Here is an example of using the MergingSettableBeanProperty class from the com.fasterxml.jackson.databind package in the Jackson library to handle a merging property:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.introspect.AnnotatedMember;
import com.fasterxml.jackson.databind.introspect.BeanPropertyDefinition;
import com.fasterxml.jackson.databind.introspect.POJOPropertyBuilder;
import com.fasterxml.jackson.databind.introspect.SettableBeanProperty;
import com.fasterxml.jackson.databind.module.SimpleModule;

public class MergingSettableBeanPropertyExample {
    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);

        SimpleModule module = new SimpleModule();
        module.addDeserializer(MyObject.class, new MyObjectDeserializer());
        mapper.registerModule(module);

        MyObject obj = new MyObject();
        obj.setMyField("myValue");
        obj.setMyField2("myValue2");

        String json = mapper.writeValueAsString(obj);
        System.out.println(json);

        MyObject obj2 = mapper.readValue(json, MyObject.class);
        System.out.println(obj2.getMyField());
        System.out.println(obj2.getMyField2());
    }
}

class MyObject {
    private String myField;
    private String myField2;

    public String getMyField() {
        return myField;
    }

    public void setMyField(String myField) {
        this.myField = myField;
    }

    public String getMyField2() {
        return myField2;
    }

    public void setMyField2(String myField2) {
        this.myField2 = myField2;
    }
}

class MyObjectDeserializer extends JsonDeserializer<MyObject> {
    @Override
    public MyObject deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        MyObject obj = new MyObject();
        JsonNode node = parser.getCodec().readTree(parser);
        obj.setMyField(node.get("my_field").asText());
        obj.setMyField2(node.get("my_field_2").asText());
        return obj;
    }
}

class MyPOJOPropertyBuilder extends POJOPropertyBuilder {
    @Override
    protected SettableBeanProperty _construct(AnnotatedMember member) {
        SettableBeanProperty property = super._construct(member);
        if (property != null) {
            return new MergingSettableBeanProperty(property);
        }
        return property;
    }
}