mysql:mysql-connector-java:jar:unknown was not found in http://maven.aliyun.com/nexus/content/groups/public during a previous attempt. This failure was cached in the local repository and resolution is not reattempted until the update interval of nexus-ali

这是一个 Maven 依赖问题，可能是由于您的本地仓库中缺少 mysql-connector-java 这个包，或者是您的 Maven 配置文件中没有正确配置阿里云的镜像地址。您可以尝试清空本地仓库再重新构建项目，或者添加以下配置到您的 Maven 配置文件中：

<mirrors>
  <mirror>
    <id>aliyun</id>
    <mirrorOf>*</mirrorOf>
    <name>阿里云公共仓库</name>
    <url>https://maven.aliyun.com/repository/public</url>
  </mirror>
</mirrors>

这样 Maven 就会从阿里云的公共仓库中下载依赖了。