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
二、源码解析执行流程
2.1》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());
2.2》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");
}
2.3》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()));
}
}
}
三、结论
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
四 、实践
4.1》maven settings.xml配置
<?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">
<pluginGroups></pluginGroups>
<proxies></proxies>
<servers>
<server>
<id>nexus-releases</id>
<username>admin</username>
<password>admin123</password>
</server>
<server>
<id>nexus-snapshots</id>
<username>admin</username>
<password>admin123</password>
</server>
</servers>
<mirrors>
<mirror>
<id>nexus-releases</id>
<mirrorOf>nexus-releases</mirrorOf>
<url>http://localhost:8081/nexus/content/groups/public</url>
</mirror>
<mirror>
<id>nexus-snapshots</id>
<mirrorOf>nexus-snapshots</mirrorOf>
<url>http://localhost:8081/nexus/content/groups/public-snapshots</url>
</mirror>
</mirrors>
<profiles>
<profile>
<id>nexus</id>
<repositories>
<repository>
<id>nexus-releases</id>
<url>http://nexus-releases</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</repository>
<repository>
<id>nexus-snapshots</id>
<url>http://nexus-snapshots</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>nexus-releases</id>
<url>http://nexus-releases</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</pluginRepository>
<pluginRepository>
<id>nexus-snapshots</id>
<url>http://nexus-snapshots</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</pluginRepository>
</pluginRepositories>
</profile>
</profiles>
<activeProfiles>
<activeProfile>nexus</activeProfile>
</activeProfiles>
</settings>
4.2》项目所在pom.xml配置
<distributionManagement>
<!-- 两个ID必须与 setting.xml中的<server><id>nexus-releases</id></server>保持一致-->
<repository>
<id>nexus-releases</id>
<name>Nexus Release Repository</name>
<url>http://localhost:8081/nexus/content/repositories/releases</url>
</repository>
<snapshotRepository>
<id>nexus-snapshots</id>
<name>Nexus Snapshot Repository</name>
<url>http://localhost:8081/nexus/content/repositories/snapshots</url>
</snapshotRepository>
</distributionManagement>
