{"id":286,"date":"2025-04-22T13:00:00","date_gmt":"2025-04-22T13:00:00","guid":{"rendered":"https:\/\/springmasteryhub.com\/?p=286"},"modified":"2025-04-16T16:34:13","modified_gmt":"2025-04-16T16:34:13","slug":"spring-framework-essentials-understanding-componentscan","status":"publish","type":"post","link":"https:\/\/springmasteryhub.com\/?p=286","title":{"rendered":"Spring Framework Essentials: Understanding @ComponentScan"},"content":{"rendered":"\n

@ComponentScan<\/code> is an annotation that tells Spring where to find classes annotated as Spring beans. Using this annotation, we can instruct Spring to create beans only for the specified location. Spring will use the package provided in the annotation to look for beans to create.<\/p>\n\n\n\n

If no package is defined in the annotation, Spring will scan recursively from the class where this annotation is declared.<\/p>\n\n\n\n

You can also use this annotation to scan multiple packages and configure exclusions to avoid creating certain beans.<\/p>\n\n\n\n

If this annotation is not specified, Spring will scan all the classes and jars present on the classpath.<\/p>\n\n\n\n

Let\u2019s take a look at a code example.<\/p>\n\n\n\n

In this example, we are creating a component scan without a parameter, so Spring will scan from this package and all the subpackages from this declaration.<\/p>\n\n\n\n

