Version: 9.4.25.v20191220 |

Chapter 33. Troubleshooting
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## Chapter 33. Troubleshooting

This is a collection of helpful tricks and tips that we have come across to address odd issues that might arise.

## 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 Oracle Bug 4774421 for more information.

### Remedy

The remedy is to avoid hot replacing Jar or WAR files, which can be difficult if you are using the 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 setExtractWAR option set to true. This causes the WAR to be extracted to a 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 WebAppContext.setCopyWebInf(true), which (re)copies just the WEB-INF directory to a different location.
- Deploy an unpacked WAR file with the setCopyWebDir option set to true. This causes the directory to be extracted to a new location.

If you have problems with Windows file-locking preventing static file editing (such as JSP or HTML), use the WebAppContext .setCopyWebDir(true) option.

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