问题： 反序列化xml时出现Exception in thread “main” com.thoughtworks.xstream.security.ForbiddenClassException:，
是因为这一行代码 XStream.setupDefaultSecurity(xStream); 导致的
解决：
将 XStream.setupDefaultSecurity(xStream); 的顺序修改一下即可

    public XmlStream() {
        xmlResolver = () -> {
            XStream xStream = new XStream(new DomDriver("UTF-8"));
            //将这一行代码写在此处即可
             XStream.setupDefaultSecurity(xStream);
            xStream.allowTypes(new Class[]{Animal.class, Animal.Dog.class, Animal.Dogs.class});
            xStream.processAnnotations(new Class[]{Animal.class, Animal.Dogs.class, Animal.Dog.class});
            xStream.aliasSystemAttribute(null, "class");
            xStream.aliasSystemAttribute(null, "serialization");
            
            //XStream.setupDefaultSecurity(xStream);
            return xStream;
        };
    }