When writing jsp with IDEA, I can't always change it and watch it. I read various solutions to modify the update source and classes, or add the jrebel plug-in (have to be cracked), but it didn't achieve the effect, and then I accidentally found that the version did not match. Installed a tomcat9 (previously it was tomcat8.5, it ran fine in eclipse)
jdk9 + tomcat9 + idea2018.1.1
Maybe it's the reason why I only use jsp. It can be updated in real time without modifying this, but it's better to set it to update classes and resources