1.5 Servlet

	The Java term for CGI application is Servlet, as mentioned above that CGI application is different from plain
	HTML document. To write and save data on the server you cannot rely on web server alone.

	Web server have the ability to deliver static HTML pages only. But it cannot create real time pages that respond
	to client request. What you need is a helper application. Which is called CGI or Servlet in Java world.

	Servlet is a Java program that runs in a Web server, as opposed to an applet that runs in a client browser.
	Typically, the servlet takes an HTTP request from a browser, generates dynamic content (such as by querying a
	database), and provides an HTTP response back to the browser.

	Alternatively, it can be accessed directly from another application component or send its output to another
	component. Most servlets generate HTML text, but a servlet might instead generate XML to encapsulate data
	(Wright and Smith 2005).

	Servlet programming also offers advantages over earlier models of server-side Web application development,
	including the following as stated by (Wright and Smith 2005):

		Servlets outperform earlier technologies for generating dynamic HTML, such as server-side "includes" or
		CGI scripts. Once a servlet is loaded into memory, it can run on a single lightweight thread; CGI scripts must
		be loaded in a different process for every request.

1.5 Servlet

		Servlet technology, in addition to improved scalability, offers the well-known Java advantages of object
		orientation, platform independence, security, and robustness.

		Servlets are fully integrated with the Java language and its standard APIs, such as JDBC for Java database
		connectivity.

		Servlets are fully integrated into the J2EE framework, which provides an extensive set of services that your
		Web application can use, such as Java Naming and Directory Interface (JNDI) for component naming and
		lookup, Java Transaction API (JTA) for managing transactions, Java Authentication and Authorization
		Service (JAAS) for security, Remote Method Invocation (RMI) for distributed applications, and Java Message
		Service (JMS).

		A servlet handles concurrent requests (through either a single servlet instance or multiple servlet instances,
		depending on the thread model), and servlets have a well-defined lifecycle. Also, servlets can optionally be
		loaded when OC4J starts, so that any initialization is handled in advance instead of at the first user request.

		The servlet request and response objects provide a convenient way to handle HTTP requests and send text
		and data back to the client.

1.5 Servlet

		Because servlets are written in the Java programming language, they are supported on any platform that
		has a Java virtual machine and a Web server that supports servlets. Servlets can be used on different
		platforms without recompiling. You can package servlets together with associated files such as graphics,
		sounds, and other data to make a complete Web application. This simplifies application development and
		deployment.

An Example

		Suppose that we want the current time of server to be shown up on web page, you cannot do this with static
		HTML page, you need something more dynamic, you need servlet:

1.5 Servlet

		In order to run this example you need to do other things (e.g. configure something called the deployment
		descriptor (DD)). This is not our focus now we just want to show you how simple servlet looks like.

		In the previous figure, Lines from 4 to 7 are standard servlet declarations. We will talk about that in coming
		topics. Don't worry about them now.

		Lines from 8 to 13 are the core, we use PrintWriterobject which we get from response object to write HTML
		tags to the response object, and through HTML tags we have put the current date of server.

It should display:

		This is how you create a dynamic web page in a servlet. You have to print the whole thing to an output
		stream (it's really part of the HTTP response stream that you're printing to). But trying to format the HTML
		inside a servlet out.println() is much sophisticated, this is one of the worst parts about servlets. If only there
		was a way to put Java inside an HTML page instead of putting HTML inside a Java class, yes there is, are
		you heard about JSP? (Bates, Sierra and Basham 2008).