Why might Maven ignore updated classes during install?

I've been seeing odd behaviour from my Maven 2.2.1 installation whilst doing war installs.

Occasionally, I will update a class but the updated version is not packaged up in the artifact produced by mvn install.

So far, I have determined that an updated .class file is produced in the target directory, and that the class of the same name in the produced .war is not the same (different date modified, different size)

Running Maven from the command line with the -X flag produced debug output for the class like:

[DEBUG] * WEB-INF/classes/mypackage/MyClass.class is up to date.

I think I've also had the same problem before where the file that was cached(?) was an incomplete compile from Eclipse, causing 'Unresolved Compilation Problem' errors from the Maven build, but a working artifact from an Eclipse export.

• How doe开发者_如何学编程s Maven determine whether a file 'is up to date' during the install process?
• Where are the files Maven is comparing to?
• Can I force Maven to build a package from scratch?
• Any other ideas would be appreciated!

So far, I have determined that an updated .class file is produced in the target directory, and that the class of the same name in the produced .war is not the same (different date modified, different size)

Just to be sure, the classes should be built under target\classes, not target.

• Can I force Maven to build a package from scratch?

You can force a full build by running

mvn clean install

This performs a clean (essentially removes the target directory) before running the install phase.

Also - check for copies of your classes outside of the Maven build directory. In this case as it is a webapp, check src/main/webapp/WEB-INF/classes