java.lang.ClassNotFoundException: org.apache.tools.ant.Main

This error should not be occuring when you install Ant out-of-the-box and run it. However, on the rare occasions it does occur - the solution is quite simple.

java.lang.ClassNotFoundException: org.apache.tools.ant.Main
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at org.apache.tools.ant.launch.Launcher.run(Launcher.java:244)
        at org.apache.tools.ant.launch.Launcher.main(Launcher.java:67)

Take a look at the ANT_HOME/lib folder - and ensure that the ant.jar is in there and showing a size of 1MB or higher.

It is usually due to a corrupted version of ant.jar in the above path.

Executing multiple mvn commands from a Windows bat file

When running Maven, if you try to run multiple Maven commands in a batch (.bat) file, it only runs the first one and exits to the command prompt

mvn clean
mvn package

This occurs since mvn itself is a bat file. To overcome this, you need to stop Windows passing control to the mvn.bat script by using the call command for each call to mvn.

call mvn clean
call mvn package

Additionally, to catch failures you will need to do this

call mvn clean
echo Exit Code = %ERRORLEVEL%
if not "%ERRORLEVEL%" == "0" exit /b

call mvn package
echo Exit Code = %ERRORLEVEL%
if not "%ERRORLEVEL%" == "0" exit /b

A failure throws an ERRORLEVEL higher than 0. Otherwise it will keep moving ahead even if it fails. Note: if you're using maven 2.0.7 or older, there is a possibility that the mvn does not return an ERRORLEVEL > 0 for the process to exit. Lots of examples are available here http://www.google.co.uk/search?hl=en&q=mvn+exit+ERRORLEVEL&meta= A simple test to check if your version allows this - run the commands below in a bat file.

call mvn unknown
echo Exit Code = %ERRORLEVEL%

You should get a Failure with exit code 1 as below. If it does not fail, then upgrade to a higher version of Maven in which the issue is fixed.

D:\maven-2.0.7\bin>call mvn unknown
[INFO] Scanning for projects...
[INFO] ----------------
[ERROR] BUILD FAILURE
[INFO] ----------------
[INFO] Invalid task 'unknown': you must 

specify a valid lifecycle phase, 

or a goal in the format plugin:goal or  

pluginGroupId:pluginArtifactId:pluginVersion:goal

[INFO] ----------------
[INFO] For more information, run Maven 

with the -e switch
[INFO] ----------------
[INFO] Total time: < 1 second
[INFO] Finished at: Tue Mar 10 12:07:12 

GMT+05:30 2009
[INFO] Final Memory: 1M/2M
[INFO] ----------------
Exit Code = 1

Update Learnt the hard way that the call to mvn must immediately be followed by the checking of the ERRORLEVEL. Our build.bat script measures time taken for each step like below:

time /t
call mvn install
time /t
if not "%ERRORLEVEL%" == "0" exit /b

In this case, it loses the ERRORLEVEL value from the mvn command. Hence we need to ensure:

time /t
call mvn install
if not "%ERRORLEVEL%" == "0" exit /b
time /t