EDIT

package eu.etaxonomy.taxeditor.editor.handler;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;

import java.util.UUID;

import org.eclipse.core.commands.AbstractHandler;

import org.eclipse.core.commands.ExecutionEvent;

import org.eclipse.core.commands.ExecutionException;

import org.eclipse.jface.viewers.ISelection;

import org.eclipse.jface.viewers.IStructuredSelection;

import org.eclipse.ui.PartInitException;

import org.eclipse.ui.handlers.HandlerUtil;

import eu.etaxonomy.cdm.model.description.IndividualsAssociation;

import eu.etaxonomy.cdm.model.occurrence.SpecimenOrObservationBase;

import eu.etaxonomy.taxeditor.editor.EditorUtil;

import eu.etaxonomy.taxeditor.editor.view.derivate.DerivateViewEditorInput;

import eu.etaxonomy.taxeditor.model.MessagingUtils;

public class OpenDerivateViewHandler extends AbstractHandler {

    @Override

    public Object execute(ExecutionEvent event) throws ExecutionException {

        Set<UUID> selectedElementUUIDs = new HashSet<UUID>();

        //check if parameter is set

        Object parameter = event.getObjectParameterForExecution("eu.etaxonomy.taxeditor.specimenUuidParameter");

        if(parameter instanceof UUID){

            selectedElementUUIDs.add((UUID) parameter);

        }

        else{

            //if not, try with current selection

            ISelection currentSelection = HandlerUtil.getCurrentSelection(event);

            if(currentSelection instanceof IStructuredSelection){

                Iterator<?> selectionIterator = ((IStructuredSelection) currentSelection).iterator();

                while(selectionIterator.hasNext()){

                    Object object = selectionIterator.next();

                    if(object instanceof SpecimenOrObservationBase<?>){

                        selectedElementUUIDs.add(((SpecimenOrObservationBase<?>) object).getUuid());

                    }

                    else if(object instanceof IndividualsAssociation){

                        SpecimenOrObservationBase specimen = ((IndividualsAssociation) object).getAssociatedSpecimenOrObservation();

                        if(specimen!=null){

                            selectedElementUUIDs.add(specimen.getUuid());

                        }

                    }

                }

            }

        }

        if(!selectedElementUUIDs.isEmpty()){

            DerivateViewEditorInput input = new DerivateViewEditorInput(selectedElementUUIDs);

            try {

                EditorUtil.open(input);

            } catch (PartInitException e) {

                MessagingUtils.error(OpenDerivateViewHandler.class, "Could not open Derivative Editor", e);

            } catch (NullPointerException npe){

                MessagingUtils.messageDialog("Failed to open Editor", OpenDerivateViewHandler.class, "Could not open Derivative Editor. The derivate hierarchy is corrupted!", npe);

            }

        }

        else{

            MessagingUtils.informationDialog("Empty selection", "No Specimen selected.");

        }

        return null;

    }

}