springboot自動裝配原理

springboot核心是自動裝配

spring ioc的升級過程

1. xml方式
2. 注解方式
3. javaconfig方式
4. springboot提供的自動裝配

springboot自動裝配的核心

1. EnableAutoConfiguration
2. @Import(AutoConfigurationImportSelector.class)
3. ImportSelector.selectImports
4. META-INF/spring.factories
   ImportSelector.selectImports返回的就是javaconfig類，再根據Condition篩選后，決定是否執行注入
   官方提供的自動裝配配置在spring-boot-autoconfigure中的META-INF/spring.factories中，如spring-boot-starter-data-redis
   非官方需要自己提供spring.factories，如mybatis-spring-boot-autoconfigure中定義了META-INF/spring.factories

通過繼承ImportSelector.selectImports實現spring注入

@SpringBootApplication
@EnableSelectImportService
public class SelectImportApp {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SelectImportApp.class);
        SelectImportService service = context.getBean(SelectImportService.class);
        service.hello();
    }
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(MySelectImport.class)
public @interface EnableSelectImportService {
}

public class MySelectImport implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{SelectImportService.class.getName()};
    }
}

public class SelectImportService {
    public void hello(){
        System.out.println("hello selectimport");
    }
}