{"id":126739,"date":"2024-05-28T21:48:33","date_gmt":"2024-05-28T20:48:33","guid":{"rendered":"https:\/\/www.baeldung.com\/spring-boot-autowire-multiple-implementations"},"modified":"2024-05-28T21:48:33","modified_gmt":"2024-05-28T20:48:33","slug":"autowiring-an-interface-with-multiple-implementations","status":"publish","type":"post","link":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/2024\/05\/28\/autowiring-an-interface-with-multiple-implementations\/","title":{"rendered":"Autowiring an Interface With Multiple Implementations"},"content":{"rendered":"

\"\"<\/p>\n

1. Introduction<\/h2>\n
<\/div>\n

In this article, we’ll explore autowiring an interface with multiple implementations in Spring Boot, ways to do that, and some use cases.<\/strong> This is a powerful feature that allows developers to inject different implementations of the interface into the application dynamically.<\/p>\n

2. Default Behavior<\/h2>\n
<\/div>\n

Usually, when we have multiple interface implementations and try to autowire that interface into the component, we’ll get an error – “required a single bean, but X were found”. <\/strong>The reason is simple: Spring doesn’t know which implementation we want to see in that component. Fortunately, Spring provides multiple tools to be more specific.<\/p>\n

3. Introducing Qualifiers<\/h2>\n
<\/div>\n

With the\u00a0@Qualifier<\/em> annotation, we specify which bean we want to autowire among multiple candidates.<\/strong> We can apply it to the component itself to give it a custom qualifier name:<\/p>\n

