Q:

NotSerializableException when Tomcat startup

I'm trying to solve this.  I'm using NetBeans 8.0 and TomCat 8.0.9, when server start up throws this NSE:
11-Sep-2014 00:01:43.578 WARNING [http-apr-8080-exec-191] org.apache.catalina.session. StandardSession.doWriteObject No puedo serializar atributo de sesión com.sun.faces.application.view.activeViewMaps para sesión 9AA3A199643F6FDA808F5269DDF0EA86
 java.io. NotSerializableException: model. Estado_civil
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
at java.io. ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at java.util. ArrayList.writeObject(ArrayList.java:762)
at sun.reflect. GeneratedMethodAccessor151.invoke(Unknown Source)
at sun.reflect. DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect. Method.invoke(Method.java:483)
at java.io. ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
at java.io. ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io. ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io. ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io. ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io. ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io. ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at java.util. HashMap.internalWriteEntries(HashMap.java:1777)
at java.util. HashMap.writeObject(HashMap.java:1354)
at sun.reflect. GeneratedMethodAccessor239.invoke(Unknown Source)
at sun.reflect. DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect. Method.invoke(Method.java:483)
at java.io. ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
at java.io. ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io. ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io. ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at java.util. LinkedHashMap.internalWriteEntries(LinkedHashMap.java:333)
at java.util. HashMap.writeObject(HashMap.java:1354)
at sun.reflect. GeneratedMethodAccessor239.invoke(Unknown Source)
at sun.reflect. DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect. Method.invoke(Method.java:483)
at java.io. ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
at java.io. ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io. ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io. ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io. ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441)
at java.util. Collections$SynchronizedMap.writeObject(Collections.java:2691)
at sun.reflect. GeneratedMethodAccessor1935.invoke(Unknown Source)
at sun.reflect. DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect. Method.invoke(Method.java:483)
at java.io. ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
at java.io. ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
at java.io. ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io. ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io. ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at org.apache.catalina.session. StandardSession.doWriteObject(StandardSession.java:1710)
at org.apache.catalina.session. StandardSession.writeObjectData(StandardSession.java:1116)
at org.apache.catalina.session. StandardManager.doUnload(StandardManager.java:401)
at org.apache.catalina.session. StandardManager.unload(StandardManager.java:320)
at org.apache.catalina.session. StandardManager.stopInternal(StandardManager.java:487)
at org.apache.catalina.util. LifecycleBase.stop(LifecycleBase.java:232)
at org.apache.catalina.core. StandardContext.stopInternal(StandardContext.java:5397)
at org.apache.catalina.util. LifecycleBase.stop(LifecycleBase.java:232)
at org.apache.catalina.core. StandardContext.reload(StandardContext.java:3773)
at org.apache.catalina.manager. ManagerServlet.reload(ManagerServlet.java:984)
at org.apache.catalina.manager. ManagerServlet.doGet(ManagerServlet.java:345)
at javax.servlet.http. HttpServlet.service(HttpServlet.java:618)
at javax.servlet.http. HttpServlet.service(HttpServlet.java:725)
at org.apache.catalina.core. ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core. ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server. WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core. ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core. ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.filters. SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
at org.apache.catalina.core. ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core. ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core. StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core. StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator. AuthenticatorBase.invoke(AuthenticatorBase.java:615)
at org.apache.catalina.core. StandardHostValve.invoke(StandardHostValve.java:136)
at org.apache.catalina.valves. ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves. AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core. StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector. CoyoteAdapter.service(CoyoteAdapter.java:526)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
at org.apache.coyote. AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:277)
at org.apache.tomcat.util.net. AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2381)
at org.apache.tomcat.util.net. AprEndpoint$SocketProcessor.run(AprEndpoint.java:2370)
at java.util.concurrent. ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent. ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads. TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang. Thread.run(Thread.java:745)

model. Estado_civil is POJO and isn't referenced.  I delete every code could call this POJO I'm using an empty Bean and an empty XHTML. 
I undeployed the project from the server using netbeans and clean and built the project again. 
I can't understand why throws this exception. 

A:

You are storing an Object that doesn't implement Serializable in a HttpSession:
...
at java.io. ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at org.apache.catalina.session. StandardSession.doWriteObject(StandardSession.java:1710)
...

When Tomcat shuts down it attempts to save the session state to a file using the Java Serialization API.  When it starts up again it attempts to restore the session state. 
From the method name  - doWriteObject - I would say it's attempting to store something persistently. 
In order to disable this feature entirely you need to add:
<Manager pathname="" />

To your context.xml.  The context.xml is located in /META-INF/context.xml and will look something like:
<Context>
    <Manager pathname="" />
</Context>

For more information consult the Tomcat documentation

