public void json(HttpServletRequest request,HttpServletResponse response){ 
  Map<String,Object>map=new HashMap<String, Object>(); 
  String id = request.getParameter("id");      //接收ajax请求带过来的id 
  String level = request.getParameter("level");   //接收ajax请求带过来的level 
  String callback=request.getParameter("callback"); //接收ajax请求带过来的callback参数 
  if ("1".equals(level)) {             //如果level是'1',则查询第一级目录内容 
    map.put("results", this.carBrandService.findByAttr(null, "first_letter asc")); //调用查询方法，结果放入map 
  } else if ("2".equals(level)) {          //如果level是'2',则查询第二级目录内容 
    map.put("results", this.carSerieService.findByAttr("parent_id="+id, "first_letter asc"));//调用查询方法，结果放入map 
  } else if ("3".equals(level)) {          //如果level是'3',则查询第三极目录内容 
    map.put("results", this.carModelYearService.findByAttr("parent_id="+id, "jian_pin desc"));//调用查询方法，结果放入map 
  } 
  map.put("level",level); 
  if (null==callback) {               //如果接收的callback值为null,则是不跨域的请求,输出json对象 
    HttpAdapter.printlnObject(response, map); 
  }else{                      //如果接收的callback值不为null,则是跨域请求，输出跨域的json对象 
  HttpAdapter.printlnJSONPObject(response, map, callback); 
  } 
} 

/** 
 * 打印对象 
 * @param response 
 * @param object 
*/ 
public static void printlnObject(HttpServletResponse response,Object object){ 
  PrintWriter writer=getWriter(response); 
  writer.println(JSON.toJSONString(object)); 
} 
/** 
 * 打印跨域对象 
 * @param response 
 * @param object 
*/ 
public static void printlnJSONPObject(HttpServletResponse response,Object object,String callback){ 
  PrintWriter writer=getWriter(response); 
  writer.println(callback+"("+JSON.toJSONString(object)+")"); 
} 

function loadData(obj,level,id,value){ 
  $.ajax({  
    url:'http://192.168.1.106:8086/carBrand/json.html"htmlcode">

function loadData(obj,level,id,value){ 
  $.ajax({  
    url:'http://192.168.1.106:8086/carBrand/json.html"http://跨域/...xx.js"></script>是一致的(qq空间就是大量采用这种方式来实现跨域数据交换的) .JSONP是一种脚本注入(Script Injection)行为,所以也有一定的安全隐患.

注意,jquey是不支持post方式跨域的.