function getJson(){
  $.ajax({
    type:"get",
    dataType:"json",
    url:"<%=basePath %>getJson",
    success:function(data){
      for(var i=0;i<jsonData.length;i++){
        alert("Id："+data[i].id+"  username："+data[i].username);
      }
    },
 　　　　error:function(e){
　　　　　　alert(e);
　　  }
  })
}

  @ResponseBody
  @RequestMapping("/getJson")
  public Object getJson(){
    return new Object();
  }

@RequestMapping("/getJson")
  public void getJson(HttpServletResponse response){
　　　　　Object obj = new Object();
　   JSONObject json = JSONObject.fromObject(obj);
    JsonUtils.ajaxJson(json.toString(), response);
  }

import java.io.IOException;

import javax.servlet.http.HttpServletResponse;

public class JsonUtils {
  public static void ajaxJson(String jsonString,HttpServletResponse response) {
    ajax(jsonString, "application/json",response);
  }
  public static void ajax(String content, String type,HttpServletResponse response) {
    try {
      response.setContentType(type + ";charset=UTF-8");
      response.setHeader("Pragma", "No-cache");
      response.setHeader("Cache-Control", "no-cache");
      response.setDateHeader("Expires", 0);
      response.getWriter().write(content);
      response.getWriter().flush();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}