Introduction to Java 2 platform, Enterprise Edition (J2EE)
This article will explain Introduction to Java Platform Enterprise Edition J2EE and present an overview of what it is and what it can do. In addition, we will also take a look at how to start J2EE and the development of J2EE applications.Future articles take a look at some of the main J2EE technologies, such as Java Servlets, JavaServer Pages (JSP), Enterprise JavaBeans (EJB) and Java Message Service (JMS).
What is J2EE?
Using the Java 2 Platform, Standard Edition (J2SE) as a foundation, Java 2 Platform, Enterprise Edition (J2EE) relies on it to provide the types of services needed to build multi-scale, distributed, layer-based application components. Essentially, the J2EE is a collection of APIs that can be used to build such systems, although this is only half the image. J2EE is also a standard for the creation and implementation of corporate applications, maintained together with the API specifications it defines and the services that J2EE provides. In other words, this means that Java’s “write once, run anywhere” promises also apply to corporate applications:
- Business applications can be run on different platforms that support the Java 2 platform.
- Business applications are portable among the application servers that support the J2EE specifications.
What does J2EE understand?
J2EE consists of many APIs that can be used to create enterprise applications. Although the total API list seems initially impressive, it is important to note that some are mainly used by the J2EE environment in which the application is running, while some provide services that your specific application may not require. Therefore, it is worth remembering that it is not necessary to use all of them to build J2EE applications. To complete, however, the complete list of technologies that make up the J2EE is the following:
- Java Servlets
- JavaServer Pages (JSP)
- Enterprise JavaBeans (EJB)
- Java Message Service (JMS)
- Java Naming and Directory Interface (JNDI)
- Java Database Connectivity (JDBC)
- Java Transaction Service (JTS)
- Java Transaction API (JTA)
- J2EE connector architecture (J2EE-CA or JCA)
From the developer’s point of view, the main technologies are EJB, JSP, Java Servlets, JDBC and JMS, although the JNDI is used to locate EJBs and other corporate resources. For now, let’s take a quick look at some of these technologies.
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What is Enterprise JavaBeans?
The EJB is an important part of the J2EE specification and defines a model for building reusable server-side components. There are three types of enterprise beans currently supported by J2EE – session beans, entity beans, and message-driven beans.
Session beans can be viewed as extensions for the client application and are typically used to model business processes. There are two types of session bean – stateful and stateless. Session beans with status information are generally used to record the conversation status of a single client between requests while session beans without status information are shared between any number of clients at any time.
Entity beans are typically used to model persistent business entities and, in particular, data in a database. A common assignment is to model an entity bean in a table, with one instance of that bean for each row in the table. There are two forms of persistence: persistence administered by container and administered by bean. In persistence managed by container, an assignment is defined at the time of implementation between the persistent properties in the bean and the columns in the table. With the persistence managed by the bean, the developers write the JDBC code that executes the create, read, update and delete operations.
Finally, message-driven beans allow the functionality to run asynchronously, usually triggered by message-oriented middleware JMS messages.
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What is the Java message service (JMS)?
JMS is a Java API that presents an interface in message-oriented middleware, such as IBM MQSeries, SonicMQ and so on. As JDBC, JMS provides Java applications with a mechanism to integrate with these systems, presenting a common programming interface, regardless of the subtype message system.Functionally, the JMS allows messages to be sent and received using a point-to-point paradigm or publish / sign.
The steps to execute a J2EE application – construction, package and implementation
There are several stages involved in the construction and execution of a J2EE application. The first step is to build it. J2EE is now supported by many tools (commercial and open source) and can certainly be useful in removing some of the complexity involved during the development process.
After creating your application, the next step is to package it. Here, the type of J2EE component you used will determine how you package your application. However, at a high level, it is only about grouping all its components and classes into one file (for example, JAR). In addition to the compiled code, some of the characteristics associated with certain components must be configured using implementation descriptors. These are simply XML files that describe how the component will behave when running within the J2EE environment.
The final step in the process is called implementation. As J2EE is, in essence, a collection of APIs and specifications, it is necessary to install an application server – the software that implements these specifications and provides the services on which they depend on their J2EE components to run.
J2EE is a very broad platform and, in principle, the range of technologies and APIs may seem overwhelming. By building your knowledge of J2EE piece by piece, technology by technology, you will soon be in a good position to start designing and building J2EE systems. In the next month, we will begin our tour of the various J2EE technologies by examining more closely the web layer (Java Servlets and JSP), including a discussion on how they fit into the J2EE, how Java Servlets and JSP coexist and also the kind of things that both are capable of.
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