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From Christopher Schultz <>
Subject Re: Force recompile of JSP in Tomcat 6
Date Thu, 30 Jul 2009 16:30:46 GMT
Hash: SHA1


On 7/22/2009 5:41 PM, David Wall wrote:
> In a production environment in which JSPs do not change frequently, I'd
> like to reduce the overhead of checking for JSP recompiles, assuming
> that such checks are in fact costly

You might want to look at the Tomcat code to see just how costly these
check are. I suspect they are less costly than you think.

> and instruct Tomcat to recompile a given JSP should it change. In our
> environment, the JSP is written out by our web app.
> I noted the page.jsp?jsp_precompile=true type of option, but this seems
> to have no effect if Tomcat's web.xml sets the JspServlet param
> development=false.

This is probably a security feature. If anyone could force your app
server to recompile your JSPs at will, they could launch a DOS attack by
constantly recompiling all your JSPs. Not only would it eat up CPU time
by performing the actual compilation, but during the recompile, the JSP
is probably locked by the compiling thread so that other requests for
that same JSP are delayed until the recompile is complete. That means
that other users will be affected by the recompile request, and
everything sucks for everyone.

You may need to hack the Tomcat code in order to allow this behavior. If
you choose to do this, consider making it a nice patch and submitting it
as an enhancement.

I can see separate configuration parameters for Tomcat:

development=true|false sets the two below flags to true|false
jspUpToDateCheck=true|false enables checking JSPs for up-to-date status
allowJspPrecompileParam=true|false enables the precompilation

This would allow you to configure Tomcat to allow recompiles, but not to
do up-to-date checks. This makes sense when, for example, your JSPs are
in the WEB-INF directory and cannot be accessed directly.

- -chris
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