Question

Without thinking about it too much, I’ve been doing something like the following:

1) building a list of SomeBean objects based on the results of a database call

2) putting that list in my command object

3) building a form based on that command object where users can modify attributes of the SomeBeans

4) extracting data out of the post-submit command object and writing the updated data to my database

My code looks something like this:

public class UpdateThingsinListController extends SimpleFormController {      protected Object formBackingObject(final HttpServletRequest request)           throws Exception {      List<SomeBean> beans = database.getBeans();      Command comamnd = new UpdateThingsCommand()     command.setList(beans);      return command;    }     protected ModelAndView onSubmit(final HttpServletRequest request,           final HttpServletResponse response, final Object commandArg,           final BindException errors) throws Exception {      database.setBeans(commandArg.getList());             }   } 

my jsp looks somthething like:

<form:form>     <c:forEach var='bean' items='${beans}' varStatus='status'>         <form:checkbox path='beans[${status.index}].someBooleanProperty' />${bean.name} <br>         </c:forEach> </form:form> 

The code works fine, but it’s just dawned on me that my ‘beans’ list is getting created twice (sessionform must be false in my case) — once when displaying the form, once when binding. If anything changes on the second creation (a bean is missing, the results are in a different order), my binding will get messed up, and I’ll get fired. I’m beginning to think that any biding scheme where a command object needs to be merged with a form submission is very risky.

So, my question is — how do folks ensure that form submissions get bound to lists correctly? Is there another way to do it besides list index? Object ids maybe?

thanks,

-Morgan

Answer 1

If you can’t depend on the List always being the same whenever you retrieve it, then you have to use a different collection – a map.

Another approach would be to cache your List somewhere. Perhaps some AOP around your database.getBeans method.