extjs+hibernate+spring+json开发应用，如何解决级联对象json化？

hibernate的级联对象，一对一、一对多、多对多，怎样才能转化成json格式的字符串？
例：public class Resource {
private static final long serialVersionUID = -7009425391300130055L;

private Long id;
private String name;
private String type;
private String className;
private String methodName;
private Module module;

private Set authorizations = new HashSet(0); //authorizations为Authorization的集合

private String descn;
         //。。。。。。setter,getter方法略。
  }
  public class Authorization {
private static final long serialVersionUID = 7373331899233513702L;

private Long id;
private String name;
private Right right;
private Resource resource;

private Module module;
         //。。。。。。setter,getter方法略。
  }
  public class Module {
private static final long serialVersionUID = -4990110851439538814L;

private Long id;

private String name;

private Module parentModule;

private String serviceKeyName; //服务关键字

private String url;

private String displayPicPath;

private Set resources = new HashSet(0);

private Set authorizations = new HashSet();

private Set childModules = new HashSet(0);

private String descn; //描述
           //。。。。。。setter,getter方法略。
  }
  当从数据库获得一个Resource时，如何将其转化成json格式的数据？
  我是这样做的,在action中：
  (1)得到resource集合：resources
  (2)将resources转成json:
  String str = new JSONSerializer().include("authorizations").deepSerialize(resources);
  //System.out.println("{success:" + true +",resources:"+ str +"}");
  try {
httpServletResponse.getWriter().write("{success:" + true +",resources:"+ str + "}");
} catch (IOException e) {
e.printStackTrace();
  }
 
  可是后台异常：
  java.lang.IllegalArgumentException: object is not an instance of declaring class
  Error trying to serialize path: [ authorizations.module.annotation ]