MUST READ : J2EE ESSENTIAL DEFINITIONS

J2EE ESSENTIALS



J2EE specification defines the following J2EE components:

• Application clients and applets are components that run on the client.
• Java Servlet and JavaServer Pages™ (JSP™) technology
components are web components that run on the server.
• Enterprise JavaBeans™ (EJB™) components (enterprise beans)
are business components that run on the server.

J2EE Clients
A J2EE client can be a web client or an application client.




Web Clients
A web client consists of two parts: (1) dynamic web pages containing various types of markup language (HTML, XML, and so on), which are generated by web components running in the web tier, and (2) a web browser, which renders the pages received from the server. A web client is sometimes called a thin client. Thin clients usually do not query databases, execute complex business rules, or connect to legacy applications. When you use a thin client, such heavyweight operations are off-loaded to enterprise beans executing on the J2EE server, where they can leverage the security, speed, services, and reliability of J2EE server-side technologies.

Applets
An applet is a small client application written in the Java programming language that executes in the Java virtual machine installed in the web browser.

Web Components
J2EE web components are either servlets or pages created using JSP technology (JSP pages). Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.

Business Components
Business code, which is logic that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans running in the business tier.

There are three kinds of enterprise beans: session beans, entity beans, and message- driven beans. A session bean represents a transient conversation with a client.When the client finishes executing, the session bean and its data are gone. In contrast, an entity bean represents persistent data stored in one row of a database table. If the client terminates or if the server shuts down, the underlying services
ensure that the entity bean data is saved. A message-driven bean combines features of a session bean and a Java Message Service (JMS) message listener, allowing a business component to receive JMS messages asynchronously.

Enterprise Information System Tier
The enterprise information system tier handles EIS software and includes enterprise infrastructure systems such as enterprise resource planning (ERP), mainframe transaction processing, database systems, and other legacy information systems.

Container Types

J2EE server
The runtime portion of a J2EE product. A J2EE server provides EJB and
web containers.

Enterprise JavaBeans (EJB) container
Manages the execution of enterprise beans for J2EE applications. Enterprise beans and their container run on the J2EE server.

Web container
Manages the execution of JSP page and servlet components for J2EE applications. Web components and their container run on the J2EE server.

Application client container
Manages the execution of application client components. Application clients and their container run on the client.

Applet container
Manages the execution of applets. Consists of a web browser and Java Plugin running on the client together.

SOAP Transport Protocol
Client requests and web service responses are transmitted as Simple Object Access Protocol (SOAP) messages over HTTP to enable a completely interoperable exchange between clients and web services, all running on different platforms and at various locations on the Internet.



WSDL Standard Format
TheWeb Services Description Language (WSDL) is a standardized XML format for describing network services. The description includes the name of the service, the location of the service, and ways to communicate with the service.

UDDI and ebXML Standard Formats
Other XML-based standards, such as Universal Description, Discovery and Integration (UDDI) and ebXML, make it possible for businesses to publish information on the Internet about their products and web services, where the information can be readily and globally accessed by clients who want to do business.

Packaging Applications
A J2EE application is delivered in an Enterprise Archive (EAR) file, a standard Java Archive (JAR) file with an .ear extension. Using EAR files and modules makes it possible to assemble a number of different J2EE applications using some of the same components. No extra coding is needed; it is only a matter of assembling (or packaging) various J2EE modules into J2EE EAR files. An EAR file (see Figure 1–6) contains J2EE modules and deployment descriptors.
A deployment descriptor is an XML document with an .xml extension that
describes the deployment settings of an application, a module, or a component. Because deployment descriptor information is declarative, it can be changed without the need to modify the source code. At runtime, the J2EE server reads the deployment descriptor and acts upon the application, module, or component accordingly.

J2EE Product Provider
The J2EE product provider is the company that designs and makes available for purchase the J2EE platform APIs, and other features defined in the J2EE specification.

Tool Provider
The tool provider is the company or person who creates development, assembly, and packaging tools used by component providers, assemblers, and deployers.

Application Component Provider
The application component provider is the company or person who creates web components, enterprise beans, applets, or application clients for use in J2EE applications.

Enterprise Bean Developer
An enterprise bean developer performs the following tasks to deliver an EJB JAR file that contains the enterprise bean(s):
• Writes and compiles the source code
• Specifies the deployment descriptor
• Packages the .class files and deployment descriptor into the EJB JAR file

Web Component Developer
A web component developer performs the following tasks to deliver a WAR file containing the web component(s):
• Writes and compiles servlet source code
• Writes JSP and HTML files
• Specifies the deployment descriptor
• Packages the .class, .jsp, and.html files and deployment descriptor into
the WAR file

Application Assembler
The application assembler is the company or person who receives application modules from component providers and assembles them into a J2EE application EAR file.

Application Deployer and Administrator
The application deployer and administrator is the company or person who configures and deploys the J2EE application, administers the computing and networking infrastructure where J2EE applications run, and oversees the runtime environment. Duties include such things as setting transaction controls and security attributes and specifying connections to databases.

