Spring Boot - How to create a custom serialization for " java.time.LocalDateTime" class

I have developed a rest service with Spring Boot. I want return a json response with the birthday of the user as milliseconds. How to serialize a java.time.LocalDateTime object to milliseconds ?

My model class:

    @Entity(name = "users")
    public class User implements Serializable {

        @Id
        @GeneratedValue
        @Column(name = "user_id")
        private Long id;

        @Column(name = "first_name")
        private String firstName;

        @Column(name = "last_name")
        private String lastName;



        @Column(name = "date_of_birth")
        private LocalDateTime dateOfBirth;  

 . . .

    }

current response:

{
 . . .
"dateOfBirth":[2018,7,25,7,0],
. . . 
}

preferred response:

{
 . . .
"dateOfBirth": 1532786354419,
. . . 
}