前提：
1.第三方包，gradle引入
2.项目在上午可以正常运行，下午就包错，错误日志如下
Could not resolve com.mob:MobToolsMC:+.
Required by:
project :app
> Failed to list versions for com.mob:MobToolsMC.
> Unable to load Maven meta-data from https://mvn.mob.com/android/com/mob/MobToolsMC/maven-metadata.xml.
> Could not HEAD ‘https://mvn.mob.com/android/com/mob/MobToolsMC/maven-metadata.xml’.
> sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
? Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
经过一天一夜的baidu+google，各种操作，无意中解决问题。
回忆、总结+记录下，应该是这两点：
1.证书导入，参考https://blog.csdn.net/qq_35250752/article/details/86305049
2.
最后，出个题目，大家巩固巩固基础，如下，打印什么？
