How to do map inversion with Guava with non-unique values?

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You can do this:

Map<K, V> map = ...;
ListMultimap<V, K> inverse = Multimaps.invertFrom(Multimaps.forMap(map), 
    ArrayListMultimap.<V,K>create());

Do note that pretty much any time you write Map<K, List<V>> or Map<K, Set<V>> or some such, a ListMultimap<K, V> or SetMultimap<K, V> is what you really want.

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