【SpringBoot】@Import 注解的使用的三种方式

最新推荐文章于 2025-02-16 16:27:35 发布

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#spring boot #后端 #java

本文详细介绍了SpringBoot中@Import注解的使用，包括直接导入普通Java类、自定义注解导入以及使用ImportSelector和ImportBeanDefinitionRegistrar动态注册Bean。通过示例展示了如何通过这些方式将Bean注入到Spring容器中。

SpringBoot @Import注解使用

作用

一句话概括：向Spring注入Bean。

三种使用方式

导入普通的 Java 类
自定义的 ImportSelector
ImportBeanDefinitionRegistrar

导入普通的java类

import + Configuration 实现注入

还是请我们的User.java 出场吧，定一个User类

public class User {
}

定义UserConfig.java

@Import({User.class})
@Configuration
public class UserConfig {

}

测试

依旧还是修改启动类的代码，通过上下文去获取，这里是根据类型去获取的哈，通过名称的话是获取不到的，不知道注入的bean的名称。

@SpringBootApplication
public class BootImportsApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BootImportsApplication.class, args);
        Object user = context.getBean(User.class);
        System.out.println(user);
    }

}

输出结果：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

2023-07-03 14:00:34.105  INFO 14848 --- [           main] xx.imports.BootImportsApplication        : Starting BootImportsApplication on ZJZL-20210402GJ with PID 14848 (F:\idea-project\xy-integration-middleware\boot\boot-imports\target\classes started by Administrator in F:\idea-project\xy-integration-middleware)
2023-07-03 14:00:34.118  INFO 14848 --- [           main] xx.imports.BootImportsApplication        : No active profile set, falling back to default profiles: default
2023-07-03 14:00:35.511  INFO 14848 --- [           main] xx.imports.BootImportsApplication        : Started BootImportsApplication in 2.592 seconds (JVM running for 5.809)
xx.imports.entity.User@3a0807b7

自定义的注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({User.class})
public @interface EnableUser {

}

注意：刚才新建的UserConfig 要注释掉哦。

修改启动类

在启动类上加上注解 @EnableUser

@EnableUser
@SpringBootApplication
public class BootImportsApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BootImportsApplication.class, args);
        Object user = context.getBean(User.class);
        System.out.println(user);
    }

}

测试

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

2023-07-03 14:16:54.817  INFO 9640 --- [           main] xx.imports.BootImportsApplication        : Starting BootImportsApplication on ZJZL-20210402GJ with PID 9640 (F:\idea-project\xy-integration-middleware\boot\boot-imports\target\classes started by Administrator in F:\idea-project\xy-integration-middleware)
2023-07-03 14:16:54.828  INFO 9640 --- [           main] xx.imports.BootImportsApplication        : No active profile set, falling back to default profiles: default
2023-07-03 14:16:55.918  INFO 9640 --- [           main] xx.imports.BootImportsApplication        : Started BootImportsApplication in 1.957 seconds (JVM running for 7.231)
xx.imports.entity.User@3174cb09

ImportSelector

如果定义太多注解,那么在main方法上要添加太多注解…因此使用ImportSelector ,ImportSelector 是一个接口，
该接口中只有一个 selectImports 方法，用于返回全类名数组。所以利用该特性我们可以给容器动态导入 N 个 Bean。
因为这两个bean都是通过@Enable类型注解来将配置类注册到IOC容器中，所以我们现在要做的就是将这两个bean一次性都注册到IOC容器中。
在Spring中，要将多个类进行注册，可以使用selector的方式。

新建Role.java

由于需要多个类注入，我们新建一个Role类

public class Role {
}

新建一个ApplicationSelector.java

用来返回多个类名数组

public class ApplicationSelector implements ImportSelector {

    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        return new String[]{
                User.class.getName(),
                Role.class.getName()
        };
    }
}

定义EnableApplicationSelector 注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({ApplicationSelector.class})
public @interface EnableApplicationSelector {
}

注意：这里需要将之前定义的 UserConfig、 EnableUser注释掉哦。

修改启动类

@EnableApplicationSelector
@SpringBootApplication
public class BootImportsApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BootImportsApplication.class, args);
        Object user = context.getBean(User.class);
        System.out.println(user);

        Object role = context.getBean(Role.class);
        System.out.println(role);
    }
}

测试

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

2023-07-03 14:27:08.124  INFO 14616 --- [           main] xx.imports.BootImportsApplication        : Starting BootImportsApplication on ZJZL-20210402GJ with PID 14616 (F:\idea-project\xy-integration-middleware\boot\boot-imports\target\classes started by Administrator in F:\idea-project\xy-integration-middleware)
2023-07-03 14:27:08.135  INFO 14616 --- [           main] xx.imports.BootImportsApplication        : No active profile set, falling back to default profiles: default
2023-07-03 14:27:09.219  INFO 14616 --- [           main] xx.imports.BootImportsApplication        : Started BootImportsApplication in 2.336 seconds (JVM running for 6.605)
xx.imports.entity.User@42a9a63e
xx.imports.entity.Role@62da83ed

ImportBeanDefinitionRegistrar

ImportBeanDefinitionRegistrar 是一个接口，它可以手动注册bean到容器中，从而可以对类进行个性化的定制。

新建 EImportBeanDefinitionRegistrar

实现ImportBeanDefinitionRegistrar接口，并实现其中的方法

public class EImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata annotationMetadata, BeanDefinitionRegistry beanDefinitionRegistry) {
        RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(User.class);
        // 注册一个名字叫做 halo 的 bean
        beanDefinitionRegistry.registerBeanDefinition("haloUser", rootBeanDefinition);
    }
}

新建 EImportUserConfig.java

@Import({EImportBeanDefinitionRegistrar.class})
@Configuration
public class EImportUserConfig {
}

修改一下启动类

这里我们通过bean的名称获取

@SpringBootApplication
public class BootImportsApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BootImportsApplication.class, args);
        Object user = context.getBean("haloUser");
        System.out.println(user);
    }
}

测试

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

2023-07-03 14:32:20.845  INFO 2564 --- [           main] xx.imports.BootImportsApplication        : Starting BootImportsApplication on ZJZL-20210402GJ with PID 2564 (F:\idea-project\xy-integration-middleware\boot\boot-imports\target\classes started by Administrator in F:\idea-project\xy-integration-middleware)
2023-07-03 14:32:20.860  INFO 2564 --- [           main] xx.imports.BootImportsApplication        : No active profile set, falling back to default profiles: default
2023-07-03 14:32:22.476  INFO 2564 --- [           main] xx.imports.BootImportsApplication        : Started BootImportsApplication in 2.949 seconds (JVM running for 7.532)
xx.imports.entity.User@5a4bef8