Spring Boot Web Application: throwing java.lang.IllegalStateException: getOutputStream() has already been called for this response

Question

In Spring Boot Web Application throwing java.lang.IllegalStateException: getOutputStream() has already been called for this response.

I have in memory database h2 with ORM Relation of @ManyToOne, @ManyToMany, my class look like

@Entity
public class Book {
    @Id
    @GeneratedValue
    private Long id;
    private String isbn;
    private String title;
    private String description;
    @ManyToOne
    private Author author;
    @ManyToOne
    private Publisher publisher;
    @ManyToMany
    private List<Reviewer> reviewers;

    protected Book() {
    }

    public Book(String isbn, String title, Author author, Publisher publisher) {
        this.isbn = isbn;
        this.title = title;
        this.author = author;
        this.publisher = publisher;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    public String getTitle() {
        return title;
    }
}

and testing class

public class StartupRunner implements CommandLineRunner {
    protected final Log logger = LogFactory.getLog(getClass());

    @Autowired
    private BookRepository bookRepository;

    @Autowired
    private AuthorRepository authorRepository;

    @Autowired
    private PublisherRepository publisherRepository;

    @Override
    public void run(String... args) throws Exception {
        logger.info("Number of books: " + bookRepository.count());
        Author author = new Author("Alex", "Antonov");
        author = authorRepository.save(author);
        Publisher publisher = new Publisher("Packt");
        publisher = publisherRepository.save(publisher);
        Book book = new Book("978-1-78528-415-1", "Spring Boot Recipes", author, publisher);
        bookRepository.save(book);
    }

    @Scheduled(initialDelay = 1000, fixedRate = 10000)
    public void run() {

        logger.info("Number of books: " + bookRepository.count());
    }

}

main class

public class StartupRunner implements CommandLineRunner {
    protected final Log logger = LogFactory.getLog(getClass());

    @Autowired
    private BookRepository bookRepository;

    @Autowired
    private AuthorRepository authorRepository;

    @Autowired
    private PublisherRepository publisherRepository;

    @Override
    public void run(String... args) throws Exception {
        logger.info("Number of books: " + bookRepository.count());
        Author author = new Author("Alex", "Antonov");
        author = authorRepository.save(author);
        Publisher publisher = new Publisher("Packt");
        publisher = publisherRepository.save(publisher);
        Book book = new Book("978-1-78528-415-1", "Spring Boot Recipes", author, publisher);
        bookRepository.save(book);
    }

    @Scheduled(initialDelay = 1000, fixedRate = 10000)
    public void run() {

        logger.info("Number of books: " + bookRepository.count());
    }

}

Trying to access the data http://localhost:8080/books/978-1-78528-415-1 throwing above exception

Answer 1

Not an ideal solution but I was able to get mine working after adding an eager fetch type to the mapped children (ie fetch=FetchType.EAGER )

@ManyToMany (fetch=FetchType.EAGER)
private List<Reviewer> reviewers;