开始 controller 方法写的是
@RequestMapping( value = "/add", method = RequestMethod.POST )
public String add( @RequestBody Map<String, Object> params ) {
报错 Content type 'application/x-www-form-urlencoded;charset=UTF-8' not supported
改成
@RequestMapping( value = "/add", method = RequestMethod.POST )
public String add( @RequestParam Map<String, Object> params ) {
就不报错了。