How to get length of json object array?

Question

I wrote a restService and my service returns me two different result :

{"Response": {
"cars":[
{"id":"1",
"name":"test1"},
{"id":"2",
"name":"test2"},
{"id":"3",
"name":"test3"}
],
"books":[
{"id":"4",
"name":"example1"},
{"id":"5",
"name":"example2"},
{"id":"6",
"name":"example3"}    
]}}

and second ,

{"Response": {
"cars":{
"id":"1",
"name":"test1"},
"books":{
"id":"4",
"name":"example1"}
}}

I will show the result in my dataTable with javascript. For this, I want to learn length of cars or books. If result >1 I can get length, cars or books act as an array,but if result <1 it acts as an object and I can't get length of objects .In my restService, I defined as an ArrayList the cars and books. Is there any solutions for this ? Thanks for responses.

var len = Array.isArray(Response.cars) ? Response.cars.length : 1 — adeneo
– adeneo, Commented Sep 17, 2014 at 15:15
@adeneo I tried this but when I write Response.cars[i] in a for loop, it can't show to me because of it is a object — Ozkan Ciftci
– Ozkan Ciftci, Commented Sep 17, 2014 at 15:44
Look closely, Array.isArray(Response.cars) <- that's how you know it's an array, if that fails, it's not an array, so you don't do a for loop at all. — adeneo
– adeneo, Commented Sep 17, 2014 at 15:52
Thanks @adeneo, yes you are right , it is a solution to learn it's an array or not,I'm sure it is an array, and I want to do a for loop at all. — Ozkan Ciftci
– Ozkan Ciftci, Commented Sep 17, 2014 at 16:21

folkol · Accepted Answer · 2014-09-17 15:16:08Z

3

The problem lies with your REST Service, make it always return a list of cars, even if there is only one car.

answered Sep 17, 2014 at 15:16

folkol

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7 Comments

jsuddsjr Over a year ago

I've also seen lots of examples of returning a "count" variable with your JSON, just to make it easier to work with.

folkol Over a year ago

Yes, that is unfortunately pretty common. My personal opinion is that metadata like that does not belong in a JSON response. Either use an array for that data, or pass the metadata in a separate structure. (Or use XML and pass the count as an attribute, if you want to be able to read it without parsing the full structure)

Ozkan Ciftci Over a year ago

@folkol but my REST Service returns list of Response, not list of cars ?

folkol Over a year ago

Yes, but I was talking about the value called "cars", make sure that it is always a list, even when there is only one car (Or no cars for that matter).

Ozkan Ciftci Over a year ago

List<Car> cars= new ArrayList<Car>(); cars= result.getSelectedCars(); Response.setCars(cars); I think you want to say like this , but it did not work

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