Avoid duplicate field generated by JsonTypeInfo in Jackson

Question

I'm using Jackson Databind 2.7.2 and I have the following annotations on an interface:

@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.PROPERTY,
        property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value = SubType1.class, name = "SubType1"),
        @JsonSubTypes.Type(value = SubType2.class, name = "SubType2")})
public interface Common {
     String getType();
}

getType is overridden (implemented) in SubType1 and SubType2. The problem is that when an instance of SubType1 or SubType2 is mapped to JSON it contain two fields called type with the same value:

{
  "type" : "SubType1",
  ... // Other properties
  "type" : "SubType1"
}

How can I prevent jackson from rendering duplicate fields?

user_19999230 · Answer

If anyone happens to have this error, it can be solved by changing the default include property

@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.EXISTING_PROPERTY,
    visible = true,
    property = "type"
)

By default Jackson uses JsonTypeInfo.As.PROPERTY

Reference: https://fasterxml.github.io/jackson-annotations/javadoc/2.4/com/fasterxml/jackson/annotation/JsonTypeInfo.As.html

Avoid duplicate field generated by JsonTypeInfo in Jackson

2 Answers