(ajax) 406 error when receiving json data from controller - ajax

Question

I have some Ajax methods which receives data from controller with HashMap object and everything worked fine.
This time,
I'm trying to retrieve the data with json type.
However, my server responses with error 406 (not acceptable).
I don't understand why the server cannot receive json type
I followed every step introduced in stackoverflow
(adding additional bean tag, changing content type , and so on..)
None of them worked
Here's my codes below.
#RequestMapping(value="/report/getMember", produces="application/json",
method=RequestMethod.GET)
public #ResponseBody JSONArray getMember(){
List<HashMap<String,String>> result_dep = reportDao.getDep();
List<MemberForReport> result_member = reportDao.getMemberForReport();
String[] dep_list = new String[result_dep.size()];
for(int i=0; i<result_dep.size(); i++){
dep_list[i] = result_dep.get(i).get("dep");
}
HashMap<String, ArrayList<String>> hash_list = new HashMap<String, ArrayList<String>>();
for(int i=0; i<dep_list.length; i++){
ArrayList<String> member_list = new ArrayList<String>();
for(int j=0; j<result_member.size(); j++){
if(dep_list[i].equals(result_member.get(j).getDep())){
member_list.add(result_member.get(j).getName());
}
}
hash_list.put(dep_list[i], member_list);
}
JSONArray arry = new JSONArray();
List keys = new ArrayList(hash_list.keySet());
for(int i=0; i<keys.size(); i++){
JSONArray arry_child = new JSONArray();
JSONObject json_folder = new JSONObject();
json_folder.put("title", keys.get(i));
json_folder.put("isFolder", true);
for(int j=0; j<hash_list.get(keys.get(i)).size(); j++){
JSONObject json_child = new JSONObject();
json_child.put("title", hash_list.get(keys.get(i)).get(j));
arry_child.put(json_child);
}
json_folder.put("children", arry_child);
arry.put(json_folder);
}
System.out.println("result \n"+arry.toString());
return arry;
}
my jquery code
$.ajax({
url: "/asec/document/report/getMember",
type: "get",
ContentType: "application/json",
success: function(data){
alert(data);
// alert ("dd");
},
error: function(request, status, error){
console.log(request.getAllResponseHeaders());
}
});