Re: [Springframework-developer] Ordering HandlerMappings and other beans

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Agreed. What about SimpleUrlHandlerMapping, as it's not the default?

----- Original Message -----
From: "jürgen höller [werk3AT]" <jue...@we...>
To: <spr...@li...>
Sent: Monday, April 07, 2003 5:14 PM
Subject: RE: [Springframework-developer] Ordering HandlerMappings and other
beans

A naming issue: UrlHandlerMapping should probably be called
DefaultUrlHanderMapping or some other more meaningful name. Especially with
AbstractUrlHandlerMapping in addition to BeanNameUrlHandlerMapping, naming a
concrete implementation UrlHandlerMapping seems inappropriate.

Of course, this would mean a name change that affects ControllerServlet
context config files. But I think that we should prefer proper names and
proper structure to backward compatibility, at least as long as there isn't
an official release.

Juergen

-----Original Message-----
From: jürgen höller [werk3AT]
Sent: Monday, April 07, 2003 5:09 PM
To: spr...@li...
Subject: [Springframework-developer] Ordering HandlerMappings and other
beans

Hi Rod, everyone,

I've just developed a custom HandlerMapping strategy for one of our
applications and faced the issue that I wanted to retrieve beans of a
certain class from the ApplicationContext in a specifyable order. Looking
for a solution, I've recognized that exactly the same issue occurs with
HandlerMappings themselves too. Currently, ControllerServlet solves this via
sorting by bean name ("a.urlMap", "b.urlMap"), but frankly, I've never
particularly liked that solution.

So I've applied a new approach to both HandlerMapping order and the problem
in the custom application. Details of the HandlerMapping solution follow:

- I've introduced a Ordered interface to com.interface21.core, featuring one
single method "int getOrder()", and an associated OrderComparator. The
getOrder() method simply returns an int value, higher value meaning greater
in terms of sorting resp. lower priority. This is somewhat analogous to
Servlet load-on-startup values. OrderComparator sorts by order value,
treating non-Ordered objects as greatest resp. lowest priority.

- ControllerServlet now sorts HandlerMappings (and HandlerAdapters, for
consistency's sake) by sorting them with OrderComparator, rather than by
bean name. Non-Ordered instances are thus applied in an arbitrary order, but
instances can choose to implement Ordered to be able to specify a higher
priority. Of course, the obvious way is adding an "order" bean property with
getter and setter, to allow specifying the order value in the
ApplicationContext configuration.

- There's AbstractUrlHandlerMapping now, an abstract base class for
url-based HandlerMapping implementations. In addition to refactored things
like unified handler initialization code (propagating ApplicationContext and
LocaleResolver) for both BeanNameUrlHandlerMapping and UrlHandlerMapping, it
offers a property-based Ordered implementation.

An example snippet from an applicationContext.xml file:

<bean name="myUrlMap"
class="com.interface21.web.servlet.handler.UrlHandlerMapping">
<property name="order">0</property>
<property name="mappings">
/example.do=exampleController
</property>
</bean>

<bean name="yourUrlMap"
class="com.interface21.web.servlet.handler.UrlHandlerMapping">
<property name="order">1</property>
<property name="mappings">
/example.do=/exampleFormController
/exampleForm.do=exampleFormController
</property>
</bean>

According to the order values, myUrlMap gets applied first, thus
"/example.do" will lead to exampleController's execution. If one sets
myUrlMap's order value to "2" or omits its order line, yourUrlMap will get
applied first, thus "/example.do" will lead to exampleFormController's
execution.

I consider this more elegant and more flexible than sorting by bean name.
After all, servlets don't get started in the order of their name for a
reason... ;-) Fortunately, an application developer doesn't have to care
about the Ordered interface if he doesn't want to: A single HandlerMapping
definition doesn't need to specify an order value, and a HandlerMapping
implementation doesn't need to implement Ordered.

If noone objects, I will check in the changes promptly, as they go hand in
hand with other things like the UrlHandlerMapping refactoring and some
ControllerServlet polishing.

Juergen

DI Jürgen Höller
Senior System Architect
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