Spring MVC - Cannot map request parameters as a Map parameter in method?

Question

What I want to do is passing a map to the method in Controller using @RequestParam, but it seems not working. While this is working in Struts 2 as value binding.

Below is what I am trying: In JSP using JQuery:

var order = {};
order['seq'] = "ASC";
var criteria = {};
criteria['label'] = "Directory";

$.post(context + 'menu/list',
    {"orders" : order,
     "criterias" : criteria}

The parameters I am trying to post is an 'map' object order and criteria for listing menu. In Java:

    @RequestMapping("/{collection}/list")
public @ResponseBody Map<String, ? extends Object> list(@PathVariable String collection,
        @RequestParam("criterias") Map<String, String> criteria,
        @RequestParam("orders") Map<String, String> order) {

However, when I print out the map criteria & order in Java, it takes all value as below:

Criteria: {criterias[label]=Directory, orders[seq]=ASC}
Order: {criterias[label]=Directory, orders[seq]=ASC}

Can @RequestParam in Spring be used to init a Map parameter?

Ken Chen · Accepted Answer · 2010-05-23 13:29:07Z

OK. Seems I find the reason.

In HandlerMethodInvoker.java

@SuppressWarnings("unchecked")
private Object resolveRequestParam(String paramName, boolean required, String defaultValue,
        MethodParameter methodParam, NativeWebRequest webRequest, Object handlerForInitBinderCall)
        throws Exception {

    Class<?> paramType = methodParam.getParameterType();
    if (Map.class.isAssignableFrom(paramType)) {
        return resolveRequestParamMap((Class<? extends Map>) paramType, webRequest);
    }}


private Map resolveRequestParamMap(Class<? extends Map> mapType, NativeWebRequest webRequest) {
    Map<String, String[]> parameterMap = webRequest.getParameterMap();
    if (MultiValueMap.class.isAssignableFrom(mapType)) {
        MultiValueMap<String, String> result = new LinkedMultiValueMap<String, String>(parameterMap.size());
        for (Map.Entry<String, String[]> entry : parameterMap.entrySet()) {
            for (String value : entry.getValue()) {
                result.add(entry.getKey(), value);
            }
        }
        return result;
    }
    else {
        Map<String, String> result = new LinkedHashMap<String, String>(parameterMap.size());
        for (Map.Entry<String, String[]> entry : parameterMap.entrySet()) {
            if (entry.getValue().length > 0) {
                result.put(entry.getKey(), entry.getValue()[0]);
            }
        }
        return result;
    }
}

When it checks that if my @RequestParam annotated parameter is Map class type, it puts all request parameters into this parameter as MultiValueMap or Linked HashMap

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