4

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

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3 Answers 3

Reset to default
8

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);
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2 Comments

when i insert that code in my java class in eclipse , the whole text is red underlined. I have import for Autolist and Element factory . it says Autopopulatlist is undefined , ElementFactory is not generic; it cannot be parameterized with arguments. what is the issue. do i need to define these
@Pasha There was a duplicate equals symbol in the code (I've corrected it). Maybe you have added the wrong import or your Spring Version is not the last one because now ElementFactory can be used with generics. Anyway you can use it without generics. I've provided another code in case you want to use the default constructor of Book (simpler, though most of the times it is enough to get what you need) where you don't need to use ElementFactory. In that case it will use Book() to create the objects.
1

When I have such complicated form i honestly prefer to use JSON and submit it using AJAX.

{"person":{"id":1,"books":[{"person_id":2,"book_id":3},{"person_id":2,"book_id":6},{"person_id":3,"book_id":4}]}


@RequestMapping(value = "/persons/add", method = RequestMethod.POST)
@ResponseBody
     public String add(@RequestBody Person person){ 
//ad your business logic
}

Your code will be validate by de-serializer and you will be able to save it. You can reed more about that in this post:

http://blog.springsource.com/2010/01/25/ajax-simplifications-in-spring-3-0/

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1

Binding of Set isn't possible with Spring MVC as Sets do not have indexes to work with. Although you can iterate through sets in JSP and show the results. The solutions might be -

  1. Use another type of collection like List.
  2. Wrap your Set in a POJO, use your Set for showing its containing values in JSP. Once you want to post the form containing your selection, add new property in your POJO which is String(or similar) and provide this property as your PATH in JSP tag, which will get the selection data from JSP. Then in backend code, fill your set with this value.

In case, your POJO is the also an Entity for your database creation using Hibernate, simply put @Transient on top of it. Hibernate will ignore this property while creating table.

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