Spring Boot 2 自动配置流程

https://www.bilibili.com/video/BV19K4y1L7MT?p=15

以 spring-boot-autoconfigure-2.3.4.RELEASE.jar 中的 org.springframework.boot.autoconfigure.aop.AopAutoConfiguration 为例，分析自动配置流程

package org.springframework.boot.autoconfigure.aop;

import org.aspectj.weaver.Advice;

……
@Configuration(proxyBeanMethods = false)
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)
public class AopAutoConfiguration {

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(Advice.class)
	static class AspectJAutoProxyingConfiguration {

		@Configuration(proxyBeanMethods = false)
		@EnableAspectJAutoProxy(proxyTargetClass = false)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false",
				matchIfMissing = false)
		static class JdkDynamicAutoProxyConfiguration {

		}

		@Configuration(proxyBeanMethods = false)
		@EnableAspectJAutoProxy(proxyTargetClass = true)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true",
				matchIfMissing = true)
		static class CglibAutoProxyConfiguration {

		}

	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnMissingClass("org.aspectj.weaver.Advice")
	@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true",
			matchIfMissing = true)
	static class ClassProxyingConfiguration {

		ClassProxyingConfiguration(BeanFactory beanFactory) {
			if (beanFactory instanceof BeanDefinitionRegistry) {
				BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
				AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
				AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
			}
		}

	}
}

@Configuration 说明这是一个配置类；

@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)

配置文件中是否存在 spring.aop 这个配置，如果存在了 spring.aop.auto 这个配置，并且它的值是“true”，那么这个类中的其他配置就生效，matchIfMissing = true 就算没有响应的配置，也认为满足条件，所以相当于这个配置是生效的

再来看

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(Advice.class)
	static class AspectJAutoProxyingConfiguration {

		@Configuration(proxyBeanMethods = false)
		@EnableAspectJAutoProxy(proxyTargetClass = false)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false",
				matchIfMissing = false)
		static class JdkDynamicAutoProxyConfiguration {

		}

		@Configuration(proxyBeanMethods = false)
		@EnableAspectJAutoProxy(proxyTargetClass = true)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true",
				matchIfMissing = true)
		static class CglibAutoProxyConfiguration {

		}

	}

@Configuration 说明这是一个配置类；

@ConditionalOnClass(Advice.class) 类路径中是否存在 org.aspectj.weaver.Advice 这个类，在 IDEA 中 按两下 Shift 只有选择 Classes tab 页，没有 org.aspectj.weaver.Advice这个类，所以这个类中的其他配置也就不生效了