Question about maven - maven-2

Question

Why is maven downloading dependencies from repository even if the jar exists on my local repository(one reason could be that jar doesn't have a pom), is there a way to get bypass that except with the -o option?

Answer 1

Why is maven downloading [SNAPSHOT] dependencies from repository even if the jar exists on my local repository
Because that's the expected behavior with SNASPSHOT dependencies. Unlike fixed versions, Maven will periodically try to download the most recent version of a given SNAPSHOT. That's extremely useful when you're depending on a project that is under active development. From the Maven Reference:
3.3.1.2. SNAPSHOT Versions
Maven versions can contain a string
literal to signify that a project is
currently under active development. If
a version contains the string
“SNAPSHOT,” then Maven will expand
this token to a date and time value
converted to UTC (Coordinated
Universal Time) when you install or
release this component. For example,
if your project has a version of
“1.0-SNAPSHOT” and you deploy this
project’s artifacts to a Maven
repository, Maven would expand this
version to “1.0-20080207-230803-1” if
you were to deploy a release at 11:08
PM on February 7th, 2008 UTC. In other
words, when you deploy a snapshot, you
are not making a release of a software
component; you are releasing a
snapshot of a component at a specific
time.
Why would you use this? SNAPSHOT
versions are used for projects under
active development. If your project
depends on a software component that
is under active development, you can
depend on a SNAPSHOT release, and
Maven will periodically attempt to
download the latest snapshot from a
repository when you run a build.
Similarly, if the next release of your
system is going to have a version
"1.4", your project would have a
version "1.4-SNAPSHOT" until it was
formally released.
As a default setting, Maven will not
check for SNAPSHOT releases on remote
repositories. To depend on SNAPSHOT
releases, users must explicitly enable
the ability to download snapshots
using a repository or pluginRepository
element in the POM.
When releasing a project, you should
resolve all dependencies on SNAPSHOT
versions to dependencies on released
versions. If a project depends on a
SNAPSHOT, it is not stable as the
dependencies may change over time.
Artifacts published to non-snapshot
Maven repositories such as
http://repo1.maven.org/maven2 cannot
depend on SNAPSHOT versions, as
Maven's Super POM has snapshot's
disabled from the Central repository.
SNAPSHOT versions are for development
only.
If you really want to change this behavior, you can change the updatePolicy of your snapshot enabled repository:
<repositories>
<repository>
<id>my-repo</id>
<name>My Corporate Repository</name>
<url>http://repo.mycompany.com/maven2</url>
<layout>default</layout>
...
<snapshots>
<enabled>true</enabled>
<updatePolicy>never</updatePolicy>
<checksumPolicy>fail</checksumPolicy>
</snapshots>
</repository>
Switching to never will force you to use a manual update (using mvn -U). But beware, this is usually not what people want and expect with SNAPSHOTs.
For the record, Maven 3 has a -nsu, --no-snapshot-updates command line option allowing to Suppress SNAPSHOT updates.
See also
3.2. The POM
Repositories in the POM reference

Answer 2

You could generate a pom in your local repository by installing the file manually:
mvn install:install-file
-Dfile=[FILE]
-DgroupId=[GROUP]
-DartifactId=[ARTIFACT]
-Dversion=[VERSION]
-Dpackaging=jar
-DgeneratePom=true
-DcreateChecksum=true
EDIT: You wouldn't want to do this for snapshots.