What is Java Server Page

1
What is Java Server Page?

• JSP Page is simply a HTML page that contains
  snippets of code that execute application logic
  to generate dynamic content
• This application logic could be present in a Java
  Bean, Enterprise Java Bean, RMI Object or Corba
  Object

2
JSP Servlets

• Creating dynamic HTML output in servlets is a
  tedious work
• If changes are required in the dynamic HTML
  output of a servlet, the servlet has to be
  recompiled
• If dynamic output is generated using JSP, changes
  could be made and need not be recompiled.
• It is just like making changes to basic HTML.

3
Java Server Pages

• JSP is similar to server-side includes.
• The main difference is that instead of embedding
  a ltSERVLETgt tag in an HTML page, actual snippets
  of servlet code can be embedded.
• Each block of servlet code is surrounded by
  leading lt tag and a closing tag gt

4
Four predefined variables

• request
• The servlet request, an HttpServletRequest
  object
• response
• The Servlet response, an HttpServletResponse
  object
• out
• The Output writer, a PrintWriter object
• in
• The input reader, a Bufferedreader object
•  

5
Example(hello.jsp)

• ltHTMLgt
• ltHEADgtltTITLEgtHellolt/TITLEgtlt/HEADgt
• ltBODYgt
• ltH1gt
• lt if ( request.getParameter (name )
  null)
• out.println(Hello World)
• else
• out.println(Hello,request.getParameter(name)
  )
• gt
• lt/H1gt
• lt/BODYgtlt/HTML

6
Background Servlet

• When the page is run, the server automatically
  creates, compiles , loads, and runs a special
  servlet corresponding to hello.jsp.
• The static portions of the HTML pages are
  generated by the workhorse servlet using
  out.println() commands.

7

• import java .io.
• import java.x.servlet.
• import javax.servlet.
• import javax.servlet.http.
• public class _hellojsp extends HttpServlet
• public void _jspservice (HttpServletrequest
  request,HttpServletResponse response)
• response.setContentType(text/html)
• PrintWriter out response.getWriter()
• Bufferedreader in request.getReader()
• out.println(ltHTMLgt)
• out.println(ltHEADgtltTITLEgtHellolt/TITLEgtlt/HEADgt
  )
• out.println(ltBODYgt)
• out.println(ltH1gt)
• if (request.getParameter(name) null)
• out.println(Hello World)
• else
• out.println(Hello,request.getParameter(name
  ))
• out.println(lt/H1gt )
• out.println(lt/BODYgtlt/HTMLgt)

8

• When the JSP page is accessed for the first time,
  server takes a short time to respond because the
  server has to create compile the Background
  Servlet.
• When the JSP files contents changes, the server
  takes a short time because the server has to
  recompile the BackgroundServlet.

9
Expression

• Expressions are variables or constants that are
  inserted into the data returned by the web server
  
• Expressions are defined by lt and gt
• Any Java expressions between the two tags is
  evaluated, the result is converted to a string,
  and the text is included directly in the page.
• For example,lt h gt prints the value of the
  variable h.

10
Directives

• A JSP directive begins with lt_at_ and ends with gt.
  
• It allows a JSP page to control certain aspects
  of Background Servlet.
• Directives can be used from JSP to set
  background Servlets content type, import a
  package, extend a different superclass, implement
  an interface and handle either GET or POST
  REQUESTSgt

11
Content Type

• specifies the content type of generated page
• lt _at_ content_type text/plain gt
• The default content type is text/html
•  

12
import keyword

• specifies a list of classes the servlet should
  import.
• Multiple classes can be given in a
  comma-seperated list or given through multiple
  import directives.
• For example
• lt_at_ import java.io.util.Hashtablegt
• lt_at_ import java.io., java.io.util.Hashtable
  gt

13
extends

• Specifies the superclass the servlet should
  extend.
• For example
• lt_at_ extends GenericServletgt
• The Default superclass is HttpServlet

14
implements

• Implements
• specifies a list of interfaces the servlet should
  implement.
• Multiple interfaces can be given in a
  comma-separated list or given through multiple
  implement directives.
• For example
• lt_at_ implements Serializablegt
• The default is not to implement anything

15
method

• Specifies the servlet method that should contain
  the generated code and handle client requests.
• The default is service,which handles all
  requests.
• For example
• lt_at_ method doPost gt

16
language

• Specifies the scripting language used by the
  back-end. The default language is java.
• Some servers can allow other languages.
• For example
• lt language javagt

17

• Example
•  
• lt_at_ methoddoPost gt
• ltHTMLgt
• ltHEADgtltTITLEgtHellolt/TITLEgtlt/HEADgt
• ltBODYgt
• ltH1gt
• lt if (request.getParameter(name)null) gt
• Hello World
• lt else gt
• Hello, ltrequest.getParameter(name) gt
• lt gt
• lt/H1gt
• lt/BODYgtlt/HTMLgt
•  
•