How to retain values of mulitple checkboxes upon form submission using Spring?

I've looked at numerous posts on this topic but I am having a difficult time applying the solutions to my problem. I have a form that has multiple checkboxes and these checkbox values come from a list. When I submit the form I'm checking for errors and if the form has errors then it keeps the user on the same page. However, after I "submit" the form with errors, it removes my checked checkboxes. I'd like these to stay checked. Here's what I have for my code:

How the checkboxes are displayed on the form:

 <div class="control-group">
                <label class="control-label" for="moduleIds"><spring:message code="label.modules"/></label>
                <div class="controls">
                    <c:forEach items="${modules}" var="module">
                        <label class="checkbox"><input type="checkbox" name="moduleIds" value="${module.id}" /> ${module.title}</label>
                    </c:forEach>
                    <form:errors path="moduleIds" cssClass="form-errors" />
                </div>
            </div>

Here's my controllers for loading the form then submitting it. The form is backed by the "assignTraining" object which will take the values of the checkboxes and add them to a list that is a field of the assignTraining object. "Modules" is the attribute that populates the checkboxes:

@RequestMapping(method = RequestMethod.GET, value = "/select")
public final String select(final ModelMap model) {
    model.addAttribute("modules", moduleDao.findByDeletedFalse());
    model.addAttribute("assignTraining", new AssignTraining());
    return "userTraining/select";
}

/**
 * Save new training for a user.
 * 
 * @return The tile definition to view a user's training.
 */
@RequestMapping(method = RequestMethod.POST, value = "/save")
public final String save(final ModelMap model, @Valid AssignTraining assignTraining, BindingResult result) {
    String formFile;

    if (result.hasErrors()) {
        formFile = "userTraining/select";
        //add something here maybe?

    } else {
        List<Module> modules = moduleDao.findAll(new ArrayList<Long>(assignTraining.getModuleIds()));
        List<TrainingEntry> trainingEntries = TrainingEntryUtil.scheduleTraining(assignTraining.getTmNumber(),
                                                                                 modules);
        for (TrainingEntry entry : trainingEntries) {
            trainingEntryDao.save(entry);
        }
        formFile = "redirect:/userTraining/view?tmNumber=" + assignTraining.getTmNumber();
    }

    return formFile;

}

Where I've commented "add something here?", I was thinking of setting a ModelAttribute of the selected checkbox values and then using that attribute in my jsp page, but I'm not sure where to start. Any help is much appreciated.