Why do I get ServletException - ClassNotFoundException?

Question

When I go to my webApplication I get the following exception:

Error 500: javax.servlet.ServletException: Filter [Encoding]: Could not find required filter class - my.packagename.filter.EncodingFilter.class

In the console I get:

com.ibm.ws.webcontainer.webapp.WebApp logServletError SRVE0293E: [Servlet Error]-[action]: java.lang.ClassNotFoundException: class java.lang.ClassNotFoundException: my.packagename.filter.EncodingFilter

In my web.xml I have the following configuration:

<filter>
    <filter-name>Encoding</filter-name>
    <filter-class>my.packagename.filter.EncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
</filter>

I verified that this class exists in my project (projectName\src\my\packagename\filter\EncodingFilter.java) and that it implements the Filter interface.

What could be wrong? How can I solve this?