Problem when querying table by WebService

So, I'm creating a WebService in Java, after creating the class to connect to MySQL database and the class "UserData" to run the application I solved testing using soapUI, when I do the test it claims to me the error: / p>

<faultstring>The ServiceClass object does not implement the required method in the following form: OMElement listarUsuarios(OMElement e)</faultstring>

Looking for similar questions I saw that the problem might be in service.xml, so I switched, but it still did not work. Follow the service.xml:

<service name="UsuarioDAO" >
   <description>
       Please Type your service description here
   </description>
   <messageReceivers>
       <messageReceiver mep="http://www.w3.org/ns/wsdl/in-only" class="org.apache.axis2.rpc.receivers.RPCInOnlyMessageReceiver" />
       <messageReceiver  mep="http://www.w3.org/ns/wsdl/in-out"  class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/>
   </messageReceivers>
   <parameter name="ServiceClass">mainWS.UsuarioDAO</parameter></service>

I'm using SoapUI 5.4, Tomcat 7.0.85, Axis 2-1.7.