Best practice to convert list object to list objectDto java

Question

I have done do get all my data and convert from object to objectDto. But, somehow, I feel like my code is not good yet. Here I need your help, I need any reference/advice to make my code better (in performance). Here is my working code:

    @Override
    public List<BookDto> findAll() throws Exception {
        try {
            List<Book> list = bookDao.findAll();
            List<BookDto> listDto = new ArrayList<>();

            for (Book book : list) {
                BookDto bookDto = new BookDto();
                Set<AuthorDto> listAuthorDto = new HashSet<AuthorDto>();
                Set<Author> dataAuthor = new HashSet<Author>();
                book.getAuthor().iterator().forEachRemaining(dataAuthor::add);

                BeanUtils.copyProperties(book, bookDto, "author", "category");
                bookDto.setCategory(book.getCategory().getCategory());

                for (Author author : dataAuthor) {
                    AuthorDto authorDto = new AuthorDto();
                    BeanUtils.copyProperties(author, authorDto);
                    listAuthorDto.add(authorDto);
                }

                bookDto.setAuthor(listAuthorDto);
                listDto.add(bookDto);
            }
            return listDto;
        } catch (Exception e) {
            throw new Exception(e);
        }
    }

and here is the output that I need (already achieved with above code):

[
    {
        "title": "book1",
        "year": "2013",
        "author": [
            {
                "name": "john",
                "address": "NY"
            },
            {
                "name": "angel",
                "address": "LA"
            }
        ],
        "category": "science"
    },
    {
        "title": "book2",
        "year": "2014",
        "author": [
            {
                "name": "john",
                "address": "NY"
            }
        ],
        "category": "science"
    },
    {
        "title": "book3",
        "year": "2009",
        "author": [
            {
                "name": "angel",
                "address": "LA"
            }
        ],
        "category": "comedy"
    }
]

Solution

Instead of re-inventing the wheel and writing this by yourself you better use an existing library/tool, which is made for this.

I would recommend to use ModelMapper which is a great library for DTO/entity mapping, you will just need one line to convert your entity to DTO, something like:

ModelMapper modelMapper = new ModelMapper();
BookDto bookDTO = modelMapper.map(book, BookDto.class);

You can check the library's Examples page or the Entity To DTO Conversion for a Spring REST API tutorial to get deeper into this library.

Comments

[sklott]

Probably using some existing library, like e.g. "Gson", will eliminate any need in your custom code at all.

[Abhijeet Farakate]

You can use a library like model mapper.

[Dzmitry Prakapenka]

I prefer mapstruct, for the possibility to see the result of code generation after mapping and code post-processing.

[Akza]

why it is ridiculous? I thought it might be useful to trace error...?

[cнŝdk]

Well they are several ways of doing it, we just need to choose the suitable one ;)