我如何驗證selectOneMenu的值？

我正在驗證我的表單，並且我可以獲取文本框的值，但始終檢索空值 uiClass變量（Error: java.lang.NullPointerException）：任何建議？我如何驗證selectOneMenu的值？

例外：

WARNING: /jsf/report/Edit.xhtml @39,99 listener="#{studentController.validate}": java.lang.NullPointerException 
javax.el.ELException: /jsf/report/Edit.xhtml @39,99 listener="#{studentController.validate}": java.lang.NullPointerException 
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:111) 
    at com.sun.faces.facelets.tag.jsf.core.DeclarativeSystemEventListener.processEvent(EventHandler.java:131) 
    at javax.faces.component.UIComponent$ComponentSystemEventListenerAdapter.processEvent(UIComponent.java:2464) 
    at javax.faces.event.SystemEvent.processListener(SystemEvent.java:106) 
    at com.sun.faces.application.ApplicationImpl.processListeners(ApplicationImpl.java:2168) 
    at com.sun.faces.application.ApplicationImpl.invokeComponentListenersFor(ApplicationImpl.java:2116) 
    at com.sun.faces.application.ApplicationImpl.publishEvent(ApplicationImpl.java:288) 
    at com.sun.faces.application.ApplicationImpl.publishEvent(ApplicationImpl.java:246) 

Caused by: java.lang.NullPointerException 
    at entities.StudentController.validate(StudentController.java:163) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
    at java.lang.reflect.Method.invoke(Method.java:597) 

@ManagedBean() 
@SessionScoped 
public class StudentController implements Serializable { 
    public void validate(ComponentSystemEvent event) { 
     FacesContext fc = FacesContext.getCurrentInstance(); 
     UIComponent components = event.getComponent(); 

     UIInput uiName = (UIInput) components.findComponent("frmStudent:name"); 
     UIInput uiClass = (UIInput) components.findComponent("frmStudent:myclass"); 

     String name = uiName.getLocalValue().toString(); 
     String myclass = uiClass.getLocalValue().toString(); 

     if (name.equals("") || name == null || name.isEmpty()) { 
      FacesMessage msgName = new FacesMessage("Please enter name !"); 
      fc.addMessage(components.getClientId(), msgName); 
      fc.renderResponse(); 
     } else if (myclass.equals("") || myclass == null || myclass.isEmpty()) { 
      FacesMessage msgClass = new FacesMessage("Please select a class !"); 
      fc.addMessage(components.getClientId(), msgClass); 
      fc.renderResponse(); 
     } 
    } 
}

我XHTML

<h:message for="textPanel" style="color:red;" /> 
<h:panelGrid id="textPanel" columns="4"> 
    <f:event listener="#{studentController.validate}" type="postValidate" /> 
    <h:inputText id="name" value="#{studentController.selected.name}" size="20" /> 
    <h:selectOneMenu id="myclass" value="#{studentController.selected.myclass}" style="width:180px;"> 
     <f:selectItem itemLabel="Select ..." itemValue="#{null}" noSelectionOption="true" /> 
     <f:selectItems value="#{studentController.classItems}"/> 
    </h:selectOneMenu> 
</h:panelGrid>

來源

2012-10-19 Bryan

請發佈你的異常棧跟蹤，除此之外，你應該改變'name.equals（「」）|| name == null'用於'name == null ||' name.equals（「」）'，因爲如果名稱爲'null'，它將導致NPE – higuaro

我使用名稱進行測試，因此除selectOneMenu的值外，其他都是OK。是的，我現在會發布例外 – Bryan

你爲什麼不使用所需的屬性？

<h:inputText id="name" required="true" requiredMessage="Please enter name !" value="#{studentController.selected.name}" size="20" /> 
    <h:selectOneMenu id="myclass" required="true" requiredMessage="Please select a class !" value="#{studentController.selected.myclass}" style="width:180px;"> 
     <f:selectItem itemLabel="Select ..." itemValue="#{null}" noSelectionOption="true" /> 
     <f:selectItems value="#{studentController.classItems}"/> 
    </h:selectOneMenu>

來源

2012-10-21 10:02:05

我如何驗證selectOneMenu的值？

回答

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