Springboot启动过程

Posted 2023-03-09

参考技术A 元注解

元标签有 @Retention、@Documented、@Target、@Inherited、@Repeatable 5 种。

FactoryBean getObject

1. 静态注入

2. 动态引入

基于ImportSelector接口实现

3. 基于ImportBeanDefinition

4. spring.factories

@conditional 加载到容器的条件

第一个决定要加载的类型, 第二个决定是否加载?

扩展下. 其实springCloud组件 很多用到@Import @Conditional , 还有些select等, 顺藤摸瓜 我简答列列举几个:

@SpringBootApplication-->@EnableAutoConfiguration

@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

@Import(AutoConfigurationImportSelector.class)

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration

重点说下Selector:

public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered

最顶层继承了ImportSelector 和 Aware接口:

public interface ImportSelector



protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes)
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
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;


protected Class<?> getSpringFactoriesLoaderFactoryClass()
return EnableAutoConfiguration.class;


其实最终是寻找EnableAutoConfiguration对应的类组合, EnableAutoConfiguration来自package org.springframework.boot.autoconfigure;

所以最终初始化时, 是加载了spring-boot-autoconfigure里面的spring.factories的内容, 简单列举出现:

说明下:

SpringFactoriesLoader属于Spring框架私有的一种扩

展方案，其主要功能就是从指定的配置文件META-INF/spring.factories加载配置。

public final class SpringFactoriesLoader