I know how spring BeanPostProcessor works but I exactly don't get any such scenarios where BeanPostProcessor might be very helpful. If someone has implemented BeanPostProcessor in his/her application, then please give a brief about that.
The BeanPostProcessor interface is arguably the most basic and useful tool of the Spring IoC container. Take a look at the implementing classes in the javadoc.
You typically use Spring to inject beans into other beans. Spring uses AutowiredAnnotationBeanPostProcessor to achieve this. After the bean has been instantiated, this BeanPostProcessor scan the bean's fields for #Autowired targets. If it finds any, it tries to resolve a bean from the context to inject. You can find the source code here.
Related
I am debugging a Java application which uses the Spring IoC Container. I have a breakpoint set in one of the methods of a class annotated as a #Component. I would like to get my hands on the Spring Application Context which manages this bean (to access some different bean, which hasn't been injected into this class).
Since I don't want to modify the code, implementing ApplicationContextAware is out of question.
How could I do this? Is this even possible?
You can do it, no need to implement ApplicationContextAware.
You can #Autowire the application context
private #Autowired ApplicationContext appContext;
EDIT
without any code modification, what you need is a good profiling tool. MaybeJProfiler can do the trick, or some free alternative.
Basically #Autowire and #Configurable do the same. What is the difference between these two annotation?
Please pardon me.
#Configurable allows you to inject dependencies without explicit bean definition while #Autowire used to inject the explicitly defined beans.
I have a requirement that I want to initialize a bean before any other bean in my application context. One way to do is to use "depends-on" on every other bean but its too verbose as I have many beans in my application-context.
Is there any other way to do this. I have read abt implementing ServletContext for this but I dont think this will work as this has nothing to do with Spring.
Please let me know your thoughts on it.
Thanks,
Raunak
Make sure that your bean comes first in your context.xml and it will be instantiated first. You can make a simple test to verify.
How should each class in an application retrieve the Spring application context? Or, stated another way, how many times should an application invoke new ClassPathXmlApplicationContext("applicationContext.xml")?
Usually a class does not need the application context, but it needs some of the objects Spring injects. And this is configured in that applicationContext.
As such an application typically calls new ClassPathXmlApplicationContext("applicationContext.xml") only once.
With dependency injection, you shouldn't have to, in general. But if your class really needs to be aware of the application context, implement the ApplicationContextAware interface. Spring will automatically call the setApplicationContext method defined in that interface to provide your class with the application context.
Note that if you're trying to gain access to filesystem resources, you should use ResourceLoaderAware. If you want access to the message source, then don't implement an interface; instead, inject a reference to the MessageSource bean.
I think you should take the advice from the answer to your other question here. Implementing ApplicationContextAware or ServletContextAware (if you are in a servlet container) is the best way to get the context.
Look up how spring handles Dependency Injection or Inversion of Control.
Once.
Actually you should let Spring do the heavy lifting and build/configure the classes rather than the other way around.
The whole idea is that all classes can be built without having to call the outside world for dependencies, which are 'magically' provided by the Spring framework.
This approach was invented to get away from the ServiceLocator pattern to which you are alluding, i.e. get a reference to an object to get the dependencies you need, ala JNDI.
I am using Java-based Spring configuration in my project, specifying bean construction in #Bean-annotated methods in #Configuration. Recently, Recently, I've started to think that maybe it would've been better to use #Autowired to remove all non-important beans from #Configuration, leaving only small "root" set of them (key services and technical beans like those of Spring MVC).
Unfortunately, it seems that Spring can notice implementations for #Autowired dependencies only if they are inside component-scanned package which I cannot do without resorting to some XML.
Is there any way to use #Autowired with Java-based configuration without explicitly specifying each bean?
If I understand you correctly, you're expecting Spring to auto-discover the DaoImpl class based on the autowired dependency on the Dao interface.
This isn't going to happen - you either need to use component scanning, or you need to explicitly declare the bean, either as <bean> or #Bean.
The reason for this is that Java provides no mechanism to discover classes which implement a given interface, the classloader just doesn't work that way.
If you are implementing the Idao via dao and you are looking to #Autowire that dependency into your reference var... you need to first:
define the bean so you (in Java Based Config) simply return the impl class to the interface. The bean name is that of your method name.
When you autowire this, it will search for a matching name between your reference variable you are looking to autowire and your declaration.
THEN you will be fine. Hope this helps.