Invoking PostConstruct for each bean in a list - spring

Question

I have the following pseudo code:
#Bean
public List<BeanB> beanB(
List<BeanA> beansA) {
List<BeanB> beansB = new ArrayList<>();
for (BeanA beanA : beansA) {
beansB.add(new BeanB(beanA))
}
return beansB;
}
#Bean
public BeanC beanC(
List<BeanB> beansB) {
return new BeanC(beansB);
}
Now the challenge is when the list of BeansB is constructed post construct is not invoked on those beans in the list. Is there any idiomatic way to trigger post construct invocation on those beans.

Answer 1

This does not work well as #PostConstruct is called by Spring. and from your code, for List<BeanB>, Spring will only try to find #PostConstruct in List. If it can find it, it will execute the #PostConstruct code.
I suspect you are writing beanA as follow in case you have #PostConstruct in beanA's class like below.
#Bean
public BeanA beanA_1() {
return new BeanA();
}
#Bean
public BeanA beanA_2() {
return new BeanA();
}
// which naming List of Bean B as beanB does not seems a good idea though
#Bean
public List<BeanB> beanB(List<BeanA> beansA) {
List<BeanB> beansB = new ArrayList<>();
for (BeanA beanA : beansA) {
beansB.add(new BeanB(beanA))
}
return beansB;
}
To make it work, there are multiple ways, I will just suggests some of them.
Creating a new Class, says BeanBCollectionWrappe to wrap the List of BeanB. And to make the code a bit more robust, I am implementing InitializingBean instead of #PostConstruct which is essentially the same, but allow me to ensure the method is afterPropertiesSet but not any methods.
public class BeanBCollectionWrapper implements InitializingBean {
private List<BeanB> beansB;
public void afterPropertiesSet() throws Exception {
for (BeanB beanB: beansB) {
beanB.afterPropertiesSet();
}
}
// getter and setter
}
public class BeanB implements InitializingBean {
public void afterPropertiesSet() throws Exception {
// ...
}
}
The Wrapper code can definitely be a bit better by use of Generics, like replacing BeanB to <T extends InitializingBean>.
And for the last Part,
#Bean
public BeanC beanC(BeanBCollectionWrapper wrapper) {
return new BeanC(wrapper.getBeansB());
}
Another method can be done by implementing BeanPostProcessor.
For example,
#Component
public class BeanBListBeanPostProcessor implements BeanPostProcessor{
#Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (beanName.equals("beanB")) {
List<BeanB> beanBList = (List) bean;
for (BeanB beanB : beanBList) {
try {
beanB.afterPropertiesSet();
} catch (Exception exception) {
exception.printStackTrace();
}
}
}
return null;
}
}
public class BeanB implements InitializingBean {
public void afterPropertiesSet() throws Exception {
// ...
}
}