为什么我的弹簧启动错误控制器不起作用？

I have a simple spring boot web application (running under Tomcat) and I cannot figure out how to get an error handler to work. So far I've created the web application and controllers and they all work fine. That is, they display Thymeleaf templates. Upon error. I get the default white label error page.I have a simple spring boot web application (ru