How to convert String to List object in spring MVC

Question

I am trying Spring MVC example. I have a testBean which has List type variable like

  private List<HashMap<String, String>> books;

In my controller I have

@RequestMapping(value = "/booksList", method = RequestMethod.POST)
    public String displayBooks(@ModelAttribute TestBean testBean, Model model, HttpSession   session) {
     // some code here
}

In my jsp page I have

<form:form action="booksList.html" method="post" modelAttribute="testBean">
        <form:hidden path="books" />
   <input type="submit" value="submit">
</form:form>

When I submit this form I am getting this error

Cannot convert value of type [java.lang.String] to required type [java.util.HashMap] for property 'books[0]'.

How can I solve this error ? please help

Updated:

I have seen that I can do this way also.

 @InitBinder
public void initBinder(WebDataBinder binder) {              
        binder.registerCustomEditor(List.class, "testBean", new CustomCollectionEditor(List.class) {                
        @Override           
        protected Object convertElement(Object element) {
            TestBean testBean = new TestBean();                
            if (element != null) {
                List<HashMap<String, String>> id = (List<HashMap<String, String>>) element;
                testBean.setFilters(id);
            }
            return testBean;
        }
        });       
   }

But I don't understand the above method fully there may be some mistakes in what I have written. And I don't know how and from where I can call convertElement(Object element) method. i do understand initBinder(WebDataBinder binder) will call jsut before my controller method public String displayBooks(...). Even I don't know if its the right way of doing this.

millhouse · Accepted Answer · 2012-01-12 23:55:33Z

1

As you have it above, you're trying to represent an extremely complex type (a List of Maps) with a single text field. Your first step should be working out how you want to display that information in a web form. Then try using "canned data" (e.g. a TestBean that you've loaded up with fake books) and see if your form looks how you expect it to.

You might find it easier if you change the way your books collection is stored. Having such a complex type as part of a "bean" while allowed, is probably not recommended. Consider using a List<BookBean> where a BookBean holds a collection of BookDetailBean, and a BookDetailBean holds that String-to-String relationship that you previously had in your Map.

answered Jan 12, 2012 at 23:55

millhouse

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