A "processAction method not implemented" error is shown in the log

Issue

Many processAction method not implemented errors are thrown in the server log:

ERROR [http-nio-8080-exec-1][PortletServlet:117] null

javax.portlet.PortletException: javax.portlet.PortletException: processAction method not implemented

at com.liferay.portal.kernel.portlet.LiferayPortlet.callActionMethod(LiferayPortlet.java:192) ~[portal-kernel.jar:?]

at com.liferay.portal.kernel.portlet.bridges.mvc.MVCPortlet.callActionMethod(MVCPortlet.java:439) ~[portal-kernel.jar:?]

at com.liferay.portal.kernel.portlet.LiferayPortlet.processAction(LiferayPortlet.java:82) ~[portal-kernel.jar:?]

at com.liferay.portal.kernel.portlet.bridges.mvc.MVCPortlet.processAction(MVCPortlet.java:256) ~[portal-kernel.jar:?]

...

Caused by: javax.portlet.PortletException: processAction method not implemented

at javax.portlet.GenericPortlet.processAction(GenericPortlet.java:223) ~[portlet.jar:3.0.1]

at com.liferay.portal.kernel.portlet.LiferayPortlet.callActionMethod(LiferayPortlet.java:187) ~[portal-kernel.jar:?]

... 191 more

Environment

Liferay DXP 7.1+.

Resolution

One of the causes could be that the action name used in the url is not declared or have a different name.
For example, if we define:
```
@ProcessAction(name="submitMyAction")
...
```
We should declare the same name in the url: submitMyAction

Another example would be within a MVCActionCommand at the time of specifying the property mvc.command.name:

@Component(
immediate = true,
property = {
"javax.portlet.name=" + JournalPortletKeys.JOURNAL,
"mvc.command.name=/journal/add_folder"
},
service = MVCActionCommand.class
)
public class AddFolderMVCActionCommand extends BaseMVCActionCommand {

  @Override
  protected void doProcessAction(
    ActionRequest actionRequest, ActionResponse actionResponse)
   throws Exception {
   
   ...
  
  }

...

}

The value of this property should be same of the URL parameter MyPortlet_javax.portlet.action