From a google code search for “package com.samskivert.util” “class StringUtil” I get a result in http://samskivert.googlecode.com, also the POM of getdown contains
<dependency>
<groupId>com.samskivert</groupId>
<artifactId>samskivert</artifactId>
<version>1.0</version>
<scope>compile</scope>
<optional>true</optional>
</dependency>
clearly the optional flag is wrong here ;). So the package lies in a separate project and needs to be added to the classpath. You probably should check all dependencies with scope compile, runtime or provided, put them in the classpath or just package them into the getdown.jar.