java - Referencing Environment Variables in web.xml

Question

I'm pre-packaging a JSP web-app that relies on some file path settings found within web.xml. These settings are unknown at packaging time, because they reference a path the customer will set when deploying the entire application (of which the web-app is a management interface).

It seems that the easiest way to avoid tokens and file modifications in my installer script, is to ask the user for an install location, set this location as an environment variable (e.g JAVA_HOME), and have web.xml always reference that variable.

Is there a way to reference an environment variable value from within web.xml? Google searches lead to the J2EE method of SETTING environment variables from ejb xml files. This is not what I'm looking for.

Answer 1

You can use Ant-style variable substitution in any of the tomcat xml config files, such as:

<servlet-mapping>
    <servlet-name>mvc-dispatcher</servlet-name>
    <url-pattern>${foo}</url-pattern>
</servlet-mapping>

Where foo is a Java System Property (sysprop).

You can't use OS Environment Variables (envvars) directly, I think...

To use envvars, you can put

set "CATALINA_OPTS=-DsomeJavaSysProp=%SOME_OS_ENVVAR%"

in bin/setenv.bat (or similarly in bin/setenv.sh for *nix). You may need to create that file. Tomcat will run this file when it starts.

As CATALINA_OPTS is an envvar (as opposed to a command line option), it should not be visible by other users on the system (save ancient Unixes), though I haven't tested this.

http://tomcat.apache.org/tomcat-7.0-doc/config/

If you are using Spring, you can create a <context:property-placeholder/> bean and then directly use envvars or sysprops in Spring XML config files (though not web.xml).