`` vs. ``: What are Their Key Differences and When Should I Use Each?

vs. : Clarifying Their Differences

While and both deal with annotations, there are notable differences in their functionality:

• Enables annotations defined on beans already registered in the application context.
• Does not scan packages for bean definitions.

• Combines the functionality of by scanning packages and registering beans within the application context.
• Supports annotation-based bean definition.

Example to Illustrate the Differences

To demonstrate the distinct roles of these tags, consider the following scenario:

• Package structure:

  com.xxx.B
  com.xxx.C
  com.yyy.A

• XML configuration with only:

  <component-scan base-package="com.xxx"></component-scan>

• In this scenario, only beans annotated with @Component within the "com.xxx" package will be registered in the application context. Bean "A" from "com.yyy" will be omitted.

Similar Functionality

Despite their different approaches, and achieve similar goals:

• Activation of annotation-based bean definition
• Registration of bean post processors for annotation handling

Interoperability and Recommendations

While both tags can be used separately, they can also coexist within the same XML configuration:

• If is present, it implies the use of on all beans registered within the application context. This ensures annotation support for both scanned and manually registered beans.
• It is not necessary to include both tags if using as it covers both annotation processing and package scanning.

Additional Considerations

• The "annotation-config" attribute on is a legacy feature that has no practical use.
• While multiple instances of and can be defined, only one instance of each is effectively processed by Spring.
• Spring handles annotation-processing setups to ensure they run only once, even with multiple bean registrations.

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