Missing Maven dependencies in Eclipse Project

I have faced a couple of times this issue. There is a workaround that sometimes works, however it is not always true.

modify .classpath xml file, adding the following tag:

<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
 <attributes>
 <attribute name="maven.pomderived" value="true"/>
 <attribute name="org.eclipse.jst.component.nondependency" value=""/>
 </attributes>
</classpathentry>

Several tips & tricks appear at: http://stackoverflow.com/questions/4262186/missing-maven-dependencies-in-eclipse-project

UPDATE1: another usual mistake is not to have the maven directory structure:

src/main/java