本以为是 jdk编译版本和运行版本不匹配，idea里面是 1.9 ，本地安装是1.8 的 ，修改成一致的1.8还是 会报错；

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:compile (default-compile) on project demo: Fatal error compiling: 无效的目标发行版: 1.9 -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

苦思了一晚上， 想起来 可能是mvn配置的问题， 好久没看mvn的相关知识了；
如下图，在settings.xml文件里配置了 ==jdk为1.9 ==所以才会报 这个 maven 插件的错误；

	<profile>
	  <id>jdk-1.8</id>
	  <activation>
	    <activeByDefault>true</activeByDefault>
	    <jdk>1.8</jdk>
	  </activation>
	  <properties>
	    <maven.compiler.source>1.8</maven.compiler.source>
	    <maven.compiler.target>1.8</maven.compiler.target>
	    <maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
	  </properties>
	</profile>