A deployer or system administrator performs the following tasks to install and configure a J2EE application:
• Adds the J2EE application (EAR) file created in the preceding phase to
the J2EE server
• Configures the J2EE application for the operational environment by
modifying the deployment descriptor of the J2EE application
• Verifies that the contents of the EAR file are well formed and comply with
the J2EE specification
• Deploys (installs) the J2EE application EAR file into the J2EE server

Enterprise JavaBeans Technology
An Enterprise JavaBeans™ (EJB™) component, or enterprise bean, is a body of code having fields and methods to implement modules of business logic. You can think of an enterprise bean as a building block that can be used alone or with other enterprise beans to execute business logic on the J2EE server.

Web container Web components are supported by the services of a runtime platform called a web container. A web container provides services such as request dispatching, security, concurrency, and life-cycle management. It also gives web components access to APIs such as naming,transactions, and email.

Java EE server: The runtime portion of a Java EE product. A Java EE server provides EJB and web containers


Java Servlet Technology
Java servlet technology lets you define HTTP-specific servlet classes. A servlet class extends the capabilities of servers that host applications that are accessed by way of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers.

JavaServer Pages Technology
JavaServer Pages™ (JSP™) technology lets you put snippets of servlet code directly into a text-based document. A JSP page is a text-based document that contains two types of text: static data (which can be expressed in any text-based format such as HTML, WML, and XML)

Java Message Service API
The Java Message Service (JMS) API is a messaging standard that allows J2EE application components to create, send, receive, and read messages. It enables distributed communication that is loosely coupled, reliable, and asynchronous.

Java Transaction API
The Java Transaction API (JTA) provides a standard interface for demarcating transactions. The J2EE architecture provides a default auto commit to handle transaction commits and rollbacks. An auto commit means that any other applications that are viewing data will see the updated data after each database read or
write operation.

Java Naming and Directory Interface
The Java Naming and Directory Interface™ (JNDI) provides naming and directory functionality. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, a J2EE application can store and retrieve any type of named Java object.

JavaServer Faces
JavaServer Faces technology is a user interface framework for building web applications.
A GUI component framework.
The following features support the GUI components:
• Input validation
• Event handling
• Data conversion between model objects and components
• Managed model object creation
• Page navigation configuration

What are Web Services?
Web services are application components
Web services communicate using open protocols
Web services are self-contained and self-describing
Web services can be discovered using UDDI
Web services can be used by other applications
XML is the basis for Web services
How Does it Work?
The basic Web services platform is XML + HTTP.
XML provides a language which can be used between different platforms and programming languages and still express complex messages and functions.
The HTTP protocol is the most used Internet protocol.
Web services platform elements:
SOAP (Simple Object Access Protocol)
UDDI (Universal Description, Discovery and Integration)
WSDL (Web Services Description Language)

A few years ago Web services were not fast enough to be interesting.
Interoperability has Highest Priority
When all major platforms could access the Web using Web browsers, different platforms could interact. For these platforms to work together, Web-applications were developed.
Web-applications are simple applications that run on the web. These are built around the Web browser standards and can be used by any browser on any platform.
Web Services take Web-applications to the Next Level
By using Web services, your application can publish its function or message to the rest of the world.
Web services use XML to code and to decode data, and SOAP to transport it (using open protocols).
With Web services, your accounting department's Win 2k server's billing system can connect with your IT supplier's UNIX server.

Web Services have Two Types of Uses
Reusable application-components.
There are things applications need very often. So why make these over and over again?
Web services can offer application-components like: currency conversion, weather reports, or even language translation as services.
Connect existing software.
Web services can help to solve the interoperability problem by giving different applications a way to link their data.
With Web services you can exchange data between different applications and different platforms.

What is SOAP?
SOAP is an XML-based protocol to let applications exchange information over HTTP.
Or more simple: SOAP is a protocol for accessing a Web Service.
SOAP stands for Simple Object Access Protocol
SOAP is a communication protocol
SOAP is a format for sending messages
SOAP is designed to communicate via Internet
SOAP is platform independent
SOAP is language independent
SOAP is based on XML
SOAP is simple and extensible
SOAP allows you to get around firewalls
SOAP is a W3C standard
What is WSDL?
WSDL is an XML-based language for locating and describing Web services.
WSDL stands for Web Services Description Language
WSDL is based on XML
WSDL is used to describe Web services
WSDL is used to locate Web services
WSDL is a W3C standard

What is UDDI?
UDDI is a directory service where companies can register and search for Web services.
UDDI stands for Universal Description, Discovery and Integration
UDDI is a directory for storing information about web services
UDDI is a directory of web service interfaces described by WSDL
UDDI communicates via SOAP
UDDI is built into the Microsoft .NET platform

Thanks @ Regards
RK
http://rkj2me.blogspot.com