関連ワード:  java stream map list of objects    java stream map list of objects to hashmap    java 8 map to list of objects    java stream create map from list of objects    java stream convert map to list of objects    java stream map list of objects to list of strings    java 8 create map from list of objects    java 8 convert map to list of objects    java stream map list to single object    java stream map list of objects to another list of objects