maven的mirror和repository加载顺序

一、概述

maven的settings.xml文件里面有proxy、server、repository、mirror的配置，在配置仓库地址的时候容易混淆

proxy是服务器不能直接访问外网时需要设置的代理服务，不常用

server是服务器要打包上传到私服时，设置私服的鉴权信息

repository是服务器下载jar包的仓库地址

mirror是用于替代仓库地址的镜像地址

下面查看源码来确定repository和mirror的优先顺序

二、初始化远程仓库

在maven的远程仓库初始化时会执行newRepositorySession方法，会创建mirror、proxy、authentication和其它系统环境信息：

this.mavenRepositorySystem.injectMirror(request.getRemoteRepositories(), request.getMirrors());
this.mavenRepositorySystem.injectProxy(session, request.getRemoteRepositories());
this.mavenRepositorySystem.injectAuthentication(session, request.getRemoteRepositories());

三、遍历注入镜像

在injectMirror方法中：

public void injectMirror(List<ArtifactRepository> repositories, List<Mirror> mirrors)
  {
    if ((repositories != null) && (mirrors != null)) {
      for (ArtifactRepository repository : repositories)
      {
        Mirror mirror = getMirror(repository, mirrors);
        injectMirror(repository, mirror);
      }
    }
  }

遍历repositories，获得mirror然后注入mirror

注：这里不用担心repositories没数据，因为在之前的初始化repositories方法中会判断没有配置"central"中央仓库的时候加入默认仓库

private void injectDefaultRepositories(MavenExecutionRequest request)
    throws MavenExecutionRequestPopulationException
  {
    Set<String> definedRepositories = this.repositorySystem.getRepoIds(request.getRemoteRepositories());
    if (!definedRepositories.contains("central")) {
      try
      {
        request.addRemoteRepository(this.repositorySystem.createDefaultRemoteRepository(request));
      }
      catch (Exception e)
      {
        throw new MavenExecutionRequestPopulationException("Cannot create default remote repository.", e);
      }
    }
  }

public ArtifactRepository createDefaultRemoteRepository(MavenExecutionRequest request)
    throws Exception
  {
    return createRepository("https://repo.maven.apache.org/maven2", "central", true, "daily", false, "daily", "warn");
  }

三、匹配镜像

在getMirror方法中：

public static Mirror getMirror(ArtifactRepository repository, List<Mirror> mirrors)
  {
    String repoId = repository.getId();
    if ((repoId != null) && (mirrors != null))
    {
      for (Mirror mirror : mirrors) {
        if ((repoId.equals(mirror.getMirrorOf())) && (matchesLayout(repository, mirror))) {
          return mirror;
        }
      }
      for (Mirror mirror : mirrors) {
        if ((matchPattern(repository, mirror.getMirrorOf())) && (matchesLayout(repository, mirror))) {
          return mirror;
        }
      }
    }
    return null;
  }

忽略不常用的layout配置，第一个循环优先寻找mirrorOf与repositoryId完全相同的mirror

第二个循环通过规则来匹配mirror，matchPattern的方法：

static boolean matchPattern(ArtifactRepository originalRepository, String pattern)
  {
    boolean result = false;
    String originalId = originalRepository.getId();
    if (("*".equals(pattern)) || (pattern.equals(originalId)))
    {
      result = true;
    }
    else
    {
      String[] repos = pattern.split(",");
      for (String repo : repos) {
        if ((repo.length() > 1) && (repo.startsWith("!")))
        {
          if (repo.substring(1).equals(originalId))
          {
            result = false;
            break;
          }
        }
        else
        {
          if (repo.equals(originalId))
          {
            result = true;
            break;
          }
          if (("external:*".equals(repo)) && (isExternalRepo(originalRepository))) {
            result = true;
          } else if ("*".equals(repo)) {
            result = true;
          }
        }
      }
    }
    return result;
  }

如果是mirrorOf是*号就匹配，如果不是就遍历可能是逗号分隔的mirrorOf值，同时看是否是!号排除的

在找到mirror后会执行injectMirror方法，把匹配的mirror注入到repository里面：

private void injectMirror(ArtifactRepository repository, Mirror mirror)
  {
    if (mirror != null)
    {
      ArtifactRepository original = createArtifactRepository(repository.getId(), repository.getUrl(), repository.getLayout(), repository
        .getSnapshots(), repository.getReleases());

      repository.setMirroredRepositories(Collections.singletonList(original));

      repository.setId(mirror.getId());
      repository.setUrl(mirror.getUrl());
      if (StringUtils.isNotEmpty(mirror.getLayout())) {
        repository.setLayout(getLayout(mirror.getLayout()));
      }
    }
  }

四、总结

1、在mirrorOf与repositoryId相同的时候优先是使用mirror的地址

2、mirrorOf等于*的时候覆盖所有repository配置

3、存在多个mirror配置的时候mirrorOf等于*放到最后

4、只配置mirrorOf为central的时候可以不用配置repository

我的settings.xml一般这样设置：

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>X:\工具\maven资源\repository</localRepository>
  <pluginGroups></pluginGroups>
  <proxies></proxies>
  <servers></servers>
  <mirrors>
    <mirror>
      <id>nexus-aliyun</id>
      <name>Nexus aliyun</name>
	  <mirrorOf>central</mirrorOf>
      <url>http://maven.aliyun.com/nexus/content/groups/public</url>
    </mirror>
    <mirror>
      <id>nexus-mine</id>
      <name>Nexus mine</name>
	  <mirrorOf>*</mirrorOf>
      <url>http://xx.xx.xx.xx/nexus/content/groups/public</url>
    </mirror>
  </mirrors>
  <profiles></profiles>
</settings>

nexus-aliyun使用阿里云的镜像作为central中央仓库

nexus-mine作为私服，mirrorOf配置为*来提供中央仓库中不存在的jar包