IDEA如果出現卡頓，Index瘋狂掃描，建議清空一下如下目錄
~/Library/Caches/IntelliJIdea2017.3
Resource nexus-maven-repository-index.prpperties does not exist
解決辦法
For me the solution was to delete the folder ~/.m2/repository. This made Maven to re-index everything correctly.
方法0：刪除Maven的本地倉庫（一般沒啥用，可以往下看，其他方法）
Failed trials, that may work for someone else:
方法1：Build, Execution, Deployment → Build Tools → Maven → Repositories : Selecting the repositories and click updates.
方法2：Build, Execution, Deployment → Build Tools → Maven: Giving more memory JVM
方法3：Delete folder ~/.IntelliJIdea2016.3/system/caches