Spring Inheritance - abstract

Question

I came across this link which explains how to bean can be inherited. Assuming that the HelloWorld class in this example is represented as a bean using the @Component annotation, how to create another bean that inherits this bean? Can I use extends to inherit a HelloWorld bean and add @Component to a new class to extend an existing bean to show it as a new bean with additional features?

Answer 1

First you make your abstract configuration, which is achieved not , denoting it as @Configuration , for example:

 // notice there is no annotation here public class ParentConfig { @Bean public ParentBean parentBean() { return new ParentBean(); } } 

Then you expand it, for example:

 @Configuration public class ChildConfig extends ParentConfig { @Bean public ChildBean childBean() { return new ChildBean(); } } 

The result will be the same as if you did this:

 @Configuration public class FullConfig { @Bean public ParentBean parentBean() { return new ParentBean(); } @Bean public ChildBean childBean() { return new ChildBean(); } } 

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Edit : Answer the next question in a comment.

If Spring selects both classes, parent and child, there are problems with duplicate beans, so you cannot distribute it directly . Even if you override the methods, beans from the superclass will also be instantiated by ParentConfig .

Since your parent class is already compiled , you have 2 options:

• Talk to the author of the parent class and ask him to change it.

• Change @ComponentScan packages.

To clarify solution 2:

If the parent class is in the com.parent.ParentConfig package and the child class is the com.child.ChildConfig package, you can configure component scanning to only get classes under com.child .

You can specify component scan packages using the @ComponentScan("com.child") annotation @ComponentScan("com.child") in the main configuration file (assume the application class).