spring cloud gateway使用zookeeper作为注册中心调用其它服务的时候报了下面这个错误：

ava.lang.NullPointerException: nullat io.netty.util.NetUtil.isValidIpV4Address(NetUtil.java:648) ~[netty-common-4.1.29.Final.jar:4.1.29.Final]at io.netty.util.NetUtil.createByteArrayFromIpAddressString(NetUtil.java:368) ~[netty-common-4.1.29.Final.jar:4.1.29.Final]at reactor.ipc.netty.options.InetSocketAddressUtil.attemptParsingIpString(InetSocketAddressUtil.java:132) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]at reactor.ipc.netty.options.InetSocketAddressUtil.createForIpString(InetSocketAddressUtil.java:80) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]at reactor.ipc.netty.options.InetSocketAddressUtil.createInetSocketAddress(InetSocketAddressUtil.java:69) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]at reactor.ipc.netty.options.ClientOptions.createInetSocketAddress(ClientOptions.java:253) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]at reactor.ipc.netty.http.client.HttpClientOptions.getRemoteAddress(HttpClientOptions.java:87) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]at reactor.ipc.netty.http.client.MonoHttpClientResponse.lambda$subscribe$0(MonoHttpClientResponse.java:76) ~[reactor-netty-0.7.10.RELEASE.jar:0.7.10.RELEASE]

调用的地址是http://zks_servers_1:18001，zks_servers_1是服务的hosts配置的名称，空指针异常跟踪发现是下面这个问题导致的：

//类HttpClientOptionspublic final InetSocketAddress getRemoteAddress(URI uri) {Objects.requireNonNull(uri, "uri");boolean secure = isSecure(uri);int port = uri.getPort() != -1 ? uri.getPort() : (secure ? 443 : 80);boolean shouldResolveAddress = !this.useProxy(uri.getHost());return this.createInetSocketAddress(uri.getHost(), port, shouldResolveAddress);}

uri.getHost()返回值是null，也就是说根据上面的调用地址，没有获取到对应的host。
uri的创建方式是：

//类MonoHttpClientResponse
MonoHttpClientResponse(HttpClient parent, String url, HttpMethod method, Function<? super HttpClientRequest, ? extends Publisher<Void>> handler) {this.parent = parent;boolean isWs = Objects.equals(method, HttpClient.WS);try {this.startURI = new URI(parent.options.formatSchemeAndHost(url, isWs));} catch (URISyntaxException var7) {throw Exceptions.bubble(var7);}this.method = isWs ? HttpMethod.GET : method;this.handler = handler;}

创建方式是调用URI的new URI(String)方法，知道原因之后在本地测试：

try {URI uri = new URI("http://zks_servers_1:18001/test.html");String host = uri.getHost();System.out.println(host);} catch (URISyntaxException e) {e.printStackTrace();}

确实获取不到host，查看源码发现：

 /*** Returns the host component of this URI.**   <li><p> A domain name consisting of one or more <i>labels</i>*   separated by period characters ({@code '.'}), optionally followed by*   a period character.  Each label consists of <i>alphanum</i> characters*   as well as hyphen characters ({@code '-'}), though hyphens never*   occur as the first or last characters in a label. The rightmost*   label of a domain name consisting of two or more labels, begins*   with an <i>alpha</i> character. </li>* </ul>** The host component of a URI cannot contain escaped octets, hence this* method does not perform any decoding.** @return  The host component of this URI,*          or {@code null} if the host is undefined*/public String getHost() {return host;}

谷歌翻译：

由一个或多个标签组成的域名由句点字符代码'.'分隔，可选地后跟一个英文句号角色。 每个标签由alphanum字符组成以及连字符字符代码' - '，虽然连字符永远不会作为标签中的第一个或最后一个字符出现。 最右边包含最少长度最少两个并且以英文字符开始的标签

举例如下：
www.baidu.com，这个域名包含三个标签www、baidu、com；
www.baidu-zhidao.com，这个域名包含三个标签www、baidu-zhidao、com；
这个例子就是说明每个标签都可以使用-连接；

然后看一下，我的报错的服务名称zks_servers_1，这个名称没有以【.】分割，包含了非法字符【_】最后以单个数字结尾也不符合要求。
实际上测试发现zks-servers-1这样也是不正确的，不知道是不是翻译的有问题，这个结果和翻译不太匹配。

总而言之，修改服务器的hosts配置就行了。