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From "Sergey Vladimirov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DBCP-335) NPE with MySQL PreparedStatement
Date Tue, 01 Jun 2010 08:30:40 GMT

    [ https://issues.apache.org/jira/browse/DBCP-335?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12873920#action_12873920
] 

Sergey Vladimirov commented on DBCP-335:
----------------------------------------

Marcus,

In your example code DBCP is not used. If you have exceptions with provided example - it is
not DBCP related.

Anyway, if you need to periodicaly check if connection alive, it much better to use DBCP to
do so. In fact, DBCP already has properties to check if connection alive:

validationQuery - query used to validate connection
testWhileIdle - set to true to check connection while they are in the pool
timeBetweenEvictionRunsMillis - time between checks (and evictions)

And one more thing about example. Personally i believe (IMHO) it is not correct to call Statement.execute()
without synchronization.

> NPE with MySQL PreparedStatement
> --------------------------------
>
>                 Key: DBCP-335
>                 URL: https://issues.apache.org/jira/browse/DBCP-335
>             Project: Commons Dbcp
>          Issue Type: Bug
>    Affects Versions: 1.4
>         Environment: CloudFoundry, Linux, Sun Java 1.6.0_04, Grails 1.2.2, MySQL Connector
5.1.12
>            Reporter: Marcus Better
>
> My Grails application using MySQL and DBCP often throws an exception as below. I can
trigger it by making a simultaneous requests (three at a time) on differend threads in a ThreadPoolExecutor.
The requests would all use the same query. This triggers the exception with a few percent
probability.
> I have tried with DBCP 1.2.2 and 1.4.
> There is a similar-looking [MySQL bug|http://bugs.mysql.com/bug.php?id=41628] but they
blame the pool...
> {code}
> Exception in thread "pool-1-thread-12" java.lang.NullPointerException
>         at com.mysql.jdbc.PreparedStatement.fillSendPacket(PreparedStatement.java:2475)
>         at com.mysql.jdbc.PreparedStatement.fillSendPacket(PreparedStatement.java:2451)
>         at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2205)
>         at org.apache.commons.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96)
>         at org.apache.commons.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:96)
>         at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
>         at org.hibernate.loader.Loader.getResultSet(Loader.java:1808)
>         at org.hibernate.loader.Loader.doQuery(Loader.java:697)
>         at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
>         at org.hibernate.loader.Loader.loadEntity(Loader.java:1881)
>         at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:71)
>         at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:65)
>         at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3072)
>         at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:434)
>         at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:415)
>         at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:165)
>         at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:121)
>         at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:905)
>         at org.hibernate.impl.SessionImpl.immediateLoad(SessionImpl.java:863)
>         at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:95)
>         at org.codehaus.groovy.grails.orm.hibernate.proxy.HibernateProxyHandler.unwrapProxy(HibernateProxyHandler.java:80)
>         at org.codehaus.groovy.grails.orm.hibernate.cfg.GrailsHibernateUtil.unwrapProxy(GrailsHibernateUtil.java:322)
>         at org.codehaus.groovy.grails.orm.hibernate.cfg.GrailsHibernateUtil$unwrapProxy.call(Unknown
Source)
>         at org.codehaus.groovy.grails.plugins.orm.hibernate.HibernatePluginSupport$__clinit__closure88.doCall(HibernatePluginSupport.groovy:401)
>         at sun.reflect.GeneratedMethodAccessor381.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>         at java.lang.reflect.Method.invoke(Method.java:597)
>         at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:266)
>         at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:51)
>         at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:151)
>         at org.codehaus.groovy.grails.plugins.orm.hibernate.HibernatePluginSupport$__clinit__closure88.call(HibernatePluginSupport.groovy)
>         at sun.reflect.GeneratedMethodAccessor380.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>         at java.lang.reflect.Method.invoke(Method.java:597)
>         at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:86)
>         at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:234)
>         at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1049)
>         at groovy.lang.ExpandoMetaClass.invokeMethod(ExpandoMetaClass.java:923)
>         at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:880)
>         at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:924)
>         at groovy.lang.ExpandoMetaClass.invokeMethod(ExpandoMetaClass.java:923)
>         at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:880)
>         at org.codehaus.groovy.runtime.InvokerHelper.invokePogoMethod(InvokerHelper.java:739)
>         at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:722)
>         at org.codehaus.groovy.runtime.metaclass.ClosureMetaMethod$1.invoke(ClosureMetaMethod.java:135)
>         at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:234)
>         at groovy.lang.MetaClassImpl.getProperty(MetaClassImpl.java:1594)
>         at groovy.lang.ExpandoMetaClass.getProperty(ExpandoMetaClass.java:951)
>         at groovy.lang.MetaClassImpl.getProperty(MetaClassImpl.java:3287)
>         at groovy.lang.ExpandoMetaClass.getProperty(ExpandoMetaClass.java:964)
>         at org.codehaus.groovy.runtime.callsite.PogoMetaClassGetPropertySite.getProperty(PogoMetaClassGetPropertySite.java:48)
>         at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGroovyObjectGetProperty(AbstractCallSite.java:241)
>         at org.example.MyService.onApplicationEvent(MyService.groovy:52)
>         at org.example.MyService.onApplicationEvent(MyService.groovy)
>         at org.springframework.context.event.SimpleApplicationEventMulticaster$1.run(SimpleApplicationEventMulticaster.java:92)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
>         at java.lang.Thread.run(Thread.java:619)
> {code}

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