How to remove null attributes while constructing the JSON response

Question

So I'm building a simple API in Spring Boot that retrieves specific books and their authors form a database. The book has an id, name, year that it was published and a foreign key for the Author of that book. Here is the model:

@Entity @Table(name="book", schema = "book_store") public class Book { @Id private long id; private String name; private int released; @ManyToOne @JoinColumn(name="author_id") private Author author; public Book() { } public Book(String name, int released, Author author){ this.name=name; this.released=released; this.author=author; } //And also the getters and setters

Here is the repository:

public interface BookRepository extends JpaRepository<Book, Long> { }

And the service implementaiton:

@Service public class BookServiceImplementation implements BookService { @Autowired private BookRepository bookRepository; public List<Book> getAll(){ return bookRepository.findAll(); } public List<Book> getWithoutAuthor(){ List<Book> newList=bookRepository.findAll(); newList.forEach(p ->p.setAuthor(null)); return newList; } }

So when I go to /api/book/noAuthor it calls the getWithoutAuthor() method and returns this JSON response:

[{"id":1,"name":"Anna Karenina","released":1877,"author":null}, {"id":2,"name":"War And Peace","released":1869,"author":null}, {"id":3,"name":"To Kill A Mockingbird","released":1960,"author":null}, {"id":4,"name":"Go Set A Watchman","released":2015,"author":null}, {"id":5,"name":"The Catcher In The Rye","released":1951,"author":null}, {"id":6,"name":"Franny And Zooey","released":1961,"author":null}]

The author is being set to null which is what I want however is there a way to make the response no return "author":null at all?

Because in this case the "author" field is pretty much useless and I want to remove it completely because I want to have a cleaner response.

I also tried to create a custom JSON response by building a list of Maps with keys and values. While the method does work it does not return a List of Books which is what I want for the controller to return in the end.

Does anyone know a different method?

Jonathan JOhx · Accepted Answer · 2020-04-19 16:27:57Z

You might add simply @JsonInclude annotation then include non null values.

@JsonInclude(JsonInclude.Include.NON_NULL) @ManyToOne @JoinColumn(name="author_id") private Author author;

Lucbel · Accepted Answer · 2020-04-19 16:30:29Z

In that case what I usually do is as you say return in the controller an list of custom entities that will be the books without author. This is the most easy way, the controller layer is responsible of parsing the answer.

I will add a crazy idea just for fun:

in repository

@Query("select id,name,released from Book") // you get all except the author List<Book> findBooksWithoutAuthor();

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