INTRODUCTION TO J2EE

Java Enterprise Edition

- Sahil Kukreja

(C.S.E – 5th B)

WHAT IS J2EE ?

Java EE is Oracle’s enterprise Java computing platform.

Platform provides an API and runtime environment for developing and running  enterprise software.

Java EE extends the Java Platform, Standard Edition (Java SE/J2SE), providing an API for object – relational mapping, distributed and multi-tier architectures.

WHAT MAKES A PLATFORM?

J2EE is neither a hardware(it can run on any hardware with apt JVM) , nor a software exactly (J2EE-compatible systems available).

So what sort of a platform is J2EE ?

In the world of software, a platform is a combination of hardware and software necessary to run applications.

PLATFORM REQUIREMENTS

Consistency : Consistency is a basic platform requirement. Applications depend on platforms to provide a specific set of well-known services.

Adoption : Adoption provides established platforms with enormous momentum and market clout.

Openness : Some degree of openness is necessary for software vendors to develop products for a platform.

Specification : The platform specification defines the platform, usually in terms of required APIs, policies, and interfaces.

J2EE – BUILDING BLOCKS

Servlets : A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP.

JSP : With JSP you could write HTML in a JSP file, and the server would automatically create a servlet from the page. JSP also allows you to write blocks of Java code inside the JSP.

Web Frameworks : The shortcomings of plain servlets and JSP sparked the creation of many Web frameworks that intended to make Web application development easier.

A timeline with the release dates of some Web frameworks. Most of them are Java frameworks, but some other ones are included.

J2EE HISTORY

The original J2EE specification was developed by Sun Microsystems.The year 2000 has seen J2EE compliancy move out of realm of marketing and into nine shipping products. JSR 58 specifies J2EE 1.3 and JSR 151 specifies the J2EE 1.4 specification. The Java EE 5 specification was developed under JSR 244 and the final release was made on May 11 2006.

In short, the server side java industry has gone through a whirl wind of change.

Overview of J2EE architecture

JAVA WEB APPLICATION SERVERS

Understanding the differences between a web server, a servlet container and an application server is important when learning how a Java Web application is presented to its end users.

The servlet/application/EJB container terms are a bit ambiguous, but we will try to come to a workable definition.

Let’s take a look.

1. WEB SERVER

A Web server handles the HTTP protocol. When the Web server receives an HTTP request, it responds with an HTTP response.

The Web server itself does not dynamically generate responses, it just handles receiving the request and sending the response.

The most commonly used Web servers are Apache, Microsoft IIS and nginx.

2. WEB CONTAINER

A Web container (or servlet container) is a program that provides an environment for the servlets and JSP to run.

The Web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access rights.

So a Web container provides a runtime environment for a subset of the Java EE specification, usually only the JSP and Servlet parts.

The most common Web container are  Tomcat and Jetty.

3. Application Server

An application server is a server that provides support for the entire Java EE specification.In addition it provides the capabilities of a Web Container as well as of a Web Server.

J2EE DEPLOYMENT

How do you present a Web application to the server?

Web applications are packaged in WAR and EAR files. Web containers (e.g. Tomcat) accept WAR files. Application servers (e.g. Glassfish) accept WAR files and EAR files.

A Java EE application is delivered in a Java Archive (JAR) file, a Web Archive (WAR) file, or an Enterprise Archive (EAR) file.

A WAR or EAR file is a standard JAR file with a .war or .ear extension.

1. JAR : JAVA ARCHIVE

A JAR is an archive file format typically used to aggregate many Java class files and associated metadata and resources into one file to distribute application software or libraries on the Java platform.

A manifest file is a specific file contained within a JAR archive. It is used to define information about the JAR.

Application client modules are packaged as JAR files with a .jar extension.

2. WAR : Web Application ARchive

A WAR file is a JAR file used to distribute a Web Module.The top-level directory of a web module is the document root of the application.The structure of a WAR file looks like this:

3. EAR : Enterprise Archive

When a large Web application is deployed, all its .jar and .war files are packaged as JAR file with .ear extension and deployed into an application server.Deploying EAR files requires an application server such as Glassfish.Web containers such as Tomcat can not deploy EAR files, only WAR files.EAR file structure :

FUTURE OF JAVA TECHNOLOGY

When Java was developed initially , even its developers were not sure in which direction the technology will grow. And actually Java has taken an unexpected turn around as a development technology.

Some people say there is no need of separate Core Java, which is now known as J2SE. J2SE comprise of core Java components and libraries like core language library, utilities, SWT, Swing, Networking, Security etc.

Let us examine possible directions where there are chances Java will grow as development technology.

NEW TRENDS

People are always in search of implementing J2EE, a way that it can be used optimally. Several new frameworks, practices and design patterns are developed to make proper utilization of advantages of J2EE.

Some of them are discussed here :

Design Patterns : For enterprise applications , it is very important that they are well designed prior to start of their development phase because they are large in scale. Some of the design patterns are MVC (Model-View-Controller), DAO (Data Access Objects) and many more.

Frameworks : 

Some organizations have developed their own frameworks over the top of J2EE. Also such frameworks implement best J2EE practices to achieve high performance and other advantages of J2EE.Some popular J2EE frameworks are Struts, Spring etc.

J2EE Best Practices :

Ways to utilize J2EE framework that it can perform at its best with its all advantages like scalability, remote access etc.

Such practices are used by many developers and proven to be useful to achieve such goals in J2EE applications. and are also known as J2EE best practices.

New Technologies The Java community which is controlled by Sun keeps including new features and technologies to J2EE such as JFS (Java Faces Service), Java.net, Java gaming, Java AI etc.

Go Mobile Mobile phone applications are very wide scope area where Java is being used for its portability and independence.

Most of mobile phones operate over Java implementations.

Embedded

Java is gaining more popularity to develop embedded applications. The reason after such popularity is its platform independence.

The principle of reusability is gaining more popularity among embedded applications community and so Java.

SUMMARY

After examining scope, usage and potential of different areas of Java technology we can summarize that it has still long way to go. Java has got a lot of potential to develop and grow in many areas. For existing areas like desktop applications and enterprise applications there are chances for Java to gain better role. Also it has got to grow in new areas of embedded applications in future.

SOURCES

http://encyclopedia2.thefreedictionary.com/J2EE

http://www.j2eebrain.com/java-J2ee-j2ee-history.html

http://pic.dhe.ibm.com/infocenter/wbihelp/v6rxmx/index.jsp?topic=%2Fcom.ibm.wics_developer.doc%2Fdoc%2Faccess_dev_j2ee%2Faccess_dev_j2ee15.htm

http://www.exforsys.com/tutorials/j2ee/future-of-java-technology.html

THANKYOU !