Java Server Pages (JSP) is a technology that allows developers to embed Java code in HTML pages to create dynamic web content. JSP pages are compiled into servlets, so they can benefit from the full functionality of the Java programming language. The JSP lifecycle involves compilation, initialization, execution, and cleanup similar to a servlet lifecycle. Key tags like scriptlets allow inserting Java code directly into JSP pages to generate dynamic output.

1. Java server pages

2. DEFINITION FOR JSP
Java Server Pages (JSP) is a technology
for developing web pages that support dynamic
content which helps developers insert java code
in HTML pages by making use of special JSP tags,
most of which start with <% and end with %>.
EXAMPLE
We can collect input from users through
web page forms

3. In the early days of the Web, the Common
Gateway Interface (CGI) was the only tool for
developing dynamic web content. However, CGI is
not an efficient solution.
For every request that comes in, the web
server has to create a new operating-system
process, load aninterpreter and a script, execute
the script, and then tear it all down again.
This is very taxing for the server and doesn't
scale well when the amount of traffic increases.

4.  Active Server Pages (ASP)
 PHP
 ColdFusion
 Server-Side Includes (SSI)
 JavaScript
 Pure Servlet
 Static HTML

5. The advantages of JSP are twofold.
First, the dynamic part is written in Java,
not Visual Basic or other MS specific
language, so it is more powerful and easier
to use. Second, it is portable to other
operating systems and non-Microsoft Web
servers.

6. PHP1 is an open source web scripting language.
Like JSP and ASP, PHP allows a page author to
include scripting code in regular web pages to
generate dynamic content.
PHP has a C-like syntax with some features
borrowed from Perl, C++, and Java.
The current version, compiles a page when it's
requested, executes it and merges the result of
executing the scripts with the static text in the
page, before it's returned to the browser.

7. The dynamic parts of a page are generated by
inserting HTML/XML -like elements, known as the
ColdFusion Markup Language (CFML), into web pages.
The latest version of ColdFusion also includes
elements for communication with Java servlet and
Enterprise JavaBeans.
Custom elements can be developed in C++ or Java to
encapsulate application specific functions, and CFML
extensions are available from third parties.

8. Server Side Iincludes is really
only intended for simple inclusions,
not for "real" programs that use form
data, make database connections,
and the like.

9. JavaScript can generate
HTML dynamically on the client but
can hardly interact with the web
server to perform complex tasks like
database access and image
processing etc.

10. It is more convenient to write
(and to modify!) regular HTML than
to have plenty of println statements
that generate the HTML.

11. Regular HTML, of course, cannot
contain dynamic information.

12. A JSP life cycle can be defined as
the entire process from its creation
till the destruction which is similar
to a servlet life cycle with an
additional step which is required to
compile a JSP into servlet.

13. Compilation
Initialization
Execution
Cleanup

15. When a browser asks for a JSP, the JSP
engine first checks and the JSP engine compiles
the page. If the page has never been compiled
and JSP has been modified.
The compilation process involves three steps:
 Parsing the JSP.
 Turning the JSP into a servlet.
 Compiling the servlet.

16. When a container loads a JSP it invokes the
jspInit() method before servicing any requests. If
you need to perform JSP-specific initialization,
override the jspInit() method.
Example:
public void jspInit()
{ // Initialization code...
}
Typically initialization is performed only
once and as with the servlet init method

17. This phase of the JSP life cycle represents all
interactions with requests until the JSP is destroyed.
Whenever a browser requests a JSP and the page
has been loaded and initialized, the JSP engine
invokes the _jspService() method in the JSP.
The _jspService() method takes an
HttpServletRequest and an HttpServletResponse as
its parameters as follows

18. Example
void _jspService (HttpServletRequest request,
HttpServletResponse response)
{
// Service handling code...
}

19. The destruction phase of the JSP life cycle
represents when a JSP is being removed from use
by a container.
The jspDestroy() method is the JSP
equivalent of the destroy method for servlets.
Example
public void jspDestroy()
{
// Your cleanup code goes here.
}

20. SCRIPLET
A scriptlet can contain any number of
JAVA language statements, variable or
method declarations, or expressions that are
valid in the page scripting language.
Syntax of Scriptlet
<% code fragment %>

21. <html>
<head><title>Hello World</title></head>
<body>
Hello World!<br/>
<%
out.println("Your IP address is " +
request.getRemoteAddr());
%>
</body>
</html>

23. A declaration declares one or more
variables or methods that you can use in Java
code later in the JSP file.
Syntax of JSP DECLARATIONS
<%! declaration; %>
Example
<%! int a, b, c=0; %>
<%! Circle a = new Circle(2.0); %>

24. <%! int day = 3; %>
<html>
<head><title>SWITCH...CASE Example</title></head>
<body>
<%
switch(day) {
case 0:
out.println("It's Sunday.");
break;
case 1:
out.println("It's Monday.");
break;
case 2:
out.println("It's Tuesday.");
break;

25. case 3:
out.println("It's Wednesday.");
break;
case 4:
out.println("It's Thursday.");
break;
case 5:
out.println("It's Friday.");
break;
default:
out.println("It's Saturday.");
}
%>
</body>
</html>

26. This would produce following result:
It's Wednesday.