@SpringBootApplication详解-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_43130076/article/details/123630247

@SpringBootApplication是Spring Boot核心注解，整合了@Configuration、@EnableAutoConfiguration和@ComponentScan。它用于启动自动配置和组件扫描，从META-INF/spring.factories加载自动配置类，并根据条件选择导入。

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@SpringBootApplication

等同于

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {}

1、@SpringBootConfiguration

1.1、@Configuration

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Indexed
@Configuration
public @interface SpringBootConfiguration {
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

2、@ComponentScan

指定要扫描哪个包，有两个自定义的扫描器

3、@EnableAutoConfiguration

@AutoConfigurationPackage
@Import({AutoConfigurationImportSelector.class})

3.1、@AutoConfigurationPackage

3.1.1、@Import({Registrar.class})

3.1.1.1、Registrar.class

static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
    Registrar() {
    }

    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        AutoConfigurationPackages.register(registry, (String[])(new AutoConfigurationPackages.PackageImports(metadata)).getPackageNames().toArray(new String[0]));
    }

    public Set<Object> determineImports(AnnotationMetadata metadata) {
        return Collections.singleton(new AutoConfigurationPackages.PackageImports(metadata));
    }
}

3.2、@Import({AutoConfigurationImportSelector.class})

3.2.1、AutoConfigurationImportSelector方法

public String[] selectImports(AnnotationMetadata annotationMetadata) {
    if (!this.isEnabled(annotationMetadata)) {
        return NO_IMPORTS;
    } else {
        AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(annotationMetadata);
        return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    }
}

3.2.1.1、getAutoConfigurationEntry方法

protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
    if (!this.isEnabled(annotationMetadata)) {
        return EMPTY_ENTRY;
    } else {
        AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
        List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
        configurations = this.removeDuplicates(configurations);
        Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
        this.checkExcludedClasses(configurations, exclusions);
        configurations.removeAll(exclusions);
        configurations = this.getConfigurationClassFilter().filter(configurations);
        this.fireAutoConfigurationImportEvents(configurations, exclusions);
        return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);
    }
}

3.2.1.1.1、getCandidateConfigurations方法

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
    Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");
    return configurations;
}