import javax.validation.constraints.NotNull;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.Email;
import javax.validation.constraints.Size;

public class User {

    @NotNull(message = "Id must be not null")
    private Long id;

    @Email(message = "Email must be valid")
    @NotEmpty(message = "Email must be not null/empty")
    private String email;

    @Size(min = 8, message = "Password must be of min 8 characters")
    @NotEmpty(message = "Password must be not null/empty")
    private String password;

    // Constructor, Setters and Getters
}