You need to add the following line (mutatis mutandis):
<Context docBase="/var/lib/tomcat7/webapps/oaipmh" path="/oaipmh"/>
… in the server.xml Tomcat7 that, e.g., in my system
lives in: /var/lib/tomcat7/conf/server.xml.
E.g., in my system:
$ cat /var/lib/tomcat7/conf/server.xml | tail -20
<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true">
<!-- SingleSignOn valve, share authentication between web applications
Documentation at: /docs/config/valve.html -->
<!--
<Valve className="org.apache.catalina.authenticator.SingleSignOn" />
-->
<!-- Access log processes all example.
Documentation at: /docs/config/valve.html
Note: The pattern used is equivalent to using pattern="common" -->
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
prefix="localhost_access_log." suffix=".txt"
pattern="%h %l %u %t "%r" %s %b" />
<Context docBase="/var/lib/tomcat7/webapps/oaipmh" path="/oaipmh"/>
</Host>
</Engine>
</Service>
</Server>
… followed of course by a server restart:
sudo /etc/init.d/tomcat7 restart
I was then able to view the static content by pointing my browser at: http://localhost:8080/oaipmh/