Upgrading from Tomcat 7 to Tomcat 8

When we upgraded from Apache Tomcat 7.0.21 to 7.0.56, all that we did, was copy over every single file in the TOMCAT_HOME/conf directory into the new installation and everything worked perfectly. When I did the same thing upgrading to Tomcat 8.0.15, it blew apart. Tomcat would not even start. The exception in the logs was:

java.lang.classnotfoundexception org.apache.catalina.core.jasperlistener

The fix was to find the original server.xml and splice in our local stuff into it -- like the context and the appBase and the listening port.  Once we did that, it worked like a charm.

Hope this helps someone.

java.lang.UnsupportedClassVersionError: Unsupported major.minor version 51.0

One of my programming guys was getting this error:

java.lang.UnsupportedClassVersionError:  Unsupported major.minor version 51.0

and Tomcat failed to start.

The message from the tomcat logs was:

SEVERE: Catalina.start: 
org.apache.catalina.LifecycleException: Failed to start component [StandardServer[8005]]

The fix was simple.  He was compiling at JRE version 1.7 and the JRE on the server was 1.6.  This was easily fixed in Eclipse under Project Properties > Java Compiler.

Hope this helps someone.