SpringBoot自动装配原理笔记

@SpringBootApplication
@MapperScan("com.xx.mapper")
public class SpringBootVipDemoApplication {
    public static void main(String[] args) {
        // 基于配置文件的方式
        ApplicationContext ac1 = new ClassPathXmlApplicationContext("");
        // 基于Java配置类的方式
        ApplicationContext ac2 = new AnnotationConfigApplicationContext(SpringBootVipDemoApplication.class);
		// run 方法的返回对象是 ConfigurableApplicationContext 对象
        ConfigurableApplicationContext ac3 = SpringApplication.run(SpringBootVipDemoApplication.class, args);
    }
}

@SpringBootApplication
@MapperScan("com.xx.mapper")
public class SpringBootVipDemoApplication {

    public static void main(String[] args) {
        // 基于配置文件的方式
        ApplicationContext ac1 = new ClassPathXmlApplicationContext("");
        // 基于Java配置类的方式
        ApplicationContext ac2 = new AnnotationConfigApplicationContext(SpringBootVipDemoApplication.class);
        // run 方法执行完成后返回的是一个 ApplicationContext 对象
        // 到这儿我们是不是可以猜测 run 方法的执行 其实就是Spring的初始化操作[IoC]
        ApplicationContext ac3 = SpringApplication.run(SpringBootVipDemoApplication.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}
)}
)

@Target({ElementType.TYPE}) // 表明 修饰的注解的位置 TYPE 表示只能修饰类
@Retention(RetentionPolicy.RUNTIME) // 表明注解的作用域
@Documented // API 文档抽取的时候会将该注解 抽取到API文档中
@Inherited  // 表示注解的继承

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
// 上面是3个元注解
// @Configuration 注解修饰的Java类是一个配置类
@Configuration
// @Indexed
@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 {};
}

    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(annotationMetadata);
            // 返回的就是需要注册到IoC容器中的对象对应的类型的全类路径名称的字符串数组
            // ["com.bobo.pojo.User","com.bobo.pojo.Person", ....]
            return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
        }
    }

    protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return EMPTY_ENTRY;
        } else {
            // 获取注解的属性信息
            AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
            // 获取候选配置信息 加载的是 当前项目的classpath目录下的 所有的 spring.factories 文件中的 key 为
            // org.springframework.boot.autoconfigure.EnableAutoConfiguration 的信息
            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 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);
            // 因为会加载多个 spring.factories 文件，那么就有可能存在同名的，
            // removeDuplicates方法的作用是 移除同名的
            configurations = this.removeDuplicates(configurations);
            // 获取我们配置的 exclude 信息
            // @SpringBootApplication(exclude = {RabbitAutoConfiguration.class})
            // 显示的指定不要加载那个配置类
            Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
            this.checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            // filter的作用是 过滤掉咱们不需要使用的配置类。
            configurations = this.getConfigurationClassFilter().filter(configurations);
            this.fireAutoConfigurationImportEvents(configurations, exclusions);
            return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);
        }
    }