often their methods correspond to use cases and use services of one or many Entity Beans ƒ E.g. Methods which provides appropriate data for the presentation layer

ƒ Session Beans encapsulate Entity Beans ƒ Session Beans represent a classical facade Entity Bean Client

Session Bean

Entity Bean Entity Bean

Entity Bean

EJB-Container

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

ƒ Important: ƒ Value Objects have to be serializable

J2EE - Servlets ƒ ƒ ƒ ƒ

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

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Servlets can access components running in the EJB container (-> Session Beans) But: html-code is generated using println-statements

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ƒ The web container forwards the request to the servlet. ƒ The servlet processes it and generates the content dynamically. ƒ The web container then transmits the response back to the web server and finally to the client.

ƒ PrintWriter out = resp.getWriter(); ƒ out.println("