SpringBoot3.0.1自动装配_springboot3.0 自动装配

SpringBoot的自动装配是SpringBoot的核心，而SpringBoot的启动类上的@SpringBootApplication注解中包括@SpringBootConfiguration、@EnableAutoConfiguration和@ComponentScan三个注解，其中@EnableAutoConfiguration就是自动装配的核心注解。

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
//自动装配的核心注解
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
}

对@EnableAutoConfiguration进行跟踪，@Import({AutoConfigurationImportSelector.class})就是负责自动装配。

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({AutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
 
    Class<?>[] exclude() default {};
 
    String[] excludeName() default {};
}

跟踪AutoConfigurationImportSelector.class，其中有个getAutoConfigurationEntry方法，用于自动获取配置了类信息。

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);
        }
    }

其中getCandidateConfigurations方法用于获取候选配置

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        List<String> configurations = ImportCandidates.load(AutoConfiguration.class, this.getBeanClassLoader()).getCandidates();
        Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you are using a custom packaging, make sure that file is correct.");
        return configurations;
    }

其中的ImportCandidates.load方法解析出配置文件的路径"META-INF/spring/%s.imports"，也就是spring-boot-autoconfigure包下的META-INF下的spring中的org.springframework.boot.autoconfigure.AutoConfiguration.imports文件

文件中就包括了自动加载的类，在具体的装配时，会进行条件判断，符合了才会自动装配，也就是判断项目中是否真的引入了依赖。