浅谈Spring中@Import注解的作用和使用

浅谈Spring中@Import注解的作用和使用

@Import用来导入@Configuration注解的配置类、声明@Bean注解的bean方法、导入ImportSelector的实现类或导入ImportBeanDefinitionRegistrar的实现类。

@Import注解的作用

查看Import注解源码

/**

* Indicates one or more {@link Configuration @Configuration} classes to import.

*

*

Provides functionality equivalent to the {@code } element in Spring XML.

* Only supported for classes annotated with {@code @Configuration} or declaring at least

* one {@link Bean @Bean} method, as well as {@link ImportSelector} and

* {@link ImportBeanDefinitionRegistrar} implementations.

*

*

{@code @Bean} definitions declared in imported {@code @Configuration} classes

* should be accessed by using {@link org.springframework.beans.factory.annotation.Autowired @Autowired}

* injection. Either the bean itself can be autowired, or the configuration class instance

* declaring the bean can be autowired. The latter approach allows for explicit,

* IDE-friendly navigation between {@code @Configuration} class methods.

*

*

May be declared at the class level or as a meta-annotation.

*

*

If XML or other non-{@code @Configuration} bean definition resources need to be

* imported, use {@link ImportResource @ImportResource}

*

* @author Chris Beams

* @since 3.0

* @see Configuration

* @see ImportSelector

* @see ImportResource

*/

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface Import {

/**

* The @{@link Configuration}, {@link ImportSelector} and/or

* {@link ImportBeanDefinitionRegistrar} classes to import.

*/

Class>[] value();

}

分析类注释得出结论：

声明一个bean

导入@Configuration注解的配置类

导入ImportSelector的实现类

导入ImportBeanDefinitionRegistrar的实现类

@Import注解的使用

声明一个bean

package com.example.demo.bean;

public class TestBean1 {

}

package com.example.demo;

import com.example.demo.bean.TestBean1;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

@Import({TestBean1.class})

@Configuration

public class AppConfig {

}

导入@Configuration注解的配置类

package com.example.demo.bean;

public class TestBean2 {

}

package com.example.demo.bean;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

@Configuration

public class TestConfig {

@Bean

public TestBean2 getTestBean2(){

return new TestBean2();

}

}

package com.example.demo;

import com.example.demo.bean.TestBean1;

import com.example.demo.bean.TestConfig;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class})

@Configuration

public class AppConfig {

}

导入ImportSelector的实现类

package com.example.demo.bean;

public class TestBean3 {

}

package com.example.demo.bean;

import org.springframework.context.annotation.ImportSelector;

import org.springframework.core.type.AnnotationMetadata;

public class TestImportSelector implements ImportSelector {

@Override

public String[] selectImports(AnnotationMetadata importingClassMetadata) {

return new String[]{"com.example.demo.bean.TestBean3"};

}

}

package com.example.demo;

import com.example.demo.bean.TestBean1;

import com.example.demo.bean.TestConfig;

import com.example.demo.bean.TestImportSelector;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class,TestImportSelector.class})

@Configuration

public class AppConfig {

}

导入ImportBeanDefinitionRegistrar的实现类

package com.example.demo.bean;

public class TestBean4 {

}

package com.example.demo.bean;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;

import org.springframework.beans.factory.support.RootBeanDefinition;

import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;

import org.springframework.core.type.AnnotationMetadata;

public class TestImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

@Override

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(TestBean4.class);

registry.registerBeanDefinition("TestBean4", rootBeanDefinition);

}

}

package com.example.demo;

import com.example.demo.bean.TestBean1;

import com.example.demo.bean.TestConfig;

import com.example.demo.bean.TestImportBeanDefinitionRegistrar;

import com.example.demo.bean.TestImportSelector;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class,TestImportSelector.class,TestImportBeanDefinitionRegistrar.class})

@Configuration

public class AppConfig {

}

最后，我们来看下导入结果：

package com.example.demo;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.springframework.boot.test.context.SpringBootTest;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;

@RunWith(SpringRunner.class)

@SpringBootTest

public class DemoApplicationTests {

@Test

public void test() {

AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(AppConfig.class);

String[] beanDefinitionNames = annotationConfigApplicationContext.getBeanDefinitionNames();

System.out.println("--------------------------------------------------------");

for (String beanDefinitionName: beanDefinitionNames) {

System.out.println(beanDefinitionName);

}

System.out.println("--------------------------------------------------------");

}

}

打印结果如下：

--------------------------------------------------------

org.springframework.context.annotation.internalConfigurationAnnotationProcessor

org.springframework.context.annotation.internalAutowiredAnnotationProcessor

org.springframework.context.annotation.internalRequiredAnnotationProcessor

org.springframework.context.annotation.internalCommonAnnotationProcessor

org.springframework.context.event.internalEventListenerProcessor

org.springframework.context.event.internalEventpNgmtDRMJListenerFactory

appConfig

com.example.demo.bean.TestBean1

com.example.demo.bean.TestConfig

getTestBean2

com.example.demo.bean.TestBean3

TestBean4

--------------------------------------------------------

可以看出TestBean1,TestBean2,TestBean3,TestBean4通过不同的4种导入方法被导入SpringIOC容器中。

版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。