@SpringBootApplication 之 @ComponentScan

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原理

@SpringBootApplication 是一个复合注解，包括

• @SpringBootConfiguration
• @EnableAutoConfiguration
• @ComponentScan

Note：

@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

• excludeFilters：Specifies which types are not eligible for component scanning
• @Filter：Filter annotation
• FilterType.CUSTOM：Filter candidates using a given custom implementation
• classes：Filter specific class, include TypeExcludeFilter, AutoConfigurationExcludeFilter

 

@ComponentScan 源码

Note：

• 通常自定义一个Spring Bean，一般在类上加上注解 @Component、@Service、@Controller，定义好后，需要使用@ComponentScan 来告诉Spring IoC 容器去哪里装载自定义的Spring Bean
• @SpringBootApplication 包含了@ComponentScan，所以@SpringBootApplication注解所在包及其子包目录下的Spring Bean都会被扫描并装载到Spring IoC容器。
• 如果自定义的一个Spring Bean，不在@SpringBootApplication 注解所在包及其子包目录下，需要手动加上@ComponentScan 注解并指定自定义Spring Bean所在的包。

 

示例

Project Directory

 

Maven Dependency

<?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 http://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>2.3.12.RELEASE</version>
        <relativePath/>
    </parent>

    <groupId>org.fool</groupId>
    <artifactId>hellospring</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

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

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

</project>

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