springboot自动配置原理浅析

Posted 2021-10-25 霜序0.2℃

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springboot自动配置原理浅析

springboot版本2.5.5

注解@SpringBootApplication的源码:

@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 {}

我们可以看到

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan

ComponentScan

其中ComponentScan注解用于扫描,注解后面跟着的是springboot自定义的扫描器,这个最后我们再谈

SpringBootConfiguration

这个是SpringBootConfiguration的源码,我们可以看出

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
@Indexed
public @interface SpringBootConfiguration {}

我们看到有Configuration注解,无非就是配置类,只不过SpringBootApplication是主配置类

EnableAutoConfiguration

源码:

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

其中有着

@AutoConfigurationPackage

AutoConfigurationPackage

“自动配置包”

再看看源码:

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

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

Import是什么,就是自动给容器导入组件

我们看看这个类的源码:(好吧,实属套娃了)

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));
    }
}

作用是给容器里面批量注册组件

registerBeanDefinitions方法中的参数AnnotationMetadata注解变化信息,相当于源信息,所以我们找到标记这个合成注解的类(被SpringBootApplication标记了的类)

方法内部:

AutoConfigurationPackages.register(registry, (String[])(new AutoConfigurationPackages.PackageImports(metadata)).getPackageNames().toArray(new String[0]));