I apologize, but there is no such class called JsonKey in the Apache Commons IO library. JsonKey is not a class from Apache Commons IO. It's probably a custom class.

You can use @JsonProperty annotation from Jackson library to specify the name of the key when serializing an object to JSON:

import com.fasterxml.jackson.annotation.JsonProperty;

public class MyClass {

    @JsonProperty("my_field")
    private String field;

    public MyClass(String field) {
        this.field = field;
    }

    public String getField() {
        return field;
    }
}

In this example, the field is annotated with @JsonProperty("my_field") which will be used as the key when serializing the MyClass object to JSON.

Make sure that you are using jackson as serializer.