https://beam.apache.org/releases/javadoc/2.71.0/org/apache/beam/sdk/values/PCollectionViews.MultimapViewFn.html
PCollectionViews.MultimapViewFn (Apache Beam 2.71.0)
declaration: package: org.apache.beam.sdk.values, class: PCollectionViews, class: MultimapViewFn
apache beam