Handling map-like request parameters in Spring MVC - spring-mvc

Question

Say I have a form for a list of questions where I need a 0/1 answer. I could easily model a static list with radios, something like
<input type="radio" name="question1" value="0">
<input type="radio" name="question1" value="1">
<br>
<input type="radio" name="question2" value="0">
<input type="radio" name="question2" value="1">
#RequestMapping("/answer")
public String answer(Integer question1, Integer question2) {
But I have a dynamic list of questions instead, where each question has a numeric ID. I therefore tried to model it like the following (the HTML is dynamically created with an iteration on the question list):
<input type="radio" name="question[42]" value="0">
<input type="radio" name="question[42]" value="1">
<br>
<input type="radio" name="question[51]" value="0">
<input type="radio" name="question[51]" value="1">
where 42 and 51 are the question id.
I was expecting to capture all values in a Map parameter of my Spring controller, like so:
#RequestMapping("/answer")
public String answer(#RequestAttribute("question") HashMap<Integer, Integer> question) {
It didn't work (the method isn't called).
I also tried with string ids:
<input type="radio" name="question['42']" value="0">
#RequestMapping("/answer")
public String answer(#RequestAttribute("question") HashMap<String, Integer> question) {
Same as before.
It only works if I use a map of string/string, but in this case I get all request parameters in the map, which I will then need to parse:
#RequestMapping("/answer")
public String answer(#RequestAttribute("question") HashMap<String, String> question) {
--> question.keys: "question[42]", "question[51]"
So what is the proper way of handling dynamic radios, or more generally map-like request parameters?

Answer 1

I don't know why, but it works if I put the map inside a bean:
public class QuestionForm {
private HashMap<Long, String> question;
public HashMap<Long, String> getQuestion() {
return question;
}
public void setQuestion(HashMap<Long, String> question) {
this.question = question;
}
}
#RequestMapping("/answer")
public String answer(QuestionForm questionForm) {