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https://issues.apache.org/jira/browse/LUCENE-5956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14614613#comment-14614613
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Uwe Schindler commented on LUCENE-5956:
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bq. What I'm trying to do, which should work, and appears to be working, is to
rename all org.apache.lucene for a given version to some.other.place.luceneN.
At the moment, at least classname lookups appear to be working. (Other weird
things are going on, but I don't have the foggiest idea what's going on there
yet.)
You have to load them in different classloaders, see my reply on user mailing
list:
{quote}
Hi,
It could be the reason for this is your classpath:
If you load all Lucene Versions into the same classloader (but with different
package names - I assume you use Maven Shade plugin to do this), Lucene 3 will
load perfectly, yes; Lucene 4 will also load perfectly, yes! But when it tries
to load Lucene 5, it will fail to load all shipped codecs. Codecs are not
identified by their Java package name, but by the symbolic name (like
"Lucene50") as written into the index. The SPI interface of Lucene will load
all codecs from classpath and save them in a lookup map based on the symbolic
name. If the Lucene 4 JAR file are placed before Lucene 5 JARs, the "slots" for
codec names are already taken (because the Lucene 5 loader will see the Lucene
4 codecs first), so loading Lucene 5 variants of old codecs is a no-op. This
may cause those problems, because Lucene 5 ships with "modified" versions of
the old Lucene 4 codecs - but they are not identical.
You can only workaround by loading the Lucene JARs into completely different
classloaders (don't forget to also set context classloader!). In that case you
would not even need to change package names!
{quote}
> Add runnable index upgrader
> ---------------------------
>
> Key: LUCENE-5956
> URL: https://issues.apache.org/jira/browse/LUCENE-5956
> Project: Lucene - Core
> Issue Type: New Feature
> Reporter: Ryan Ernst
>
> As a spinoff from discussion in LUCENE-5940, I'd like to add a new module
> "lucene-upgrader", move {{IndexUpgrader}} to this, and add embed older
> versions of lucene (just enough to upgrade indexes) in the built version of
> the module's jar. This would be runnable from the command line with
> something like:
> {{java -jar lucene-upgrader-4.11.0.jar /path/to/index}}
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