★ wanayoo — archive 1999 http://wdvl.internet.com/Authoring/Java/Servlets/java_server.html

Java Server Pages

April 5, 2000

As described earlier JSP build on the ASP technology and use Java as a programming language.

We saw the WelcomeServlet which takes myName as a parameter from HTML-form and displays a personalized welcome message. Now let's see how to achieve the same with a JSP:

Welcome.jsp:

		
<HTML>
 <HEAD>
 <B> Welcome  <%= request.getParameter("myName")%>
</B>
 </HEAD> 
</HTML>

That's all ! Suddenly life's become easy huh?

The code between "<%" and "%>" is executed at the server and the HTML, with the results, is passed back to the client.

One important fact about JSP one should always keep in mind is: every JSP is internally converted into a servlet. So even if it looks simple it it is probably going to put more 'load' on your m/c. A rule of thumb is 'if you have a lot of HTML code and some 'run time variables' use JSP. If you need a lot of processing, a servlet is the best choice. Actually one can 'interleave' servlets and JSP. We will see that in the next section.

There are some pre-defined objects (such as request, response and session) available to each JSP. We can use all the normal programming constructs such as:

<% if ((request.getParameter("myName") == "Harshal") {%>
       <B> Hey we have the same name !</B>
<%  } else { %>
       <B> Welcome <%= request.getParameter("myName") %> </B>
<%} %>

Finally, we can call methods of an external program - Java bean.