Naming Beans

Every bean has one or more identifiers. These identifiers must be unique within the container that hosts the bean. A bean usually has only one identifier. However, if it requires more than one, the 13 extra ones can be considered aliases.

XML Based Configuration

In XML-based configuration metadata, each bean has one or more identifiers. These identifiers must be unique within the container that hosts the bean. Typically, a bean has a single identifier, but if additional identifiers are needed, they can be considered aliases (up to 13 extra aliases).

To specify bean identifiers, you can use the id attribute, the name attribute, or both:

• The id attribute allows you to specify exactly one identifier for the bean.
• The name attribute enables you to specify multiple identifiers (aliases) for the same bean, separated by commas (,), semicolons (;), or white spaces.

Example:

<bean id="myBean" name="alias1, alias2; alias3">
<!-- Bean definition -->
</bean>

Here, myBean is the primary identifier, while alias1, alias2, and alias3 are additional aliases.

Identifiers and aliases are conventionally alphanumeric (e.g., myBean, someService), but they can include special characters.

Annotation Based Configuration

In annotation-based configuration, you use Spring annotations such as @Component, @Service, @Repository, or @Controller to define beans. By default, the identifier for a bean is derived from the class name, with the first letter converted to lowercase (e.g., MyBean becomes myBean).

However, in the (unusual) special case when there is more than one character and both the first and second characters are upper case, the original casing gets preserved. These are the same rules as defined by java.beans.Introspector.decapitalize (which Spring uses).

You can explicitly define a unique identifier for the bean by providing a value within the annotation:

@Component("customBeanId")
public class MyBean {
// Bean implementation
}

In this example, the bean identifier is customBeanId.

If you need to define additional aliases for the bean, you can use the @AliasFor annotation with custom annotations or define multiple names explicitly using the @Bean annotation in a configuration class:

@Configuration
public class AppConfig {

    @Bean(name = {"primaryBeanId", "alias1", "alias2"})
    public MyBean myBean() {
        return new MyBean();
    }
}

Here:

• primaryBeanId is the main identifier.
• alias1 and alias2 are additional aliases.

As in XML-based configuration, identifiers and aliases must be unique within the application context and can contain special characters if necessary.