Frequently Asked Questions: Develop a plugin for the SPS

I get a NullpointerException after restarting my servlet engine.

This could be caused by several things:

1. Check, if you have implemented the getProfileInformation. This ensures that the SPS stores this information in the database during the registration process of a sensor instance. If you omitted implementing this method, the SPS assumes there is no sensor configuration.

Starting the SPS fails with a ClassNotFoundException, but the class is there and on the buildpath of the plugin.

When running the SPS within an eclipse WTP project (e.g. for development) and you have an extra plugin project, you have to ensure that the plugin and its 3rd party libraries are on the SPS classpath during runtime. You must add all dependend libraries (and the plugin project itself) as a module dependency of the SPS project.

I get a NoClassDefFoundError javax/servlet/http/HttpServletRequest (or similar) after starting my servlet engine.

This could be caused by spaces within your server runtime path. WTP eclipse does not check, so that (for example you have tomcat installed at c:\Program Files\Apache) the parts of the path before the last space (in the example, c:\Program Files) are not recognized during runtime and the location cannot be resolved (including runtime libs). We recommend to have a separate tomcat only for WTP dev (faster start/stop) running on a different port than other servlet engines (which may run other components, like WNS, SES, SOS, etc you may need during development). Make sure the path to your dev tomcat does not contain any space.

-- HenningBredel - 2012-03-16