@Service\r\n@Qualifier("goodServiceA-custom-name")\r\npublic class GoodServiceA implements GoodService {\r\n    \/\/ implemantation\r\n}<\/code><\/pre>\n
After that, we annotate parameters with @Qualifier<\/em> to specify which implementation we want:<\/p>\n
@Autowired\r\npublic SimpleQualifierController(\r\n    @Qualifier("goodServiceA-custom-name") GoodService niceServiceA,\r\n    @Qualifier("goodServiceB") GoodService niceServiceB,\r\n    GoodService goodServiceC\r\n) {\r\n        this.goodServiceA = niceServiceA;\r\n        this.goodServiceB = niceServiceB;\r\n        this.goodServiceC = goodServiceC;\r\n}<\/code><\/pre>\n
In the example above, we can see that we used our custom qualifier to autowire GoodServiceA<\/em>. At the same time, for GoodServiceB<\/em>, we do not have a custom qualifier:<\/p>\n
@Service\r\npublic class GoodServiceB implements GoodService {\r\n    \/\/ implementation\r\n}\r\n<\/code><\/pre>\n
In this case, we autowired the component by class name. The qualifier for such autowiring should be in the camel case, for example “myAwesomeClass” is a valid qualifier if the class name was “MyAwesomeClass“<\/em>.<\/p>\n
The third parameter in the above code is even more interesting. We didn’t even need to annotate it with @Qualifier<\/em>, because Spring will try to autowire the component by parameter name by default<\/strong>, and if GoodServiceC<\/em> exists we’ll avoid the error:<\/p>\n
@Service \r\npublic class GoodServiceC implements GoodService { \r\n    \/\/ implementation \r\n}<\/code><\/pre>\n
4. Primary Component<\/h2>\n
<\/div>\n
Furthermore, we can annotate one of the implementations with @Primary<\/em>. Spring will use this implementation if there are multiple candidates and autowiring by parameter name or a qualifier is not applicable:<\/strong><\/p>\n
@Primary\r\n@Service\r\npublic class GoodServiceC implements GoodService {\r\n    \/\/ implementation\r\n}<\/code><\/pre>\n
It is useful when we frequently use one of the implementations and helps to avoid the “required a single bean” error.<\/p>\n
5. Profiles<\/h2>\n
<\/div>\n
It is possible to use Spring profiles to decide which component to autowire.<\/strong> For example, we may have a FileStorage<\/em> interface with two implementations – S3FileStorage<\/em> and AzureFileStorage<\/em>. We can make S3FileStorage<\/em> active only on the prod<\/em> profile and AzureFileStorage<\/em> only for the dev<\/em> profile.<\/p>\n
@Service\r\n@Profile("dev")\r\npublic class AzureFileStorage implements FileStorage {\r\n    \/\/ implementation\r\n}\r\n@Service\r\n@Profile("prod")\r\npublic class S3FileStorage implements FileStorage {\r\n    \/\/ implementation\r\n}\r\n<\/code><\/pre>\n
6. Autowire Implementations Into a Collection<\/h2>\n
<\/div>\n
Spring allows us to inject all available beans of a specific type into a collection.<\/strong> Here is how we autowire all implementations of the GoodService<\/em> into a list:<\/p>\n
@Autowired\r\npublic SimpleCollectionController(List<GoodService> goodServices) {\r\n    this.goodServices = goodServices;\r\n}\r\n<\/code><\/pre>\n
Also, we can autowire implementations into a set, a map, or an array. When using a map, the format typically is Map<String, GoodService><\/em>, where the keys are the names of the beans, and the values are the bean instances themselves:<\/p>\n
@Autowired\r\npublic SimpleCollectionController(Map<String, GoodService> goodServiceMap) {\r\n        this.goodServiceMap = goodServiceMap;\r\n}\r\npublic void printAllHellos() {\r\n    String messageA = goodServiceMap.get("goodServiceA").getHelloMessage();\r\n    String messageB = goodServiceMap.get("goodServiceB").getHelloMessage();\r\n    \/\/ print messages\r\n}<\/code><\/pre>\n
Important note: Spring will autowire all candidate beans into a collection regardless of qualifiers or parameter names, as long as they are active.<\/strong> It ignores beans annotated with @Profile<\/em> that do not match the current profile. Similarly, Spring includes beans annotated with @Conditional<\/em> only if the conditions are met\u00a0(more details in the next section).<\/p>\n
7. Advanced Control<\/h2>\n
<\/div>\n
Spring allows us to have additional control over which candidates are selected for autowiring.<\/p>\n
For more precise conditions on which bean becomes a candidate for autowiring, we can annotate them with @Conditional<\/em>.<\/strong> It should have a parameter with a class that implements the Condition<\/em> (it is a functional interface). For example, here is the Condition<\/em> that checks if the operating system is Windows:<\/p>\n
public class OnWindowsCondition implements Condition {\r\n    @Override \r\n    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {\r\n        return context.getEnvironment().getProperty("os.name").toLowerCase().contains("windows");\r\n    } \r\n}<\/code><\/pre>\n
Here is how we annotate our component with @Conditional<\/em>:<\/p>\n
@Component \r\n@Conditional(OnWindowsCondition.class) \r\npublic class WindowsFileService implements FileService {\r\n    @Override \r\n    public void readFile() {\r\n        \/\/ implementation\r\n    } \r\n}<\/code><\/pre>\n
In this example, WindowsFileService<\/em> will become a candidate for autowiring only if matches()<\/em> in OnWindowsCondition<\/em> returns true.<\/p>\n
We should be careful with @Conditional<\/em> annotations for non-collection autowiring since multiple beans that match the condition will cause an error.<\/p>\n
