Question

I have been trying for last 3 days still i am not able to solve my problem

I have Person Class

@SuppressWarnings("rawtypes")
 @OneToMany(cascade = CascadeType.ALL, fetch=FetchType.LAZY, mappedBy="person")
 @JoinColumn(name="person_id")
 public Set<Book> books = new HashSet<Book>();

class Book

book_id
person_id

In my JSP form i have

<c:forEach items="${BookList}" var="var1" varStatus="counter">
     <input type="checkbox" name="books[${counter.index}].book_id" value="${var1.book_id}" >${var1.book_name}</input>
    </c:forEach>

I am inserting the books in table depending upon the check boxes
The book list is populated from refrenceData model.

COntroller

@RequestMapping(value = "/persons/add", method = RequestMethod.GET)
    public String getAdd(Model model) {
        logger.debug("Received request to show add page");

        // Create new Person and add to model
        // This is the formBackingOBject
        model.addAttribute("personAttribute", new Person());

        // This will resolve to /WEB-INF/jsp/addpage.jsp
        return "hibernate/addpage";
    }



@RequestMapping(value = "/persons/add", method = RequestMethod.POST)
public String add(@Valid @ModelAttribute("personAttribute") Person person, BindingResult result) {
        logger.debug("Received request to add new person");

        if (result.hasErrors()) 
    return "hibernate/addpage";
        else
        personService.add(person);

    // This will resolve to /WEB-INF/jsp/addedpage.jsp
        return "hibernate/addedpage";
    }

Now if i have single Book object then this works ok and data is entered in DB but if i have set then it says invalid property book[1]

After searching a lot on SO and Google i leart that i have two option

PropertyEditor
AutoPopulatingList

I don’t know how to use them in my case. Can anyone help me , where do i have to use them and how to use it

Answer 1

Look at this question Bind objects in a Set collection

You need to use another type of Collection. I’d recommend to use a List instead of a Map. When you send from the form a parameter with a name like:

name="books[0].book_id"

SpringMVC will look in the property called books (which is a Set for you) and then it will try to get the first element by doing books.get(0). Set don’t have a get because Set has not an order.

For the implementation of the list you can use AutoPopulatingList. It is an implementation of a lazy List which will create an object if it doesn’t exist. For example if you invoke books[0].id and you haven’t added a book in the position 0 of the list it will throw a NullPointerException, but if you use AutoPopulatingList it will create a new Book and addd it in that position if that position is empty.

public List<Book> books = new AutoPopulatingList<Book>(new ElementFactory<Book>() {
    @Override
    public Book createElement(final int index) throws ElementInstantiationException {
         //call the constructor as you need
         return new Book();
    }       
});

if you you are going to instanciate it with the default constructor of Book (that is Book()), you can use a syntax like this one:

public List<Book> books = new AutoPopulatingList<Book>(Book.class);