関連ワード:  java 8 list to map    java 8 list to map group by    java 8 list to map example    java 8 list to map with multiple values    java 8 list to map group by multiple fields    java 8 list to map based on condition    java 8 list to map ignore duplicate    java 8 list to map remove duplicates    java 8 list to map stream    java 8 list to map with duplicate keys