Handful of sand

I wanted dynamic configuration of my logback TurboFilter and i couldn’t find a good way to configure my logback TurboFilter through logback.xml. My requirement was to configure the filter based on a property from a properties file. I could have read the properties file in the filter class but i instead decided to use my Spring configuration for wiring in properties. To reap that benefit, the filter had to be a bean in the Spring context. Something like this when configured in XML

<bean id="turboFilter" class="com.nielsen.mmp.fw.logging.DynamicLoggerDisablingFilter">
    <property name="disabledLoggers" value="${disabledLoggers}"/>
</bean>

Now all i needed was some glue code that would make logback use this filter. Its been quite a while since i saw a need for a Spring BeanFactoryPostProcessor. I added a simple filter discovering post-processor that would discover all the TurboFilters defined in the Spring context and let logback know.

Map filterBeans = BeanFactoryUtils.
                            beansOfTypeIncludingAncestors(beanFactory,
                                                    TurboFilter.class);
    for (TurboFilter filter : filterBeans.values()) {
        LoggerContext loggerContext = (LoggerContext) LoggerFactory.getILoggerFactory();
	loggerContext.addTurboFilter(filter);
    }

Because we have hierarchical BeanFactories i had to use this BeanFactoryUtils.beansOfTypeIncludingAncestors(…) method. The usual BeanFactory.getBeansOfType() checks only in that beanFactory instance. It does not go through the parent beanFactories.

I wish Joran had a way (documented) to use values from properties file when configuring. Something like the following would have been neat.

    <configuration>
        <properties id="props" source="my-app.properties"/>
        <filter id="myTurboFilter" class="x.x.x.MyTurboFilter">
              <myFilterProperty>$props.propertyKey</myFilterProperty>
        </filter>
    </configuration>

Edit:
So i was mistaken. Joran does support properties file based customization just the way i had outlined. But, but, but, i don’t see it allowing property file overriding (ie a property file overriding the base property file) which is what we needed for our app. So my post processor is still going to be useful.