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The <o:hashParam> is a component that extends the standard <f:viewParam> with support for setting hash query parameter values in bean and automatically reflecting updated model values in hash query string.

The "hash query string" is the part in URL after the # which could be formatted in the same format as a regular request query string (the part in URL after the ?). An example:

https://example.com/page.xhtml#foo=baz&bar=kaz

This specific part of the URL (also called hash fragment identifier) is by default not sent to the server. This component will on page load send it anyway and on every ajax request update the hash query string in client side when the model value has changed in server side. *

Usage

It's very similar to the <o:viewParam>.

<f:metadata>
    <o:hashParam name="foo" value="#{bean.foo}" />
    <o:hashParam name="bar" value="#{bean.bar}" />
</f:metadata>

This only requires that the JSF page has at least one {@link UIForm} component, such as <h:form> or <o:form>, otherwise the <o:hashParam> won't be able to fire the ajax request which sets the with hash query parameter values in bean. In such case an error will be printed to JS console when the project stage is Development.

You can use the render attribute to declare which components should be updated when a hash parameter value is present.

<f:metadata>
    <o:hashParam name="foo" value="#{bean.foo}" render="fooResult" />
    <o:hashParam name="bar" value="#{bean.bar}" />
</f:metadata>
...
<h:body>
    ...
    <h:panelGroup id="fooResult">
        ...
    </h:panelGroup>
    ...
</h:body>

You can use the default attribute to declare a non-null value which should be interpreted as the default value. In other words, when the current model value matches the default value, then the hash parameter will be removed.

<f:metadata>
    <o:hashParam name="foo" value="#{bean.foo}" />
    <o:hashParam name="bar" value="#{bean.bar}" default="kaz" />
</f:metadata>

When #{bean.foo} is "baz" and #{bean.bar} is "kaz" or empty, then the reflected hash query string will become https://example.com/page.xhtml#foo=baz. If #{bean.bar} is any other value, then it will appear in the hash query string.