Also, we will get an error if no candidates are found. Because of this, when integrating @Conditional<\/em> with autowiring, it makes sense to set an optional injection. This ensures that the application can still proceed without throwing an error if it does not find a suitable bean. There are two approaches to achieve this:<\/p>\n
@Autowired(required = false)\r\nprivate GoodService goodService; \/\/ not very safe, we should check this for null\r\n@Autowired\r\nprivate Optional<GoodService> goodService; \/\/ safer way<\/code><\/pre>\n
When we autowire into the collection, we can specify the order of the components by using @Order<\/em> annotation:<\/strong><\/p>\n
@Order(2) \r\npublic class GoodServiceA implements GoodService { \r\n    \/\/ implementation\r\n } \r\n@Order(1) \r\npublic class GoodServiceB implements GoodService {\r\n    \/\/ implementation \r\n}<\/code><\/pre>\n
If we try to autowire List<GoodService><\/em>, GoodServiceB<\/em> will be placed before GoodServiceA<\/em>. Important note: @Order <\/em>doesn’t work when we are autowiring into the Set<\/em>.<\/p>\n
8. Conclusion<\/h2>\n
<\/div>\n
In this article, we discussed the tools Spring provides for the management of the multiple implementations of the interface during autowiring. These tools and techniques enable a more dynamic approach when designing a Spring Boot application. However, like with every instrument, we should ensure their necessity, as careless use can introduce bugs and complicate long-term support.<\/p>\n
As always, the examples are available over on GitHub<\/a>.<\/p>\n
\"\"<\/p>\n
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\"\"<\/p>\n
Quick tutorial on how to autowire an interface with multiple implementations in Spring Boot.<\/p>\n
<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/div>\n","protected":false},"author":2156,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"site-container-style":"default","site-container-layout":"default","site-sidebar-layout":"default","disable-article-header":"default","disable-site-header":"default","disable-site-footer":"default","disable-content-area-spacing":"default","footnotes":""},"categories":[22],"tags":[61,122,127,129,124,128,125,132,131,133,126,130,123,66,94,88,97,56,64,65,60,112,40,75,95,104,33,120,105,101,98,115,30,29,41,86,70,69,68,72,71,26,118,108,87,46,55,48,52,54,51,50,83,62,58,57,109,35,59,63,85,79,82,96,80,27,81,114,44,42,43,45,38,39,110,117,100,111,116,73,89,90,92,91,93,84,78,37,102,34,36,77,67,74,99,113,119,28,121,32,47,49,53,103,31,76],"class_list":["post-126739","post","type-post","status-publish","format-standard","hentry","category-mobile","tag-airpods","tag-anime","tag-anime-characters","tag-anime-cosplay","tag-anime-edits","tag-anime-merchandise","tag-anime-movies","tag-anime-news","tag-anime-recommendations","tag-anime-reviews","tag-anime-series","tag-anime-streaming","tag-animes","tag-app-store","tag-app-store-samsung","tag-appgallery","tag-appgallery-oneplus","tag-apple","tag-apple-music","tag-apple-tv","tag-apple-watch","tag-bbc-sport","tag-best-mobile-games","tag-bixby","tag-bixby-xiaomi","tag-champions-league","tag-cyberpunk","tag-cyberpunk-2077","tag-fantasy-football","tag-fifa","tag-football","tag-formula-1","tag-fortnite","tag-free-fire","tag-free-mobile-games","tag-freebuds-pro","tag-galaxy-a52","tag-galaxy-note-20","tag-galaxy-s21","tag-galaxy-watch-4","tag-galaxy-z-fold-3","tag-game","tag-games","tag-golf","tag-harmonyos","tag-how-to-backup-iphone","tag-how-to-factory-reset-iphone","tag-how-to-reset-iphone","tag-how-to-restore-iphone","tag-how-to-unlock-iphone","tag-how-to-unlock-iphone-5","tag-how-to-unlock-iphone-6","tag-huawei","tag-ios","tag-ipad","tag-iphone","tag-live-soccer","tag-lol","tag-macbook","tag-macos","tag-mate-40-pro","tag-mi-11-lite","tag-mi-home-security-camera-basic-1080p","tag-mi-home-security-camera-basic-1080p-huawei","tag-mi-smart-band-6","tag-minecraft","tag-miui","tag-mlb-scores","tag-mobile-game-design","tag-mobile-game-development","tag-mobile-game-marketing","tag-mobile-game-monetization","tag-mobile-games","tag-mobile-gaming","tag-nba-scores","tag-nba-standings","tag-nfl","tag-nfl-scores","tag-nhl-scores","tag-one-ui","tag-oneplus","tag-oneplus-9-pro","tag-oneplus-buds-pro","tag-oneplus-nord-ce-5g","tag-oxygenos","tag-p40-pro-plus","tag-poco-x3-pro","tag-pokemon","tag-premier-league","tag-pubg","tag-pubg-mobile","tag-redmi-note-10-pro","tag-samsung","tag-samsung-pay","tag-soccer","tag-sports","tag-steam","tag-steeam","tag-top-10-anime","tag-valorant","tag-when-do-the-iphone-7-come-out","tag-when-does-the-iphone-7-come-out","tag-when-is-the-iphone-7-coming-out","tag-world-cup","tag-xbox-series-x","tag-xiaomi"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/posts\/126739","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/users\/2156"}],"replies":[{"embeddable":true,"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/comments?post=126739"}],"version-history":[{"count":0,"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/posts\/126739\/revisions"}],"wp:attachment":[{"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/media?parent=126739"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/categories?post=126739"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gamefootballmobileanimeiphone.com\/index.php\/wp-json\/wp\/v2\/tags?post=126739"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}