The role of @ Import annotations as well as how to use

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1. @Import注解提供了@Bean注解的功能,在Spring 4.2之后,@Import可以直接指定实体类,加载这个类定义到context中.

2. @Import的优先于本身的的类定义加载.

Straight talk [email protected]比较常用的用法

直接指定类

新建类ImportTest1

public class ImportTest1 {
    

    public void run() {
    
        System.out.println("======ImportTest1=======");
    }
}

新建配置类ImportTest2,并标注注解@Import,The annotation internally specifies the class to be loaded,Here it is handed overSpring IOC容器管理.

@Configuration
@Import(ImportTest1.class)
public class ImportTest2 {
    

    @Bean
    public ImportTest2 importTest2(){
    
		return new ImportTest2();
	}
}

通过@Autowired就可以直接使用这个类了.

@RestController
public class ProducerController {
    

    @Autowired
    private ImportTest1 importTest1;

    @GetMapping("/imported")
    public String imported() {
    

        importTest1.run();
        return String.valueOf(ThreadLocalRandom.current().nextInt(100));
    }
}

实现ImportSelector接口

新建类ImportTest1

public class ImportTest1 {
    

    public void run() {
    
        System.out.println("======ImportTest1=======");
    }
}

实现ImportSelector接口,实现selectImports方法,Specify the full class name you want to load.

public class ImportSelectorTest implements ImportSelector {
    
    @Override
    public String[] selectImports( AnnotationMetadata annotationMetadata) {
    
        return new String[]{
    "com.issa.producer.csdn.imported.ImportTest1"};
    }
}

在配置类中使用@Import注解指定ImportSelector的实现类.

@Configuration
@Import(ImportSelectorTest.class)
public class ImportTest2 {
    

    public void run() {
    
        System.out.println("======ImportTest2=======");
    }
}

通过@Autowired就可以直接使用这个类了.

@RestController
public class ProducerController {
    

    @Autowired
    private ImportTest1 importTest1;

    @GetMapping("/imported")
    public String imported() {
    

        importTest1.run();
        return String.valueOf(ThreadLocalRandom.current().nextInt(100));
    }
}

Custom annotation integrationImportSelector接口

自定义注解

@Retention(RetentionPolicy.RUNTIME)
@Documented
@Target(ElementType.TYPE)
@Import(ImportTest.class)
public @interface EnableSelector {
    

    @AliasFor("name")
    String value() default "";

    @AliasFor("value")
    String name() default "";
}

注解处理

public class ImportTest implements ImportSelector {
    

    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
    
        Map<String, Object> map = annotationMetadata.getAnnotationAttributes(EnableSelector.class.getName(), true);
        assert map != null;
        String name = (String) map.get("name");
        if (Objects.equals(name, "ImportTest1")) {
    
            return new String[]{
    "com.issa.producer.csdn.imported.ImportTest1"};
        }
        return new String[0];
    }
}

注解使用

@Configuration
@EnableSelector("ImportTest1")
public class ImportTest2 {
    

    public void run() {
    
        System.out.println("======ImportTest2=======");
    }
}

参考：https://spring.io、https://cloud.tencent.com/developer/article/1811376