Defining JSP (Java Server Pages)
Q
What exactly are Java Server Pages (JSP)?
Can you please give an example how they can be effectively used?
A
Java Server Pages are Sun's very weak and probably doomed attempt at selling a server side include (SSI) solution that competes with Microsoft's Active Server Pages (ASP). :)
That said, let me try to explain.
A Server Side Include is a bit of code that is embedded into an HTML page that, when processed by a web server, will be executed such that the results of the execution replace the SSI code when the web server sends the processed HTML page out to the browser.
Consider a simple, traditional SSI example that could be named
date.shtml....
<HTML>
<HEAD>
<TITLE>Date Test</TITLE>
</HEAD>
<BODY>
The date is:
<!--#exec cmd = "date" -->
</BODY>
</HTML>
When a web browser requests date.shtml, the web server will get the file and notice that it has a special <!--#exec..> tag.
When it sees the tag, it will say to itself, "hey, I have to do something with this.
I have to execute a command and insert the results of the command into the page."
In the case above, the web server will execute the date command and then send out the modified HTML page to the browser which might now look like the following:
<HTML>
<HEAD>
<TITLE>Date Test</TITLE>
</HEAD>
<BODY>
The date is:
12-AUG-1999 13:31:44 BST
</BODY>
</HTML>
Notice that the web browser would never have seen <!--#exec cmd = "date" --> because the web server did the replacement on the server-side (hence the name, Server-Side Includes).
Well, traditional SSI kinda sucks because you are limited to the commands provided by the operating system on which the web server runs... in the case above, we rely on the date command provided by UNIX (and fortunately DOS as well).
This however, can be a very limited set of commands and may not be cross-platform.
As a result, we saw the proliferation of proprietary server side include solutions such as Cold Fusion or Net Objects several years ago.
These companies provided a much larger set of tags, but they were still limited to the tags implemented by the vendor.
I think Cold Fusion has like 70 commands these days, quite impressive and full-featured, but... still only 70 commands.
What was needed was a way to write fully executable code that could be embedded in HTML and executed at the web server.
Microsoft released ASP which allowed you to use VBScript to access MS COM objects.
Sun released JSP which allowed you to use Java to define executable code that is run by the web server before a page is sent out to the browser.
ASP and JSP each require a web server that knows how to do the work and both are somewhat platform dependent.
To tell you the truth, I don't like either all that much.
I find embedded Perl/CGI (a la MOD_PERL or VELOCOGEN) to be a more maintainable solution for server side development.
But hey, each to their own :)
As it so happens, I am writing a book on ASP at the moment, so I am not saying that it is useless to learn, just that I might choose another solution if my job depended on it and I would not be shocked if ASP and JSP went the way of SSI.
Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com
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