@ManagedProperty注释类型返回null

@Stateless
public class BookService
{
    @PersistenceContext(unitName="persistentUnit")
    protected EntityManager entityManager;

    public BookModel find(Long id) {
       return entityManager.find(BookModel.class, id);
    }
}

@ManagedBean(name = "bookBean")
@RequestScoped
public class BookBean implements Serializable
{
    @EJB
    private BookService bookService;

    @ManagedProperty(value="#{param.id}")
    private Long id;

    private DataModel<BookModel> books;
    private BookModel currentBook;

    @PostConstruct
    public void init() {
        if (id == null) {
           // UPDATE: Retrieve a list of books.
        } else { 
           // UPDATE: id shouldn't be null here.
           // Get detail info about a book using the id
           currentBook = bookService.find(id);
        }
    }

    public Long getId() {
       return id;
    } 

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

    public BookModel getCurrentBook() {
       return currentBook;
    }

    public void setCurrentBook(BookModel currentBook) {
       this.currentBook = currentBook;
    }
 }

id

bookedit.jsf?id=5418

EntityManager#find

EntityManager#find

EntityManager#find