JSP is great for hosted environments (ie: shared development
environments, ISP's and large companies) where many different kinds of
people are putting pages on the servlet engine may not know much more
than HTML. Part of the reason it is so nice is that with the HTML'ish
syntax JSP is so easy to learn!
However, if one really looks at that statement in more detail it becomes
apparent that this might not be such a good thing. Consider the
following snippet of Java code:
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Hashtable strings = new Hashtable();
int i=0;
while (true)
{
strings.put ("dead"+i, new StringBuffer(999999));
}
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What this does is that it creates a Hashtable and then goes into a tight
loop. At the same time, it creates a new StringBuffer object that has a
default size of 999999. Therefore, creating what amounts to a memory
leak in the Java Virtual Machine (which all of the hosted applications
share).
As soon as all of the memory is gone, every single hosted application
will start to receive the dreaded "OutOfMemoryError". The reason why
this is so bad has already been explained earlier. Essentially JSP pages
themselves cannot catch OOME errors and the entire servlet engine will
suddenly become useless, all because of what amounts to a few lines of
badly written Java code.
Remember, it is a bad idea to put Java code into a JSP page. Tell that
to the 14 year old kid who is being hosted on your ISP's servlet engine
who really does not care that others might be affected by these actions.
Velocity does not have this issue because there is no while loop in the
Velocity Template Language. The only looping construct in Velocity is a
#foreach and that loops over an array that has a finite amount of
elements. It is also possible to disable the #foreach directive and
limit the amount of recursive nesting that is possible. Note: it is
possible to modify Velocity to add a #while directive to the template
language.
There is nothing in JSP or Struts that prevents people from embedding
Java code in the page.
You make the decision.
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