Setup tomcat7 is easy. Just do
sudo apt-get install tomcat7and http://localhost:8080/ will work already. The default source files are in /usr/share/tomcat7, while the default path is in /var/lib/tomcat7/webapps/ROOT.
First install those five packages from Help > Install New Software... > (Work with) Luna > Web, XML, Java EE and OSGi Enterprise development.
Eclipse Java EE Developer Tools
Eclipse Java Web Developer Tools
Eclipse Web Developer Tools
JST Server Adapters
JST Server Adapters Extensions
Goes to Windows > Performances > Server > Runtime Environment and add the one just installed, with Tomcat installation directory as /usr/share/tomcat7. It is also possible to install a local version of tomcat7 using download and install and specify folder path; however, what is installed is just identical duplications and there's not much differences.
Goes to File > New > Others > Server > server and add a new Tomcat v7.0 server, choose the server runtime environment we just set up. If we setup/remove several times, sometimes it happens that the Server Name is blank, and there's no way to type anything in it. It is a known bug in Eclipse. Just do
cd ~/workspace/.metadata/.plugins/org.eclipse.core.runtime/.settings/
rm org.eclipse.jst.server.tomcat.core.prefs
rm org.eclipse.wst.server.core.prefs
then everything is reset.
The Java EE (rather than Java) prospective is needed to be switched to.
Change the privacy policy of /usr/share/tomcat7 so Eclipse (and other normal users) can use it.
cd /usr/share/tomcat7
sudo ln -s /var/lib/tomcat7/conf conf
sudo ln -s /etc/tomcat7/policy.d/03catalina.policy conf/catalina.policy
sudo ln -s /var/log/tomcat7 log
sudo chmod -R 777 /usr/share/tomcat7/conf
Copy all files in /usr/share/tomcat7/conf (inside folders seems unnecessary because they are backups) to ~/workspace/Servers/Tomcat v7.0 Server at localhost-config. Then either stop the original Tomcat by
sudo service tomcat7 stop
sudo update-rc.d tomcat7 disable
Or choose another port for the Ecplise instance (I am choosing this way) by changing 8080 to 8181 (or whatever unused port) and 8005 to 8115 in ~/workspace/Servers/Tomcat v7.0 Server at localhost-config/server.xml.
The Servers view can be shown from Windows > Show View > Others > Servers, and right now it should be started successfully. Right now http://localhost:8181/ will gives 404 errors.
Just use File > New > Others > Web > Dynamical Web Project wizard to start a new servlet project. Put whatever servlet code into /src folder by adding File > New > Others > Web > Servlet class. Eclipse is complaining import errors. Go to project Properties > Java Build Path > Libraries > Add External Jars... and add all the things in /usr/share/tomcat7/lib in it. Then Run on Server will work, and the page can be viewed from http://localhost:8181/project_name/ClassName.