Class not found exception after upgrade

Problem:

You might be getting the following exception after an upgrade.

SEVERE [localhost-startStop-1] org.apache.tomcat.jdbc.pool.ConnectionPool.init Unable to create initial connections of pool.
java.sql.SQLException: Unable to load class: org.postgresql.Driver from ClassLoader:java.net.URLClassLoader@548c4f57;ClassLoader:ParallelWebappClassLoader
context: analytics
delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@548c4f57

at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:292)
at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:212)
at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:736)
at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:668)
at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:483)
at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:154)
at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:118)
at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:107)
at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:560)
at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:244)
at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:839)
at org.apache.naming.NamingContext.lookup(NamingContext.java:159)
at org.apache.naming.NamingContext.lookup(NamingContext.java:827)
at org.apache.naming.NamingContext.lookup(NamingContext.java:173)
at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1015)
at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:556)
at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:252)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:94)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5154)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1140)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)

Caused by: java.lang.ClassNotFoundException: Unable to load class: org.postgresql.Driver from ClassLoader:java.net.URLClassLoader@548c4f57;ClassLoader:ParallelWebappClassLoader
context: analytics
delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@548c4f57

at org.apache.tomcat.jdbc.pool.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:56)
at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:280)
... 31 more
Caused by: java.lang.ClassNotFoundException: org.postgresql.Driver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1328)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1156)
at java.lang.Class.forName0(Native Method)

Solution:

There might be other reasons.  One of the reasons is that the Tomcat user does not have access rights to lib/postgres jar .