public Class<Protocol> get(String protocolName) {
        final Class<Protocol> protocolClass = protocols.get(protocolName);
        if (protocolClass == null) {
            throw new IllegalArgumentException("Procotol with name " + protocolName + " not registered.");
        }
        return protocolClass;
    }
Protocol factory

@author <a href="mailto:wangyuxuan@dangdang.com">Yuxuan Wang</a>
config-toolkit/src/main/java/com/dangdang/config/service/file/protocol/Protocols.java