问题
After importing a newly created Vaadin 14.0.x project, and using the Import Project feature to create a Maven-driven project in IntelliJ 2019.3 EAP, I get a message saying "Cannot resolving symbol". The error message offers me a button to "Add library … to classpath". But the necessary libraries are already loaded by Maven as dependencies. So this makes no sense.
I retried the import 3 times. On each effort I opened another project to run the File > Invalidate Caches / Restart menu item. This action avoids known IntelliJ bugs/anti-features with creating a new project with same name as a deleted project.
Eventually I tried using the Open feature of the "Welcome to IntelliJ IDEA` panel. Amazingly, no such problem. All the classes are recognized by the IntelliJ code editor.
Bizarre, as I am opening each time a fresh unzipped copy of the original project created by the Getting Started with Vaadin page. There is some major difference between using Open versus Import Project in IntelliJ.
回答1:
The best advice is "dont use the Import Project" feature. It's always been a little buggy / cumbersome ;)
Simply check out your project, and open the project's root folder (containing the parent pom.xml) in IntelliJ.
Incidentally, after checking out from git, the "Would you like to open this project in IntelliJ?" has also been buggy in the past. As a habit I answer "no" to this question and use File -> Open to open the new project manually.
回答2:
Avoid Create project from existing sources option
I suspect that when you chose the Import Project route, you accepted the default option in the resulting dialog box. Do not use that option.
❌
That option, Create project from existing sources will fail in your situation. The documentation for that dialog unfortunately does not explain the first item. But option seems to expect a fully-formed project folder. Yours is not, apparently.
Use Import project from external model option
Instead, choose the second option, Import project from external model. Select Maven from the list, in your case, for a Vaadin 14 project.
✅
Note that with this option, you go through a series of dialogs Wizard-style. Whereas, with the first option, you directly opened the project.
Using this second option, and completing the series of dialogs, will yield an operational Vaadin 14 project.
来源：https://stackoverflow.com/questions/58987498/after-importing-a-maven-project-into-intellij-2019-3-the-bundled-classes-are-no