Check the "<servlet-name>" attributes in "<servlet>" and "<servlet-mapping>" properties in the web.xml. They may be different, so a mapping cannot be established correctly.
Error "Exception in thread "main" java.lang.UnsupportedClassVersionError: JVMCFRE003 bad major version; class="org"/apache/maven/cli/MavenCli, offset=6"
The Maven build is running with Java 6. Choose Run As > Maven Build... (with the ellipsis on the end) and change the JRE (second tab) to Java 1.8.