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
问题产生原因是：pom引入的依赖包undertow与websocket依赖包中的tomcat冲突了导致,如下：
<!--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>
解决方案：
<!--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>