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SingleToMultiValueMapAdapter and MultiToSingleValueMapAdapter expose adapted entry values (singleton lists and first values, respectively) through entrySet() and equals(), but delegated hashCode() to the target map whose entry values differ. As a consequence, an adapter could be equal to a regular map while having a different hash code. This commit computes hashCode() from the adapted entries, as defined by the Map.hashCode() contract. Closes spring-projectsgh-37469 Signed-off-by: lejuho <zedd1324@gmail.com>
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Overview
Fixes #37469.
SingleToMultiValueMapAdapter(returned byMultiValueMap.fromSingleValue()) exposes singleton-list values throughentrySet()and compares those inequals(), buthashCode()delegated to the underlying single-value map. As a result, the adapter could be equal to a regularMap<K, List<V>>with the same entries while reporting a different hash code, breaking theMap.hashCode()contract and lookups in hash-based collections.The symmetric
MultiToSingleValueMapAdapter(returned byMultiValueMap.asSingleValueMap()) has the same problem in the opposite direction: it exposes the first value per key, buthashCode()delegated to the underlying multi-value map.Changes
SingleToMultiValueMapAdapter.hashCode()now sums the hash codes of its adapted entries.MultiToSingleValueMapAdapter.hashCode()now sumshash(key) ^ hash(firstValue)for each entry, using the same first-value adaptation asget(), so keys mapped to an empty list contribute like anullvalue instead of failing.Testing
SingleToMultiValueMapAdapterTests: equal/hashCode/HashSetlookup against a regular map, including anullvalue.MultiValueMapTests:asSingleValueMap()equal/hashCode/HashSetlookup against a regular map, and hashCode with an empty value list, for all maps under test.Result: BUILD SUCCESSFUL. The new tests fail without the fix (12 failures).