1.5 Introduction to J2EE APIs

1.5 Introduction to J2EE APIs

1.5.1 Servlets:-

-          At a high level.

-          Java Servlets are the Java equivalent of CGI scripts.

-          That can be used to perform processing and the servicing of client requests on a web server.

-          From an implementation perspective, servlets are simply Java classes.

-          That implement a predefined interface.

-          One use for servlets is that they can be used to dynamically generate content.

-          For presentation to the user.

-          And this is achieved by embedding markup language (e.g. HTML) inside the Java code.

-          As Servlets are written in Java, they have access to the rich library of features provided by Java.

-          Including access to databases and other enterprise resources such as EJB.

1.5.2. Java Server Pages (JSP):-

-          JSP is another technology for presenting information to the user over the web.

-          And uses a paradigm where Java code is embedded into the HTML

-          The opposite of servlets, and much like Microsoft ASP.

-          Pages are written as HTML files with embedded Java source code known as scriptlets.

-          One of the pitfalls in using JSP is that it is very easy to build large pages.

-          Containing lots of embedded Java code and business logic.

-          For this reason, JSPs provide easy integration with JavaBeans and another feature called JSP tag extensions.

-          These custom tags (also known as custom actions) allow re-usable functionality to be encapsulated into XML

-          Like tags that can be easily used on the pages by both page developers and designers.

1.5.3 Enterprise JavaBeans (EJB) :-

-          EJB is a major part of the J2EE specification.

-          And defines a model for building server-side, reusable components.

-          There are three types of enterprise beans currently supported by J2EE :

1)      Session beans,

2)      Entity beans and

3)      Message-driven beans.

-          Session beans can be seen as extensions to the client application.

-          And are typically used to model business processes.

-          There are two types of session bean :

1)      Stateful and

2)      Stateless.

-           Stateful session beans are typically used to record conversational state for a single client between requests.

-          Whereas stateless session beans are shared between any number of clients at any one time.

-          Entity beans are typically used to model persistent business entities.

-          And, in particular, data in a database.

-          A common mapping is to model an entity bean on a table.

-          There being one instance of that bean for every row in the table.

-          There are two ways that persistence can be achieved :

1)      Container managed and

2)      Bean managed persistence.

-          In container managed persistence, a mapping is defined at deployment time.

-          Between the persistent properties in the bean and the columns in the table.

-          With bean managed persistence, developers write the JDBC code that performs the create, read, update and delete operations.

-          Finally, message-driven beans allow functionality to be executed on an asynchronous basis.

-          Typically triggered by JMS messages from message-oriented middleware.

1.5.4 Java Message Service (JMS) :-

-          JMS is Java API that presents an interface into message-oriented middleware such as :

1)      IBM MQSeries,

2)      SonicMQ and

3)      so on.

-          Like JDBC, JMS provides Java applications a mechanism to integrate with such systems by presenting a common programming interface.( Irrespective of the underlying messaging system).

-          Functionally, JMS allows messages to be sent and received using a point-to-point or publish/subscribe paradigm.

1.5.5 Java Mail :-

 

-           The Java Mail API provides classes that allow we work with e – mail.

-          Specifically it allows sending & receiving e – mail by using a wide variety of protocols. Such as:

1)      POP

2)      SMTP

3)      IMAP

 

-          We can create e – mails that conform to a large number of MIME type.

-          MIME – Multi Purpose Internet Mail Extension.

-          Because the API uses JAF to provide support for a number of MIME types.

-          JAF – Javabean Activation Framework.

-          We can create HTML messages that contain embedded graphics & even have attachments.

-          Most internet application requires the ability to send e – mail messages.

-          We can use this API together with JAF to send from :

1)      JSP

2)      Servlets or

3)      EJB

 

 

1.5.6 Java Server Faces (JSF) :-

-          This technology is a user interface framework for building web applications

-          The main component of JSF technology is as follows:

1)      A GUI component framework :

§  A flexible model for rendering components in different kinds of HTML or different markup languages & technologies.

§  A Rendered (turn into) object generates the markup to render the component.

§  And converts the data that can be represented in a view.

 

-          So, JSF does :

1)      A standard rendered kit for generating HTML markup.

2)      Input validation.

3)      Event handling.

4)      Data conversion between model objects & components.

5)      Page navigation configuration.

 

1.5.7 Java Naming Directory Interface (JNDI) :-

-          It is an extension to the Java platform.

-          And provide multiple naming & directory services.

-          A naming services provides a mechanism for locating distributed objects.

-          A director services organize the distributed objects & other resources. Such as:

1)      Files in to a hierarchical structures.

-          Directory services allow resources to be linked virtually.

-          So as to be located in directory service hierarchy.

-          They are different types of directory services.

-          JNDI allows the different types of directory services to be linked.

-          Thus client can any type of directory services.