How does jackson @JsonGetter and @JsonSetter work

Question

I am using jackson 2.10.0 (https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core/2.10.0), following is a simple test case

The Person class is defined as follows, for the setters, I have used the @JsonSetter annotation, and didn't use @JsonGetter for the getters,

import com.fasterxml.jackson.annotation.JsonProperty;

public class Person {
    private String firstName;
    private String lastName;

    public String getFirstName() {
        return firstName;
    }

    @JsonSetter("first_name")
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    @JsonSetter("last_name")
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

}

Then, I create a Person object ,and serialize it as string,

import com.fasterxml.jackson.databind.ObjectMapper;


public class Person3Test2 {
    public static void main(String[] args) throws Exception {
        Person p = new Person();
        p.setFirstName("abc");
        p.setLastName("def");
        String str = new ObjectMapper().writeValueAsString(p);
        System.out.println(str);
    }
}

It will call Person's getters, since it doesn't use @JsonGetter, so I think the output should be

{"firstName":"abc","lastName":"def"}

But, I am surprised to find that it is :

{"first_name":"abc","last_name":"def"}

It looks that the @JsonSetter has affected the getter output, I would ask what's the behavior here.

Answer 1

@JsonSetter will effect during serialization also here is the github issue, if you want different name just use another annotation @JsonGetter on get method

Documentation may be wrong; @JsonSetter does not only affect deserialization. While it can indeed be used for asymmetric naming (similar to @JsonProperty itself with "split" annotation), its scope is not limited. It may have been at some point, but after unification of property handling (in 1.8 or so), there is less separation between various property accessors.

I can review Javadocs to make it clear that none of annotations is strictly limited in scope -- some may only be relevant to one or the other, but none is intentionally separated.