Deep copy of properties one object to anothe from jackson? - json

Question

I am performing an UPDATE operation such that all the non-null properties set in the incoming POJO shall be copied into another object (same type) and this shall happen for nested properties too.
Ex:
POJO:
public class Person {
private String homePhoneNumber;
private String officePhoneNumber;
private Address address;
public String getHomePhoneNumber() {
return homePhoneNumber;
}
// getter/setters
}
public class Address {
private String street;
private String houseNumber;
public String getStreet() {
return street;
}
// getter/setters
}
// Source
Person sourcePerson = new Person();
sourcePerson.setHomePhone("123");
Address address1 = new Address();
address1.setStreet("Street");
sourcePerson.setAddress(address1);
//Dest person
Person destPerson = new Person();
destPerson.setOfficePhone("456");
destPerson.setHomePhone("123");
Address address2 = new Address();
address2.setStreet("Street2");
address2.setHouseNumber("246");
destPerson.setAddress(address2);
ObjectMapper mapper = new ObjectMapper();
//skip setters for null values
mapper.setDefaultSetterInfo(JsonSetter.Value.forValueNulls(Nulls.SKIP));
Person result = mapper.updateValue(destPerson, sourcePerson);
So I want to copy all non-null properties set in sourcePerson to get copied in destPerson i.e overriding only those properties of destperson which sourcePerson has set, keeping other properties unchanged.
Using
Person result = mapper.updateValue(destPerson, sourcePerson);
is not working for nested properties. It's replacing the whole Address object from source to destination
I searched through jackson to find merge feature in jackson which:
mapper.setDefaultMergeable(true);
However, adding this configuration is making null values in sourcePerson nullify those in destPerson too, which seems strange.
mapper.configOverride(Address.class).setMergeable(true);
This above configuration works for what I wanted. But I have many POJO nested resources, so I don't want specific configurations for each POJO.
Is this can be achieved with jackson in a clean way ?

Answer 1

You can start by enabling error reporting with respect to merging
com.fasterxml.jackson.databind.MapperFeature#IGNORE_MERGE_FOR_UNMERGEABLE
This needs to be false.
It's indeed strange that mapper.configOverride() sort of works, but not mapper.setDefaultMergeable().
I don't see setters in your example. Aren't you using #JsonSetter annotations in Person class by any chance? Then they would override mapper configuration.
In jackson-databind Unit Tests I see they are using mapper.readerForUpdating() rather than mapper.updateValue():
private final ObjectMapper MAPPER = objectMapperBuilder()
// 26-Oct-2016, tatu: Make sure we'll report merge problems by default
.disable(MapperFeature.IGNORE_MERGE_FOR_UNMERGEABLE)
.build();
public void testBeanMergingWithNullDefault() throws Exception
{
// By default `null` should simply overwrite value
ConfigDefault config = MAPPER.readerForUpdating(new ConfigDefault(5, 7))
.readValue(aposToQuotes("{'loc':null}"));
assertNotNull(config);
assertNull(config.loc);
// but it should be possible to override setting to, say, skip
// First: via specific type override
// important! We'll specify for value type to be merged
ObjectMapper mapper = newObjectMapper();
mapper.configOverride(AB.class)
.setSetterInfo(JsonSetter.Value.forValueNulls(Nulls.SKIP));
config = mapper.readerForUpdating(new ConfigDefault(137, -3))
.readValue(aposToQuotes("{'loc':null}"));
assertNotNull(config.loc);
assertEquals(137, config.loc.a);
assertEquals(-3, config.loc.b);
// Second: by global defaults
mapper = newObjectMapper();
mapper.setDefaultSetterInfo(JsonSetter.Value.forValueNulls(Nulls.SKIP));
config = mapper.readerForUpdating(new ConfigDefault(12, 34))
.readValue(aposToQuotes("{'loc':null}"));
assertNotNull(config.loc);
assertEquals(12, config.loc.a);
assertEquals(34, config.loc.b);
}
Also worth trying using com.fasterxml.jackson.annotation.JsonMerge directly in Person class.