Jackson library: custom mapping of a Java object in a JSON element

Question

I have two class

public class Person { private long id; private String name; private Gender gender; // getter and setter omitted }

and

public class Gender { private long id; private String value; // getter and setter omitted }

By default the JSON mapping with Jackson library of a Person object is:

{ id: 11, name: "myname", gender: { id: 2, value: "F" } }

I'd like to known how to configure Jackson to obtain:

{ id: 11, name: "myname", gender: "F" }

I don't want mapping all the Gender object but only its value property.

Héctor Valls · Accepted Answer · 2015-03-20 09:51:23Z

You can use a custom serializer:

 public class GenderSerializer extends JsonSerializer<Gender> { public GenderSerializer() { } @Override public void serialize(Gender gender, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException { jgen.writeString(gender.getValue()); } }

And in your Person class:

public class Person { private long id; private String name; @JsonSerialize(using = GenderSerializer.class) private Gender gender; }

Muhammad Suleman · Accepted Answer · 2015-03-20 09:42:41Z

you might wanna see this for custom mapping OR if you need a short cut then you can change getter/setter of gender like this

public String getGender(String type){ this.getGender().getValue(); } public void setGender(String value){ Gender gender = new Gender(); gender.setId(2); gender.setValue(value); this.gender = gender; }

further you can also put condition for setting male/female on value= M/F

Thank you! you brought me in the right direction. I found this link: baeldung.com/jackson-custom-serialization that is what I'm looking for.

StaxMan · Accepted Answer · 2015-03-20 19:13:29Z

No need for custom serializer/deserializer if you can modify Gender class. For serialization you can use @JsonValue, for deserialization simple constructor (optionally annotated with @JsonCreator):

public class Gender { @JsonCreator // optional public Gender(String desc) { // handle detection of "M" or "F" } @JsonValue public String asString() { // name doesn't matter if (...) return "M"; return "F"; } }

Alternatively you could use a static factory method instead of constructor; if so, it must be annotated with @JsonCreator. And return type of method annotated with @JsonValue can be anything that Jackson knows how to serialize; here we use String, but Enum, POJO and such are fine as well.

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