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https://issues.apache.org/jira/browse/SOLR-5526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877902#comment-13877902
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Hoss Man commented on SOLR-5526:
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Hey Vitaliy,
For the most part, these tests look great -- just a few minor things i think we
should try to clean up...
* QParserPlugin.standardPlugins's javadoc needs to point out the importance of
these names being static & final so people aren't surprised by these tests
when new parsers are added in the future.
* TestStandardQParsers is doing something sufficiently odd that it really needs
some javadocs explaining why it exists (ie: mention the class loading problems
associated if there is a standardPlugin that has a non-static, non-final name,
with an {{@see}} this issue, {{@see QParserPlugin.standardPlugins}}, etc...)
* we should probably make TestStandardQParsers assert that the static & final
name it finds in each class matches the name associated in
QParserPlugin.standardPlugins.
* solrconfig-query-parser-init.xml has a cut & paste comment referring to an
unrelated test.
* TestInitQParser should have a javadoc comment explaining what the point of
the test is
* TestInitQParser should actaully do a query using the "fail" parser registered
in the config, to help future-proof us against someone unwittingly changing the
test config in a way that defeats the point of the test.
...if you want to take a crack at this that would be great, if not i'll try to
make some time later this week.
> Query parser extends standard cause NPE on Solr startup
> -------------------------------------------------------
>
> Key: SOLR-5526
> URL: https://issues.apache.org/jira/browse/SOLR-5526
> Project: Solr
> Issue Type: Bug
> Components: query parsers
> Affects Versions: 4.5.1, 4.6, 5.0
> Environment: Linux, Java 1.7.0_45
> Reporter: Nikolay Khitrin
> Priority: Blocker
> Attachments: NPE_load_trace, SOLR-5526-final-names.patch,
> SOLR-5526-final-names.patch, SOLR-5526-tests.patch, SOLR-5526.patch,
> SOLR-5526.patch
>
>
> Adding any custom query parser extending standard one with non-final field
> {{NAME}} lead to messy {{NullPointerException}} during Solr startup.
> Definition of standard parsers is located in
> {{QParserPlugin.standardPlugins}} static array. The array contains names from
> static {{NAME}} fields and classes for each plugin.
> But all of listed parsers are derived from {{QParserPlugin}}, so we have
> circular dependency of static fields.
> Normally, class loader start initializing {{QParserPlugin}} before all listed
> plugins in {{SolrCore.initQParsers}}, and array elements referenced to
> {{NAME}} plugins' fields are filled properly.
> Custom parsers are instantiated before standard parsers. And when we subclass
> plugin with non-final {{NAME}} field and add it to Solr via
> {{solrconfig.xml}}, class loader start loading our class before
> {{QParserPlugin}}. Because {{QParserPlugin}} is a superclass for plugin, it
> must be initialized before subclasses, and static dereferencing cause null
> elements in {{standardPlugins}} array because it filled before {{NAME}} field
> of loading plugin's superclass.
> How to reproduce:
> # Checkout Solr (trunk or stable)
> # Add the following line to solr/example/solr/collection1/conf/solrconfig.xml
> {{<queryParser name="fail" class="solr.search.LuceneQParserPlugin"/>}}
> # Call ant run-example in solr folder
> Possible workarounds:
> * dev-workaround: add {{int workaround =
> QParserPlugin.standardPlugins.length;}} as a first line to
> {{SolrCore.initQParsers}}
> * user-workaround: add plugin with final {{NAME}} field (edismax) to
> solrconfig.xml before subclasses of standard plugins.
> {{<queryParser name="workaround"
> class="solr.search.ExtendedDismaxQParserPlugin"/>}}
>
> Possible fix:
> Move {{standardPlugins}} to new final class to break circular dependency.
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