jsf - Unable to understand <h:head> behaviour

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jsf - Unable to understand <h:head> behaviour

posted Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

jsf - Unable to understand <h:head> behaviour

I have a template composition Button.xhtml which contains a <p:commandLink>:

<ui:composition
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:p="http://primefaces.org/ui">
    <p:commandLink value="View" action="#{printClass.printPdf}"/>
</ui:composition>

The link's purpose is to generate PDF.

I have a template client defaultPage.xhtml where the Button.xhtml is been included.

<ui:composition template="../../WebPages/MasterPage/Template.xhtml">
    <ui:define name="MainContent">
        <ui:include src="../../WebPages/Facelets/Button.xhtml"/>
    </ui:define>
</ui:composition>

The last one is Template.xhtml which inserts the MainContent template definition inside a <h:form>.

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core">
    <h:body>
        <h:form>
            <ui:insert name="MainContent" />
        </h:form>
    </h:body>
</html>

When I place <h:head></h:head> in Template.xhtml, then the <p:commandLink> in Button.xhtml stops working, but CSS of page works perfect. When I remove the <h:head></h:head> or replace it by <head></head> then the <p:commandLink> starts working, but CSS stops working.

How is this caused and how can I solve it?

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1 Reply

深蓝 · Answer 1 · 2021-10-23T18:25:51+0000

The <h:head> will auto-include all necessary JavaScript files for ajax behavior and CSS files for layout. When you remove it, then CSS will not be auto-included and ajax behavior will not be enabled. The <p:commandLink> would then act like as a plain vanilla link.

The <h:head> is absolutely necessary for proper functioning of JSF and PrimeFaces components and applying of the PrimeFaces look'n'feel. So you should not remove or replace it.

Let's concentrate on the problem of the failing <p:commandLink>. There are relatively a lot of possible causes, which are all mentioned in this answer: commandButton/commandLink/ajax action/listener method not invoked or input value not updated

You didn't show a fullworthy SSCCE, so it's impossible to copy'n'paste'n'run your code to see the problem ourselves (work on that as well in your future questions). So, I'll just mention the most probable cause for this problem based on the symptoms: you're nesting <h:form> components in each other. Placing the <h:form> in the master template is also a design smell. You should rather place it in the template client. Als note that the <p:dialog> should have its own form but that the <p:dialog> should by itself not be nested in another form.

Update: based on the comments, you're trying to return a whole PDF file as a response to an ajax request. This will indeed not work. The ajax engine expects a XML response with information about changes in the HTML DOM tree. A PDF file isn't valid information. Also, JavaScript has for obvious security reasons no facilities to programmatically trigger a Save As dialogue whereby possibly arbitrary content is provided.

You can't download files by ajax. You have to turn off ajax. In case of <p:commandLink> there are basically 2 solutions:

Use ajax="false".
```
<p:commandLink ... ajax="false" />
```
Just use <h:commandLink> instead.
```
<h:commandLink ... />
```

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jsf - Unable to understand <h:head> behaviour

jsf - Unable to understand <h:head> behaviour

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