SpringBoot的自动装配机制和Starter的实现原理分析

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan

@Configuration
@ConditionalOnClass(DataSource.class)
public class DataSourceAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public DataSource dataSource() {
        // 自动配置数据源
    }
}

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.example.MyAutoConfiguration

my-starter
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com
│   │   │       └── example
│   │   │           ├── MyService.java         // 服务类
│   │   │           └── auto
│   │   │               └── MyAutoConfiguration.java // 自动配置
│   │   └── resources
│   │       └── META-INF
│   │           └── spring.factories           // 注册自动配置
└── pom.xml

@Configuration
@ConditionalOnClass(MyService.class)
public class MyAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public MyService myService() {
        return new MyService();
    }
}

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.example.auto.MyAutoConfiguration

<!-- pom.xml 示例 -->
<artifactId>my-spring-boot-starter</artifactId>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-autoconfigure</artifactId>
    </dependency>
</dependencies>

// 用户项目中直接注入服务
@RestController
public class DemoController {
    @Autowired
    private MyService myService; // 自动注入 Starter 提供的 Bean
    @GetMapping("/demo")
    public String demo() {
        return myService.execute();
    }
}