@Override
        protected LoadingCache<String, UserEntity> initialValue() {
          CacheLoader<String, UserEntity> loader = new CacheLoader<String, UserEntity>() {
            @Override
            public UserEntity load(String key) throws Exception {
              //fallback mechanism, mostly for unit tests
              return userDAO.findUserByName(key);
            }
          };

          return CacheBuilder.newBuilder()
              .expireAfterWrite(20, TimeUnit.SECONDS)
              .build(loader);
        }
The key property ids for a privilege resource.
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/UserPrivilegeResourceProvider.java