var _url = (xxx.contextPath + '/documenttype/getextension/'+ val);
    $.getJSON(_url).done(function (data) {
        if(data){
            $('#documents').attr('accept', data);
        }
    }).fail(function( jqxhr, textStatus, error ) {
        var err = textStatus + ", " + error;
        alert(err);
    });

@ResponseBody
@RequestMapping(value = "/getextension/{typeId}", method =
RequestMethod.GET)
public String findExtension(@PathVariable Long typeId) {
    String ext = getEntityService().findExtension(typeId);
    // json requires string with double quotes
    ext = new StringBuilder(""").append(ext).append(""").toString();
    return ext;
}

[{"id":40,"createdBy":1,"createdDate":"21/11/2017
12:49","updatedBy":1,"updatedDate":"21/11/2017 12:49","version":0,"group":
{"id":23,"createdBy":1,"createdDate":"21/11/2017
12:49","updatedBy":1,"updatedDate":"21/11/2017
12:49","version":0,"code":"ALTDISPUTERES","name":"Alternative Dispute
Resolution","store":
{},"systemGenerated":false,"position":0,"displayAll":false,"handler":.....