Eu utilizo um gecao de dependente do result, e para alimentar meus comobox eu utiliza includ.
<dl>
<dt><label for="leitor.cidade">Cidade:</label></dt>
<dd><select name="leitor.cidade.id" id="leitor.cidade" />
<option value="">Selecione</option>
<c:forEach items="${listaCidade}" var="cidade">
<option value="${ciadade.id}">${cidade.descCidade}</option>
</c:forEach>
</select></dd>
</dl>
exception
br.com.caelum.vraptor.InterceptionException: an exception was raised while executing resource method
br.com.caelum.vraptor.interceptor.ExecuteMethodInterceptor.intercept(ExecuteMethodInterceptor.java:86)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:56)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.ParametersInstantiatorInterceptor.intercept(ParametersInstantiatorInterceptor.java:77)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.InstantiateInterceptor.intercept(InstantiateInterceptor.java:42)
br.com.caelum.vraptor.core.InstantiatedInterceptorHandler.execute(InstantiatedInterceptorHandler.java:47)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.InterceptorListPriorToExecutionExtractor.intercept(InterceptorListPriorToExecutionExtractor.java:46)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.FlashInterceptor.intercept(FlashInterceptor.java:80)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.ResourceLookupInterceptor.intercept(ResourceLookupInterceptor.java:67)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:56)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.DefaultRequestExecution.execute(DefaultRequestExecution.java:70)
br.com.caelum.vraptor.VRaptor$1.insideRequest(VRaptor.java:92)
br.com.caelum.vraptor.ioc.spring.SpringProvider.provideForRequest(SpringProvider.java:56)
br.com.caelum.vraptor.VRaptor.doFilter(VRaptor.java:89)
root cause
org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: br.com.biblioteca.entidades.cadastros.Bairro
org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:242)
org.hibernate.type.EntityType.getIdentifier(EntityType.java:430)
org.hibernate.type.ManyToOneType.isDirty(ManyToOneType.java:265)
org.hibernate.type.TypeFactory.findDirty(TypeFactory.java:619)
org.hibernate.persister.entity.AbstractEntityPersister.findDirty(AbstractEntityPersister.java:3151)
org.hibernate.event.def.DefaultFlushEntityEventListener.dirtyCheck(DefaultFlushEntityEventListener.java:501)
org.hibernate.event.def.DefaultFlushEntityEventListener.isUpdateNecessary(DefaultFlushEntityEventListener.java:227)
org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:150)
org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)
org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:49)
org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
br.com.biblioteca.Dao.cadastros.LeitorDao.salva(LeitorDao.java:24)
br.com.biblioteca.controller.cadastros.LeitorController.adiciona(LeitorController.java:27)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
br.com.caelum.vraptor.interceptor.ExecuteMethodInterceptor.intercept(ExecuteMethodInterceptor.java:57)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:56)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.ParametersInstantiatorInterceptor.intercept(ParametersInstantiatorInterceptor.java:77)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.InstantiateInterceptor.intercept(InstantiateInterceptor.java:42)
br.com.caelum.vraptor.core.InstantiatedInterceptorHandler.execute(InstantiatedInterceptorHandler.java:47)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.InterceptorListPriorToExecutionExtractor.intercept(InterceptorListPriorToExecutionExtractor.java:46)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.FlashInterceptor.intercept(FlashInterceptor.java:80)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.interceptor.ResourceLookupInterceptor.intercept(ResourceLookupInterceptor.java:67)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:54)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.ToInstantiateInterceptorHandler.execute(ToInstantiateInterceptorHandler.java:56)
br.com.caelum.vraptor.core.DefaultInterceptorStack.next(DefaultInterceptorStack.java:65)
br.com.caelum.vraptor.core.DefaultRequestExecution.execute(DefaultRequestExecution.java:70)
br.com.caelum.vraptor.VRaptor$1.insideRequest(VRaptor.java:92)
br.com.caelum.vraptor.ioc.spring.SpringProvider.provideForRequest(SpringProvider.java:56)
br.com.caelum.vraptor.VRaptor.doFilter(VRaptor.java:89)