How to convert List into Map>, with Java 8 streams and custom List and Map suppliers?

Question

It\'s easy to convert List into Map>. For example:

public Map> ge         


        

Answer 1

You could use this solution, if you plan to create a map similar to Map>:

Map> ds= requestList.stream().collect(
    Collectors.groupingBy(TagRequest::getProperty_1, HashMap::new, 
    Collectors.mapping(TagRequest::getProperty_2, Collectors.toList()))
);

If you plan to create a map similar to Map>, you may use:

Map> ds= requestList.stream().collect(
    Collectors.groupingBy(TagRequest::getProperty_1, HashMap::new, 
    Collectors.mapping(TagRequest::getProperty_2, Collectors.toSet()))
);