Split a JsonArray

Question

I'd like to split a JsonArray from the package javax.json and I can't find a convenient method that does the job. I looked through the documentation and I can only think of iterating over the JsonArray and adding the items manually using the JsonArrayBuilder.

Is there a more convenient way to split the array?

Please note that I can't use another package (such as google.gson).

Thanks in advance.

edit: I have a JsonArray of size N and I'd like to split it by indexes from and to and save the result as a JsonArray.

something like this:

JsonArray array1 = getJsonArrayOfSize(10);
JsonArray array2 = array1.split(2,5);

Convert your JsonArray to List and then split each items in List. — Vishwa Ratna
– Vishwa Ratna, Commented Dec 30, 2019 at 9:56

Michał Ziober · Accepted Answer · 2019-12-30 11:21:18Z

You can use subList method:

import javax.json.Json;
import javax.json.JsonArray;
import javax.json.JsonArrayBuilder;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class JsonApp {

    public static void main(String[] args) {
        List<Integer> ints = IntStream.range(1, 10).boxed().collect(Collectors.toList());
        JsonArrayExt array = new JsonArrayExt(ints);

        JsonArray array1 = array.subList(2, 5);
        System.out.println(array);
        System.out.println(array1);
    }
}

class JsonArrayExt {
    private final JsonArray array;

    public JsonArrayExt(List<Integer> ints) {
        this(Json.createArrayBuilder(ints).build());
    }

    public JsonArrayExt(JsonArray array) {
        this.array = Objects.requireNonNull(array);
    }

    public JsonArray subList(int fromIndex, int toIndex) {
        JsonArrayBuilder builder = Json.createArrayBuilder();
        array.subList(fromIndex, toIndex).forEach(builder::add);

        return builder.build();
    }

    @Override
    public String toString() {
        return array.toString();
    }
}

Above code prints:

[1,2,3,4,5,6,7,8,9]
[3,4,5]

Amit Kumar Lal · Accepted Answer · 2019-12-30 11:13:29Z

2

with Gson

List<MyModel> myModelList = gson.fromJson(jsonArray.toString(), listType);

Updated

you can create a utility for the same if you only want to use javax.json package. Below is the complete sample code with only javax.json.* package.

import java.io.StringReader; import java.util.List;

import javax.json.Json; import javax.json.JsonArray; import javax.json.JsonObject; import javax.json.JsonReader; import javax.json.JsonValue;

public class Converter {
    public static void main(String[] args) {
        String str =     "{\r\n" + 
                         "\"name\":\"John\",\r\n" + 
                         "\"age\":30,\r\n" + 
                         "\"cars\":[ \"Ford\", \"BMW\", \"Fiat\" ]\r\n" + 
                         "}";

        JsonReader reader = Json.createReader(new StringReader(str));
        JsonObject object = reader.readObject();
        JsonArray array = object.getJsonArray("cars");
        System.out.println(getJsonArrayFromIndex(1, 2, array));
        System.out.println(getJsonArrayFromIndex(0, 2, array));
        System.out.println(getJsonArrayFromIndex(0, 1, array));
    }

    public static List<JsonValue> getJsonArrayFromIndex(int start, int end, JsonArray array) {
        return array.subList(start, end);       
    }
}

output

[BMW]
[Ford, BMW]
[Ford]

edited Dec 30, 2019 at 11:13

answered Dec 30, 2019 at 10:09

Amit Kumar Lal

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1 Comment

Vishwa Ratna Over a year ago

Please note that I can't use another package (such as google.gson). DId you read that?

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