Jackson json deserialization with integer(primitive data) as the key into POJO

Question

In one of the APIs, I'm receiving this as the Json response: You can check this response sample here Sample Json resopnse

{
    "histogram" : {
        "1" : "12",
        "2" : "20",
        "3" : "50",
        "4" : "90",
        "5" : "10"
     }
}

In order to deserialize this response, How does one even write the POJO classes ?

In java, since we are not allowed to have numbers as the variable names, how does one convert this into a POJO?

For instance, how can I create something like this:

public class MyPOJO {
    Histogram histogram;

    public static class Histogram {
        // I KNOW THIS IS WRONG !!
        String 1;
        String 2;
        String 3;
        String 4;
    }
}

Does jackson provide any annotations to handle these?

Answer 1

For this JSON:

{
  "histogram": {
    "1": "12",
    "2": "20",
    "3": "50",
    "4": "90",
    "5": "10"
  }
}

You can consider one of the the following approaches:

Using a Map<String, String> to hold the values

The histogram can the parsed into a Map<String, String>:

public class HistogramWrapper {

    @JsonProperty("histogram")
    private Map<String, String> histogram;

    // Getters and setters omitted
}

Using attributes annotated with @JsonProperty

Alternatively, you can define a Histogram class and annotate its attributes with @JsonProperty:

public class HistogramWrapper {

    @JsonProperty("histogram")
    private Histogram histogram;

    // Getters and setters omitted
}

@JsonIgnoreProperties(ignoreUnknown = true)
public class Histogram {

    @JsonProperty("1")
    private String _1;

    @JsonProperty("2")
    private String _2;

    @JsonProperty("3")
    private String _3;

    @JsonProperty("4")
    private String _4;

    @JsonProperty("5")
    private String _5;

    // Getters and setters omitted
}

Parsing the JSON

To parse the JSON, do as following:

ObjectMapper mapper = new ObjectMapper();
String json = "{\"histogram\":{\"1\":\"12\",\"2\":\"20\","
            + "\"3\":\"50\",\"4\":\"90\",\"5\":\"10\"}}";

HistogramWrapper wrapper = mapper.readValue(json, HistogramWrapper.class);