How to suppress Java warnings for specific directories or files such as generated code

I'm using a parser generator that creates somewhat ugly code. As a result my Eclipse project has several dozen warnings emanating from generated source files. I know I can use the @SuppressWarning annotation to suppress particular warnings in particular elements, but any annotations I add by hand will be lost when the parser generator runs again. Is there a way to configure Eclipse to suppress warnings for a particular file or directory?

Starting with version 3.8 M6, Eclipse (to be exact: the JDT) has built-in functionality for this. It is configurable through a project's build path: Project properties > Java Build Path > Compiler > Source

Announced here: Eclipse 3.8 and 4.2 M6 - New and Noteworthy, called Selectively ignore errors/warnings from source folders. That's also where the screenshot is from. This is the new feature developed on the previously linked Bug 220928.

There is a ticket for this, Bug 220928, that has since been completed for Eclipse 3.8. Please see this answer for details.

If you're stuck with Eclipse 3.7 or lower: The user "Marc" commenting on that ticket created (or at least links to) a plugin called 'warningcleaner' in comment 35. I'm using that with a lot of success while waiting for this feature to be integrated into Eclipse.

It's really quite simple:

1. Install plugin.
2. Right-click project and select "Add/remove generated code nature".
3. Open the project settings (right-click and select "properties").
4. Open the tab 'Warning Cleaner'.
5. Select the source folders you want to ignore the warnings from.