code: public static AVObject parseAVObject(String objectString) {
      if (StringUtil.isEmpty(objectString)) {
        return null;
      }
      // replace leading type name to compatible with v4.x android sdk serialized json string.
      objectString = objectString.replaceAll("^\\{\\s*\"@type\":\\s*\"[A-Za-z\\.]+\",", "{");
  //    objectString = objectString.replaceAll("^\\{\\s*\"@type\":\\s*\"cn.leancloud.AV(Object|Installation|User|Status|Role|File)\",", "{");
  
      // replace old AVObject type name.
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVObject\",", "\"@type\":\"cn.leancloud.AVObject\",");
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVInstallation\",", "\"@type\":\"cn.leancloud.AVInstallation\",");
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVUser\",", "\"@type\":\"cn.leancloud.AVUser\",");
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVStatus\",", "\"@type\":\"cn.leancloud.AVStatus\",");
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVRole\",", "\"@type\":\"cn.leancloud.AVRole\",");
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.AVFile\",", "\"@type\":\"cn.leancloud.AVFile\",");
  
      objectString = objectString.replaceAll("\"@type\":\\s*\"com.avos.avoscloud.ops.[A-Za-z]+Op\",", "");
  
      return JSON.parseObject(objectString, AVObject.class, Feature.SupportAutoType);
    }
docs: create AVObject instance from json string which generated by AVObject.toString or AVObject.toJSONString.
  
  @param objectString
  @return null if objectString is null