Setting Runtime Property in Web Application

I am planning to use JGroups开发者_开发百科 in a web application.

JGroups by default uses IPv6 for multicasting of messages. JGroups can only be configured to use IPv4 by setting a property like the following (see docs)

-Djava.net.preferIPv4Stack=true

This does not work if set in code. What are my options when running a war file in an application server for setting this property, specifically tomcat and glassfish?

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It seems to me the following route might work. First, add a ServletContextListener to your web app and register it in web.xml before JGroups is loaded.

Now, inside the contextInitialized method, use System.setProperty("java.net.preferIPv4Stack", "true").

Disclaimer: not tested.

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Unless you have a specific reason to put this in code, it can easily be configured for Tomcat by setting the environment variable CATALINA_OPTS (to -Djava.net.preferIPv4Stack=true). I think the proper place to do this is to create ${CATALINA_HOME}/bin/setenv.sh and place the setting in there.