今天把一个去年没做完的项目翻出来做时，发现maven无法正常导入依赖。检查了一遍项目配置，没发现有什么问题。而且依赖在本地仓库存在。
随后发现报错：Failed to transfer file:*********. Return code is: 501 , ReasonPhrase:HTTPS Required. 这时候好像发现了什么重点————我们需要将maven配置修改一下：
<!-- 中央仓库1 -->
<mirror>
<id>repo1</id>
<mirrorOf>central</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>https://repo1.maven.org/maven2/</url>
</mirror>
<!-- 中央仓库2 -->
<mirror>
<id>repo2</id>
<mirrorOf>central</mirrorOf>
<name>Human Readable Name for this Mirror.</name>
<url>https://repo2.maven.org/maven2/</url>
</mirror>
随后发现可以正常导入依赖了。
在stackoverflow上查了下，发现有人也遇到了这个问题：
Recently Maven build jobs running in Jenkins are failing with the below exception saying that they could not pull dependencies from Maven Central and should use HTTPS. I am not sure how to change the requests from HTTP to HTTPS. Could someone guide me on this matter?
回答如下：
Effective January 15, 2020, The Central Repository no longer supports insecure communication over plain HTTP and requires that all requests to the repository are encrypted over HTTPS.
所以这个问题的根源就是maven中央仓库现在只支持HTTPS协议，我们改一下就行。
