Overriding properties in a Spring Bean with BeanFactoryPostProcessor

12 / May / 2012 by Vivek Krishna 0 comments

I was going through the source code of one of the Grails Plugins where I found the use of Spring’s BeanDefinitionRegistryPostProcessor to override some configurations that are available in DataSource.groovy. That involved a complete over riding of a PropertyValue definition.


It set me thinking about whether there is a way to override bean properties like String, Integer etc in a simpler way after the bean has initialized. In comes BeanFactoryPostProcessor, which provides a wonderful hook to do just that.


I created a small grails project and added a class CustomBean which looked like this :

class CustomBean {
       String customVariable

I registered a customBean on resources.groovy using

beans = {
    customBean(CustomBean) {
        String value = "Test Data From resources.groovy"
        println "Setting value ${value}"
        customVariable = value


This sets the initial value of customVariable as “Test Data From resources.groovy”.

If you are wondering what the customBeanPostprocessor is, that is just what I am going to explain next.
The bean implements the BeanFactoryPostProcessor interface and overrides the methods which provides us with hooks to modify the properties of the bean.


The class definition is:

import groovy.util.logging.Log4j
import org.springframework.beans.factory.config.BeanPostProcessor

class CustomBeanPostprocessor implements BeanPostProcessor{

    Object postProcessBeforeInitialization(Object bean, String beanName) {
        return bean

    Object postProcessAfterInitialization(Object bean, String beanName) {
        if(beanName == 'customBean') {
            log.debug("Setting custom value inside post processor")
            bean.customVariable = "Set from Post Processor"
        return bean

What amazed me is the elegance with which the developers of the framework has provided entry points into its internals without forcing the users to shave the yak.


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