What are the types of Maven repositories? How to configure private repositories and mirrors?

Maven repositories are used to store and manage various artifacts generated during the build process, including dependencies, plugins, and project artifacts. Maven repositories are divided into three types: local repository, central repository, and remote repository.

1. Local Repository:

• Location: Default in the .m2/repository folder under the user directory
• Purpose: Store dependencies downloaded from remote repositories and project build artifacts
• Configuration: Customize location through <localRepository> tag in settings.xml
• Advantage: Avoid repeated downloads, improve build speed, support offline builds

2. Central Repository:

• URL: https://repo.maven.apache.org/maven2
• Purpose: Public repository maintained by Maven official, containing a large number of open source projects
• Features: Can be used without configuration, maintained by Maven community
• Limitation: Projects uploaded to the central repository need to meet strict requirements

3. Remote Repository:

• Purpose: Private repositories built by enterprises or teams, or third-party public repositories
• Common implementations: Nexus, Artifactory, Archiva
• Configuration method:

xml
<repositories>
    <repository>
        <id>company-repo</id>
        <url>https://repo.company.com/maven2</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
    </repository>
</repositories>

Repository Search Order:

1. Local repository: First check if the required artifact already exists locally
2. Remote repositories: Search remote repositories in the configured order
3. Central repository: If remote repositories cannot find it, finally search the central repository

Mirror Configuration: Mirrors are used to replace remote repositories, usually for accelerating downloads or using enterprise internal repositories:

xml
<mirrors>
    <mirror>
        <id>aliyun-maven</id>
        <mirrorOf>central</mirrorOf>
        <name>Aliyun Maven Mirror</name>
        <url>https://maven.aliyun.com/repository/public</url>
    </mirror>
</mirrors>

Repository Authentication Configuration: For private repositories requiring authentication, configure in settings.xml:

xml
<servers>
    <server>
        <id>company-repo</id>
        <username>admin</username>
        <password>password</password>
    </server>
</servers>

Best Practices:

• Use domestic mirrors to accelerate central repository access
• Build private repositories within enterprises to manage internal dependencies
• Distinguish between releases and snapshots repositories to avoid unstable version pollution
• Regularly clean the local repository to free up disk space
• Use mvn dependency:purge-local-repository to clean local dependencies