If you use Jetty you might notice that once it's running you can't edit any static files because it says they are already in use and locked.
Why ? Because Jetty buffers static content for webapps such as html files, css files, images etc and uses memory mapped files to do this if the NIO connectors are being used. The problem is that on Windows, memory mapping a file causes the file to be locked, so that the file cannot be updated or replaced. This means that effectively you have to stop Jetty in order to update a file.
In case this happens follow these steps:
1. Extract the runjettyrun_1.0.1.jar in the eclipse plugin directory
2. Extract the jetty-6.1.6.jar in the lib directory of the previous jar.
3. Edit the file org\mortbay\jetty\webapp\webdefault.xml and change the "useFileMappedBuffer" to false. It should look like the following:
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<init -param> <param -name>useFileMappedBuffer</param> <param -value>false</param> </init>
4. Pack everything back up and overwrite the runjettyrun jar in the plugin directory.
5. If you still get the error after step 4 start eclipse.exe with -clean and then recreate the Jetty configuration. (It just need to replace whatever jar's it copies in your workspace .plugins dir)