Caused by: java.lang.ClassCastException: 
io.undertow.websockets.jsr.ServerWebSocketContainer cannot be cast to org.apache.tomcat.websocket.server.WsServerContainer

    at org.springframework.web.socket.server.standard.TomcatRequestUpgradeStrategy.getContainer(TomcatRequestUpgradeStrategy.java:84)

    at org.springframework.web.socket.server.standard.TomcatRequestUpgradeStrategy.getContainer(TomcatRequestUpgradeStrategy.java:47)

    at org.springframework.web.socket.server.standard.AbstractStandardUpgradeStrategy.getSupportedExtensions(AbstractStandardUpgradeStrategy.java:88)

    at org.springframework.web.socket.server.support.AbstractHandshakeHandler.doHandshake(AbstractHandshakeHandler.java:272)

    at org.springframework.web.socket.server.support.WebSocketHttpRequestHandler.handleRequest(WebSocketHttpRequestHandler.java:166)

    ... 56 common frames omitted

<!--undertow-->

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-undertow</artifactId>

</dependency>

<!--websocket依赖包中本身也依赖tomcat-->

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-websocket</artifactId>

 </dependency>

        <!--websocket-->

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-websocket</artifactId>

            <exclusions>

                <exclusion>

                    <groupId>org.springframework.boot</groupId>

                    <artifactId>spring-boot-starter-tomcat</artifactId>

                </exclusion>

            </exclusions>

        </dependency>