Java 8 Stream API toMap converting to TreeMap

Question

public class Message {
    private int id;
    private User sender;
    private User receiver;
    private String text;   
    private Date senddate;
..
}

Answer 1

If your list is sorted then just use this code for sorted map.

Map> pMonthlyDataMap = list
                .stream().collect(Collectors.groupingBy(WdHour::getName, TreeMap::new, Collectors.toList()));