Dynamic Property Configuration

[fenrick]

Hi,

What I am looking to achieve is kinda of like the PropertyPlaceholderConfigurer, in that I would like configuration values within my bean config to be derived from external values.

While the PropertyPlaceholderConfigurer allows for setting values from a list of property files, I would like it to be derived from a configuration hierarachy - implemented using a similiar pattern to the Chain-of-Command structure.

I have achieved this using a bean implementing the MethodInvokingFactoryBean; but I realise that this is both cludgy and dependant upon a perscribed bean heirachy.

eg:
Configuration Setup:

    <!-- Cache Configuration Source -->
    <bean id="CacheConfigSource" class="jolyon.spring.services.config.EHCacheConfigSource">
        <property name="cache">
            <bean id="ConfigCache" class="org.springframework.cache.ehcache.EhCacheFactoryBean">
                <property name="cacheManager">
                    <bean id="EhCacheManagerFactoryBean" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"/>
                </property>
                <property name="cacheName">
                    <value>ConfigCache</value>
                </property>
                <property name="eternal">
                    <value>false</value>
                </property>
                <property name="timeToLive">
                    <value>120</value>
                </property>
                <property name="timeToIdle">
                    <value>120</value>
                </property>
                <property name="diskPersistent">
                    <value>false</value>
                </property>
                <property name="maxElementsInMemory">
                    <value>10000</value>
                </property>
                <property name="overflowToDisk">
                    <value>true</value>
                </property>
                <property name="diskExpiryThreadIntervalSeconds">
                    <value>120</value>
                </property>
            </bean>
        </property>
    </bean>
    <!-- Hibernate Configuration Source -->
    <bean id="HibernateConfigSource" class="jolyon.spring.services.config.HibernateConfigSource">
        <property name="sessionFactory">
            <ref bean="sessionFactory"/>
        </property>
        <property name="transactionManager">
            <ref bean="transactionManager"/>
        </property>
    </bean>
    <!-- Property File Configuration Source -->
    <bean id="PropertyFileConfigSource" class="jolyon.spring.services.config.PropertyFileConfigSource">
        <property name="basenames">
            <list>
                <value>config</value>
            </list>
        </property>
    </bean>
    <!-- Configuration Bean -->
    <bean id="ConfigBeanTarget" class="jolyon.spring.services.config.ConfigBeanImpl">
        <property name="configSourcesNames">
            <list>
                <value>CacheConfigSource</value>
                <value>PropertyFileConfigSource</value>
            </list>
        </property>
    </bean>
    <bean id="ConfigBean" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="proxyInterfaces">
            <value>jolyon.spring.services.config.ConfigBean</value>
        </property>
        <property name="target">
            <ref bean="ConfigBeanTarget"/>
        </property>
    </bean>
    <bean id="StringConfigSetting" abstract="true" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
        <property name="targetObject">
            <ref bean="ConfigBean"/>
        </property>
        <property name="targetMethod">
            <value>getConfigString</value>
        </property>
        <property name="singleton">
            <value>false</value>
        </property>
    </bean>
    <bean id="ListConfigSetting" abstract="true" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
        <property name="targetObject">
            <ref bean="ConfigBean"/>
        </property>
        <property name="targetMethod">
            <value>getConfigList</value>
        </property>
        <property name="singleton">
            <value>false</value>
        </property>
    </bean>

Property extract:

                <property name="outputFileName">
                    <bean parent="StringConfigSetting">
                        <property name="arguments">
                            <value>GenerateCourseCategoryDataFile.OutputFileName</value>
                        </property>
                    </bean>
                </property>

I am unable to find out what precisely I need to do to convert my ConfigBean instance into operating like a PropertyPlaceholderConfigurer, therefore allowing configuration settings to be pulled from a hierachy, without implementation linkages and verbose bean configuration.

Is this possible? Short of implementing an entire bean factory postprocessor for this specific task.

[irbouho]

You may need to implement the BeanFactoryPostProcessor interface.

HTH.

[snwiem]

I did that already using the jakarta commons configuration library.

All i did was extending the PropertyPlaceHolder with an property accepting 'org.apache.commons.configuration.Configuration'.

Next i overwrote the resolvePlaceholder with

protected String resolvePlaceholder(String placeholder, Properties properties) {
	String value = null;
	if ( true == this.configurationOverwrite && null != this.configuration ) {
		value = resolvePlaceholder( placeholder, this.configuration );
	}
	if ( null == value ) {
		value = super.resolvePlaceholder( placeholder, properties );
	}
	if ( null == value && null != this.configuration ) {
		value = resolvePlaceholder( placeholder, this.configuration );
	}
	return( value );
}

That does the trick for a singel jakarta common configuration bean. To be a little bit more convenient i additionally provide an CompositeConfigurationWrapper which extends the CompositeConfiguration class to be a little bit more convenient in combining several configuration resources using the constructor-arg pattern.

public class CompositeConfigurationWrapper extends CompositeConfiguration {

	protected static final Log log = LogFactory.getLog( CompositeConfigurationWrapper.class );
	
	/**
	 * Standard constructor.
	 * 
	 * Nothing special about this one.
	 *
	 */
	public CompositeConfigurationWrapper() {
		super();
	}

	/**
	 * Constructor for usage in spring context definitions.
	 *  
	 * @param configurations A list of org.apache.commons.configuration.Configuration instances.
	 */
	public CompositeConfigurationWrapper( List configurations ) {
		super();
		this.addConfigurations( configurations );
	}
	
	/**
	 * Setter for a list of configuration beans.
	 * 
	 * @param configurations A list of org.apache.commons.configuration.Configuration instances.
	 */
	public void addConfigurations( List configurations ) {
		if ( log.isDebugEnabled() ) {
			log.debug( "[addConfigurations] BEGIN" );
		}
		synchronized( this ) {
			for ( Iterator i = configurations.iterator(); i.hasNext(); ) {
				super.addConfiguration( (Configuration)i.next() );
			}
		}
		if ( log.isDebugEnabled() ) {
			log.debug( "[addConfigurations] END" );
		}
	}
}

Cascading configuration using placeholders is now very easy.

greets
Sebastian

[Costin Leau]

Btw, Spring Modules (springmodules.dev.java.net) already has support for Jakarta Commons. There will be a new release (0.3) in the very near future.