JsonTypeInfo property seems to appear twice in JSON

Hi, I have the following class:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "messageType", visible = true)
@JsonSubTypes({  
  @Type(value = InstanMessage.class, name = "insant_sensor_data_sync"),  
  @Type(value = TimedMessage.class, name = "response_timed_sensor_data_sync") })
public abstract class Message {

@JsonProperty
protected String source;

@JsonProperty
protected String sourceId;

@JsonProperty
protected Long timestamp;

@JsonProperty
protected MessageType messageType;

@JsonProperty
protected String errorMessage;
}

When serializing:

public void serializes_InstantSensorDataSyncMessage() throws Exception {
    InstantSensorDataSyncMessage message = new InstantSensorDataSyncMessage();
    message.setTimestamp(12345L);
    message.setSource("Sun");
    message.setSourceId("1A2B3C");
    System.out.println(asJson(message));
    //assertThat(asJson(message), is(fixture("fixtures/instantSensorDataSync.json")));
}

public static String asJson(Object object) throws IOException {
    return MAPPER.writeValueAsString(object);
}

I got:

{"messageType":"insant_sensor_data_sync","source":"Sun","sourceId":"1A2B3C",
  "timestamp":12345,"messageType":null,"errorMessage":null,"payload"}

Why does messageType appear TWICE?

And is there’s a way NOT to make JsonTypeInfo property always appear first in the JSON?

version:

   <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.2.0</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.2.0</version>
    </dependency>

     <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.2.0</version>
    </dependency>

Thanks so much.

[cowtowncoder]

This is not the correct issue tracker, check out jackson-databind. But as to the problem; no, it should not occur with new versions (2.7.4), although there may be some edge cases with inclusion of EXTERNAL_PROPERTY. If you do observe such behavior, please file a bug at jackson-databind; this repo is for Streaming part (JsonParser, JsonGenerator); object handling is implemented at higher layer.

[tsuda7]

I’ve succeeded by removing the field messageType, but sustaining the annotation as it is.