CODEWITHSUNDEEP
springspring-bootdependency-injection
Sagar
Sagar

Reputation: 5596

Spring boot : configuration inheritance

I have 

package com.parent.spring;
public abstract class ParentConfig {

@Bean
public String bParent() {
   return "parent bean";
}

then

package com.child.spring;
public class ChildConfig extends ParentConfig {
  @Bean
  public String bChild() {
     return "child bean";
  }
}

and here's how I am starting my spring boot app

@SpringBootApplication
@ComponentScan(basePackages = { "com.child.spring","com.parent.spring" })
public class MyMain {
    public static void main(String args[]) throws Exception {
        SpringApplication.run(MyMain.class, args);
    }
}

I want to load beans from child config first and the from parent config. However, opposite is happening. Don't want to use depends on option as this is just an example, in reality I have lot of beans in child and parent config. Also, I have bunch of other configuration classes in parent package so I don't want to remove that from component scan. Any nicer solution on this ?

Upvotes: 3

Views: 5775

Answers (2)

Mark Bramnik
Mark Bramnik

Reputation: 42471

Could you please explain more your use case so that we could provide you the best solution we can :) ?

In general its a wrong approach to treat @Configuration files as regular java classes and use all the power of java as a language for the code in this files. You mention inheritance, how about complicated if-conditions, loops, recursion, anyone? :) My point is that you don't really want to end up with complicated code in configuration and to debug it.

Now regarding the inheritance itself. This is not a good idea, because given the fact that its not a regular java class combined with the understanding of how exactly spring uses these configuration files, you'll understand that configuration gives nothing to you here. Think about configurations as a place where you state which beans should be loaded. Spring will take care of the rest. I do understand that you have some use case in mind, but it simply doesn't fit Spring approach.

As for your statement:

I want to load beans from child config first and the from parent config.

Could you please explain why do you need this? When spring loads it scans all the configurations first but doesn't create beans (not yet). Instead it "translates" the information found in these @Configuration classes to a "metadata" (this is called "Bean Definitions" in terms of spring). All the bean definitions from all the configurations....

Only after that Spring starts beans instantiation (it also knows by this time what bean should be created first, for example if you have something like):

class A {
   private B b;
   public A(B b) {this.b = b;}   
 }

class B {
   ....
}

Then its obvious that Spring should create Bean "B" first.

Upvotes: 1

davidxxx
davidxxx

Reputation: 131346

I want to load beans from child config first and the from parent config.

You want to explain to the framework how to do its work ?
Spring Configurations and more generally Spring beans are loaded and added in the context in a order that Spring considers the right to satisfy all dependencies requirements.
Besides, configuration inheritance is not documented as a way to achieve such a thing.
Specifying explicitly the order for specific beans is possible but it should be the exception and not the norm while you seem want to do that exception the norm.

Upvotes: 1

Related Questions