Spring中@Import注解的作用和使用

转自Spring中@Import注解的作用和使用

Import注解源码

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

	/**
	 * {@link Configuration @Configuration}, {@link ImportSelector},
	 * {@link ImportBeanDefinitionRegistrar}, or regular component 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注解的作用

1. 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 {
}

2. 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 {
}

3. 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 {
}

4. 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.internalEventListenerFactory
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。