So I finally got fed up with the limitations of JSF navigation rules and I went
ahead and implemented a stateless navigation system for Seam. There were four
main reasons why I wanted this:
(1) to centralize orchestration in one place, instead of having it split
between pages.xml and faces-config.xml
(2) to be able to specify request parameters when redirecting
(3) to be able to specify conversation begin/end according to an outcome
(4) to be able to have a value binding which evaluates the outcome, in addition
to the action method binding - this lets me get rid of the ugly outcomes
returned by action methods, and reduces the coupling of the model to the view.
(5) to support various "result types", other than a JSF view (eg. a file
download, a http error, etc).
What I have today can do what you can do with JSF navigation rules, for example:
<page view-id="/getDocument.jsp">
| <navigation>
| <outcome value="success">
| <redirect view-id="/editDocument.jsp"/>
| </outcome>
| <outcome value="not-found">
| <redirect view-id="/404.jsp"/>
| </outcome>
| </navigation>
| </page>
Is equivalent to:
<navigation-rule>
| <from-view-id>/getDocument.jsp</from-view-id>
| <navigation-case>
| <from-outcome>success</from-outcome>
| <to-view-id>/editDocument.jsp"</to-view-id>
| <redirect/>
| </navigation-case>
| <navigation-case>
| <from-outcome>not-found</from-outcome>
| <to-view-id>/404.jsp"</to-view-id>
| <redirect/>
| </navigation-case>
| </navigation-rule>
And:
<page view-id="*">
| <navigation action="#{documentHome.get}">
| <outcome value="success">
| <render view-id="/editDocument.jsp"/>
| </outcome>
| </navigation>
| </page>
Is equivalent to:
<navigation-rule>
| <navigation-case>
| <from-action>#{documentHome.get}</from-action>
| <from-outcome>success</from-outcome>
| <to-view-id>/editDocument.jsp"</to-view-id>
| </navigation-case>
| </navigation-rule>
But it can also do this:
<page view-id="/getDocument.jsp">
| <navigation outcome="#{documentHome.document!=null}">
| <outcome value="true">
| <redirect view-id="/editDocument.jsp"/>
| </outcome>
| <outcome value="false">
| <redirect view-id="/404.jsp"/>
| </outcome>
| </navigation>
| </page>
This lets you write a DocumentHome.get() method with a void return type! This
is much more transparent to the model.
You can also do this:
<page view-id="/editDocument.jsp">
| <navigation action="#{documentHome.update}">
| <null-outcome>
| <redirect view-id="/document.jsp">
| <param name="documentId"
value="#{documentHome.document.id}"/>
| </redirect>
| </null-outcome>
| </navigation>
| </page>
(Yay!)
Soon I'll also add <begin-conversation/> and <end-conversation/> to the case
handling. Eventually I'll also add support for other things in addition to and
.
OK, so, what I need feedback on is the actual XML format. What I have there
today is a little less verbose than the JSF XML, but has one higher level of
indentation (which makes it more complex). The reason for this is that I want
to allow different actions to specify different outcome expressions, and
different lists of cases, eg:
<page view-id="/getDocument.jsp">
|
| <navigation action="#{documentHome.get}"
| outcome="#{documentHome.document!=null}">
| <outcome value="true">
| <redirect view-id="/editDocument.jsp">
| <param name="documentId"
value="#{documentHome.document.id}"/>
| </redirect>
| </outcome>
| <outcome value="false">
| <redirect view-id="/404.jsp"/>
| </outcome>
| </navigation>
|
| <navigation action="#{logout.logout}">
| <null-outcome>
| <redirect view-id="/login.jsp"/>
| <null-outcome>
| </navigation>
|
| </page>
So the question is should I go for something more similar to the JSF XML (one
less level of nesting):
<page view-id="/getDocument.jsp">
|
| <navigation action="#{documentHome.get}">
| <outcome expression="#{documentHome.document!=null}"
| value="true"/>
| <redirect view-id="/editDocument.jsp">
| <param name="documentId" value="#{documentHome.document.id}"/>
| </redirect>
| </navigation>
|
| <navigation action="#{documentHome.get}">
| <outcome expression="#{documentHome.document==null}"
| value="true"/>
| <redirect view-id="/404.jsp"/>
| </navigation>
|
| <navigation action="#{logout.logout}">
| <redirect view-id="/login.jsp"/>
| </navigation>
|
| </page>
Or does it make it easier to learn if we stay even more like standard JSF:
<page view-id="/getDocument.jsp">
|
| <navigation>
| <from-action>#{documentHome.get}</from-action>
|
<outcome-expression>#{documentHome.document!=null}</outcome-expression>
| <from-outcome>true</from-outcome>
| <redirect>
| <to-view-id>/editDocument.jsp</to-view-id>
| <param name="documentId" value="#{documentHome.document.id}"/>
| </redirect>
| </navigation>
|
| <navigation>
| <from-action>#{documentHome.get}</from-action>
|
<outcome-expression>#{documentHome.document==null}</outcome-expression>
| <from-outcome>true</from-outcome>
| <redirect>
| <to-view-id>/404.jsp"</to-view-id>
| </redirect>
| </navigation>
|
| <navigation action="#{logout.logout}">
| <redirect>
| <to-view-id>/login.jsp"</to-view-id>
| </navigation>
|
| </page>
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