未知字段的Jackson json arraylist

Question

I have a JSON string like this:

{
    "123": {
        "hi": {
            "name": "John",
            "phone": "12345"
        }
    },
    "124": {
        "hi": {
            "name": "James",
            "phone": "12345"
        }
    },
    "125": {
        "hi": {
            "name": "Leo",
            "phone": "12347"
        }
    }
}

The JSON is ordered externally: 123, 124, 125 I just want to get the value of the last field ("125" : {...} ) but I don't know its name, is auto-generated. What's the best way?

I'm trying mapping to an arrayList of JsonNodes , but I don't find the right way.

Answer 1

You can also do it using @JsonAnySetter annotation. Please, see below example. POJO class:

class Node {

    private Integer key = Integer.MIN_VALUE;
    private JsonNode value;

    @JsonAnySetter
    public void set(String newKey, JsonNode newValue) {
        if (Integer.valueOf(newKey) > key) {
            value = newValue;
        }
    }

    public JsonNode getValue() {
        return value;
    }

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

Example usage:

ObjectMapper mapper = new ObjectMapper();
Node node = mapper.readValue(json), Node.class);
System.out.println(node);

Prints:

{"hi":{"name":"Leo","phone":"12347"}}

Answer 2

I did it putting the JSON string in a JsonNode, data and mapping to a NavigableMap.

NavigableMap<String, JsonNode> updates = mapper.readValue(data.traverse(), new TypeReference<TreeMap<String, JsonNode>>() {});
Entry<String, JsonNode> lastEntry = updates.lastEntry();
String lastUpdate = lastEntry.getValue().toString();