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[[troubleshooting-zip-exceptions]]
=== Troubleshooting Zip Exceptions

A Zip exception occurs when Jetty rereads a Jar or WAR file.

The JVM maintains a cache of zip file indexes, and does not support hot replacement of zip files.
Thus if you redeploy a web application using the same WAR or Jar files, exceptions occur when Jetty rereads the jars.
See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4774421[Oracle Bug 4774421] for more information.

[[remedy]]
==== Remedy

The remedy is to avoid hot replacing Jar or WAR files, which can be difficult if you are using the
link:#configuring-specific-webapp-deployment[Webapp Provider].
You can use the following techniques to reduce exposure to this issue:

* Deploy unpacked classes in the `WEB-INF/classes` directory rather than as a Jar file under `WEB-INF/lib`.
* Deploy all WAR and Jar files with a version number in their filename or path.
If the code changes, a new version number applies, avoiding the cache problem.
* Deploy a packed WAR file with the link:{JDURL}/org/eclipse/jetty/webapp/WebAppContext.html#setExtractWAR(boolean)[setExtractWAR] option set to true.
This causes the WAR to be extracted to a link:#ref-temporary-directories[temporary directory] and thus to a new location.
This might not be sufficient if you want to hot-replace and re-extract the WAR, so you might also need to use link:{JDURL}/org/eclipse/jetty/webapp/WebAppContext.html#setCopyWebInf(boolean)[WebAppContext.setCopyWebInf(true)], which (re)copies just the WEB-INF directory to a different location.
* Deploy an unpacked WAR file with the link:{JDURL}/org/eclipse/jetty/webapp/WebAppContext.html#setCopyWebDir(boolean)[setCopyWebDir] option set to true.
This causes the directory to be extracted to a new location.

If you have problems with link:#troubleshooting-locked-files-on-windows[Windows file-locking] preventing static file editing (such as JSP or HTML), use the link:{JDURL}/org/eclipse/jetty/webapp/WebAppContext.html#setCopyWebDir(boolean)[WebAppContext .setCopyWebDir(true)] option.