TL;DR
There are three options to resolve.
- Upgrade to version 4.0.16 of JGroups, currently in SNAPSHOT. Edit: Now released here.
- Make sure java properties for "user.language" and "user.country" are set.
- Force JDKLogImpl with
-Djgroups.use.jdk_logger=true
. (mentioned by Perimosh)
Explanation
Ran into this issue in the following scenario.
Apache Camel + JGroups worked fine in a local environment. Deployed it elsewhere in a Docker instance, where we got the following stacktrace:
2018-11-19 13:38:03.063 INFO 582 --- [ main] o.a.camel.spring.boot.RoutesCollector : Loading additional Camel XML routes from: classpath:camel/*.xml
2018-11-19 13:38:03.064 INFO 582 --- [ main] o.a.camel.spring.boot.RoutesCollector : Loading additional Camel XML rests from: classpath:camel-rest/*.xml
2018-11-19 13:38:03.107 INFO 582 --- [ main] o.a.camel.spring.SpringCamelContext : Apache Camel 2.22.2 (CamelContext: camel-1) is starting
2018-11-19 13:38:03.111 INFO 582 --- [ main] o.a.c.m.ManagedManagementStrategy : JMX is enabled
2018-11-19 13:38:03.480 INFO 582 --- [ main] o.a.camel.spring.SpringCamelContext : StreamCaching is not in use. If using streams then its recommended to enable stream caching. See more details at http://camel.apache.org/stream-caching.html
2018-11-19 13:38:03.597 INFO 582 --- [ main] o.a.camel.spring.SpringCamelContext : Apache Camel 2.22.2 (CamelContext: camel-1) is shutting down
2018-11-19 13:38:03.616 WARN 582 --- [ main] o.a.camel.spring.SpringCamelContext : Error occurred while shutting down service: org.apache.camel.component.jgroups.cluster. JGroupsLockClusterService@10fa5af5. This exception will be ignored.
java.lang.NullPointerException: null
at org.apache.camel.component.jgroups.cluster.JGroupsLockClusterView.doStop(JGroupsLockClusterView.java:109)
at org.apache.camel.support.ServiceSupport.stop(ServiceSupport.java:102)
at org.apache.camel.impl.cluster.AbstractCamelClusterService.lambda$doStop$2(AbstractCamelClusterService.java:134)
at org.apache.camel.util.concurrent.LockHelper.doWithReadLockT(LockHelper.java:54)
at org.apache.camel.impl.cluster.AbstractCamelClusterService.doStop(AbstractCamelClusterService.java:130)
at org.apache.camel.support.ServiceSupport.stop(ServiceSupport.java:102)
at org.apache.camel.util.ServiceHelper.stopService(ServiceHelper.java:142)
at org.apache.camel.util.ServiceHelper.stopAndShutdownService(ServiceHelper.java:205)
at org.apache.camel.impl.DefaultCamelContext.shutdownServices(DefaultCamelContext.java:3663)
at org.apache.camel.impl.DefaultCamelContext.shutdownServices(DefaultCamelContext.java:3688)
at org.apache.camel.impl.DefaultCamelContext.shutdownServices(DefaultCamelContext.java:3676)
at org.apache.camel.impl.DefaultCamelContext.doStop(DefaultCamelContext.java:3567)
at org.apache.camel.support.ServiceSupport.stop(ServiceSupport.java:102)
at org.apache.camel.impl.DefaultCamelContext.stop(DefaultCamelContext.java:3220)
at org.apache.camel.spring.SpringCamelContext.stop(SpringCamelContext.java:148)
...
2018-11-19 13:38:03.679 INFO 582 --- [ main] o.a.camel.spring.SpringCamelContext : Apache Camel 2.22.2 (CamelContext: camel-1) uptime 0.570 seconds
2018-11-19 13:38:03.680 INFO 582 --- [ main] o.a.camel.spring.SpringCamelContext : Apache Camel 2.22.2 (CamelContext: camel-1) is shutdown in 0.082 seconds
2018-11-19 13:38:03.716 INFO 582 --- [ main] org.mongodb.driver.connection : Closed connection [connectionId{localValue:2, serverValue:2}] to localhost:43115 because the pool has been closed.
As you can see, Apache Camel attempts to start, but never does and ends up shutting down. Thus, JGroups gets a NPE because it expects Camel to be up.
After debugging the code, it appeared that there was an exception being thrown during the Camel start up process which was getting eaten.
From there, discovered that the creation of an instance of Slf4jLogImpl in org.jgroups.logging.LogFactory#getLog(java.lang.Class<?>)
(new Slf4jLogImpl(clazz)
) was a problem Method threw 'java.lang.ExceptionInInitializerError' exception.
:
java.lang.NullPointerException: null
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.jgroups.logging.LogFactory.getLog(LogFactory.java:101)
at org.jgroups.conf.XmlConfigurator.<clinit>(XmlConfigurator.java:33)
at org.jgroups.conf.ConfiguratorFactory.getXmlConfigurator(ConfiguratorFactory.java:210)
at org.jgroups.conf.ConfiguratorFactory.getStackConfigurator(ConfiguratorFactory.java:91)
at org.jgroups.JChannel.<init>(JChannel.java:130)
...
Running (new Slf4jLogImpl(clazz)
) the second time onward in the debugger results in the following stacktrace that mirrors the original posted issue:
java.lang.NoClassDefFoundError: Could not initialize class org.jgroups.logging.Slf4jLogImpl
at org.jgroups.logging.LogFactory.getLog(LogFactory.java:101)
at org.jgroups.conf.XmlConfigurator.<clinit>(XmlConfigurator.java:33)
at org.jgroups.conf.ConfiguratorFactory.getXmlConfigurator(ConfiguratorFactory.java:210)
at org.jgroups.conf.ConfiguratorFactory.getStackConfigurator(ConfiguratorFactory.java:91)
at org.jgroups.JChannel.<init>(JChannel.java:130)
This difference in results is due to the class loader caching the result of the Class.forName()
call previously to determine that the class definition was not found.
Finally, we tracked the previous NPE to be thrown from java.util.Locale#Locale(java.lang.String, java.lang.String, java.lang.String)
, since country was null
. This is because JGroup's org.jgroups.logging.Slf4jLogImpl
is definine a LOCALE
field using java properties for "user.language" and "user.country". The former was not set in our docker instance, so Locale.java
threw the NPE. Adding both of these java properties should fix this issue. Alternatively you can force using the JDKLogImpl
so that the Slf4jLogImpl
is never attempted to be instantiated. This was mentioned in the previous answer, by passing in -Djgroups.use.jdk_logger=true
.
Edit: Fixed in the latest version released here.
Now, it looks like this will be fixed in the upcoming JGroup release of 4.0.16.Final (https://github.com/belaban/JGroups/commit/61578c657138f02178c32a564ac9eae7c3976093#diff-93eb0f6a8a4953312098be459bd7ce76). Until then, you can get the snapshot version with the fix at https://repository.jboss.org/nexus/content/repositories/snapshots/org/jgroups/jgroups/4.0.16-SNAPSHOT/.