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You should have a clearer idea of repository management best practises through the following examples and counterexamples.
Initial configuration
This configuration come with maven without doing anything.
The "simple project" pom.
Extended usage
Without repository manager
Take a look on the "extended project" pom.
With repository manager
The "extended project" pom don't change, we just add mirrors section in the settings.xml (M2_HOME/conf/settings.xml or ~/.m2/settings.xml).
Take a look on the Mirrors definitions in settings.xml.
Complex usage
Counterexamples
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