3）此时出现如下错误：

Cannot access nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public/) in offline mode and the artifact org.apache.spark:spark-core_2.12:pom:3.0.0 has not been downloaded from it before.

4）找到原因之后我们打开Maven

5）重新打包，发现打包成功