You cannot do that without violating the
J2EE standard.
According to the spec, a WAR is a JAR-format archive file. Note the
word "file", not "directory", not "files". In a WAR file, the WEB-INF/classes "directory" is just a path within the WAR and cannot be accessed natively by the host OS filesystems.
Within a WAR, you can obtain access by using the HttpServletRequest getResource() and getResourceAsStream() methods. They don't return filesystem paths, but they do return objects that the webapp can use to read WAR resources such as property files.
Some webapp servers support the concept of optionally "exploding" a WAR. In that case, the WAR is unzipped, and there will be a physical WEB-INF/classes directory on the filesystem. However, exploded WARs are not part of the J2EE standard and any webapp that depends on a WAR having been exploded will not be standards-compliant.
Under absolutely NO circumstances should you ever WRITE to a location within a WAR. Even if the server permits it, you WILL experience pain.