Added NoCachingLookupFactory

[jc89]

NoCachingLookupFactory: LookupFactory not using Lookup cache (Setting it to null)

[jc89]

@pettermahlen i think this could be useful when you are not interested in using the ttl declared in the records

I added a few test cases, will update the README later

[pettermahlen]

@jc89 looks good, the only thing left I think should be done is something like having the DnsSrvResolverBuilder throw an IllegalStateException if the user tries to set both useLookupCache and cacheLookups to true.

[jc89]

@pettermahlen by default, previously it was basically using the Lookup cache always. In order to keep that behaviour, i set the default value for that caching flag in the lookup to true. If we add this validation, it could suddenly start breaking the build when people only update the version. We could:

• Accept this fact and go ahead and add the validation. Would also need to update the usage examples
• Refactor the two flags into an enum, picking up the caching strategy to use (Like, cachingSchema(someSchema) where the schemas could be none, caching resolutions, caching lookups.

[pettermahlen]

Sorry, I was confused. The problematic case is useLookupCache = false && cacheLookups = true. In this case, the useLookupCache configuration will be silently ignored, which I think would be confusing to the user.

Reading the above text, it's quite obvious that these two parameter names are very similar, and it's not clear what the difference between them really is. We should explain that somehow. Is it correct to say that:

• useLookupCache determines whether or not a given Lookup instance should cache its previous results, and
• cacheLookups determines whether a given thread should reuse Lookup instances for a given query between invocations.