我们将使用DTO在表示层之间来回发送数据。我们有像这样的图层：

• facade
• appService
• domain

并且我们使用推土机来帮助我们将实体转换为dto。但是我现在有两个问题：

1. 从实体到dto，我们可以使用推土机，但是从dto到实体，我们可以使用推土机吗？如果是，如何？
2. 我应该在哪里创建实体？在外观或DTOAssembler中？

例如，我必须注册一本书。这本书的实体外观如下：

Book{
   public Book(BookNumber number,String name){
      //make sure every book has a business number,
      //and the number can't change once the book is created.
      this.bookNumber = number;
      ..
   }
}

我们有一个DTOAssembler：

BookDTOAssembler{

  BookDTO toDAO(bookEntity){
  ...
  }
  BookEntiy fromDTO(book DTO,BookRepository bookRepository){
    //1.Where should i create book entity? 
    //2.Is there any effective way to convert dto to entity in java world?
  }
}

选项1

the BookManagedFacade has a registerBook function:
public registerBook(bookDTO){
   Book book = BookDTOAssembler.fromDTO(book DTO);
}

//Create book in BookDTOAssembler.fromDTO 
public static BookEntiy fromDTO(BookDTO bookDTO,BookRepository bookRepository){
    //book is never registered 
    if (0==bookDTO.getBookID()){
       Book book = new Book(bookRepository.generateNextBookNumber(),bookDTO.getName());
    }else{
       //book is been registed so we get it from Repository
       book = bookRepository.findById(bookDTO.getBookID()); 
    }
    book.setAuthor(bookDTO.getAuthor);
    ...
    return book;
}

选项2

the BookManagedFacade has a registerBook function:
public registerBook(bookDTO){
   Book book = new Book(bookRepository.generateNextBookNumber(),bookDTO.getName());
   book = BookDTOAssembler.fromDTO(book DTO,book);
}

//add another function in BookDTOAssembler.fromDTO 
public static BookEntiy fromDTO(BookDTO bookDTO,Book book){
    book.setAuthor(bookDTO.getAuthor);
    ...
    return book;
}

用一个更好？或者它可以以更好的方式实现..？