DependencyResolutionException when upgrading from Maven 2.2.1 to Maven 3.0.4

Question

I'm trying to upgrade my project from Maven 2.2.1 to Maven 3.0.4 but am running into problems with a dependency resolution. I spent a full day trying to research this by looking through Maven documentation and similar posts, but I'm still stuck. This is my first question on stackoverflow, so hopefully I've followed etiquette here well enough. Thanks for your help!

My project structure is as follows:

pom.xml (acme-parent)
child-alpha
+-----> pom.xml

In addition, I have the following files in my own repository:

http://maven.my-own-repo.com/acme/child-dep-jdk15/maven-metadata-local.xml
http://maven.my-own-repo.com/acme/child-dep-jdk15/1.0/child-dep-jdk15-1.0.jar
http://maven.my-own-repo.com/acme/child-dep-jdk15/1.0/child-dep-jdk15-1.0.pom

child-alpha/pom.xml in turn has a profile dependency on my own acme:child-dep-jdk15, which has been separately built into a jar file and has its own .pom file specifying a parent that is the same acme-parent parent as child-alpha.

Here are excerpts from the relevant files:

acme-parent pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>acme</groupId>
    <artifactId>acme-parent</artifactId>
    <name>Acme Parent Project</name>
    <version>1</version>
    <packaging>pom</packaging>

    <properties>...</properties>

    <modules>
        <module>child-alpha</module>
    </modules>

    <repositories>
        <repository>
            <id>acme-repo</id>
            <url>http://maven.my-own-repo.com</url>
        </repository>
        <repository>
            <id>central</id>
            <url>http://repo1.maven.org/maven2</url>
        </repository>
    </repositories>

    <pluginRepositories>...</pluginRepositories>

    <build>
      <plugins>...</plugins>
    </build>

    <dependencies>...</dependencies>
</project>

child-alpha pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>acme</groupId>
        <artifactId>acme-parent</artifactId>
        <version>1</version>
    </parent>
    <artifactId>child-alpha</artifactId>
    <name>Child Alpha Project</name>
    <version>1.0</version>
    <packaging>jar</packaging>

    <scm>...</scm>

    <properties>...</properties>

    <build>
      <resources>...</resources>
      <plugins>...</plugins>
    </build>

    <profiles>
        <profile>
            <id>jdk15</id>
            <activation>
                <activeByDefault>true</activeByDefault>
                <jdk>1.5</jdk>
            </activation>
            <dependencies>
                <dependency>
                    <groupId>acme</groupId>
                    <artifactId>child-dep-jdk15</artifactId>
                    <version>1.0</version>
                </dependency>
            </dependencies>
        </profile>
    </profiles>

    <dependencies>...</dependencies>
</project>

child-dep-jdk15-1.0.pom:

<project>
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>acme</groupId>
        <artifactId>acme-parent</artifactId>
        <version>1</version>
    </parent>
    <groupId>acme</groupId>
    <artifactId>child-dep-jdk15</artifactId>
    <name>Acme Child Dependency</name>
    <version>1.0</version>
    <packaging>jar</packaging>

    <build>...</build>

    <dependencies>...</dependencies>
</project>

When I tried to build child-alpha (while in the child-alpha directory), I ran the following command:

mvn -U -e clean install

And I got the following log messages and stack trace (extraneous messages removed):

Downloading: http://maven2.my-own-repo.com/acme/acme-parent/1/acme-parent-1.pom
Downloading: http://repo1.maven.org/maven2/acme/acme-parent/1/acme-parent-1.pom

[...]

[ERROR] Failed to execute goal on project child-alpha: Could not resolve dependencies for project acme:child-alpha:jar:1.0: [...]

Caused by: org.apache.maven.project.DependencyResolutionException: Could not resolve dependencies for project acme:child-alpha:jar:1.0: [...]

