JSP(Java Server Pages)
				    --------------------------

Q)What is JSP?
     =>JSP  is a Java based  web technology     from Sun Microsystems.

Q)What is the purpose of JSP technology?
=>JSP technology is used to develop Java  based dynamic websites.
                         OR
  =>In Java based web application development  JSP technology is used.

Q)What is a jsp?

      =>A jsp is a dynamic web resource    that enahances the functionality of the
      web server.

      =>A jsp is a JSP Container managed  web server side piece   of code(server side program). 

      =>A  jsp is a web component.

      =>A jsp is a a text file with any name but with ".jsp extension.

Q)What can a jsp do in a Java web application?
    =>All that a servlet can do.
Q)Can a jsp replace a servlet?
    =>Yes. But it will not do.
    Note:- In fact, each use-case is implemented using a servlet and a jsp together.

Q)When there is already Servlet technology, what was the need of JSP technology?
    =>servlets are weak in presentation. JSP is excellent in that.

Q)What is the life cycle  of a jsp?

A  JSP page(a jsp)   life cycle  is described   with  3 life cycle methods  and  6 life cycle
   phases.
   =>Life cycle methods are
                   1.)jspInit()
		   2.)_jspService()
		   3.)jspDestory()
  =>Life cycle phases   are
               1.)translation phase
	       2.)compilation phase
	       3.)initialization phase
	       4.)instantiation phase
	       5.)servicing phase
	       6.)destruction phase
Translation phase
--------------------
 =>JSP Container converting  a jsp  into  a   servlet is nothing but  translation phase of a jsp.
 =>When client request comes for a jsp for   the first time after its deployment, JSP
    engine makes a full read of the source code   of the jsp and verifies the syntactical correctness    of the JSP elements(if any) used in the    jsp. If  JSP elements are syntactically    correct,  it   converts   ".jsp"  file  into ".java"   file.
    =>".java" file created during translation phase   is nothing but the source code of a servlet.   I.e. during translation phase of a jsp, JSP container    generates a servlet. This servlet is known    as container generated servlet  OR   page
    implementation class.  
Compilation phase
---------------------
=>JSP Engine   compiling    the page implementation
    class source code  to  ".class" file  is nothing but
    compilation phase of a jsp.

    Note:- translation  and compilation  happens
    only once in the life time of a jsp unless its source
    code is modified.
Q)Explain about instantiation,initialization,servicing
and destruction phase of a jsp.

  =>Container instantiating the page implementation
  class is nothing but  instantiation phase of the jsp.

  =>Container calling jspInit() method of the
  page implementation class is nothing but initialization
  phase of  the jsp.

  =>Instantiation and initialization happens
  only once in the life time of  a jsp.

  =>jsp developer(page author) provides any resources
  required for the jsp in  jspInit() method. For eg.
  database connection creation &  PreparedStatement
  creation.
  =>Container calling _jspService() method is nothing
  but servicing phase of the jsp. for each client
  request Container calls _jspService() method.

  =>JSP container is responsible to generate 
  _jspService() method.

  =>In a jsp, jsp developer should not implement 
  _jspService() method. If required, jspInit() &
  jspDestroy() can be implemented.

  =>When application is unloaded or Container is shutdown, container calls  jspDestroy()  and marks the page implementation  class instance for garbage collection.

  =>Container calling jspDestroy() method is nothing
  but destruction phase of the jsp.

  =>destruction happens only once in the
  life time of a jsp.

  =>resources if any allocated during initialization
  phase are deallocated in jspDestroy() method.

Q)What are the constituents (contents) of a jsp?

    A jsp= HTML code+Java code+JSP elements
Note:- "writing HTML code   inside Java code is servlet
development  and vice-versa  is jsp development"

Q)Explain about   Scripting elements.
    =>JSP  Scripting elements are those JSP
    elements using which, Java code is directly
    embeded into a jsp.
    =>Scripting elements are of 3 types.
                    1.)declaration
		    2.)expression
		    3.)scriptlet
    declaration
    -------------
    =>JSP declaration is one of the three  JSP    scripting elements.
    =>It is used to place Java code directly within the    source code of a jsp.
    =>A  JSP declaration starts with  <%!      and ends with  %>
    =>With in a JSP declaration we can   place Java variables  and  Java methods.
        For eg.
	             <%!
                               int  count;
			       Connection con;
			       PreparedStatement ps;
			       public void jspInit()
			       {
			           .....
                                }
				public void jspDestroy()
				{
				}
				public void process()
				{
				}
                  %>
        =>During translation phase, Java variables	and Java methods of the JSP declaration become	the members of the page implementation 
	class. i.e. container generated servlet.
       
       =>We can have any number   JSP declarations      in a jsp.
		             
    expression
    -------------
   =>JSP expression is one of the three  JSP    scripting elements.
    =>It is used to place Java code directly within the    source code of a jsp.
    =>A  JSP expression starts with  <%=    and ends with  %>
    =>Within a JSP expression we can   write  only  one  Java expression(that too without   semi colon).

       For eg.
	       a.)      <%=   a+b    %>
	       b.)   <%=  request.getParameter("username") %>
	       c.)   <%=  sum  %>

   =>During translation phase,  Java expression of  a JSP expression is placed in  _jspService()     method of page implementation class.
   =>We can have any number of JSP expressions  in a jsp. In the same order their Java code will   be placed  in _jspService method.
 =>When a JSP expression is executed, 2 things happen in the background.
                     1.)Java expression is evaluated.
		     2.)evaluated value is written to the
		      browser stream.
scriptlet
-----------
     =>JSP scriptlet is one of the three  JSP    scripting elements.
    =>It is used to place Java code directly within the    source code of a jsp.
    =>A  JSP scriptlet starts with  <%     and ends with  %>
    =>We can place  free form of Java code  in  a JSP scriptlet. i.e. during servlet programming   whatever Java code we write in servicing method  to implement the use-case, all that Java   code we can write  in a JSP scriptlet.

     For eg.
                  <%

		        String a=request.getParameter("t1");
		        String b=request.getParameter("t2");
			int n1=Integer.parseInt(a);
			int n2=Integer.parseInt(b);
			...
                 %>
    =>During translation phase,  Java code of     a JSP Scriptlet is placed in  _jspService()  method of page implementation class.

   =>We can have any number of JSP scriptlets  in a jsp. In the same order their Java code will  be placed  in _jspService method.