springmvc ajax String类型时，报parsererror? 400 报错

springmvc ajax String类型时，报parsererror? 400 报错

后台代码

@Controller
@RequestMapping("/hello")
public class HelloController {

	@RequestMapping("/say.do")
	public @ResponseBody String say(String name) {
		System.out.println(name + " saying .......");
		
		return name + "say!";
		
	}
}

  var data = null;
  $.ajax({
   url : $.contextPath + "/hello/say.do?name=haha",
   type: "get",
   dataType : "json",
   async : false,
   success : function(rlt) {
   debugger;
    data = rlt;
   },
   error : function (req, error, errThrow) {
    debugger;
    $.error("function load json error: " + error);
   }
  });

如果后台方法say return Map对象的话，前台ajax请求就正常了，请各位高手们帮我分析分析哪出问题了，谢谢！