简单工厂加上反射

public static xxx getInstance()
    {
        Class decoderClass = null;
        if (null == instance)
        {
            try
            {
                decoderClass = Class
                    .forName(HttpAgentData.HttpSOAPDecoderClass);
            }
            catch (ClassNotFoundException e)
            {
                   ex.printStackTrace();
            }
            Constructor constructor = decoderClass.getConstructors()[0];
            try
            {
                instance = (SOAPDecoder)constructor.newInstance(null);
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
        return instance;
    }