Access Spring bean definition properties at runtime for logging - spring

Question

I want to be able to read the properties from certain bean definitions that are configured in my Spring configuration file (i.e. the one set by contextConfigLocation in my web.xml) at run time. I want to do this so that I can log property values so that I when I receive the log files for diagnosis I can see how the system integrators have set up the application.
Looking at the Spring debug logs I can see that they are read from the config file by the class XmlBeanDefinitionReader. I'm guessing there is a way that Spring provides for accessing the resulting bean definitions, but I can't find it.
By way of example these are the sort of bean definitions that for which I would like to read configurations.
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="driverClass">
<value>com.mysql.jdbc.Driver</value>
</property>
<property name="jdbcUrl">
<value>jdbc:mysql://localhost:3306/an_example_db</value>
</property>
<property name="user">
<value>exampleuser</value>
</property>
<property name="password">
<value>examplepwd</value>
</property>
</bean>
<bean id="sessionFactory"
class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
<property name="dataSource">
<ref bean="dataSource" />
</property>
<property name="packagesToScan" value="com.my.example.entity" />
<property name="hibernateProperties">
<props>
<prop key="hibernate.id.new_generator_mappings">true</prop>
<prop key="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</prop>
<prop key="hibernate.hbm2ddl.auto">validate</prop>
<prop key="hibernate.show_sql">true</prop>
<prop key="hibernate.format_sql">true</prop>
<prop key="hibernate.query.substitutions">true 1, false 0, yes 'Y', no 'N'</prop>
</props>
</property>
</bean>
Please note that these are examples only. I'd like to be able to read properties for any bean definition if that is possible.

Answer 1

You can create a bean that plugs in the post-construction phase of all beans created at which point you can perform you logging. This can be done by a bean that implements BeanPostProcessor.
Example:
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
#Component
public class BeanPostProcessorAuditChecker implements BeanPostProcessor {
#Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
#Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("Bean: " + beanName + " initialized with props: " + bean);
return bean;
}
}
Things to note:
This bean can be defined using annotations (as depicted above) or XML config as usual.
The interface is intercepting all bean constructions.
The interface method implementations are expecting you to return the bean object.
In my example I just System.out.println but you really want to SLF4J or otherwise log. Also I'm trusting that the toString() method is implemented properly exposing the properties you are interested in.
If you want to filter the logging to happen only on a subset of beans and not for all beans you'll have to do that yourself in the body of the method with reflection
Snippet:
if(bean instanceof DataSource ||
bean instanceof SessionFactory) { log.debug("{}",bean); }
Since your business domain is not known some alternatives provided:
If you can pointcut your domain you want to plugin AOP is another alternative proxy approach.
You could expose JMX on the beans and consume externally (decoupled approach)
Another decoupled approach is publishing Events using ApplicationEventPublisher. This is fyi since not advisable in your case - you are interested in construction only state properties.
Before Edit
The beans you are demonstrating are 1) singletons (by virtue of Spring default scope) and 2) properties are not likely to be changing after bean setup (via set method calls).
Under these assumptions why aren't you amassing these properties values in a props file
database.driverClass=com.mysql.jdbc.Driver
database.user=exampleuser
...
inject them in the context definition
...
<property name="user" value="#{database.user}"/>
...
and use the PropertyPlaceholderConfigurer to check the values.