How to create a Spring bean for apache logging Log class? - spring

Question

I'd like to create an autowired bean in a Dao class in order to do logging opperations. My way was hitherto static final statement like this:
private static final Log log = LogFactory.getLog(LoggedClass.class);
But now I'm trying to use IoC to turn classes decoupled.
If just add configuration in pom.xml and try to do sth like
#Autowired
Log log;
I receive an error message:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'funciDaoImpl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.apache.commons.logging.Log br.com.bb.dirco.dao.impl.FunciDaoImpl.log; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'log' defined in class path resource [com/company/project/util/PersistenceConfig.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [java.lang.Class]: : No qualifying bean of type [java.lang.Class] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [java.lang.Class] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
In order to get a logger, I had to provide a class to getLog method on LogFactory class and attribute it to Log instance. There's a way to do it using #Autowired Spring IoC? Thanks!

Answer 1

You can inject only those objects which are managed/created by Spring container. You have to register your bean (or factory method creating the bean) with container (with annotations like #Component/#Singleton/... or directly in xml)
In your case it's not very applicable since you have to have many different types (for every class) of logger objects provided by Spring and then when you inject they would have to be identified by different name/type for every class.
P.S. I don't see any problem using it the way you use it now

Answer 2

Where I work we have implemented support for #Autowired SLF4J Loggers using Springs BeanPostProcessor.
First you need to define an Logger placeholder bean in your application context. This bean is going to be injected by Spring into all bean with a #Autowired Logger field.
#Configuration
public class LoggerConfig {
#Bean
public Logger placeHolderLogger() {
return PlaceHolder.LOGGER;
}
#Bean
public AutowiredLoggerBeanPostProcessor loggerPostProcessor() {
return new AutowiredLoggerBeanPostProcessor();
}
}
Then you an AutowiredLoggerBeanPostProcessor which inspects all beans, indetify bean that contain Logger fields annotated with #Autowired (at this point should contain a reference to the Logger placeholder bean), create a new Logger for the partilcar bean an assigned it to the fields.
#Component
public class AutowiredLoggerBeanPostProcessor implements BeanPostProcessor, PriorityOrdered {
#Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
attachLogger(bean);
return bean;
}
#Override
public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
attachLogger(bean);
return bean;
}
private void attachLogger(final Object bean) {
ReflectionUtils.doWithFields(bean.getClass(), new FieldCallback() {
public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
if (Logger.class.isAssignableFrom(field.getType()) &&
(field.isAnnotationPresent(Autowired.class) ||
field.isAnnotationPresent(Inject.class))) {
ReflectionUtils.makeAccessible(field);
if (field.get(bean) == PlaceHolder.LOGGER) {
field.set(bean, LoggerFactory.getLogger(bean.getClass()));
}
}
}
});
}
#Override
public int getOrder() {
return HIGHEST_PRECEDENCE;
}
}