install Java database (JDBC) driver for MySQL

sudo apt-get install libmysql-java

# old, manuall installation
# wget http://ftp.gwdg.de/pub/misc/mysql/Downloads/Connector-J/mysql-connector-java-5.1.6.tar.gz -P /tmp
# tar xzf /tmp/mysql-connector-java-5.1.6.tar.gz -C /tmp
# cp /tmp/mysql-connector-java-5.1.6/mysql-connector-java-5.1.6-bin.jar /opt/gwt-linux/

# LINKS
http://packages.ubuntu.com/feisty/libs/libmysql-java