SpringBoot自动装配之@Import深入讲解

时间:2023-02-03 不死鸟.亚历山大.狼崽子人气:0

@Enable*底层依赖于@Import注解导入一些类，使用@Import导入的类会被Spring加载到IOC容器中。而@Import提供4中用法：

导入Bean
导入配置类
导入ImportSelector 实现类。一般用于加载配置文件中的类
导入ImportBeanDefinitionRegistrar实现类。

1 导入Bean

定义一个user实体类：

package com.enable.entity;
public class User {
}

测试功能：

package com.example.demo;
import com.enable.config.EnableUser;
import com.enable.config.UserConfig;
import com.enable.entity.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import java.util.Map;
@SpringBootApplication
@Import(User.class)
public class SpringbootApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringbootApplication.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Map<String,User> map = context.getBeansOfType(User.class);
        System.out.println(map);
    }
}

结果如下：

2 导入配置类

新建实体类：

package com.enable.entity;
public class Role {
}

package com.enable.entity;
public class User {
}

测试功能：

package com.example.demo;
import com.enable.config.EnableUser;
import com.enable.config.UserConfig;
import com.enable.entity.Role;
import com.enable.entity.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import java.util.Map;
@SpringBootApplication
@Import(UserConfig.class)
public class SpringbootApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringbootApplication.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);
    }
}

测试结果：

3 导入ImportSelector 实现类

新建实体类：

package com.enable.entity;
public class Role {
}

package com.enable.entity;
public class User {
}

编写ImportSelector：

package com.enable.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.enable.entity.Role","com.enable.entity.User"};
    }
}

测试功能：

package com.example.demo;
import com.enable.config.EnableUser;
import com.enable.config.MyImportSelector;
import com.enable.config.UserConfig;
import com.enable.entity.Role;
import com.enable.entity.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import java.util.Map;
@SpringBootApplication
@Import(MyImportSelector.class)
public class SpringbootApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringbootApplication.class, args);
        User user = context.getBean(User.class);
        System.out.println(user);
        Role role = context.getBean(Role.class);
        System.out.println(role);
    }
}

结果如下：

4 导入ImportBeanDefinitionRegistrar实现类

新建实体类：

package com.enable.entity;
public class User {
}

ImportBeanDefinitionRegistrar实现类

package com.enable.config;
import com.enable.entity.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.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;
public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(User.class).getBeanDefinition();
        registry.registerBeanDefinition("user",beanDefinition);
    }
}

测试结果：

package com.example.demo;
import com.enable.config.EnableUser;
import com.enable.config.MyImportBeanDefinitionRegistrar;
import com.enable.config.MyImportSelector;
import com.enable.config.UserConfig;
import com.enable.entity.Role;
import com.enable.entity.User;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import java.util.Map;
@SpringBootApplication
@Import(MyImportBeanDefinitionRegistrar.class)
public class SpringbootApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringbootApplication.class, args);
        Object user1 = context.getBean("user");
        System.out.println(user1);
        User user = context.getBean(User.class);
        System.out.println(user);
    }
}

结果如下：

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