Two simple commands to resolve problems with Maven installed via Homebrew

UpdateEnvironmentPlist.sh

defaults write ~/.MacOSX/environment.plist M2_HOME `brew --prefix maven`/libexec
defaults write ~/.MacOSX/environment.plist M2 `brew --prefix maven`/libexec/bin

When you install Maven via Homebrew, chances are that you run into this error, as soon as you try using it:

Exception in thread "main" java.lang.NoClassDefFoundError: org/codehaus/plexus/classworlds/launcher/Launcher
Caused by: java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

To fix it, you need to point the M2_HOME environment variable to the libexec directory within the maven installation directory (run brew --prefix maven to see the directory of the currently activated version). Setting the M2 variable isn't necessary, but might help, if the problem persists. The two commands above will automatically set the correct paths in your ~/.MacOSX/environment.plist file and should be run every time you update Maven via Homebrew. In order for the changes to take effect you have to log out and in again or restart your Mac.

Credit goes to digitalsanctum.com for figuring this out.

Thanks for the tip mate!

Thank you, This was the only solution that worked.

Thanks, this really saved me. I also did

export M2=brew --prefix maven/libexec/bin
export M2_HOME=brew --prefix maven/libexec

so that I could use maven in my open shell.

Thanks so much!

Thank you! I've been at this for too long. This fixed it

Thanks for your tips. @sanderson-sfdc

...and if like me you got
Exception in thread "main" java.lang.UnsupportedClassVersionError: org/apache/maven/cli/MavenCli : Unsupported major.minor version 51.0

Then you need to set JAVA_HOME (check you are using the correct JDK version in the command):
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home

Thanks! This just solved my problem!

I just downloaded maven zip file and extracted to my local folder in mac.
maven commands are not recognized in mac