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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?

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