package br.com.monografia.gwt.server;
public class UsuariosServiceImpl extends RemoteServiceServlet implements UsuariosService{

    @Override
    public DataEvent selectAll() {
        UsuarioDelegate delegate = new UsuarioDelegate();
        List<Usuario> dtos = null;
        try {
            dtos = delegate.selectAll();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        UsuarioRetrivedEvent theEvent = new UsuarioRetrivedEvent();
        theEvent.setDtos(dtos);
        return theEvent;
    }
    ...

package br.com.monografia.gwt.client.service;
public class UsuariosServiceClientImpl  implements UsuariosServiceClientInt{
    private UsuariosServiceAsync service;
    private ManterUsuariosWidget mainview;
    public UsuariosServiceClientImpl(String url){
        this.service = GWT.create(UsuariosService.class);
        ServiceDefTarget endpoint = (ServiceDefTarget) this.service;
        endpoint.setServiceEntryPoint(url);
        this.mainview = new ManterUsuariosWidget(this);
    }
    public void selectAll(){
        this.service.selectAll(new DefaultCallback());
    }
    ...
    private class DefaultCallback implements AsyncCallback<DataEvent>{

        @Override
        public void onFailure(Throwable caught) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onSuccess(DataEvent result) {
            mainview.handleEvent(result);

        }
    }
}

package br.com.monografia.gwt.client.events;
...
public class UsuarioRetrivedEvent  extends DataEvent {
    private Usuario dto;
    private List<Usuario> dtos;
    public UsuarioRetrivedEvent(){
        super();
    }
    public Usuario getDto() {
        return dto;
    }
    public void setDto(Usuario dto) {
        this.dto = dto;
    }
    public List<Usuario> getDtos() {
        return dtos;
    }
    public void setDtos(List<Usuario> dtos) {
        this.dtos = dtos;
    }
}

package br.com.monografia.gwt.client.events;
public class DataEvent implements Serializable{
    public DataEvent(){
        super();
    }
}

package br.com.monografia.gwt.client.gui;
public class ManterUsuariosWidget extends Composite {
public ListBox listBoxUsers;
...
    public ManterUsuariosWidget(UsuariosServiceClientImpl listener) {

        this.setListener(listener);
        ...
        listBoxUsers= new ListBox();
        apForm.add(listBoxUsers, 10, 84);
        listener.selectAll();
    }
    public void handleEvent(DataEvent event) {

        if (event instanceof UsuarioRetrivedEvent) {
            UsuarioRetrivedEvent theEvent = (UsuarioRetrivedEvent) event;
            if (theEvent.getDtos() != null) {
                        comboBoxEstados.addItem("Selecione","Selecione");
                        for (Usuario dto : theEvent.getDtos()) {
                            listBoxUsers.addItem(dto.getNomeUsuario(),dto.getNomeCompleto());
                        }
            }
        }
        ...
    }
}