spring 세팅때 문제였던 점

start.spring.io/

를 통해서 스프링을 만듦

 Could not target platform: 'Java SE 11' using tool chain: 'JDK 10 (1.10)'.

preference - Build, Execution, Deployment - build Tools - Gradle 에서
Build and run using과 Run tests using을 intellij IDEA로 변경하고 
Gradle JVM을 11버전으로 변경

 

2번째 에러

java.lang.UnsupportedClassVersionError: 
project name has been compiled by a more recent version of the Java Runtime 
(class file version 55.0), this version of the Java Runtime only recognizes class file
versions up to 54.0

file - Project Structure - Project - Project SDK 11로 변경

출처 : twofootdog.tistory.com/57