How to get Sensor Web Client running/debugging as Web Project under eclipse:

1) In Eclipse, open your project's properties (Alt+Enter or right-click, Properties)
2) Under Google | Web Toolkit, likewise select the version of the GWT SDK you're using. 
   As with the App Engine SDK, install it via the Eclipse plugin update site if needed.
3) Under Google | Web Application, check the "This project has a WAR directory" box and 
   point it to your project's src/main/webapp directory. This is the standard WAR source 
   folder for Maven Web projects. Be sure that the "Launch and deploy from this directory" 
   box is NOT checked.
4) Under Java Build Path, select the Order and Export tab and move all Maven dependencies 
   to the BOTTOM. Otherwise, GPE will see the App Engine and GWT SDKs from the Maven repo 
   on the build path and complain that they are not valid. This is because GPE expects a 
   specific SDK structure used to enable other tooling.
5) Also under Java Build Path, select the Source tab and ensure that the Build output 
   directory is enabled and pointing to target/your-project-name/WEB-INF/classes. If you 
   created the project with mvn eclipse:eclipse, this should be done for you automatically.
6) Finally, and this is very important, the first time you launch your project using 
   Run As | Web Application (or Debug), you will be prompted to select the war directly. 
   This is NOT src/main/webapp, but rather the WAR output folder, which is 
   target/your-project-name. If you make a mistake, simply go to Run | Run Configurations... 
   and remove any old configurations for the project. GPE will then ask you again next time 
   you try to Run As | Web Application.