如何在页面加载期间添加 FacesMessage?使用@PostConstruct 似乎不起作用 [英] How can I add FacesMessage during page load? Using @PostConstruct does not seem to work

问题描述

在支持 bean 的@PostConstruct 方法中，我调用了一个 EJB，它可能会返回一些我想通过 p:messages 在页面上显示的消息.但是，即使我添加了 FacesMessages，例如FacesContext.getCurrentInstance().addMessage(...), p:messages 没有被 FacesMessages 更新.

In a backing bean's @PostConstruct method, I make a call to an EJB which might return some messages that I want to display on the page via p:messages. However, even if I add the FacesMessages e.g. FacesContext.getCurrentInstance().addMessage(...), p:messages is not being updated with the FacesMessages.

如果我改为在页面上的操作上调用对 EJB 的调用(假设用户单击页面上的按钮，该按钮调用调用 EJB 的方法，然后添加 FacesMessage(s))，则消息显示按预期使用 p:messages .

If I instead invoke the call to the EJB on an action from the page (say a user clicks a button on the page which invokes a method that calls the EJB and then adds the FacesMessage(s)), then the messags show up using p:messages as expected.

如何在@PostConstruct 期间添加面孔消息并在最初呈现页面时显示它们?

How do I add Faces Messages during @PostConstruct and have them show up when the page is initially rendered?

代码:

Page1Controller.java:

Page1Controller.java:

@ManagedBean
public class Page1Controller
{
    @PostConstruct
    public void init()
    {
        FacesContext.getCurrentInstance().addMessage(null, 
            new FacesMessage("Test Message from @PostConstruct"));
    }

    public String getValue()
    {
            return "Some Value";
    }

    public void triggerMessage(ActionEvent event)
    {
            FacesContext.getCurrentInstance().addMessage(null, 
                    new FacesMessage("Test Message from Trigger Button"));      
    }

}

page1.xhtml

page1.xhtml

   <h:form>
        <p:messages showDetail="true" showSummary="true" autoUpdate="true"/>
        <h:outputText value="#{page1Controller.value}"/>
        <br/>
        <p:commandButton value="Trigger Message" 
                         actionListener="#{page1Controller.triggerMessage}"/>  
   </h:form>

推荐答案

当消息组件在添加消息之前 呈现时，可能会发生这种情况.

That can happen when the message component is rendered before the message is added.

在您的具体示例中，该 bean 首次被 <h:outputText> 组件引用，因此是在该时刻第一次构造的.但是 组件出现在您的特定示例中 之后 组件，所以 <p:messages> 组件已经呈现，因此显示消息为时已晚.

In your specific example, the bean is referenced for the first time by the <h:outputText> component and thus constructed for the first time at that moment. But the <h:outputText> component appears in your specific example after the <p:messages> component, so the <p:messages> component is already rendered and thus it's too late to show the message.

您需要以某种方式确保在呈现消息组件之前添加消息.一种方法是使用 .它在 INVOKE_APPLICATION 阶段运行，该阶段在 RENDER_RESPONSE 阶段之前.因此它在 任何 组件被渲染之前运行.因此，这是一个绝佳的机会.

You need to make sure somehow that the message is added before the message component is rendered. One way is using <f:viewAction>. It runs during INVOKE_APPLICATION phase which is before RENDER_RESPONSE phase. Thus it runs before any component is rendered. A perfect opportunity thus.

<f:metadata>
    <f:viewAction action="#{bean.onload}" />
</f:metadata>

public void onload() {
    // Add message here instead of in @PostConstruct.
}

另见:

• 什么可以<f:metadata>，<f:viewParam>和 <f:viewAction>用于?

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