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From Konstantin Kolinko <knst.koli...@gmail.com>
Subject Re: NoSuchMethodError loading class in webapp from common class loader
Date Fri, 03 May 2013 14:16:03 GMT
2013/5/3 Bryan Baugher <bjbq4d@gmail.com>:
> Hi,
>
> I am running Tomcat 7.0.28 on RHEL 6.2 with a single web app. The web app
> in question uses reflection to load some implementations of our classes
> (kind of like a service loader) knowing the class name. I am trying to add
> additional implementations by dropping them in the tomcat's lib directory
> but I keep seeing NoSuchMethodError for the constructor to the class.
>
> I know the constructor is there because if I move the jar into the web
> app's lib directory (webapp/[WEB_APP]/WEB_INF/lib) everything works.
>
> I figure this must be some class loader issue I am not understanding but
> these docs[1][2] don't seem to indicate there should be any issue.
>
> -Bryan
>
> [1] - http://tomcat.apache.org/tomcat-7.0-doc/class-loader-howto.html
>
> [2] - http://download.oracle.com/otndocs/jcp/servlet-2.4-fr-spec-oth-JSpec/

Using the common classloader is somewhat tricky,  because the "Webapp
classloader has priority" rule imposed by servlet spec does mess up
things, as explained in [1].

Your description does not have enough details, nor source code, nor
stacktaces, and with such I would guess that you have the following:

a) Your constructor has some arguments
b) The classes mentioned as argument types in that method can be
loaded both from common class loader and from webapp classloader. (If
they cannot be loaded from the former, you are also in trouble).
c) Classes loaded from different classloaders are considered different
by JVM (even if they have the same name and bytecode),.
You are asking for a method specifying its arguments by using classes
loaded by webapp classloader and they do not match the ones loaded by
common classloader

Just a guess.

Best regards,
Konstantin Kolinko

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