{"id":215,"date":"2022-11-01T19:40:39","date_gmt":"2022-11-01T19:40:39","guid":{"rendered":"https:\/\/valerio.nu\/?p=215"},"modified":"2022-11-01T19:40:40","modified_gmt":"2022-11-01T19:40:40","slug":"primary-vs-qualifier-annotations","status":"publish","type":"post","link":"https:\/\/valerio.nu\/index.php\/2022\/11\/01\/primary-vs-qualifier-annotations\/","title":{"rendered":"Primary vs Qualifier Annotations"},"content":{"rendered":"\n

Providing the Dependency Injection feature automatically in Spring Boot<\/a> applications provides great convenience to the developers. In case of multiple services deriving from an interface though, which service will the Spring Boot application inject? In this case, it might not be able to decide which service to inject.<\/p>\n\n\n\n

Let’s consider the code below, it provides two different implementations of MessageService: <\/p>\n\n\n\n

public interface MessageService {\n    void printMessage();\n}<\/code><\/pre>\n\n\n\n
@Service\npublic class ShortMessageService implements MessageService{\n    @Override\n    public void printMessage() {\n        System.out.println(\"ShortMessageService\");\n    }\n}<\/code><\/pre>\n\n\n\n
@Service\npublic class LongMessageService implements MessageService{\n    @Override\n    public void printMessage() {\n        System.out.println(\"LongMessageService\");\n    }\n}<\/code><\/pre>\n\n\n\n
@Service\npublic class ExecuteMessageService {\n    @Autowired\n    private MessageService messageService;\n\n    public void getMessage(){\n        messageService.printMessage();\n    }\n}<\/code>\n<\/code><\/pre>\n\n\n\n
The above code gives an error at compile time as we perform the scenario exemplified in the video below.<\/p>\n\n\n\n