HM-SpringBoot2.3【SpringBoot自动配置-Enable*注解】

 

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1 创建模块1

 

 

 

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.haifei</groupId>
    <artifactId>springboot9-enable</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot9-enable</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

 

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2 创建模块2

 

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.haifei</groupId>
    <artifactId>springboot10-enable-other</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot10-enable-other</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
    </dependencies>

</project>

 

---

 

 3 在模块2中创建Bean类及其配置类

package com.haifei.domain;

public class User {
}

 

package com.haifei.config;

import com.haifei.domain.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class UserConfig {

    @Bean
    public User user(){
        return new User();
    }

}

4 在模块1中获取Bean

pom.xml

+

        <dependency>
            <groupId>com.haifei</groupId>
            <artifactId>springboot10-enable-other</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>  

 

package com.haifei.springboot9enable;

import com.haifei.config.EnableUser;
import com.haifei.config.UserConfig;
import com.haifei.domain.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;

/**
 * Enable*注解
 */
//@ComponentScan("com.haifei.config")
//@Import(UserConfig.class)
@EnableUser

@SpringBootApplication
public class Springboot9EnableApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Springboot9EnableApplication.class, args);
        //获取Bean（由于该Bean是其他模块中的Bean，需要在pom中导入依赖坐标）
        Object user = context.getBean("user");
        System.out.println(user);

        /*
        不能直接获取bean-user，NoSuchBeanDefinitionException: No bean named 'user' available
        原因：
            @SpringBootApplication的元注解@ComponentScan指定扫描范围仅为当前引导类所在包及其子包
            而这个bean-user在springboot10-enable-other模块中的com.haifei.config包下
            此类属于springboot9-enable模块中的com.haifei.springboot9enable包下
         */

        /*
        解决方法1：使用@ComponentScan扫描com.itheima.config包
        在该类上加上注解@ComponentScan，并指定bean的配置类所在包
        com.haifei.domain.User@517566b
         */

        /*
        解决方法2：可以使用@Import注解，加载类。这些类都会被Spring创建，并放入IOC容器
        在该类上加上注解@Import，并指定bean的配置类.class
        com.haifei.domain.User@e8df99a
         */

        /*
        解决方法3：可以对Import注解进行封装
        在springboot10-enable-other模块中的com.haifei.config包下创建注解@EnableUser，并对其配置方法2中的@Import
        在该类上加上注解@EnableUser即可
        com.haifei.domain.User@2f40e5db
         */
    }

}

 

5 模块2中自定义的@EnableUser注解

package com.haifei.config;

import org.springframework.context.annotation.Import;

import java.lang.annotation.*;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented //以上三个为@Import注解的元注解
@Import(UserConfig.class)
public @interface EnableUser {
}