json转map方法

json转map方法
Map<String,CityPo> map = new HashMap<String,CityPo>();
 CityPo po = new CityPo();
 po.setBuildCfgID(123);
 po.setCurHp(456);
 Hero hero = new Hero();
 hero.setStrAge("11");
 hero.setStrName("strName");
 po.setHero(hero);
   map.put( "name",po);   
 JSONObject json = JSONObject.fromObject( map ); //将map转成json
  Map tmp = (Map)JSONObject.toBean(json, Map.class); //将json转回map
  可是转回的map是Map<String,Object>的，有没有办法转成Map<String, CityPo>

ps: Map tmp = (Map)JSONObject.toBean(json, Map.class); 其中的Map.class为何不让设Map<String,CityPo>.class?

------解决方案--------------------------------------------------------
 Java codeCityPo po = new CityPo();
    po.setBuildCfgID(123);
    po.setCurHp(456);
    Hero hero = new Hero();
    hero.setStrAge("11");
    hero.setStrName("strName");
    po.setHero(hero);
    map.put("name", po);
    JSONObject json = JSONObject.fromObject(po); // 将map转成json
    CityPo poo = (CityPo) JSONObject.toBean(json, CityPo.class);
    System.out.println(poo);
------解决方案--------------------------------------------------------我这边有个JAR包能够带泛型转org.codehaus.jackson.map.ObjectMapper本身从网上下，用法以下：Java codeObjectMapper mapper = new ObjectMapper();
Map<String, CityPo> tmp = mapper.readValue(json, new TypeReference<Map<String, CityPo>>() {});
------解决方案--------------------------------------------------------JAR包名是：jackson，有两部分，一个是jackson-core-asl，一个是jackson-mapper-asl
------解决方案--------------------------------------------------------
Map tmp = (Map)JSONObject.toBean(json, Map.class);  改为Map<String,CityPo> tmp = (Map<String,CityPo>)JSONObject.toBean(json, Map.class);