【spring】@import的用法

一、用法

• 1.指定普通类
• 2.指定配置类
• 3. 指定实现了ImportSelector接口的类,通过ImportSelector可以一次性注册多个，返回一个string[]数组中，数组中每一个值是类的完整路径
• 4.通过实现了ImportBeanDefinitionRegistrar接口的类，可以一次性注册多个，通过BeanDefinitionRegistry来动态注册BeanDefinition
• 5.通过实现了DeferredImportSelector(ImportSelector的子类)可以一次性注册多个，返回一个string[]每一个值是完整类路径，与ImpoertSelector的区别：顺序靠后，SpringBoot用的一种方式

二、代码示例

2.1 指定普通类

package com.learning.beanimport;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description 配置类
 **/
@Configuration
@ComponentScan
@Import(UserService.class)
public class ImportConfig {
}

package com.learning.beanimport;

/**
 * @Author wangyouhui
 * @Description 业务类
 **/
public class UserService {
	public void print(String hello) {
		System.out.println(hello);
	}
}

package com.learning.beanimport;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @Author wangyouhui
 * @Description 应用类
 **/
public class Application {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(ImportConfig.class);
		UserService userService = (UserService)annotationConfigApplicationContext.getBean("userService");
		userService.print("hello");
	}
}

2.2 指定配置类

package com.learning.beanimport.configclass;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @Author wangyouhui
 * @Description 配置类
 **/
@Configuration
@ComponentScan
public class Config {
	@Bean
	public UserService userService(){
		return new UserService();
	}
}

package com.learning.beanimport.configclass;

import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description 配置类
 **/
@Import(Config.class)
public class ImportConfig {
}

package com.learning.beanimport.configclass;

/**
 * @Author wangyouhui
 * @Description 业务类
 **/
public class UserService {
	public void print(String hello) {
		System.out.println(hello);
	}
}

package com.learning.beanimport.configclass;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @Author wangyouhui
 * @Description 应用类
 **/
public class Application {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(ImportConfig.class);
		UserService userService = (UserService)annotationConfigApplicationContext.getBean("userService");
		userService.print("hello");
	}
}

2.3 指定实现了ImportSelector接口的类

package com.learning.beanimport.importselector;

/**
 * @Author wangyouhui
 * @Description 业务类
 **/
public class UserService {
	public void print(String hello) {
		System.out.println(hello);
	}
}

package com.learning.beanimport.importselector;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;


/**
 * @Author wangyouhui
 * @Description 配置类
 **/
@ComponentScan
@Configuration
@Import(ImportSelector.class)
public class ImportConfig {
}

package com.learning.beanimport.importselector;

import org.springframework.core.type.AnnotationMetadata;

/**
 * @Author wangyouhui
 * @Description 实现ImportSelector接口的类
 **/
public class ImportSelector implements org.springframework.context.annotation.ImportSelector {
	@Override
	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
//		return new String[]{"com.learning.beanimport.importselector.UserService"};
		return new String[]{UserService.class.getName()};
	}

}

package com.learning.beanimport.importselector;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @Author wangyouhui
 * @Description 应用类
 **/
public class Application {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(ImportConfig.class);
		UserService userService = annotationConfigApplicationContext.getBean(UserService.class);
		userService.print("hello");
	}
}

2.4 指定实现了ImportBeanDefinitionRegistrar接口的类

package com.learning.beanimport.importbeandefinitionregister;

/**
 * @Author wangyouhui
 * @Description 业务类
 **/
public class UserService {
	public void print(String hello) {
		System.out.println(hello);
	}
}

package com.learning.beanimport.importbeandefinitionregister;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.core.type.AnnotationMetadata;

/**
 * @Author wangyouhui
 * @Description bean定义注册器
 **/
public class ImportBeanDefinitionRegistrar implements org.springframework.context.annotation.ImportBeanDefinitionRegistrar {
	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		// 创建BeanDefinition
		GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
		beanDefinition.setBeanClass(UserService.class);
		// 注册BeanDefinition
		registry.registerBeanDefinition("userService", beanDefinition);
	}
}

package com.learning.beanimport.importbeandefinitionregister;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

/**
 * @Author wangyouhui
 * @Description 配置类
 **/
@Configuration
@ComponentScan
@Import(ImportBeanDefinitionRegistrar.class)
public class ImportConfig {
}

package com.learning.beanimport.importbeandefinitionregister;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @Author wangyouhui
 * @Description 应用类
 **/
public class Application {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(ImportConfig.class);
		UserService userService = (UserService)annotationConfigApplicationContext.getBean("userService");
		userService.print("hello");
	}
}