Code is available at local git server. That same server is also hosting multiple tomcat. Jenkins build should pull the git to collect code, prepare mysql DB, execute ant target, finally place the resultant war file at particular webapps folder. Apart from all these build specific tasks, jenkins should shutdown the associated tomcat before ant task and start it again after placing the war file in webapps
On debian, add the official jenkins repo and add signature .
wget -q -O - https://jenkins-ci.org/debian/jenkins-ci.org.key | sudo apt-key add - echo "deb http://pkg.jenkins-ci.org/debian binary/" > /etc/apt/sources.list.d/jenkins.list apt-get update