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package<\/span> <\/span>org.spring.mastery.config<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.context.annotation.ComponentScan;<\/span><\/span>\nimport<\/span> org.springframework.context.annotation.Configuration;<\/span><\/span>\n<\/span>\n@<\/span>Configuration<\/span><\/span>\n@<\/span>ComponentScan<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>AppConfig<\/span> {<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
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package<\/span> <\/span>org.spring.mastery.service<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.stereotype.Service;<\/span><\/span>\n<\/span>\nimport<\/span> javax.annotation.PostConstruct;<\/span><\/span>\n<\/span>\n@<\/span>Service<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>MyService<\/span> {<\/span><\/span>\n<\/span>\n    @<\/span>PostConstruct<\/span><\/span>\n    <\/span>public<\/span> <\/span>void<\/span> <\/span>init<\/span>() {<\/span><\/span>\n        System.out.<\/span>println<\/span>(<\/span>"<\/span>MyService initialized<\/span>"<\/span>);<\/span><\/span>\n    }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
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package<\/span> <\/span>org.spring.mastery.repository<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.stereotype.Repository;<\/span><\/span>\n<\/span>\nimport<\/span> javax.annotation.PostConstruct;<\/span><\/span>\n<\/span>\n@<\/span>Repository<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>MyRepository<\/span> {<\/span><\/span>\n<\/span>\n    @<\/span>PostConstruct<\/span><\/span>\n    <\/span>public<\/span> <\/span>void<\/span> <\/span>init<\/span>() {<\/span><\/span>\n        System.out.<\/span>println<\/span>(<\/span>"<\/span>MyRepository initialized<\/span>"<\/span>);<\/span><\/span>\n    }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
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package<\/span> <\/span>org.spring.another<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.stereotype.Service;<\/span><\/span>\n<\/span>\nimport<\/span> javax.annotation.PostConstruct;<\/span><\/span>\n<\/span>\n@<\/span>Service<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>ExcludedService<\/span> {<\/span><\/span>\n<\/span>\n    @<\/span>PostConstruct<\/span><\/span>\n    <\/span>public<\/span> <\/span>void<\/span> <\/span>init<\/span>() {<\/span><\/span>\n        System.out.<\/span>println<\/span>(<\/span>"<\/span>ExcludedService initialized<\/span>"<\/span>);<\/span><\/span>\n    }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
In this setup, MyService<\/code> and MyRepository<\/code> will be created as beans because they are in sub-packages of org.spring.mastery<\/code>. However, ExcludedService<\/code> will not be loaded because it is outside the package hierarchy.<\/p>\n\n\n\n
This is the log line:<\/p>\n\n\n\n
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2025-04-10T11:09:56.876-03:00  INFO 19296 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'<\/span><\/span>\nMyRepository initialized<\/span><\/span>\nMyService initialized<\/span><\/span>\n<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
We can also scan specific packages. Remember, we can use multiple packages in the @ComponentScan<\/code> annotation.<\/p>\n\n\n\n
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package<\/span> <\/span>org.spring.mastery.config<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.context.annotation.ComponentScan;<\/span><\/span>\nimport<\/span> org.springframework.context.annotation.Configuration;<\/span><\/span>\n<\/span>\n@<\/span>Configuration<\/span><\/span>\n@<\/span>ComponentScan<\/span>(<\/span>basePackages<\/span> <\/span>=<\/span> {<\/span>"<\/span>org.spring.mastery.service<\/span>"<\/span>, <\/span>"<\/span>org.spring.mastery.repository<\/span>"<\/span> })<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>AppConfig<\/span> {<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
In this example, we are scanning org.spring.mastery.service<\/code> and org.spring.mastery.repository<\/code>. Any beans in these packages will be created, while ExcludedService<\/code> will still not be loaded.<\/p>\n\n\n\n
The logs look like this:<\/p>\n\n\n\n
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2025-04-10T11:14:26.887-03:00  INFO 17868 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'<\/span><\/span>\nMyRepository initialized<\/span><\/span>\nMyService initialized<\/span><\/span>\n<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
If we want to add components outside the org.spring.mastery<\/code> structure, we can specify it in the @ComponentScan<\/code> annotation like this:<\/p>\n\n\n\n
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package<\/span> <\/span>org.spring.mastery.config<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.context.annotation.ComponentScan;<\/span><\/span>\nimport<\/span> org.springframework.context.annotation.Configuration;<\/span><\/span>\n<\/span>\n@<\/span>Configuration<\/span><\/span>\n@<\/span>ComponentScan<\/span>(<\/span>basePackages<\/span> <\/span>=<\/span> {<\/span>"<\/span>org.spring.mastery.service<\/span>"<\/span>, <\/span>"<\/span>org.spring.mastery.repository<\/span>"<\/span>, <\/span>"<\/span>org.spring.another<\/span>"<\/span> })<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>AppConfig<\/span> {<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
Now, the components from the other subpackages will also be loaded:<\/p>\n\n\n\n
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2025-04-10T11:15:49.313-03:00  INFO 3080 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'<\/span><\/span>\nMyRepository initialized<\/span><\/span>\nMyService initialized<\/span><\/span>\nExcludedService initialized<\/span><\/span>\n<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
If we do not want to load some specific beans or packages, we can create exclusions like this:<\/p>\n\n\n\n
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package<\/span> <\/span>org.spring.mastery.config<\/span>;<\/span><\/span>\n<\/span>\nimport<\/span> org.springframework.context.annotation.ComponentScan;<\/span><\/span>\nimport<\/span> org.springframework.context.annotation.Configuration;<\/span><\/span>\nimport<\/span> org.springframework.context.annotation.FilterType;<\/span><\/span>\nimport<\/span> org.springframework.stereotype.Service;<\/span><\/span>\n<\/span>\n@<\/span>Configuration<\/span><\/span>\n@<\/span>ComponentScan<\/span>(<\/span><\/span>\n    <\/span>basePackages<\/span> <\/span>=<\/span> {<\/span>"<\/span>org.spring.mastery.service<\/span>"<\/span>, <\/span>"<\/span>org.spring.mastery.repository<\/span>"<\/span>},<\/span><\/span>\n    <\/span>excludeFilters<\/span> <\/span>=<\/span> @<\/span>ComponentScan.Filter<\/span>(<\/span>type<\/span> <\/span>=<\/span> FilterType.ANNOTATION, <\/span>classes<\/span> <\/span>=<\/span> Service.class))<\/span><\/span>\npublic<\/span> <\/span>class<\/span> <\/span>AppConfig<\/span> {<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
In this configuration, we are excluding any classes annotated with @Service<\/code> within the specified packages.<\/p>\n\n\n\n
The result log will be:<\/p>\n\n\n\n
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2025-04-10T14:59:53.710-03:00  INFO 21828 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'<\/span><\/span>\nMyRepository initialized<\/span><\/span>\nMyService initialized<\/span><\/span>\n<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Now you have learned how @ComponentScan<\/code> works. Remember, if not set, Spring will scan all classes and jars in your classpath. Have you ever forgotten to add the package to scan and wondered why Spring is not recognizing your new bean (believe me, it happens)?<\/p>\n\n\n\n
Explore this configuration and share your thoughts in the comments or on social media.<\/p>\n\n\n\n
If you like this topic, make sure to follow me. In the following days, I\u2019ll be explaining more about Spring annotations! Stay tuned!<\/p>\n\n\n\n
Willian Moya (@WillianFMoya) \/ X (twitter.com)<\/a><\/p>\n\n\n\n
Willian Ferreira Moya | LinkedIn<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
@ComponentScan is an annotation that tells Spring where to find classes annotated as Spring beans. Using this annotation, we can instruct Spring to create beans only for the specified location. Spring will use the package provided in the annotation to look for beans to create. If no package is defined in the annotation, Spring will […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[3,6],"tags":[],"class_list":["post-286","post","type-post","status-publish","format-standard","hentry","category-java","category-spring"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/posts\/286","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=286"}],"version-history":[{"count":1,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/posts\/286\/revisions"}],"predecessor-version":[{"id":288,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=\/wp\/v2\/posts\/286\/revisions\/288"}],"wp:attachment":[{"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=286"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=286"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/springmasteryhub.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=286"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}