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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 and on every window.onhashchange event send it anyway so that the Faces model gets updated, and on every Faces ajax request update the hash query string in client side when the Faces model value has changed.

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>
 

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>
 

In case you need to invoke a bean method before rendering, e.g. to preload the rendered contents based on new hash param values, then you can observe the HashChangeEvent. See the "Events" section for an usage example.

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.

Note that as it extends from the standard <f:viewParam>, its built-in conversion and validation functionality is also supported on this component.

Events

When the hash query string is changed by the client side, e.g. by following a #foo=baz&bar=kaz link, or by manually manipulating the URL, then a CDI HashChangeEvent will be fired which can be observed in any CDI managed bean as below:

 public void onHashChange(@Observes HashChangeEvent event) {
     String oldHashString = event.getOldValue();
     String newHashString = event.getNewValue();
     // ...
 }
 

This is useful in case you want to preload the model for whatever is rendered by <o:hashParam render>.