Fix the annoying tomcat shutdown class reloading problem

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: None
• Fix Version/s: --Sprint - SP, 6.1.0 CE RC1
• Component/s: Environments > App Servers
• Labels: None
• Branch Version/s:
  6.0.x, 5.2.x, 5.1.x
• Backported to Branch:
  Committed

Tomcat has a feature to null out all classes' static fields to prevent memory leak. To do that, tomcat needs to reload the class by WebappClassLoader. The reload will force to rerun all classes' static initializing blocks. If the code inside the block call any service which is already out of service, then we will see a lot of exceptions. for example:
java.lang.NullPointerException
at com.liferay.util.SystemProperties.get(SystemProperties.java:50)
at com.liferay.portal.upload.UploadServletRequestImpl.<clinit>(UploadServletRequestImpl.java:273)
at sun.misc.Unsafe.ensureClassInitialized(Native Method)
at sun.reflect.UnsafeFieldAccessorFactory.newFieldAccessor(UnsafeFieldAccessorFactory.java:25)
at sun.reflect.ReflectionFactory.newFieldAccessor(ReflectionFactory.java:122)
at java.lang.reflect.Field.acquireFieldAccessor(Field.java:918)
at java.lang.reflect.Field.getFieldAccessor(Field.java:899)
at java.lang.reflect.Field.set(Field.java:657)
at org.apache.catalina.loader.WebappClassLoader.clearReferencesStaticFinal(WebappClassLoader.java:2034)
at org.apache.catalina.loader.WebappClassLoader.clearReferences(WebappClassLoader.java:1894)
at org.apache.catalina.loader.WebappClassLoader.stop(WebappClassLoader.java:1798)
at org.apache.catalina.loader.WebappLoader.stop(WebappLoader.java:738)
at org.apache.catalina.core.StandardContext.stop(StandardContext.java:4812)
at org.apache.catalina.core.ContainerBase.removeChild(ContainerBase.java:924)
at org.apache.catalina.startup.HostConfig.undeployApps(HostConfig.java:1319)
at org.apache.catalina.startup.HostConfig.stop(HostConfig.java:1290)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:323)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1086)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1098)
at org.apache.catalina.core.StandardEngine.stop(StandardEngine.java:450)
at org.apache.catalina.core.StandardService.stop(StandardService.java:587)
at org.apache.catalina.core.StandardServer.stop(StandardServer.java:744)
at org.apache.catalina.startup.Catalina.stop(Catalina.java:648)
at org.apache.catalina.startup.Catalina$CatalinaShutdownHook.run(Catalina.java:692)

So basically we need to avoid calling service from classes' static initializing block.