Java - Deserialization Annotations with fasterXML and Jackson

Question

Here's a simple example of working code to deserialize a string list using fasterXML/Jackson in the constructor:

private List<String> xyz;

@JsonCreator
public FooBar(@JsonProperty("blargs") List<String> xyz)
{
    this.xyz = xyz
}

So, the above code works fine, and it's my understanding of how to use Jackson to deserialize a json string like such: {"blargs":["one","two","three"]}

So, here's my question:

My input json now looks like such:

{"blargs":[
    {"fooId":888,"barVal":"tacos"},
    {"fooId":222,"barVal":"hamburgers"},
    {"fooId":444,"barVal":"underpants"}
  ]
}

...but I can't figure out how to annotate the constructor to deserialize the incoming json into my map where fooId and barVal become the key/value pairs.

Here's what I'm working with so far

private Map<Integer, String> xyz;

@JsonCreator
public FooBar(@JsonProperty("blargs") ????? Map<Integer, String> xyz)
{
    this.xyz = xyz
}

note: I am calling the constructors shown above as such:

ObjectMapper mapper = new ObjectMapper();
FooBar fooBar = mapper.readValue(jsonValue, FooBar.class);

Answer 1

You can write a custom deserializer:

public static class XyzDeserializer extends JsonDeserializer<Map<Integer, String>> {

    @Override
    public Map<Integer, String> deserialize(JsonParser p,
                                            DeserializationContext ctxt) throws IOException {
        JsonNode rootNode = p.getCodec().readTree(p);
        Map<Integer, String> map = new HashMap<>();
        rootNode.forEach(n -> map.put(
                n.get("fooId").intValue(),
                n.get("barVal").asText()
        ));
        return map;
    }
}

And use it in this way:

@JsonCreator
public FooBar(
        @JsonProperty("blargs")
        @JsonDeserialize(using = XyzDeserializer.class) Map<Integer, String> xyz) {
    this.xyz = xyz;
}