If the file you're trying to open is bundled in your web app, and the code that needs to access the file is executed in a servlet or JSP, you could try starting with getServletContext().getRealPath("somefile"). That should point you in the right direction.
If your wsf file is packaged in a JAR that's in the runtime classpath, you could try someClass.getResourceAsStream("somefile"). This puts the job of finding the file on the ClassLoader.
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