Basic Sample JAVA connector Not Working

Got the sample from Java Connector Java\Samples\Samples.war. Changed the Mysql connection parameters in WEB-INF\src\ file according to local mysql setting (add 3306 port in which mysql is running on my laptop) and recompile the class also placed the updated class file under \WEB-INF\classes. getting the following message attached:

Not sure what is this I do not have this under the specified path and i.e grid/ Am I missing something here? Any help will really appreciated. I am new in this area, may my question will sound you very elementary but your answer will really help me to understand the technology and push me ahead to explore this.

in WEB-INF/web.xml all *.do paths are mapped to servlet classes.

Thnaks Stanislav… but after setting the path I am still on the same error. I have placed the classes under \Tomcat 6.0\webapps\ROOT\WEB-INF\classes\samples. and placed the samples source under \Tomcat 6.0\webapps\ROOT\samples. Not sure why servlet class mapped with url is not found. please assist.