Michael Noack created CONFIGURATION-788:
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Summary: AbstractHierarchicalFileConfiguration can lose data when
#save() is interrupted by JVM abort/power failure
Key: CONFIGURATION-788
URL: https://issues.apache.org/jira/browse/CONFIGURATION-788
Project: Commons Configuration
Issue Type: Bug
Components: File reloading
Affects Versions: 1.10
Environment: This occurs in any environment with any use of
AbstractFileConfiguration#save(), AbstractFileConfiguration#save(URL) or
AbstractFileConfiguration#save(File).
Reporter: Michael Noack
Attachments:
0001-Implemented-keep-backup-feature-for-file-configurati.patch
When saving the current configuration, either using any of the #save() Methods
or when setting a property while auto-save is enabled the method
AbstractFileConfiguration#save(URL) effectively wipes the file content when
opening the OutputStream.
If the JVM gets destroyed or the machine powered down before the new
configuration has been serialized to the file an empty file remains with no
configuration at all.
I've created a patch on top of the RELEASE_1_10_BRANCH which introduces a
mitigation. The mitigation consists of a "keep backup" flag in
AbstractFileConfiguration which, if set, creates a copy of the current
configuration file before writing into it.
When a configuration exception occurs upon loading the configuration again the
exception will be caught and loading of the backup is attempted first before
rethrowing the exception when this fails as well.
To allow existing implementations to profit from this without touching all
instances a global flag has been added to AbstractHierarchicalFileConfiguration
which is then inherited by all future delegates added to any instance of
AbstractHierarchicalFileConfiguration.
Four unit tests for this mitigation feature have been added to
TestHierarchicalXMLConfiguration.
I've uploaded a repository with the commit to github:
https://github.com/noamik/commons-configuration/tree/RELEASE_1_11_BRANCH
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