about @PostConstruct and @PreDestroy annotation

[salih ayan]

Hi to all. l have three classes below

@SpringBootApplication
public class PostConstructDenemeApplication {

	public static void main(String[] args) {
		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
		ctx.register(SpringConfig.class);
		ctx.refresh();

		Bilgisayar b1 = ctx.getBean(Bilgisayar.class);
		System.out.println(b1.hashCode());

		Bilgisayar b2 = ctx.getBean(Bilgisayar.class);
		System.out.println(b2.hashCode());

		ctx.close();
	}
}

public class Bilgisayar {
	
	public Bilgisayar() {
		System.out.println("Bilgisayar CONSTRUCTOR");
	}

}

@Configuration
public class SpringConfig {

	@Bean(name = "bilgisayar")
	@Scope(value = "singleton" )
	public Bilgisayar getBilgisayar() {
		return  new Bilgisayar();
	}
	
	@PostConstruct
	public void test() {
		System.out.println("@PostConstruct");
		
	}
	
	@PreDestroy
	public void test2() {
		System.out.println("@PreDestroy");
	}
	
	public void close() {
		System.out.println("Close...");
	}

}

if l run this code, got below output  ...

@PostConstruct
Bilgisayar CONSTRUCTOR
1340565491
1340565491
@PreDestroy

if l changed Bilgisayar

public class Bilgisayar {
	
	public Bilgisayar() {
		System.out.println("Bilgisayar CONSTRUCTOR");
	}

	@PostConstruct
	public void test() {
		System.out.println("@PostConstruct");
		
	}
	
	@PreDestroy
	public void test2() {
		System.out.println("@PreDestroy");
	}
	
	public void close() {
		System.out.println("Close...");
	}
	
}

and SpringConfig class like below

@Configuration
public class SpringConfig {

	@Bean(name = "bilgisayar")
	@Scope(value = "singleton" )
	public Bilgisayar getBilgisayar() {
		return  new Bilgisayar();
	}
	
}

output will be like below

Bilgisayar CONSTRUCTOR
@PostConstruct
407697359
407697359
@PreDestroy
Close...

you noticed the difference .. in first output  
"@PostConstruct" comes before than "Bilgisayar CONSTRUCTOR"

but in scond one
"Bilgisayar CONSTRUCTOR"  comes before than  "@PostConstruct"


why ?

[Stephan van Hulst]

The @PostConstruct method is called after an instance of its containing class is constructed. The SpringConfig is constructed before the Bilgisayar is.

So if you put the @PostConstruct method in the SpringConfig class, it will print "@PostConstruct" before it prints "Bilgisayar CONSTRUCTOR". And if you put it in the Bilgisayar class instead, then it will print "@PostConstruct" after it's called the Bilgisayar constructor, as implied by the name 'PostConstruct'.

I don't really know how to make it more obvious than that. What confuses you? What do you expect to happen and why?

[salih ayan]

hi Stephan  ...
l really grateful for your helpful answer.

What l am want to do ?

Instead of putting "@PostConstruct" and "@PreDestroy" annotation in all bean class,  l want more generic solution, which is  putting  "@PostConstruct" and "@PreDestroy" annotation in
"Configuration" class than expect to work this two methods for all bean classes.

but for only one bean class its name is "Bilgisayar", "@PostConstruct"  method which is the "Configuration" class is not working as l expect.

l dont know could l explaing my point

       

[Claude Moore]

salih ayan wrote:hi Stephan  ...
What l am want to do ?
Instead of putting "@PostConstruct" and "@PreDestroy" annotation in all bean class,  l want more generic solution, which is  putting  "@PostConstruct" and "@PreDestroy" annotation in
"Configuration" class than expect to work this two methods for all bean classes.

That's not the way Spring beans' lifecycle works.
@PreDestroy and @PostConstruct are applied only to the methods annotated with them, within a specific class.

You may want to define a common ancestor class, with @PreDestroy and @PostConstruct annotated methods, and let your managed beans extend it.

[Himai Minh]

Hi, Salih,
Since your Bilgisayar is a singleton, you only have one bean constructed. So, b1 and b2 refer to the same bean.
The @POSTConstruct method is called after the Bilgisayar bean has been created.
But we cannot control the order of the printing.

[salih ayan]

hi Claude

You may want to define a common ancestor class, with @PreDestroy and @PostConstruct annotated methods, and let your managed beans extend it.

this came to my mind...
but still l was thinking spring must have special solutions for this situation..

[salih ayan]

hi Himai

Himai Minh wrote:Hi, Salih,
Since your Bilgisayar is a singleton, you only have one bean constructed. So, b1 and b2 refer to the same bean.
The @POSTConstruct method is called after the Bilgisayar bean has been created.
But we cannot control the order of the printing.

you are telling if we write @PostConstruct methods in confugration class this method while be performed each time after each bean class is constructed but we cant notice this
because printing order to the console  is not controlled by us

[Peter Rooke]

I suspect the BeanFactoryPostProcessor interface is what your are looking for.  
Not sure why you would want to extend the actual framework itself, but it is possible.  

[Himai Minh]

Hi, Salih,
In my opinion, we cannot rely on the order of printing to determine the order of execution.
You may find this tutorial about bean life cycle helpful :https://www.youtube.com/watch?v=A4vrK4PnqV0

[Claude Moore]

Peter Rooke wrote:I suspect the BeanFactoryPostProcessor interface is what your are looking for.  
Not sure why you would want to extend the actual framework itself, but it is possible.  

If the OP wants really to do this:

Instead of putting "@PostConstruct" and "@PreDestroy" annotation in all bean class,  l want more generic solution, which is  putting  "@PostConstruct" and "@PreDestroy" annotation in
"Configuration" class than expect to work this two methods for all bean classes.

then creating one's one BeanPostProcessorBean could be a good idea. I was thinking about using a class hierarchy - if you want to use the very same method for doing something, one should put in a single ancestor class the required code.