Bdtjtk

I'm currently using memcached-tomcat-session-manager with Tomcat7 for session storage.

This is setup in the prescribed manner with the various memcached / transcoder / serializer JARs in $CATALINA_HOME/lib and $CATALINA_HOME/conf/context.xml with a <Manager> ... entry and works just fine.

A situation has arisen where I'd like to share some static properties of classes between my webapp and (my modified version of) memcached-session-manager. I believe with the current setup they are in separate classloaders, so sharing static resources between classes is not possible.

That led me to bundle all the dependencies with the /WEB_INF/lib and move the the <Manager ... definition to /META-INF/context.xml. This is not working, with Tomcat reporting:

portal_1     | 2018-12-21 01:26:27,291 [Portal] SEVERE {localhost-startStop-1}   Digester Begin event threw exception                                                                                               

portal_1     | java.lang.ClassNotFoundException: de.javakaffee.web.msm.MemcachedBackupSessionManager                                                                                                                

portal_1     |  at java.net.URLClassLoader.findClass(URLClassLoader.java:381)                                                                                                                                       

portal_1     |  at java.lang.ClassLoader.loadClass(ClassLoader.java:424)                                                                                                                                            

portal_1     |  at java.lang.ClassLoader.loadClass(ClassLoader.java:357)                                                                                                                                            

portal_1     |  at org.apache.tomcat.util.digester.ObjectCreateRule.begin(ObjectCreateRule.java:144)                                                                                                                

portal_1     |  at org.apache.tomcat.util.digester.Digester.startElement(Digester.java:1303)                                                                                                                        

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:509)                                                                                            

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.AbstractXMLDocumentParser.emptyElement(AbstractXMLDocumentParser.java:182)                                                                            

portal_1     |  at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(XMLDocumentFragmentScannerImpl.java:1339)                                                                

portal_1     |  at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2784)                                                      

portal_1     |  at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:602)                                                                                             

portal_1     |  at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:505)                                                                     

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:842)                                                                                                 

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:771)                                                                                                 

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)                                                                                                                   

portal_1     |  at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)                                                                                                  

portal_1     |  at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)                                                                                                

portal_1     |  at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1576)                                                                                                                               

portal_1     |  at org.apache.catalina.startup.ContextConfig.processContextConfig(ContextConfig.java:644)                                                                                                           

portal_1     |  at org.apache.catalina.startup.ContextConfig.contextConfig(ContextConfig.java:606)                                                                                                                  

portal_1     |  at org.apache.catalina.startup.ContextConfig.init(ContextConfig.java:842)                                                                                                                           

portal_1     |  at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:399)                                                                                                                 

portal_1     |  at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)                                                                                                          

portal_1     |  at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)                                                                                                                 

portal_1     |  at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:388)                                                                                                                  

portal_1     |  at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:103)                                                                                                                              

portal_1     |  at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:135)

portal_1     |  at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:1018)

portal_1     |  at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:994)

portal_1     |  at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:652)

portal_1     |  at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1127)

portal_1     |  at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:2021)

portal_1     |  at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)

portal_1     |  at java.util.concurrent.FutureTask.run(FutureTask.java:266)

portal_1     |  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)

portal_1     |  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)

portal_1     |  at java.lang.Thread.run(Thread.java:748)

I'm confident the dependencies are bundled in the WAR. After reading through Tomcat 7 documentation, its not clear to me if what I'm doing is possible - having classes defined within the WARs context.xml that are not in $CATALINA_HOME/lib eg the applications classloader has not been created yet.

memcached-session-manager (msm) jars must reside in $CATALINA_HOME/lib because they're using tomcat internal classes (which is not possible from within the webapp). More concretely, these jar are memcached-session-manager.jar, memcached-session-manager-tc7.jar and spymemcached.jar.

The only msm related jars that must be put in /WEB_INF/lib are serialization related jars such as msm-kryo-serializer (usually defined as dependencies in your maven/gradle/xyz build), because they must be able to access application specific classes.

See also the related msm documentation.

Regarding your goal to share information between msm and your application: Because msm jars must reside in $CATALINA_HOME/lib, conceptually it's not possible to statically "link" application code with msm code (except msm serializer related code). This is only possible with an additional indirection: the definition of some interface inside msm, where the application provides an implementation and which msm then loads via reflection. This is how serializers are hooked into msm, see the TranscoderFactory interface (loaded from $CATALINA_HOME/lib) and the KryoTranscoderFactory implementation (loaded from /WEB_INF/lib).