正确配置maven后，在cmd运行mvn help:system显示BUILD FAILURE

错误报告：
ownloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-clean-plugin:2.5: Plugin org.apache.maven.plugins:maven-clean-plugin:2.5 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-clean-plugin:jar:2.5
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-install-plugin/2.4/maven-install-plugin-2.4.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-install-plugin:2.4: Plugin org.apache.maven.plugins:maven-install-plugin:2.4 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-install-plugin:jar:2.4
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-deploy-plugin/2.7/maven-deploy-plugin-2.7.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-deploy-plugin:2.7: Plugin org.apache.maven.plugins:maven-deploy-plugin:2.7 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-deploy-plugin:jar:2.7
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-site-plugin/3.3/maven-site-plugin-3.3.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-site-plugin:3.3: Plugin org.apache.maven.plugins:maven-site-plugin:3.3 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-site-plugin:jar:3.3
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-antrun-plugin/1.3/maven-antrun-plugin-1.3.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-antrun-plugin:1.3: Plugin org.apache.maven.plugins:maven-antrun-plugin:1.3 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-antrun-plugin:jar:1.3
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-assembly-plugin/2.2-beta-5/maven-assembly-plugin-2.2-beta-5.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-assembly-plugin:2.2-beta-5: Plugin org.apache.maven.plugins:maven-assembly-plugin:2.2-beta-5 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-assembly-plugin:jar:2.2-beta-5
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-dependency-plugin/2.8/maven-dependency-plugin-2.8.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-dependency-plugin:2.8: Plugin org.apache.maven.plugins:maven-dependency-plugin:2.8 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-dependency-plugin:jar:2.8
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-release-plugin/2.3.2/maven-release-plugin-2.3.2.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-release-plugin:2.3.2: Plugin org.apache.maven.plugins:maven-release-plugin:2.3.2 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-release-plugin:jar:2.3.2
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/apache/maven/plugins/maven-metadata.xml
Downloading: http://maven.aliyun.com/nexus/content/groups/public/org/codehaus/mojo/maven-metadata.xml
[WARNING] Could not transfer metadata org.apache.maven.plugins/maven-metadata.xml from/to alimaven (http://maven.aliyun.com/nexus/content/groups/public/): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[WARNING] Could not transfer metadata org.codehaus.mojo/maven-metadata.xml from/to alimaven (http://maven.aliyun.com/nexus/content/groups/public/): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[WARNING] Failure to transfer org.apache.maven.plugins/maven-metadata.xml from http://maven.aliyun.com/nexus/content/groups/public/ was cached in the local repository, resolution will not be reattempted until the update interval of alimaven has elapsed or updates are forced. Original error: Could not transfer metadata org.apache.maven.plugins/maven-metadata.xml from/to alimaven (http://maven.aliyun.com/nexus/content/groups/public/): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[WARNING] Failure to transfer org.codehaus.mojo/maven-metadata.xml from http://maven.aliyun.com/nexus/content/groups/public/ was cached in the local repository, resolution will not be reattempted until the update interval of alimaven has elapsed or updates are forced. Original error: Could not transfer metadata org.codehaus.mojo/maven-metadata.xml from/to alimaven (http://maven.aliyun.com/nexus/content/groups/public/): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.449 s
[INFO] Finished at: 2020-03-02T21:16:27+08:00
[INFO] Final Memory: 12M/243M
[INFO] ------------------------------------------------------------------------
[ERROR] No plugin found for prefix ‘help’ in the current project and in the plugin groups [org.apache.maven.plugins, org.codehaus.mojo] available from the repositories [local (D:\Maven\maven-repository), alimaven (http://maven.aliyun.com/nexus/content/groups/public/)] -> [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/NoPluginFoundForPrefixException
这个问题网上所有的解决方法我都试过了并没有解决我的问题，镜像我也改成阿里云的了还是不行，真的是很绝望。后来思考认为配置正确的话问题只可能是出现在网络上。而且我的旧电脑可以正常运行maven，新电脑却不行。
于是我打算按照旧电脑的配置来配置一下我新电脑的网络设置。打开win10的“设置”，点击“网络和Internet”，再点击左侧“状态”里的“更改连接属性”，设置成下图所示：

返回，再点击左侧“WLAN”设置成下图所示：

最后点击左侧“代理”设置成下图所示：

最后一个“代理”那个地方的“自动检测设置”开不开视个人电脑情况而定，开了不行就关上，关上不行就打开试一试。
问题应该可以得到解决，前提是配置都正确。但是不保证每个人的问题都可以解决，具体问题具体分析嘛。
注意：每次在cmd运行mvn help:system命令错误后，先把本地仓库没下载完成的残留文件夹全部删除后再执行该命令。不然可能也会报错