Collect specific key's value from List of Maps List<String,

Question

I am parsing the JSON response from server in Java class. We have utility function to covert JSON to List<Map<String, Object>>. Now I want to collect specific key's value from all objects. For example the JSON I receive is person's data like below

[
 {
   name:'abc',
   city: 'Hyd'
 },
 {
   name:'def',
   city:'NYC'
 }
]

I wanted to try Java8 stream API to get this job done, so here is how i wrote

List<Map<String,Object>> answer = parseJSONReponse(response);
List<Object> collect = answer.stream().map(
            m -> m.entrySet().stream()
                             .filter(e-> e.getKey().equals("name"))
                             .map(e -> e.getValue())
                             .collect(Collectors.toList())
    ).flatMap(l->l.stream()).collect(Collectors.toList());

Please let me know if there is better of writing this stream API.

Tagir Valeev · Accepted Answer · 2015-11-10 08:02:32Z

3

You don't need to collect inside map, then flatMap as you're creating unnecessary intermediate lists. Just use flatMap directly:

List<Object> collect = answer.stream().flatMap(
            m -> m.entrySet().stream()
                             .filter(e-> e.getKey().equals("name"))
                             .map(e -> e.getValue())
    ).collect(Collectors.toList());

answered Nov 10, 2015 at 8:02

Tagir Valeev

101k19 gold badges233 silver badges346 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Sviatlana Over a year ago

Is it possible to get list of another types (Long for example), not Object?

Austin · Accepted Answer · 2015-11-10 07:57:43Z

0

You may consider using a parallel stream.

Note that parallelism is not automatically faster than performing operations serially, although it can be if you have enough data and processor cores. While aggregate operations enable you to more easily implement parallelism, it is still your responsibility to determine if your application is suitable for parallelism. [1]

This can be easily done by exchanging the stream() methods with parallelStream().

[1] Oracle tutorial on stream parallelism.

answered Nov 10, 2015 at 7:57

Austin

8,6553 gold badges34 silver badges40 bronze badges

Collectives™ on Stack Overflow

Collect specific key's value from List of Maps List<String,

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related