SpringBoot中自动配置原理解析

@Data
public class A{
	private Integer id=0;
	private String name="classA";
	public void print(){
		System.out.println(this.name);
	}
}

@Data
public class B{
	private Integer id=1;
	private String name="classB";
	public void print(){
		System.out.println(this.name);
	}
}

@Import({A.class,B.class})
@Configuration
public class ClassConfig{
​​​​​​​}

@Data
public class C{
    private Integer id=2;
    private String name="classC";
    public void print(){
        System.out.println(this.name);
    }
}

public class ImportSelectorTest implements ImportSelector{
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetada){
        return new String[]{"C.class"};
    }
}

@Import({ImportSelectorTest.class})
@Configuration
public class ImportSelectorConfig{
​​​​​​​}

@Data
public class D{
	private Integer id=3;
	private String name="ClassD";
	public void print(){
		System.out.println(this.name);
	}
}

//定义类实现ImPortBeanDefinitionRegistrar接口，重写其中的registerBeanDefinitions()方法
public class ImportBeanDefinitionRegistrarTest{
	@Override
	public void registerBeanDefninitions(AnnotationMetadata annotationMetadata,BeanDefinitionRegistry registry{
		RootBeanDefinition rootBeanDefinition=new RootBeanDefinition(D.class);
		registry.registerBeanDefinition("自定义名称",rootBeanDefinition);
	}
}

//使用上面的类进行导入
@Import({ImportBeanDefinitionRegistrarTest})
@Configuration
public class ImportBeanDefinitionRegistrarConfig{

}

@SpringBootApplication
public class SpringBootTestApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootTestApplication.class, args);
    }

}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    //内容省略
}

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

@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 {};
}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import({Registrar.class})
public @interface AutoConfigurationPackage {
    String[] basePackages() default {};

    Class<?>[] basePackageClasses() default {};
}

//其中的@Import注解导入了Registrar类，该类是AutoConfigurationPackages的静态类部类
static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
        Registrar() {
        }

		/**
			根据传入的元注解信息获取所在的包，将包中组件类封装为数组进行注册
		*/
        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));
        }
    }

public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
            Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector, () -> {
                return String.format("Only %s implementations are supported, got %s", AutoConfigurationImportSelector.class.getSimpleName(), deferredImportSelector.getClass().getName());
            });
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector)deferredImportSelector).getAutoConfigurationEntry(annotationMetadata);
            this.autoConfigurationEntries.add(autoConfigurationEntry);
            Iterator var4 = autoConfigurationEntry.getConfigurations().iterator();

            while(var4.hasNext()) {
                String importClassName = (String)var4.next();
                this.entries.putIfAbsent(importClassName, annotationMetadata);
            }

        }

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);
        }
    }

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;
    }