How to parse into list of pairs from json with FasterXML

You should write a custom serializer/deserializer for the Pair class.

Here is an example:

public class JacksonPair {    static final String JSON = "{ \"x\" : 1,  \n" +            "  \"y\" : 2, \n" +            "  \"the_list\" : [[1,2],[3,4]]}";    static class Demo {        public int x;        public int y;        public List<Pair<Integer, Integer>> the_list;        @Override        public String toString() {            return "Demo{" +                    "x=" + x +                    ", y=" + y +                    ", the_list=" + the_list +                    '}';        }    }    static class PairSerializer extends JsonSerializer<Pair> {        @Override        public void serialize(                Pair pair,                JsonGenerator jsonGenerator,                SerializerProvider serializerProvider) throws IOException {            jsonGenerator.writeStartArray(2);            jsonGenerator.writeObject(pair.getLeft());            jsonGenerator.writeObject(pair.getRight());            jsonGenerator.writeEndArray();        }    }    static class PairDeserializer extends JsonDeserializer<Pair> {        @Override        public Pair deserialize(                JsonParser jsonParser,                DeserializationContext deserializationContext) throws IOException {            final Object[] array = jsonParser.readValueAs(Object[].class);            return Pair.of(array[0], array[1]);        }    }    public static void main(String[] args) throws IOException {        final SimpleModule module = new SimpleModule();        module.addSerializer(Pair.class, new PairSerializer());        module.addDeserializer(Pair.class, new PairDeserializer());        final ObjectMapper objectMapper = new ObjectMapper();        objectMapper.registerModule(module);        final Demo demo = objectMapper.readValue(JSON, Demo.class);        System.out.println("toString: " + demo);        System.out.println("Input: " + JSON);        System.out.println("Output: " + objectMapper.writeValueAsString(demo));    }}

Output:

toString: Demo{x=1, y=2, the_list=[(1,2), (3,4)]}Input: { "x" : 1,    "y" : 2,   "the_list" : [[1,2],[3,4]]}Output: {"x":1,"y":2,"the_list":[[1,2],[3,4]]}