In Spring, how do I bind a list of integers to a RequestParam?

Question

I have parameters from the client that are being sent such as

ids[] = 11
ids[] = 12
ids[] = 21

On the server side, I have a Spring controller with the following method:

@RequestMapping("/delete.x")
public @ResponseBody Map<String, Object> delete(HttpServletRequest request, @RequestParam("ids[]") List<Integer> ids) {

When I try to iterate over the collection of ids as follows:

for (Integer id : ids) {

I get an exception as follows:

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer

Is Spring changing the type of ids to List<String>? No matter I suppose, how can I avoid this issue and have the ids stored as Integers inside of a List?

Answer 1

The problem you are facing is that java has type erasure. So at runtime a List<Integer> is equivalent than a List<String> and spring has no way of knowing you want Integers into your list.

A work around might be using a integer array instead of a List of integers.

@RequestMapping("/delete.x")
public @ResponseBody Map<String, Object> delete(HttpServletRequest request,
  @RequestParam("ids[]") Integer[] ids) {