TL;博士
有三个选项可以解决。
- 升级到 JGroups 的 4.0.16 版，目前在SNAPSHOT中。编辑：现在在这里发布。
- 确保设置了“user.language”和“user.country”的 java 属性。
- 强制使用 JDKLogImpl
-Djgroups.use.jdk_logger=true。（由Perimosh提到）
解释
在以下场景中遇到了这个问题。
Apache Camel + JGroups 在本地环境中运行良好。将其部署在 Docker 实例中的其他位置，我们得到以下堆栈跟踪：
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.
如您所见，Apache Camel 尝试启动，但从未启动并最终关闭。因此，JGroups 获得了 NPE，因为它预计 Camel 会启动。调试代码后，似乎在 Camel 启动过程中抛出了一个异常，该异常被吃掉了。从那里，发现在org.jgroups.logging.LogFactory#getLog(java.lang.Class<?>)( new Slf4jLogImpl(clazz)) 中创建 Slf4jLogImpl 的实例是一个问题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)
...
new Slf4jLogImpl(clazz)在调试器中第二次运行 ( ) 会产生以下堆栈跟踪，该堆栈跟踪反映了原始发布的问题：
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)
结果的这种差异是由于类加载器缓存了Class.forName()先前调用的结果以确定未找到类定义。
最后，我们跟踪了之前从 抛出的 NPE java.util.Locale#Locale(java.lang.String, java.lang.String, java.lang.String)，因为国家是null。这是因为 JGroup使用“user.language”和“user.country”的 java 属性定义了org.jgroups.logging.Slf4jLogImpl一个字段。LOCALE前者没有在我们的 docker 实例中设置，所以Locale.java扔了 NPE。添加这两个 java 属性应该可以解决这个问题。或者，您可以强制使用，JDKLogImpl以便Slf4jLogImpl永远不会尝试实例化。这在上一个答案中通过传入-Djgroups.use.jdk_logger=true.
编辑：在此处发布的最新版本中修复。
现在，看起来这将在即将发布的 4.0.16.Final 的 JGroup 版本中得到修复（https://github.com/belaban/JGroups/commit/61578c657138f02178c32a564ac9eae7c3976093#diff-93eb0f6a8a4953312098be459bd7ce76）。在那之前，您可以在https://repository.jboss.org/nexus/content/repositories/snapshots/org/jgroups/jgroups/4.0.16-SNAPSHOT/获得带有修复程序的快照版本。