maven 仓库是如何解析的？

Question

假设我的 settings.xml 定义如下

<?xml version="1.0" encoding="UTF-8"?>
<settings xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.1.0 http://maven.apache.org/xsd/settings-1.1.0.xsd" xmlns="http://maven.apache.org/SETTINGS/1.1.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <profiles>
   <profile>
     <repositories>
       <repository>
         <snapshots>
           <enabled>false</enabled>
         </snapshots>
         <id>central</id>
         <name>libs-release</name>
         <url>http://artifactory.ark.local:8080/libs-release</url>
       </repository>
       <repository>
            <id>vmware-repo</id>
            <name>VM Nexus Repo</name>
            <url>http://build-squid.eng.vm.com/nexus/content/groups/repo</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
       <repository>
         <snapshots />
         <id>snapshots</id>
         <name>libs-snapshot</name>
         <url>http://artifactory.ark.local:8080/libs-snapshot</url>
       </repository>
     </repositories>
     <pluginRepositories>
       <pluginRepository>
         <snapshots>
           <enabled>false</enabled>
         </snapshots>
         <id>central</id>
         <name>plugins-release</name>
         <url>http://artifactory.ark.local:8080/plugins-release</url>
       </pluginRepository>
       <pluginRepository>
         <snapshots />
         <id>snapshots</id>
         <name>plugins-snapshot</name>
         <url>http://artifactory.ark.local:8080/plugins-snapshot</url>
       </pluginRepository>
     </pluginRepositories>
     <id>artifactory</id>
   </profile>
 </profiles>
 <activeProfiles>
   <activeProfile>artifactory</activeProfile>
 </activeProfiles>
</settings>

在表单的多模块项目中

main
    storage
        metrics
        config
    common

假设在 metrics pom 中添加了存储库。

<repository>
  <id>cloudera</id>
  <url>https://repository.cloudera.com/artifactory/cloudera-repos/</url>
</repository>

如果在 A 中定义了一个依赖项，它在两个 cloudera 中都存在 repo 和 local nexus repo maven 将如何解析存储库？它会首先尝试从cloudera repo下载吗？如果有一些问题然后它会进入本地关系回购或它会检查仅在 cloudera 回购中，如果它不存在，它将给出错误不从本地 nexus 仓库尝试？
上面问题的答案是否根据A定义是否改变作为 metric 或存储库不存在的其他 pom 中的依赖项定义？

Maven 版本 - 3.6.3

Answer 1

这已在 maven mailing list 中得到解答。只是re-posting这里的答案

The answer depends on the following;

is it a release version or snapshot version. As if the release version is in local repo then no remote repo's are checked. 2) order your pom's are executed

I've simplified your profiles with central repo and company repo, and Aa, Ab and Ac are the same GAV but it's just so in the explanation it's easier to know what A i'm talking about.

settings

central repo (contains Aa)

company repo (contains Ab)

parent-pom

alpha -- A

bravo (has extra R repository like your cloudera, contains Ac) -- A

charlie -- A

For release version assuming empty local repo.

Build order this time alpha, bravo, charlie

Alpha needs A, and Aa is downloaded as it's in central repo and that was 1st repo in the order list

Bravo needs A, it sees Aa in local repo and uses it

Charlie needs A, it sees Aa in local repo and uses it

Same as before but maven believe build order is bravo, alpha, charlie, i.e. you've changed an internal dependency or reorder you modules section.

Bravo needs A, and Ac is downloaded as it's in R repo and that was 1st repo in the order list, which i think it's pom repo's then parent pom's then settings file.

Alpha needs A, it sees Ac in local repo and uses it

Charlie needs A, it sees Ac in local repo and uses it

Next is if A is a -SNAPSHOT dependency assuming empty local repo, Aa is v 1-1, Ab is v1-1 and Ac is v1-1

Build order this time alpha, bravo, charlie

Alpha needs A, and Aa is downloaded as it's in central repo and that was 1st repo in the order list, but it has a cache of Ab existing

Bravo needs A, it sees it doesn't have a cache of A from R repo, so looks up A from R repo, and if Ac in R repo is newer it is downloaded and used. in this case Aa is newer so Aa is used.

Charlie needs A, it sees all repo's have caches of A, and just uses the A in the local repo, in this case Aa is used.

Next is if A is a -SNAPSHOT dependency assuming empty local repo, Aa is v 1-1, Ab is v1-1 and Ac is v1-2

Build order this time alpha, bravo, charlie

Alpha needs A, and Aa is downloaded as it's in central repo and that was 1st repo in the order list, but it has a cache of Ab existing

Bravo needs A, it sees it doesn't have a cache of A from R repo, so looks up A from R repo, and if Ac in R repo is newer it is downloaded and used. in this case Ac is newer so Ac is used.

Charlie needs A, it sees all repo's have caches of A, and just uses the A in the local repo, in this case Ac is used.

As you can see it can get very messy when -SNAPSHOT's are being used and different pom's have repo. This is my hands-on experience of trial and error, debugging and troubleshooting of build processes.

Hope it was helpful.

John

maven 仓库是如何解析的？

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