Nikolay Khitrin created SOLR-5526:
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Summary: 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, 5.0
Environment: Linux, Java 1.7.0_45
Reporter: Nikolay Khitrin
Priority: Blocker
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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