Custom maven plugin execution fails with classnotfound

Question

I am writing what is essentially my first maven plugin, so this might just be a lack of google skills, but here goes.

I am using the maven-plugin-plugin to create a plugin

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-plugin-plugin</artifactId>
            <version>3.5.2</version>
            <executions>
                <execution>
                    <id>default-descriptor</id>
                    <phase>process-classes</phase>
                </execution>
            </executions>
        </plugin>

I am using maven version 3.5.2.

The plugin project builds fine, but when I try to use it in another project it fails with this error:

Caused by: java.lang.ClassNotFoundException: org.sonatype.aether.graph.Dependency
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass (SelfFirstStrategy.java:50)
at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass (ClassRealm.java:271)
....(Lots of google.inject stuff)....
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getConfiguredMojo (DefaultMavenPluginManager.java:519)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:121)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:208)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:309)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:194)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:107)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:955)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:290)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:194)
at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:498)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:356)

After some googeling I found this stackoverflow post which I don't fully understand, but I did look at the bugreport and changed my Dependency plugin version (in both the plugin project and the consumer project because I have no idea what I'm doing :) )

The error is still there in unchanged form. The error is happening in the generatesources phase which is where my plugin is running, and removing the plugin makes the error disappear, so I am fairly certain that my plugin is to blame.

Can someone explain in simple terms what is happening, and help me with a solution? Thank you much in advance.

Here is the entire plugin POM

<project>
<modelVersion>4.0.0</modelVersion>

<groupId>...</groupId>
<artifactId>...</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>maven-plugin</packaging>

<name>...</name>

<properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>



<dependencies>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-plugin-api</artifactId>
        <version>3.5.2</version>
    </dependency>

    <!-- dependencies to annotations -->
    <dependency>
        <groupId>org.apache.maven.plugin-tools</groupId>
        <artifactId>maven-plugin-annotations</artifactId>
        <version>3.5.2</version>
        <scope>provided</scope>
    </dependency>


    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-core</artifactId>
        <version>3.5.2</version>
    </dependency>
    <dependency>
        <groupId>org.apache.maven.shared</groupId>
        <artifactId>maven-dependency-tree</artifactId>
        <version>3.0.1</version>
    </dependency>

    <dependency>
        <groupId>org.alfresco</groupId>
        <artifactId>alfresco-data-model</artifactId>
        <version>5.1.g</version>
    </dependency>

    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-project</artifactId>
        <version>2.2.1</version>
        <scope>provided</scope>
    </dependency>

    <dependency>
        <groupId>com.squareup</groupId>
        <artifactId>javapoet</artifactId>
        <version>1.11.1</version>
    </dependency>



    <dependency>
        <artifactId>junit</artifactId>
        <groupId>junit</groupId>
        <version>4.11</version>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <plugins>
    <plugin>
      <artifactId>maven-dependency-plugin</artifactId>
      <version>2.9</version>
    </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-plugin-plugin</artifactId>
            <version>3.5.2</version>
            <executions>
                <execution>
                    <id>default-descriptor</id>
                    <phase>process-classes</phase>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

---

EDIT: I tried adding

    <dependency>
        <groupId>org.sonatype.aether</groupId>
        <artifactId>aether-api</artifactId>
        <version>1.8</version>
    </dependency>
    <dependency>
        <groupId>org.sonatype.aether</groupId>
        <artifactId>aether-util</artifactId>
        <version>1.8</version>
    </dependency>

But the problem persists. I tried adding it to both projects as well. Same result.

Answer 1

You shoud add the aether api dependency to your plugin pom:

   <dependency>
      <groupId>org.sonatype.aether</groupId>
      <artifactId>aether-api</artifactId>
    </dependency>