@Import注释

1.导入bean

主类

package com.example.demo03;

import com.example.demo.Role;
import com.example.demo.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;


/*
@Import的用法
1.导入bean
2.导入配置类
3.导入ImportSelector的实现类
4.导入ImportBeanDefinitionRegistrar的实现类
 */

@SpringBootApplication
@Import(User.class)

public class Demo03Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext context=SpringApplication.run(Demo03Application.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);

    }

}

2.导入配置类

配置类：

package com.example.config;

import com.example.demo.Role;
import com.example.demo.User;
import org.springframework.context.annotation.Bean;

public class UserConfig {
    @Bean
    public User user(){
        return new User();
    }
    @Bean
    public Role role(){
        return new Role();
    }

}

启动类：

package com.example.demo03;

import com.example.config.UserConfig;
import com.example.demo.Role;
import com.example.demo.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;


/*
@Import的用法
1.导入bean
2.导入配置类
3.导入ImportSelector的实现类
4.导入ImportBeanDefinitionRegistrar的实现类
 */

@SpringBootApplication
@Import(UserConfig.class)
public class Demo03Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext context=SpringApplication.run(Demo03Application.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);

    }

}

3.导入ImportSelector的实现类

ImportSelector的实现类MyImportSelector：

（这里写得是字符串"com.example.demo.User"，可以写在配置文件中动态获取，不用写死）

package com.example.config;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

public class MyImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{
                "com.example.demo.User","com.example.demo.Role"

        };
    }
}

启动类：

package com.example.demo03;

import com.example.config.MyImportSelector;
import com.example.demo.Role;
import com.example.demo.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;


/*
@Import的用法
1.导入bean
2.导入配置类
3.导入ImportSelector的实现类
4.导入ImportBeanDefinitionRegistrar的实现类
 */

@SpringBootApplication
@Import(MyImportSelector.class)
public class Demo03Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext context=SpringApplication.run(Demo03Application.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);

    }

}

4.导入ImportBeanDefinitionRegistrar的实现类

ImportBeanDefinitionRegistrar的实现类MyImportBeanDefinitionRegistrar：

package com.example.config;

import com.example.demo.User;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override//重写ImportBeanDefinitionRegistrar的方法
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry, BeanNameGenerator importBeanNameGenerator) {
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(User.class).getBeanDefinition();
        registry.registerBeanDefinition("user",beanDefinition );//IOC容器里注册了一个Bean，user是名字，类型是User.class
    }
}

启动类：

package com.example.demo03;

import com.example.config.MyImportBeanDefinitionRegistrar;
import com.example.demo.Role;
import com.example.demo.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Import;


/*
@Import的用法
1.导入bean
2.导入配置类
3.导入ImportSelector的实现类
4.导入ImportBeanDefinitionRegistrar的实现类
 */

@SpringBootApplication
@Import(MyImportBeanDefinitionRegistrar.class)
public class Demo03Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext context=SpringApplication.run(Demo03Application.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);

    }

}

实现类MyImportBeanDefinitionRegistrar注册bean时没注册类Role所以：