Java compiler level does not match the version of the installed Java project facet.

修改了编译级别之后出现如下错误提示：

Description Resource Path Location Type

Java compiler level does not match the version of the installed Java project facet. SSJ Unknown Faceted Project Problem (Java Version Mismatch)

只要在项目的properties中选择project facet然后修改java的版本即可：