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JSP Syntax

JSP supports two basic styles of delimiting its scripting elements from page content. The first looks a great deal like ASP, whereas the second can be used to create JSP that is fully XML compliant. Here, let's take a look:

To utilize the XML Style delimiters, you have to format your JSP as an XML document. This requires some additional modification, like using <jsp:root/> as your the root XML node and making sure your page is well-formed XML. This conversion and the use of the XML Style are outside the scope of this article, but if XML is important to you or your project, you should definitely investigate them further on your own time.

If you're interested in learning more about XML and JSP, the book Professional Java XML Programming with Servlets and JSP is an excellent investment -- though if you're not quite ready to roll out the dough, JavaSoft's PDF about the matter is free for the downloading.

The most important things to know as you create your JSP website are the four basic types of delimeters: directives, declarations, fragments, and expressions. The following example is a complete JSP page that uses the base style of each delimiter:

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<%@ page info="Example"
import="java.io.*,java.util.*" %>
<%! String title = "Example JSP Page" %>
<%@ include file ="header.inc" %>

Anyone can count like this:<BR>
<%
   for (int i = 1; i < 6; i++) {
     out.println(i + "<BR>");
   }
   i = 1000000;
%>
It would take a lifetime, however to count to <%= i %>.
<%@ include file ="footer.inc" %>

In line 1, the page directive sets the generated servlet info to "Example" and makes sure that "java.io.*" and "java.util.*" are imported for use in the servlet. The import is, well, important, since without these imports there would be no access to additional Java APIs.

Line 2 declares title as a class variable. This variable can now be used in any following code. Most likely, it is used by the code in header.inc, which is included in place on line 3.

Line 4 is plain page content. This is sent to the output stream.

Lines 5 through 10 define a code fragment that writes out the numbers 1 to 5, with breaks in between, to the output stream.

Line 6 is page content that includes an expression. This content is sent to the output stream with the expression inserted.

Line 7 includes the footer.inc file, which presumably has some more content we want to place at the bottom of this file.

If you followed all that, then you now have a basic understanding of JSP syntax and are armed with enough knowledge to do some small amount of damage to your website. One gotcha that you should know about is that when included files are changed, the servlet generated by the JSP is not usually regenerated. So if you make a change to an included file, make sure to tell your server to regenerate the servlet for the including JSP. Another way to do this is to re-save the including JSP. This changes the file modification timestamp, which is supposed to cause the servlet to regenerate.

Now that we've taken a look at the basic syntax, let's take a look at how we can use the access objects that JSP provides us to detect the incoming browser and respond appropriately.