SpringBoot自动装配之@Import深入讲解
作者：不死鸟.亚历山大.狼崽子
由于最近的项目需求，需要在把配置类导入到容器中，通过查询，使用@Import注解就能实现这个功能，@Import注解能够帮我们吧普通配置类（定义为Bean的类）导入到IOC容器中
@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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