How to group an object by 'name' using java 8?

Question

I have a DTO with few attributes such as id, name, desc, etc.

It has getters and setters for all its attributes.

I get a Page<MyDto> from the service which I need to group the DTOs based on name attribute.

First, I convert the Page<MyDto> to List<MyDto> by using page.getContent.

I need to convert this List into a Map<String, Object> (not Map<String,String>) by grouping the same names using Java8.

I found some examples but they didn't resolve my problem.

How can I group the MyDto list into a Map?

where the keys are the names (String), and values would be an Array<MyDto> for each name.

For example:

If `List<MyDto>` is : 
[
{"id":1, "name":"albert", "desc":"science"},
{"id":2, "name":"george", "desc":"econ"},
{"id":3, "name":"christ", "desc":"math"},
{"id":4, "name":"george", "desc":"literature"} // george repeats twice
]

The output Map should be:

{

"george":

[
{"id":2, "name":"george", "desc":"econ"},
{"id":4, "name":"george", "desc":"literature"} 
],


"christ":

[
{"id":3, "name":"christ", "desc":"math"}
],


"albert":

[
{"id":1, "name":"albert", "desc":"science"}
]

}

Possible duplicate of https://stackoverflow.com/questions/50411257/java-8-group-by-string — mano_ksp, Oct 07 '19 at 12:10
`Map> map = dtos.stream() .collect(Collectors.groupingBy(MyDto::getName));` — Michał Krzywański, Oct 07 '19 at 12:13

score 5 · Accepted Answer · answered Oct 07 '19 at 12:15

5

Simply use Collectors::groupingBy and pass method reference to MyDto::getName method which will be used as the key for your map:

List<MyDto> dtos = ...
Map<String, List<MyDto>> map = dtos.stream()
            .collect(Collectors.groupingBy(MyDto::getName));

answered Oct 07 '19 at 12:15

Michał Krzywański

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Thanks for quick response. Appreciate the help. Works as expected. – Mohammed Idris Oct 07 '19 at 12:17

How to group an object by 'name' using java 8?

1 Answers1