The process of investigating "unable to resolve artifact" is fairly
mechanical, for most cases.
The first thing to do is to see if the artifact in question makes sense
to you. Sometimes, mainly due to unexpected property value expansions
(or failure there of), Maven tries to download an artifact that it's not
supposed to. For example, if you see Maven downloading
"org.glassfish:javax.javaee:${javaee.version}", then you can tell that
somehow Maven failed to expand "javaee.version" property.
This is often hard to investigate, especially when it happens through
transitive dependencies and project inheritance. "mvn
help:effective-pom" is a possibly useful tool, as it shows you the
effective POM after all the project inheritance and what not.
If the artifact in question appears to be legitimate, the next thing to
look is to check if such an artifact is really supposed to exist. This
we do by using a browser and look at our Maven repositories. Our bits
are split across 4 repositories --- the central repository (which you
can search from
http://www.mvnrepository.com/), Glassfish repository,
java.net maven1 and java.net maven2 repositories. The latter three are
all available on
http://maven.dyndns.org/
If it's not there, then either it's a programming mistake and someone
put an incorrect version in there, or someone forgot to publish the said
artifact (this happens if that person commits a POM change before the
artifact gets deployed by Hudson.)
If it's there, then it's a download problem. The network outage could be
a cause of this, so is the proxy setting. But by far the most likely
cause is that Maven wasn't looking into the right locations. The error
message from Maven always include where Maven looked for the artifact,
so you need to check this list to make sure it contains the right
location. If it's not, then we are missing some <repository>
declarations in our POM.
In all cases, "mvn -e" is your friend --- seeing the stack trace often
helps you see the root cause, which gets masked otherwise.
Hmm... maybe I should expand this a little more and put it into Wiki.
Roberto Chinnici wrote:
> I checked out the trunk from svn and deleted my local maven repository
> and I still get a build error.
>
> My question to you is: what do you do in this kind of situations?
>
> If (I'm guessing...) it's an issue with the java.net repository taking a
> long time to be updated, do you use the on-SWAN mirror?
>
> Is there any other meaningful way to recover from this sort of problems?
>
> I first got this error several hours ago.
>
> Thanks,
> Roberto
>
>
> ====
>
> [INFO]
> ------------------------------------------------------------------------
> [ERROR] BUILD ERROR
> [INFO]
> ------------------------------------------------------------------------
> [INFO] Failed to resolve artifact.
>
> Missing:
> ----------
> 1) com.sun.enterprise:hk2-maven:jar:0.2
>
> Try downloading the file manually from the project website.
>
> Then, install it using the command:
> mvn install:install-file -DgroupId=com.sun.enterprise
> -DartifactId=hk2-maven \
> -Dversion=0.2 -Dpackaging=jar -Dfile=/path/to/file
>
> Path to dependency:
> 1)
> org.glassfish.build:maven-glassfish-plugin:maven-plugin:1.0-SNAPSHOT
> 2) com.sun.enterprise:hk2-maven:jar:0.2
>
> ----------
> 1 required artifact is missing.
>
> for artifact:
> org.glassfish.build:maven-glassfish-plugin:maven-plugin:1.0-SNAPSHOT
>
> from the specified remote repositories:
> central (http://repo1.maven.org/maven2),
> maven2.java.net (http://download.java.net/maven/2),
> glassfish-repository (http://download.java.net/maven/glassfish),
> java.net (http://download.java.net/maven/1)
>
>
> [INFO]
> ------------------------------------------------------------------------
> [INFO] For more information, run Maven with the -e switch
> [INFO]
> ------------------------------------------------------------------------
> [INFO] Total time: 2 minutes 22 seconds
> [INFO] Finished at: Fri Apr 18 13:46:04 PDT 2008
> [INFO] Final Memory: 21M/38M
> [INFO]
> ------------------------------------------------------------------------
>
>
--
Kohsuke Kawaguchi
Sun Microsystems kohsuke.kawaguchi_at_sun.com