**1. 兩個實體類** ```java @Data public class Book { private Integer bookId; } @Data public class BookDto { private Integer bookDtoId; } ``` **2. 異常處理** ```java public class Validator { /** * 該方法只有一個參數 */ public Integer validateId(Integer id) throws ValidationException { if(id == -1){ throw new ValidationException("Invalid value in ID"); } return id; } } ``` **3. 映射接口** ```java /** * 使用uses引入Validator */ @Mapper(uses = {Validator.class}) public interface BookMapper { BookMapper INSTANCE = Mappers.getMapper(BookMapper.class); /** * 當source.bookId的類型與方法validateId(Integer id)的參數類型一致時(必須一致，子類或者基本類對包裝類都不可以)， * 就會調用方法validateId(Integer id)。 * @throws ValidationException throws可有可無 */ @Mapping(source = "source.bookId", target = "bookDtoId") BookDto toDto(Book source) throws ValidationException; } ``` **4. 測試** ```java @Test public void testBookMapper() throws ValidationException { Book book = new Book(); book.setBookId(-1); //拋出異常javax.xml.bind.ValidationException: Invalid value in ID BookDto bookDto = BookMapper.INSTANCE.toDto(book); System.out.println("Book：" + book); System.out.println("BookDto：" + bookDto); } ```