io.undertow.websockets.jsr.ServerWebSocketContainer cannot be cast to org.apache.tomcat.websocket.server.WsServerContainer

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

問題產生原因是：pom引入的依賴包undertow與websocket依賴包中的tomcat沖突了導致,如下：

<!--undertow-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>
<!--websocket依賴包中本身也依賴tomcat-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
 </dependency>

解決方案：

        <!--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>