In addition to the Maven central repository, we can also configure other repositories to be used for plugin and dependency downloads. We have to remark that there are separate configuration elements for dependencies and plugin repositories, the <repositories> and <pluginRepositories> elements. For example, if we want to download both dependencies and plugins from the Java.net repository, we should declare the following:
<project>
[...]
<repositories>
<repository>
<id>java.net-Public</id>
<name>Maven Java Net Snapshots and Releases</name>
<url>https://maven.java.net/content/groups/public</url>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>java.net-Public</id>
<name>Maven Java Net Snapshots and Releases</name>
<url>https://maven.java.net/content/groups/public</url>
</pluginRepository>
</pluginRepositories>
[...]In Chapter 5, Continuous Integration and Delivery with Maven, we'll speak about the Nexus repository service that simplifies the repository management in Enterprise environments.
By default, Maven will attempt to download both releases and snapshots from the additional repositories. If we don't want these releases or snapshots to be searched on a remote repository, we have to disable them explicitly, as follows:
<repository>
<id>sample-release-id</id>
<name>A release repository</name>
<url>...</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots
</repository>
<repository>
<id>sample-snapshot-id</id>
<name>A snapshot repository</name>
<url>...</url>
<releases>
<enabled>false</enabled>
</releases>
<snapshots>
<enabled>true</enabled>
</snapshots
</repository>If we look at the effective POM of any Maven project, we'll see that snapshots are disabled in the Maven central repository configuration.
In a multimodule project, the best choice is to declare an additional repository in the parent POM so that they will be available to all the modules of the project.