Java-Jackson JSON库和ObjectMapper.readValue

Question

I have the following json data (patients.json):

{ 
    "A" : { 
        "name" : "Tom", 
        "age" : 12 
    }, 
    "B" : { 
        "name" : "Jim", 
        "age" : 54 
    } 
}

Using the Jackson JSON library, how can I get something like the following:

HashMap<String, ???> patients = objectMapper.readValue(new File("patients.json"), ???);

String Aname = patients.get("A").get("name");
int Aname = patients.get("A").get("age");

Answer 1

Deserialize your JSON into Jackson's JSON Object type, ObjectNode . You can then traverse it as you see fit.

For example

ObjectNode patients = objectMapper.readValue(new File("test.json"), ObjectNode.class);
// you can check if it is actually an ObjectNode with JsonNode#isObject()
ObjectNode nodeA = (ObjectNode)patients.get("A");

String name = nodeA.get("name").asText();
int age = (int) nodeA.get("age").asLong();

Note that the methods asXyz() return default values if the target node cannot be converted to that type. You can check with the corresponding isXyz() methods before invoking them.

Answer 2

You could create a class to map your patients to;

private static class Patient {
    @JsonProperty("name")
    private String name;
    @JsonProperty("age")
    private int age;

    public Patient() { }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Then read your json into it via jackson

HashMap<String, Patient> patients = objectMapper.readValue(new File("patients.json"), new TypeReference<HashMap<String,Patient>>() {});
Patient patientA = patients.get("A");
String patientAName = patientA.getName();
int pateintAAge = patientA.getAge();