eclipse - WebApplicationInitializer container.addServlet() returns null -

i creating basic web app maven, importing eclipse 4.2. have tomcat 7 setup server. trying configure spring data mongodb web app.

i following code-based configuration approach found here: webapplicationinitializer

when run project on server, null pointer exception in webapplicationinitializer class have created. line: container.addservlet("dispatcher", new dispatcherservlet(dispatchercontext)); returning null.

what heck missing? bit new creating web-apps scratch using annotations.

here class in question:

public class atwwebappinitializer implements webapplicationinitializer {     @override     public void onstartup(servletcontext container) throws servletexception       {       // create 'root' spring application context       annotationconfigwebapplicationcontext rootcontext = new  annotationconfigwebapplicationcontext();       rootcontext.register(springmongoconfig.class);        // manage lifecycle of root application context       container.addlistener(new contextloaderlistener(rootcontext));        // create dispatcher servlet's spring application context       annotationconfigwebapplicationcontext dispatchercontext = new annotationconfigwebapplicationcontext();       dispatchercontext.register(atwdispatcherconfig.class);        // register , map dispatcher servlet       servletregistration.dynamic dispatcher = container.addservlet("dispatcher", new dispatcherservlet(dispatchercontext));       dispatcher.setloadonstartup(1);       dispatcher.addmapping("/*");     } }  

tried adding pom:

<dependency>     <groupid>javax.servlet</groupid>     <artifactid>javax.servlet-api</artifactid>     <version>3.0.1</version>     <scope>provided</scope> </dependency> 

didn't change anything, still getting npe. read here (http://docs.oracle.com/javaee/6/api/javax/servlet/servletcontext.html) container.addservlet returns null if servlet registered? tomcat registering servlet already?

apologies wasting everyone's time, i had web.xml file registering same servlet. 1 returning null. on fixing 404, screwed controller somehow.

according servletcontext javadoc method addservlet() return null if servlet specified name registered.