Developing Distributed application using Enterprise Java Beans, J2EE Architecture, EJB Tutorial, WebLogic Tutorial.
Distributed Architecture
Two-tier application:
In the past two-tier applications were used. Two-tier applications are also know as
Tutorial Details:
client/server applications. In most of the cases these architecture were providing only the database functionality and all the business logic and presentation of the data logic were installed on the client machine. This architecture was very difficult to maintain.
Problems of Two-tier Architecture
Easy to install, but very difficult to maintain.
Problem of installing and upgrading data access software on each client machine.
It is very difficult to reuse the business and presentation logic.
These two-tier applications are not very scalable and therefore not well suited to the Internet and Intranet Applications.
Multi tiered J2EE Architecture
Sun's J2EE architecture is multi tiered architecture and it eliminates all the problems of two-tier architecture. It also eliminates the need of writing thin-client multithread applications, which were earlier used to write distributed transactional applications for the enterprise. Thin-client multi tiered applications are very fast, secure and reliable. But writing the thin-client multi tiered applications are not easy and it involves many lines of intricate code to handle transaction and state management, multithreading, resource pooling and other complex low-level details.
In the Java TM 2 Platform, Enterprise Edition (J2EE tm), low-level details are separated from the business logic. Now the developers will more concentrate on the business logic rather than the low-level details. Low-level details are managed by the application container of the application server.
J2EETM Architecture consists of following technologies:
Java Database Connectivity (JDBC)
Java Naming and Directory Interface (JNDI)
Enterprise Java Beans (EJB)
Java Server Pages (JSP)
Java Servlets
Remote Method Invocation (RMI)
Java IDL/CORBA
1. Java Database Connectivity or JDBC for short
The JDBC API allows the java programs to access the database. For more information and tutorial on JDBC visit http://www.roseindia.net/jdbc/jdbc.htm
2. Java Naming and Directory Interface (JNDI)
Sun's JNDI API is a standard extension to the Java TM platform and it allows the java applications to access naming and directory services. With the help of JNDI java application can seamlessly access the heterogeneous enterprise naming and directory services like DNS, LDAP, local file system, or objects in an application server.
Visit: http://java.sun.com/products/jndi for downloading and more information.
3. Enterprise JavaBeans or EJB for short
Sun Microsystem's definition of Enterprise JavaBeans is:
" The Enterprise JavaBeans architecture is a component architecture for developing and deployment of component-based distributed applications. Applications written using the Enterise JavaBeans are scalable, transactional, and multi-user secure. These applications may be written once, and then deployed on any server platform that supports the Enterprise JavaBeans specification."
The EJB specification defines the EJB component architecture and the interfaces between the Enterprise JavaBeans technology-enabled server and the component.
There are three types of Beans:
A) Stateless Session Beans:
These beans do not maintain the state, and the information stored in these beans are lost when the server crashes.
b) Statefull Session Beans:
These beans are also short lived and do not survive the server crashes. These beans are used to maintain the session of a client. Shopping cart is developed using the session beans.
c) Entity Beans:
These beans represents the data stored in a database. These beans survive the server crashes because it reconstruct the data from the database when server comes up. An example of an entity bean is the users information.
4. Java Server Pages or JSP for short:
Java Server Pages allows the developers to embed the java code into html pages. It is a mean by which dynamic content can be generated using the static HTML pages and the data from the database. For more information visit http://www.roseindia.net/jsp/jsp.htm
5. Java Servlets:
Java Servlets are server side components that provides a powerful mechanism for developing serverside applications. For more information and tutorial visit http://www.roseindia.net/servlets/servlets.htm .
6. Remote Method Invocation (RMI)
It is used to invoke methods on remote objects. EJB's uses the RMI for their functionality and this is not the topic that any web application developer should learn.
7. CORBA:
Java's IDL support allows the developers to integrate Java with CORBA.
8. XML:
Java and XML combination provides the portable data. And this is ideal for the exchange of data over the Internet and the Intranet.
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