CODEWITHSUNDEEP
spring
Snowy Coder Girl
Snowy Coder Girl

Reputation: 5518

Different Spring Annotation XML Declarations

There seem to be multiple XML tags for telling Spring to use annotations:

<context:annotation-config/>

<context:component-scan base-package="org.example" />

<mvc:annotation-driven />

<tx:annotation-driven transaction-manager="transactionManager" />

I think the first tag says to scan for annotations, the second says which package to scan (and optionally, can exclude/include what to search for). Then maybe the third says to scan for controller classes. And the last one to scan for data access annotations.

My problem understanding is:

  1. I would think tags 1 and 2 could be combined into one. So I don't know why they are separated.
  2. Tags 3 and 4 seem redundant to 1 and 2.

Could anyone give me a breakdown of what each tag does, and why they're not redundant? And if there are any other annotation XML tags, let me know.

EDIT

After further investigation, I believe I found some additional information:

Still not completely sure on the <mvc:annotation-driven />. I think maybe it adds further support for JSON, etc.

Upvotes: 4

Views: 5103

Answers (2)

micfra
micfra

Reputation: 2820

  1. Difference between annotation-config and component-scan

    a) <context:annotation-config/> only looks for annotations on beans in the same application context in which it is defined. This means that, if you put <context:annotation-config/> in a WebApplicationContext for a DispatcherServlet, it only checks for @Autowired beans in your controllers, and not your services. See Section 15.2, “The DispatcherServlet” for more information.

    b) Spring provides the capability of automatically detecting 'stereotyped' classes and registering corresponding BeanDefinitions with the ApplicationContext. To autodetect these classes and register the corresponding beans requires the inclusion of the component-scan element in XML where 'basePackage' would be a common parent package (or alternatively a comma-separated list could be specified that included the parent package of each class).

  2. tx:annotation-driven

    You do provide the transaction-manager instace directly within element. annotation-config and component-scan won't.

  3. mvc:annotation-driven

    This tag registers the DefaultAnnotationHandlerMapping and AnnotationMethodHandlerAdapter beans that are required for Spring MVC to dispatch requests to @Controllers. The tag configures those two beans with sensible defaults based on what is present in your classpath. Read more at Spring doc.

Upvotes: 2

skaffman
skaffman

Reputation: 403581

I would think tags 1 and 2 could be combined into one. So I don't know why they are separated.

For reasons of backwards compatibility. Old Spring apps have to keep working, and merging the tags (which were introduced in different versions of Spring) would break that by changing the default behaviour.

Tags 3 and 4 seem redundant to 1 and 2.

See above. The 4 tags do slightly different, but complimentary things. Yes, if Spring were designed from scratch, there would be fewer of them, but the functionality needs to remain seperate.

To summarise:

<context:annotation-config/> enables annotation support in the context. This was added as part of Java 5 support, at a time when Spring still supported Java 1.4

<context:component-scan base-package="org.example" /> enables automatic scanning and configuration of beans, instead of using explicit declarations. This was added in Spring 2.5.

<mvc:annotation-driven /> is an odd one. It is not required in order to support annotated controller (those work by default). What it does is to actually disable the old style of non-annotated controller, as well as adding support for things like JSON. This is required because older apps still use the older controller style.

<tx:annotation-driven> is required because Spring supports many different styles of transaction demarcation, one of which is the annotation style. This is most popular style, but by no means the only one.

Upvotes: 1

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