Caused by: org.sonatype.aether.collection.DependencyCollectionException: Failed to collect dependencies for [...]
    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:258)
    at org.sonatype.aether.impl.internal.DefaultRepositorySystem.collectDependencies(DefaultRepositorySystem.java:308)
    at org.apache.maven.project.DefaultProjectDependenciesResolver.resolve(DefaultProjectDependenciesResolver.java:150)
    ... 23 more
Caused by: org.sonatype.aether.resolution.ArtifactDescriptorException: Failed to read artifact descriptor for acme:child-dep-jdk15:jar:1.0
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:331)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:186)
    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.process(DefaultDependencyCollector.java:412)
    at org.sonatype.aether.impl.internal.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:240)
    ... 25 more
Caused by: org.apache.maven.model.resolution.UnresolvableModelException: Could not find artifact acme:acme-parent:pom:1 in acme-repo (http://maven.my-own-repo.com)
    at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:126)
    at org.apache.maven.model.building.DefaultModelBuilder.readParentExternally(DefaultModelBuilder.java:813)
    at org.apache.maven.model.building.DefaultModelBuilder.readParent(DefaultModelBuilder.java:664)
    at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:310)
    at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:232)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:322)
    ... 28 more
Caused by: org.sonatype.aether.resolution.ArtifactResolutionException: Could not find artifact acme:acme-parent:pom:1 in acme-repo (http://maven.my-own-repo.com)
    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:538)
    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:216)
    at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:193)
    at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:122)
    ... 33 more
Caused by: org.sonatype.aether.transfer.ArtifactNotFoundException: Could not find artifact acme:acme-parent:pom:1 in acme-repo (http://maven.my-own-repo.com)
    at org.sonatype.aether.connector.wagon.WagonRepositoryConnector$4.wrap(WagonRepositoryConnector.java:947)
    at org.sonatype.aether.connector.wagon.WagonRepositoryConnector$4.wrap(WagonRepositoryConnector.java:941)
    at org.sonatype.aether.connector.wagon.WagonRepositoryConnector$GetTask.run(WagonRepositoryConnector.java:669)
    at org.sonatype.aether.util.concurrency.RunnableErrorForwarder$1.run(RunnableErrorForwarder.java:60)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:680)

While using Maven 2, I've never needed the acme-parent pom.xml at the following location: http://maven2.my-own-repo.com/acme/acme-parent/1/acme-parent-1.pom

The reason we don't have the parent pom.xml on our own repo is is that we have a script used when creating version control branches that changes some values in acme-parent pom.xml depending on which branch we're on, so it would be complicated to put that pom.xml in the repo and keep it correctly updated for all the different branches we're trying to build concurrently with our continuous integration server.

In Maven 2, when doing builds of child-alpha, Maven would have no trouble finding acme-parent pom.xml one directory up, i.e. with a relative path of ../pom.xml, so it would never try going to my repositories to find it. Having the parent pom.xml in my local checkout only and not having it in the repo worked fine in Maven 2.

However, when I tried building child-alpha under Maven 3.0.4, the exception above occurred. At first, I thought I needed to explicitly set the relativePath within the tags at the top of child-alpha's pom.xml, but that didn't fix it -- and acme-parent's pom.xml is indeed already in the default relativePath of ../pom.xml, so there's no need to explicitly set it.

Then, I tried commenting out the child-dep-jdk15 dependency within the section of child-alpha's pom.xml. The child-alpha maven build completes successfully with this dependency commented out.

I don't understand why child-alpha won't build in Maven 3 when the child-dep-jdk15 dependency is in place. If Maven was able to correctly find the acme-parent pom.xml initially (per the block at the top), why is it now trying to download it from the repos when processing the child-dep-jdk15 dependency? Have I configured something incorrectly, and if so, how should I fix it?

One other thing: if I first run mvn -N install in the same directory as acme-parent's pom.xml, and then try building child-alpha, then the child-alpha build succeeds, even when keeping the dependency child-dep-jdk15 in the code. After I run that command, I'm able to verify acme-parent-1.pom is in my local .m2 directory. While this workaround may be okay for individual developers, it'd be a problem for our continuous integration server, which needs to be able to run concurrent builds for different branches.

I'd strongly prefer not to have to reconfigure my repository to host the acme-parent pom.xml due to the version control branching changes I've mentioned above.

Answer 1

In Maven 3 if you just had a failed download and have fixed it (e.g. by uploading the jar to a repository) it will cache the failure. To force a refresh add -U to the command line.

For other possible reasons of DependencyResolutionException see Maven Confluence.