maven-exec-plugin throws exception for no apparent reason

Question

I type the following in a Windows shell in the root of a Maven project that contains a class with a

public static void main(String[] args)

method that I'd like to run.

mvn exec:java -Dexec.mainClass="com.spp.config.main.SqlGeneratorHarness" -e

The class exists and is compiled in that package (i.e., target/classes/com/spp/config/main/SqlGeneratorHarness.class).

I see...

+ Error stacktraces are turned on.  
[INFO] Scanning for projects...  
[INFO] Searching repository for plugin with prefix: 'exec'.  
[INFO] ------------------------------------------------------------------------  
[ERROR] BUILD FAILURE  
[INFO] ------------------------------------------------------------------------  
[INFO] Invalid task '.mainClass=com.spp.config.main.SqlGeneratorHarness': you must specify a valid 
       lifecycle phase, or a goal in the format plugin:goal or pluginGroupId:pluginArtifactId:pluginVersion:goal
[INFO] ------------------------------------------------------------------------
[INFO] Trace org.apache.maven.BuildFailureException: Invalid task' .mainClass=com.spp.config.main.SqlGeneratorHarness': you must specify 
       a valid lifecycle phase, or a goal in the format plugin:goal or pluginGroupId:pluginArtifactId:pluginVersion:goal
       at org.apache.maven.lifecycle.DefaultLifecycleExecutor.getMojoDescriptor(DefaultLifecycleExecutor.java:1830)
       at org.apache.maven.lifecycle.DefaultLifecycleExecutor.segmentTaskListByAggregationNeeds(DefaultLifecycleExecutor.java:462)
       at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:175)
       at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:328)
       at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138)
       at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
       at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:60)
       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)
[INFO] ------------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Tue Sep 27 14:33:52 PDT 2011
[INFO] Final Memory: 3M/122M
[INFO] ------------------------------------------------------------------------

I've tried variations like

mvn exec:exec -Dexec.executable="java" [...]

and

mvn org.codehaus.mojo:exec-maven-plugin:1.2.1:java [...]

to no avail. What gives?

I'm running Maven 2.2.1, Java JDK 1.6.0_27 on Windows 7 Enterprise 64-bit.

A snippet from my pom.xml for the exec-maven-plugin is...

<plugin> 
   <groupId>org.codehaus.mojo</groupId> 
   <artifactId>exec-maven-plugin</artifactId> 
   <version>${exec-maven-plugin.version}</version> 
</plugin> 

where the version is set in the <properties>

Answer 1

So... revisiting this... if you use Windows PowerShell, you will get the exception I originally reported. If, however, you use cmd.exe, then you should be able to run the class with the command as I posted (with or without wrapping double-quotes).

Answer 2

There's something very basic going wrong. Try losing the quotation marks. They're not needed there. In fact, try starting with something simpler, like

mvn -e exec:java -Dexec.mainClass=foo 

That should give you the error "An exception occured while executing the Java class. foo", and the root cause should be a ClassNotFoundException:

Caused by: java.lang.ClassNotFoundException: foo
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)

Type it out yourself. Don't copy/paste the command from somewhere else.

Answer 3

Just a quick checklist:

1. Rename ~/.m2 folder and run mvn exec:java ... again and let Maven to download everything again from central.
2. Check that your exec plugin is downloaded from central. (Check that your local repository contains the same files as the central.)
3. Looking for suspicious repository and pluginRepository tags in the pom.xml (and parent poms as well).
4. Looking for suspicious repository, pluginRepository and mirror tags in the settings.xml.
5. Checking the project in an other machine - copy it and try to build/run exec:java in an other machine.
6. Download Maven 3.x and try to run the exec with it.