several interactions.
If you are programming the site, it is very helpful to be able to associate
some data with each visitor. For this purpose, "session"s
can be used in JSP.
A session is an object associated with a visitor. Data can be
put in the session and retrieved from it, much like a Hashtable.
A different set of data is kept for each visitor to the site.
Here is a set of pages that put a user's name in the session, and display
it elsewhere. Try out installing and using these.
First we have a form, let us call it GetName.html
<HTML>
<BODY>
<FORM METHOD=POST ACTION="SaveName.jsp">
What's your name? <INPUT TYPE=TEXT NAME=username SIZE=20>
<P><INPUT TYPE=SUBMIT>
</FORM>
</BODY>
</HTML>
The target of the form is "SaveName.jsp", which saves the user's name in
the session. Note the variable "session". This
is another variable that is normally made available in JSPs, just like
out
and request variables. (In the @page directive, you can
indicate that you do not need sessions, in which case the "session" variable
will not be made available.)
<%
String name = request.getParameter( "username" );
session.setAttribute( "theName", name );
%>
<HTML>
<BODY>
<A HREF="NextPage.jsp">Continue</A>
</BODY>
</HTML>
The SaveName.jsp saves the user's name in the session, and puts a link
to another page, NextPage.jsp.
NextPage.jsp shows how to retrieve the saved name.
<HTML>
<BODY>
Hello, <%= session.getAttribute( "theName" ) %>
</BODY>
</HTML>
If you bring up two different browsers (not different windows of the same
browser), or run two browsers from two different machines, you can put
one name in one browser and another name in another browser, and both names
will be kept track of.
The session is kept around until a timeout period. Then it is
assumed the user is no longer visiting the site, and the session is discarded.
Exercise: Add another attribute "age" to the above example.
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