Hi all,
when deploying two applications build from the riot skeleton within
the same Tomcat servlet container, you get an
IllegalStateException: Web app root system property already set to
different value: 'webapp.root' = [/Users/joe/
Workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/webapps/
webapp-A/] instead of [/Users/joe/Workspace/.metadata/.plugins/
org.eclipse.wst.server.core/tmp0/webapps/webapp-B/] - Choose unique
values for the 'webAppRootKey' context-param in your web.xml files!
I will try to explain where this comes from and how to circumvent it,
but first the quick fix for the impatient reader: Place a context
parameter named 'webAppRootKey' in every project's web.xml and assign
a value to it, that is unique for every of your projects like the
project name itself.
The webAppRootKey context parameter is introduced by Spring. Along
with the WebAppRootListener it allows exposing the web applications
root directory as a system property. The value of the context
parameter 'webAppRootKey' names the system property to use. If the
context parameter 'webAppRootKey' is not set in the application's
web.xml, Spring chooses the default value 'app.root'. While some
servlet containers like Resin do isolate each web application's
system properties, others like Tomcat do not. And that's what the
former mentioned IllegalStateException is telling us: The system
property 'app.root' already contains the root directory of the first
web application when Spring tries to assign the root directoty of the
second application to it.
Ok, that's the background information. A deeper look into the web.xml
tells us, that there ist no WebAppRootListener configured. Why does
this initialisation take place anyway? The stack trace from the
exception reveals the culprit: The Log4jConfigListener also tries to
set the webAppRootKey, because this is an interesting mechanism for
the Spring/Log4j integration. It allows log and config file locations
relative to the web applications root directory. The
Log4jConfigListener supports three init parameters at the servlet
context level: 'log4jConifgLocation', 'log4jRefreshInterval' and
'log4jExposeWebAppRoot'. See JavaDocs for more informations.
But, none of these parameters are set in the riot project skeleton's
web.xml and none of the Log4jWebConfigureres features are used by the
riot project skeleton. As long as you do stay with default log4j
setup, the Log4jConfigListener is superflous.
At the end there are three possible solutions for the initial problem:
(1) Provide any of your applications with a unique 'webAppRootKey'.
(2) Set the servlet context parameter 'log4jExposeWebAppRoot' to
'false'. This eliminates the use of log file locations relative to
the web application's root directory but still allows a log4j config
location outside the classpath.
(3) Remove the 'Log4jConfigListener' from your application's web.xml.
What do you think is the best solution and should be incorporated
into the riot skeleton project?
不知道各位怎么样，反正我遇到这个问题呢，主要是新item的web.xml里面多了log4j的listener，希望对遇到相同问题的童鞋有所帮助！！不喜勿喷！