1. 使用环境： springcloud gateway 转发 websocket 报错
2. 报错内容：

15:30:38.092 [http-nio-9999-exec-1] ERROR c.m.g.e.GlobalErrorWebExceptionHandler - [handle,38] - org.apache.catalina.connector.ResponseFacade cannot be cast to reactor.netty.http.server.HttpServerResponse
java.lang.ClassCastException: org.apache.catalina.connector.ResponseFacade cannot be cast to reactor.netty.http.server.HttpServerResponse
	at org.springframework.web.reactive.socket.server.upgrade.ReactorNettyRequestUpgradeStrategy.getNativeResponse(ReactorNettyRequestUpgradeStrategy.java:182)
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	|_ checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ HTTP GET "/sys/websocket/1" [ExceptionHandlingWebHandler]
Stack trace:
		at org.springframework.web.reactive.socket.server.upgrade.ReactorNettyRequestUpgradeStrategy.getNativeResponse(ReactorNettyRequestUpgradeStrategy.java:182)
		at org.springframework.web.reactive.socket.server.upgrade.ReactorNettyRequestUpgradeStrategy.upgrade(ReactorNettyRequestUpgradeStrategy.java:162)
		at org.springframework.web.reactive.socket.server.support.HandshakeWebSocketService.lambda$handleRequest$1(HandshakeWebSocketService.java:235)
		at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:151)
		at reactor.core.publisher.MonoFlatMap.subscribeOrReturn(MonoFlatMap.java:53)
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:57)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.Mono.subscribe(Mono.java:4252)
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:172)
		at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at com.alibaba.csp.sentinel.adapter.reactor.MonoSentinelOperator.subscribe(MonoSentinelOperator.java:40)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)

3. 报错原因： 依赖冲突
   请求时使用的是springBoot的tomcat servlet,而响应的时候使用的是gateway Netty的tomcat,所以导致类型转换异常
4. 解决办法 gateway pom文件修改：
   删除以下 或 排除以下 依赖

<dependency>
	<groupId>javax.servlet</groupId>
	<artifactId>javax.servlet-api</artifactId>
</dependency>
 <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
 </dependency>
 <dependency>
	<groupId>javax.servlet</groupId>
	<artifactId>jstl</artifactId>
</dependency>
<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-jasper</artifactId>
</dependency>