Sort List> by a particular key in the map

Question

I have a List whose contents are Map with string keys and values if type String or Long.

[{
  "name": "Abc",
  "id": 1522047548000
},
{
  "name": "Xyz",
  "id": 1522048221000
}]

How can I sort the list

Reformulate your question, I don't understand it. `{name,id}` is the value? And what is the key? — anat0lius, Apr 04 '18 at 07:15
@anat0lius keys are always string type but value is string type for name and long type for id. I want to sort based on id — user8765332, Apr 04 '18 at 07:27

score 3 · Accepted Answer · answered Apr 04 '18 at 07:30

3

Since JAVA 1.8 there is new method in java.util.Comparator called comparing. It returns comparator comparing objects by given key. https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html#comparing-java.util.function.Function-

In this case to compare by names it would look like:

 list.sort(Comparator.comparing(o -> String.valueOf(o.get("name"))));

and to compare by id:

 list.sort(Comparator.comparing(o -> (Long) o.get("id")));

answered Apr 04 '18 at 07:30

A.K.

I guess that sorting with the second comparator destroys the sorting of the first. Doesn't it? – Stefan Steinegger Apr 04 '18 at 07:38
1

@StefanSteinegger yeah, I though question is how to handle each case separately. Id's fields should never be equal. – A.K. Apr 04 '18 at 07:44
Indeed, the question is not clear. – Stefan Steinegger Apr 04 '18 at 10:24

score 1 · Answer 2 · answered Apr 04 '18 at 07:30

Using Java 8, you can dome something like this:

list.stream()
.sorted((a, b) -> a.get("id").compareTo(b.get("id"))
   .thenComparing(a.get("name").compareTo(b.get("name")));

The result is another stream, which you can collect into another list. This doesn't change the original list (which may or may not be useful).

(I'm new to Java, used to use C# the last couple of years, so I may have missed something ...)

2 Answers2