spring ajax json - 动态下拉选择

Question

我有以下脚本。这个脚本是一个JSP具有其他（级联选择）后，填充一个国家，州和城市组合框

The script is suppose to fetch the data from the controller and populate list of states for the country selected. The function is called alert("inside ajax") is displayed and calls the controller method too. The controller fetches the list of states sucessfully and returns the list of states as "Set". when the control is passed back to the json alert("received data") doesnot pop up and nothing happens after that. There are no errors displayed too. 

I have "json-lib-2.4-jdk15.jar" in my library. Do I need any more settings? or what is that I'm missing? 

杰森Java脚本如下

<script type="text/javascript"> 
    $(document).ready(function() { 
     $('#countryName').change(
     function() { 
      alert("inside ajax"); 
      $.getJSON('${findStateURL}', { 
       countryName : $(this).val(), 
       ajax : 'true' 
      }, function(data) { 
       alert("received data"); 
       alert(data); 
       var html = '<option value="">State</option>'; 
       var len = data.length; 
       alert(len); 
       for (var i = 0; i < len; i++) { 
        html += '<option value="' + data[i].name + '">' 
          + data[i].name + '</option>'; 
        alert(html); 
       } 
       html += '</option>'; 
       $('#states').html(html); 
      }); 
     }); 
    }); 

控制器方法我里面m呼叫是

@Controller 
    public class CountryController { 

     @Autowired 
     private CountryService countryService; 
     @RequestMapping(value = "/getStates.htm", method = RequestMethod.GET) 
     @ResponseBody public 
     Set<State> StatesForCountry(
     @RequestParam(value = "countryName", required = true) String countryName, Map<String, Object> map) { 
     System.out.println("countryName " + countryName); 
     System.out.println("Country Id "); 
     List<State> states = countryService.getAllStates(countryName); 
     Set<State> state_set = new HashSet<State>(states); 
     System.out.println(" no. of states set = " + state_set); 
     return state_set; 
     } 

控制器正在返回'set'中所需的值。但唯一的问题是我没有收到任何数据在 警报（“收到的数据”）;

Answer 1

重新缩进代码后，因为我们不是机器：

$(document).ready(function() { 
$('#countryName').change(
    function() { 
     alert("inside ajax"); 
     $.getJSON(
      '${findStateURL}', 
      { 
       countryName : $(this).val(), 
       ajax : 'true' 
      }, 
      function(data) { 
       alert("received data"); 
       alert(data); 
       var html = '<option value="">State</option>'; 
       var len = data.length; 
       alert(len); 
       for (var i = 0; i < len; i++) { 
        html += '<option value="' + data[i].name + '">' 
        + data[i].name + '</option>'; 
        alert(html); 
       } 
       html += '</option>'; 
       $('#states').html(html); 
      } 
     ); 
    } 
); 
}); 

如果我读的API Doc：如果JSON文件包含语法错误，请求通常会失败默默。

我建议你得到你的控制器返回的JSON（通过示例通过Firebug）并将你的JSON放入在线验证器中。也许你会发现一个错误。