Why can't maven find a plugin?

Question

If I type the command:

mvn dependency:list

The docs suggest that I'll get a list of my project's dependencies. Instead though, I get this:

[INFO] Searching repository for plugin with prefix: 'dependency'.
[INFO] -----------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] -----------------------------------------------------------
[INFO] Required goal not found: dependency:list

Call me a hopeful naive, but I had hoped maven would download any plugins it didn't have. Does anyone know what might be leading to this error? Does anyone know where maven stores information about what plugins it has installed, and where they're stored in the maven repository?

Answer 1

Have you tried mvn -cpu dependency:list (or: mvn --check-plugin-updates dependency:list)? Probably, you have older version of dependency plugin which does not have goal list

If this does not help, try upgrading Maven. Since 2.0.9 default versions are provided by the Super POM for most important plugins (dependency plug-in included), so 2.0 version will be downloaded (which has list goal).

Or you can try removing the cached version of the plug-in from the repository (~/.m2/repository/org/apache/maven/plugins/maven-dependency-plugin/, where ~ is the user home directory).

Answer 2

Try latest maven version, usually upgrades to newer versions solve issues.

Answer 3

I have gotten a similiar result from being behind the corporate firewall. Proxy settings in your config (settings.xml) might be the answer.

<proxies>
  <proxy>
   <id>proxy</id> 
   <active>true</active> 
   <username>user</username>
   <password>passwrd</password>
   <protocol>http</protocol>
   <host>example.proxy.name.com</host>
  <port>80</port>
 </proxy>
</proxies>

Answer 4

To answer my own question, thanks to some comments that were made on it, the settings.xml file had been customized and did not list the central maven repository.

Oops.

Answer 5

Many Maven troubles can be solved easier by knowing all the details of the failed attempt when posting to forums (answering many of the follow-up questions folks above posted) or mailing list, and this is accomplished by running Maven with the debug and exception option switches like so: mvn <yourgoal> -X -e

Sample output then will look like this:

[~/Documents/Temp/Scratch] mvn clean -e -X
Using Java version: 1.6
+ Error stacktraces are turned on.
Maven version: 2.0.9
Java version: 1.6.0_07
OS name: "mac os x" version: "10.5.6" arch: "x86_64" Family: "mac"
[DEBUG] Building Maven user-level plugin registry from: '/Users/mccm06/.m2/plugin-registry.xml'
[DEBUG] Building Maven global-level plugin registry from: '/Applications/Dev/apache-maven/conf/plugin-registry.xml'
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Default Project
[INFO]    task-segment: [clean]
[INFO] ------------------------------------------------------------------------
[DEBUG] Retrieving parent-POM: org.apache.maven.plugins:maven-plugins::10 for project: null:maven-clean-plugin:maven-plugin:2.2 from the repository.
[DEBUG] Retrieving parent-POM: org.apache.maven:maven-parent::7 for project: org.apache.maven.plugins:maven-plugins:pom:10 from the repository.
[DEBUG] Retrieving parent-POM: org.apache:apache::4 for project: org.apache.maven:maven-parent:pom:7 from the repository.
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Cannot execute mojo: clean. It requires a project with an existing pom.xml, but the build is not using one.
[INFO] ------------------------------------------------------------------------
[DEBUG] Trace
org.apache.maven.lifecycle.LifecycleExecutionException: Cannot execute mojo: clean. It requires a project with an existing pom.xml, but the build is not using one.
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:583)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLifecycle(DefaultLifecycleExecutor.java:499)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:478)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:330)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:291)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:142)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:336)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:129)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:287)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
        at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
        at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
        at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
Caused by: org.apache.maven.plugin.MojoExecutionException: Cannot execute mojo: clean. It requires a project with an existing pom.xml, but the build is not using one.
        at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:377)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
        ... 16 more
[INFO] ------------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Mon Feb 16 10:59:39 MST 2009
[INFO] Final Memory: 2M/7M
[INFO] ------------------------------------------------------------------------