@Override
    public String[] getPropertyNames() {
        return StringUtils.toStringArray(((Map)this.source).keySet());
    }
Spring Enumerable Property Sources support

@author <a href="mailto:shiqingshun@gmail.com">Qingshun Shi</a>
config-toolkit/src/main/java/com/dangdang/config/service/support/spring/ConfigGroupEnumerableResource.java