Overriding Module's configuration

[sotretus]

Hi,

I am developing a module that can be included by clients to add functionality to their application. This module is to be distributed as a jar file. Inside the jar I am placing the standard configuration for my beans (i.e. a 'module-context.xml' file) and all the required files to make it work.

As such, my beans are already (and correctly) wired in the module-context.xml file. Still I would like to allow a developer that uses my module to change certain bean wirings.

For instance: Imagine that my module has three Beans wired by default; BeanA, BeanA1 and BeanA2. BeanA is wired with BeanA and BeanB, according to the module-context.xml file.

A client of mine wants to create his own version of BeanA2 and discard the one the module ships with. Is there any way the user can configure in his XML config file the new BeanA2 and wire it up my already configured BeanA ?

packaged with my .jar file is the module-context.xml file :

...
<bean id="BeanA" class="...">
   <property name="beanA1" ref="BeanA1" />
   <property name="beanA2"  ref="BeanA2" />
</bean>

<!-- BeanA1 and BeanA2 are configured here as well-->
...

and I would like the user of the module to be able to do something like this (of course this syntax is invalid):

...
<bean id="CustomBeanA2" class="...">

</bean>

//inject CustomBeanA2 into BeanA
<bean overrides="BeanA">
   <property name="BeanA2" ref="CustomBeanA2" />
</bean>
...

In this way the user of the module does not have to configure every object in my beans file again. (I actually have lots of beans configured by default)

(Note: I would like to avoid strange "hacks" if possible, like creating a method named setUserCustomBeanA2 in BeanA and then autowiring byName. Inside that method checking if the instance var has already a value and if it does overwriting. I should also do something similar in the setBeanA2 method, since I have no guarantee of which setter method will be executed first)

Please let me know if I was not clear enough.

Regards
AB
Regards
Andres B.

[karldmoore]

If you have two applicationContext files each containing the same named bean e.g. bean="sameBeanName" the last one loaded should win. I'm not sure if you'd consider this a hack or not.

[sotretus]

If you have two applicationContext files each containing the same named bean e.g. bean="sameBeanName" the last one loaded should win. I'm not sure if you'd consider this a hack or not.

I don't, as long as it is clear how to set order on the config files (i.e. documented)

Also I'm not sure I understand how this fixes my issue.. unless I set all beans to lazy-init ¿? I mean.. I need both BeanA2 and CustomBeanA2 "loaded" (in that order) before BeanA is loaded so Spring wires the correct bean.

Is there any way to specify that?

Thanks for your response
regards
Andres B.

[karldmoore]

Give this example a try. You can comment out one of the various beans in the context and see what it does. Doesn't this solve your problem?

BeanOverrideExample.java

package example;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class BeanOverrideExample
{
	public static void main ( String [] args )
	{
		ApplicationContext applicationContext = new ClassPathXmlApplicationContext ( new String [] { "applicationContextOne.xml", "applicationContextTwo.xml" } );
		SimpleBean simpleBean = ( SimpleBean ) applicationContext.getBean ( "simpleBean" );
		simpleBean.sayHello ();
	}
}

SimpleBean.java

package example;

public class SimpleBean
{
	private String someOtherProperty;
	private AnotherSimpleBean anotherSimpleBean;
	
	public void setSomeOtherProperty ( String someOtherProperty ) 
	{
		this.someOtherProperty = someOtherProperty;
	}
	
	public void setAnotherSimpleBean ( AnotherSimpleBean anotherSimpleBean )
	{
		this.anotherSimpleBean = anotherSimpleBean;
	}
	
	public void sayHello ()
	{
		System.out.println ( "Hello World! " + someOtherProperty );
		anotherSimpleBean.sayHelloAlso ();
	}
}

AnotherSimpleBean.java

package example;

interface AnotherSimpleBean
{
	void sayHelloAlso ();
}

AnotherSimpleBeanOne.java

package example;

public class AnotherSimpleBeanOne implements AnotherSimpleBean
{
	public void sayHelloAlso ()
	{
		System.out.println ( "Hello World from another simple bean one" );
	}
}

AnotherSimpleBeanTwo.java

package example;

public class AnotherSimpleBeanTwo implements AnotherSimpleBean
{
	public void sayHelloAlso ()
	{
		System.out.println ( "Hello World from another simple bean two" );
	}
}

applicationContextOne.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
       
       <bean id="anotherSimpleBean" class="example.AnotherSimpleBeanOne"/>
       
       <bean id="simpleBean" class="example.SimpleBean">
       		<property name="someOtherProperty" value="applicatioContextOne.xml set this"/>
   			<property name="anotherSimpleBean" ref="anotherSimpleBean"/>
       </bean>       
</beans>

applicationContextTwo.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
       
       <bean id="anotherSimpleBean" class="example.AnotherSimpleBeanTwo"/>
       
       <!--
       <bean id="simpleBean" class="example.SimpleBean">
   			<property name="someOtherProperty" value="applicatioContextTwo.xml set this"/>
   			<property name="anotherSimpleBean" ref="anotherSimpleBean"/>
       </bean>  
       -->
            
</beans>

[sotretus]

Yeah, it indeed solves my problem! that is something I didn't imagine it could happen. Really cool!

I didn't know it would replace the AnotherSimpleBeanTwo in SimpleBean; but hey! who am I to judge!

Do you happen to know if the order of the config files specified in a web.xml (by using the corresponding spring property) is preserved?

Very useful,
Thanks
Andres B.

[karldmoore]

Yeah, it indeed solves my problem! that is something I didn't imagine it could happen. Really cool!

I didn't know it would replace the AnotherSimpleBeanTwo in SimpleBean; but hey! who am I to judge!

I thought it might be that simple, it's always nice when it is! Glad it was useful.

Do you happen to know if the order of the config files specified in a web.xml (by using the corresponding spring property) is preserved?

I think the order is preserved so the last one loaded wins, if that makes sense.