Java (at least 5 and 6, java 7 Paths solved most) has a problem with UNC and URI. Eclipse team wrapped it up here : http://wiki.eclipse.org/Eclipse/UNC_Paths
From java.io.File javadocs, the UNC prefix is "////", and java.net.URI handles file:////host/path (four slashes).
More details on why this happens and possible problems it causes in other URI and URL methods can be found in the list of bugs at the end of the link given above.
Using these informations, Eclipse team developed org.eclipse.core.runtime.URIUtil class, which source code can probably help out when dealing with UNC paths.