PropertyPlaceholderConfigurer for bean class

[bpryor]

I have just started to use Spring in a Tapestry web application. I'm currently making heavy use of Tapestry "extensions" which are managed objects just like Spring beans upon which properties can be set.

I am planning on using the Spring stack to eliminate these Tapestry extensions, making the service objects into Spring beans. The initial target use of Spring then is as a simple service manager / locator.

The application is heavily customized - a common idiom we use is to have an interface with a different concrete implementation for each client.

So what I really wanted to do was:

	<bean id="serviceBean" class="$&#123;client.service.class&#125;" />

... and use the PropertyPlaceholderConfigurer to replace the token with the actual name of the concrete service class for a client.

However, it seems that the PropertyPlaceholderConfigurer is useful only for replacing <property> values, which makes sense given its name.

Is there a better way to accomplish this using Spring?

An additional note: I would like to have a single applicationContext.xml file - each client would have their own client.properties with customized values.

[irbouho]

try the following:

  <bean id="serviceBean" class="java.lang.Class" factory-method="forName"> 
    <constructor-arg> 
      <value>$&#123;client.service.class&#125;</value>
    </constructor-arg> 
  </bean>

HTH

[bpryor]

Thanks for the suggestion. That does almost what I'm looking for, except that the service bean ends up being a java.lang.Class instead of an instance of that class. Using that idea, I found that something like this works:

	<bean id="serviceFactory" class="java.lang.Class" factory-method="forName" singleton="false">
		<constructor-arg><value>$&#123;client.service.class&#125;</value></constructor-arg>
	</bean>
	<bean id="serviceBean" factory-bean="serviceFactory" factory-method="newInstance" />

Is there a way to accomplish this with a single <bean> declaration?

[jbetancourt]

The most direct route is not possible. I don't think Spring allows migration of bean attributes to elements so that an inline bean definitions could be used here, but maybe that would be useful in many other situations. [not implying this is what you are looking for, of course].

Not possible?

   <bean id="serviceBean" factory-method="newInstance"> 
        <property name="factory-bean">
                <bean class="java.lang.Class" factory-method="forName" singleton="false"> 
                        <constructor-arg><value>$&#123;client.service.class&#125;</value></constructor-arg> 
                </bean> 
        </property>
   </bean>

Thanks for the suggestion. That does almost what I'm looking for, except that the service bean ends up being a java.lang.Class instead of an instance of that class. Using that idea, I found that something like this works:

	<bean id="serviceFactory" class="java.lang.Class" factory-method="forName" singleton="false">
		<constructor-arg><value>$&#123;client.service.class&#125;</value></constructor-arg>
	</bean>
	<bean id="serviceBean" factory-bean="serviceFactory" factory-method="newInstance" />

Is there a way to accomplish this with a single <bean> declaration?

[cmgharris]

You could write your own factory bean class, e.g. ClassInstantiatingFactoryBean, implementing FactoryBean and having the class name as a property.

Then you'd get your instance with

<bean id="serviceBean" class="foo.bar.ClassInstantiatingFactoryBean">
        <property name="className"><value>$&#123;client.service.class&#125;</value></property>
</bean>

[.NET Guy]

How about this approach? It does mean writing some code though :?

public class Activator {

    public static object createInstance (string clazz) {
          return Activator.createInstance (Class.forName (clazz));
    }

    public static object createInstance (Class clazz) {
          return clazz.newInstance ();
    }
}

 
<bean id="serviceBean" class="Activator" factory-method="createInstance">
    <constructor-arg>
      <value>$&#123;client.service.class&#125;</value>
    </constructor-arg>
  </bean>

I have (obviously) left out all error checking, etc :wink:

[bpryor]

Thanks for all the suggestions. I ended up writing a simple class instantiator factory that does a Class.forName and a newInstance() based off a className argument. I used a single bean declaration with factory-method, passing in the className as a constructor-arg.

This approach allows me to set properties on the created beans as well as specify their class.