@Override
    protected void initServletContext(final ServletContext servletContext) {
        if (Objects.isNull(this.serverContainer)) {
            this.serverContainer = (ServerContainer) servletContext.getAttribute("jakarta.websocket.server.ServerContainer");
        }
    }
Set server container.

@param serverContainer not null
shenyu-client/shenyu-client-websocket/shenyu-client-spring-websocket/src/main/java/org/apache/shenyu/client/spring/websocket/init/ShenyuServerEndpointerExporter.java