Problem 1: DownloadService2 APIs should handle null/empty/invalid Arguments.

getCachedResource and updateCachedResource should handle Null, Invalid and empty arguments.

Null or empty URL should throw IAE.
Invalid url spec should throw PatternMatchException (if it is invalid pattern), any valid patern should just match or not.

Null version and empty version should be fine. (null version matches all non versioned resources, emty version may match nothing)

Problem 2: getCachedResource returns incorrect results for versioned resources.
(non null version spec should only match versioned resources, and null version spec should only match non versioned resources)

Problem 3: getUpdateAvailableResources() API is not correct.
(it was only checking versioned resources, and was returning versioned resources for wich there was a later version available that was also cached)