问题：IDE的problem窗口中出现Error:Maven Resources Compiler: Maven project configuration required for module 'wj' isn't available. Compilation of Maven projects is supported only if external build is started from an IDE.
And there is a problem when compiling with maven package: [ERROR] (please use -source 8 or higher to enable lambda expressions)
Solution: In the IDE toolbar, select Build->ReBuild, wait for the project to be recompiled, and then the problem can be solved.