• cdi
  • components
  • contexts
  • converters
  • eventlisteners
  • exceptionhandlers
  • facesviews
  • filters
  • functions
  • managedbeans
  • renderkits
  • resourcehandlers
  • scripts
  • taghandlers
  • utils
  • validators
  • viewhandlers
-
  • cache
  • commandScript
  • componentIdParam
  • conditionalComment
  • deferredScript
  • form
  • graphicImage
  • highlight
  • messages
  • moveComponent
  • onloadScript
  • outputFormat
  • outputLabel
  • param
  • resolveComponent
  • resourceInclude
  • tree
  • viewParam

The <o:viewParam> is a component that extends the standard <f:viewParam> and provides a stateless mode of operation and fixes the issue wherein null model values are converted to empty string parameters in query string (e.g. when includeViewParams=true) and the (bean) validation never being triggered when the parameter is completely absent in query string, causing e.g. @NotNull to fail.

Stateless mode to avoid unnecessary conversion, validation and model updating on postbacks

The standard UIViewParameter implementation calls the model setter again after postback. This is not always desired when being bound to a view scoped bean and can lead to performance problems when combined with an expensive converter. To solve this, this component by default stores the submitted value as a component property instead of in the model (and thus in the view state in case the binding is to a view scoped bean).

The standard UIViewParameter implementation calls the converter and validators again on postbacks. This is not always desired when you have e.g. a required="true", but the parameter is not retained on form submit. You would need to retain it on every single command link/button by <f:param>. To solve this, this component doesn't call the converter and validators again on postbacks.

Using name as default for label

The <o:viewParam> also provides a default for the label atrribute. When the label attribute is omitted, the name attribute will be used as label.

Avoid unnecessary empty parameter in query string

The standard UIViewParameter implementation calls the converter regardless of whether the evaluated model value is null or not. As converters by specification return an empty string in case of null value, this is being added to the query string as an empty parameter when e.g. includeViewParams=true is used. This is not desired. The workaround was added in OmniFaces 1.8.

Support bean validation and triggering validate events on null value

The standard UIViewParameter implementation uses an internal "is required" check when the submitted value is null, hereby completely bypassing the standard UIInput validation, including any bean validation annotations and even the PreValidateEvent and PostValidateEvent events. This is not desired. The workaround was added in OmniFaces 2.0.

Usage

You can use it the same way as <f:viewParam>, you only need to change f: to o:.

 <o:viewParam name="foo" value="#{bean.foo}" />
Demo
  • foo: Validation Error: Value is required.

If this page is requested by a request without foo parameter which is set by <o:viewParam>, it displays the message with the name of the <o:viewParam> as label instead of its client ID.

Clicking this GET link should cause a validation error on the bar parameter which is set by <f:viewParam>, it displays the message with the client ID of the <f:viewParam> as label.

Clicking this GET link initiates a new GET request with a test parameter. Every time this link is clicked, a converter runs that attaches an ever increasing number to the displayed value:

Clicking this POST link initiates a POST request. This should not convert the value again and thus the above number should not change. This should also not trigger the required="true" validator of the <o:viewParam> and thus no validation error should show up, on contrary to when you would use the <f:viewParam>.

When starting off with URL without view parameters, clicking the GET link with includeViewParams=true would add the <f:viewParam name="bar"> with an empty value to the request URL. This doesn't happen for <o:viewParam name="foo">.

Source code
<f:metadata>
    <o:viewParam name="foo" value="#{viewParamBean.foo}" required="true" converter="testConverter" />
    <f:viewParam name="bar" value="#{viewParamBean.bar}" converter="javax.faces.Long" />
</f:metadata>

<h:messages styleClass="messages" errorClass="error" />
<p>
    If this page is requested by a request without <code>foo</code> parameter which is set by <code>&lt;o:viewParam&gt;</code>, 
    it displays the message with the <code>name</code> of the <code>&lt;o:viewParam&gt;</code> as label instead of its client ID.
</p>
<p>
    Clicking <h:link><f:param name="foo" value="test"/><f:param name="bar" value="test" />this GET link</h:link>
    should cause a validation error on the <code>bar</code> parameter which is set by <code>&lt;f:viewParam&gt;</code>,
    it displays the message with the client ID of the <code>&lt;f:viewParam&gt;</code> as label. 
</p>
<p>
    Clicking <h:link><f:param name="foo" value="test"/>this GET link</h:link> initiates a new GET request with a <code>test</code> parameter.
    Every time this link is clicked, a converter runs that attaches an ever increasing number to the displayed value:
    <b>#{viewParamBean.foo}</b>
</p>
<h:form>
    <p>
        Clicking <h:commandLink value="this POST link" /> initiates a POST request.
        This should not convert the value again and thus the above number should not change.
        This should also not trigger the <code>required="true"</code> validator of the <code>&lt;o:viewParam&gt;</code>
        and thus no validation error should show up, on contrary to when you would use the <code>&lt;f:viewParam&gt;</code>.
    </p>
</h:form>
<p>
    When starting off with <h:link>URL without view parameters</h:link>, 
    clicking <h:link includeViewParams="true">the GET link with <code>includeViewParams=true</code></h:link>
    would add the <code>&lt;f:viewParam name="bar"&gt;</code> with an empty value to the request URL.
    This doesn't happen for <code>&lt;o:viewParam name="foo"&gt;</code>.
</p>