maven snapshot updates

Question

I have a maven project with a snapshot dependency. How does maven know if the snapshot needs to be updated? Does it always update? Is it time based? A checksum based update? I know I can force an update but otherwise, how does it check?

thanks, Jeff

Answer 1

According to the docs, the default is that it will only update once a day. That is when the first build of the day is executed. You can override this behavior with the snapshot-policy element.

• always - always check when Maven is started for newer versions of snapshots
• never - never check for newer remote versions. Once off manual updates can be performed.
• daily (default) - check on the first run of the day (local time)
• interval:XXX - check every XXX minutes

http://docs.codehaus.org/display/MAVEN/Repository+-+SNAPSHOT+Handling

Answer 2

I have a maven project with a snapshot dependency. How does maven know if the snapshot needs to be updated?

Maven will compare the local POM's timestamp (stored in a repository's maven-metadata file) to the remote. See for example hibernate-core-3.5.0-SNAPSHOT in JBoss snapshots repository.

Does it always update? Is it time based? A checksum based update?

This depends on the updatePolicy of the repository or pluginRepository containing the snapshots. The default is a daily check (other possibles values are always, interval:X (where X is an integer in minutes) or never.

When you use SNAPSHOT internally for a project under active development, it is very common to set the <updatePolicy>always</updatePolicy> for the internal repository.