SpringBoot自动装配原理

详解

SpringBoot版本：

java 复制代码

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.5</version>
        <relativePath/>
</parent>

@SpringBootAppliation由以下三个注解组成：

java 复制代码

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
...
}

@EnableAutoConfiguration又由以下两个注解组成：

java 复制代码

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
...
}

java 复制代码

// org.springframework.boot.autoconfigure.AutoConfigurationImportSelector
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
		ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {

// Return the auto-configuration class names that should be considered. By default, this method will load candidates using ImportCandidates.
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    // 这一步会提取项目中所有的META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports的文件，并且提取
    // 文件中所有的类名。像图AutoConfiguration.imports-1会在configurations中加1个元素，图AutoConfiguration.imports-2会在
    // configurations中加5个元素。
		List<String> configurations = ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader())
			.getCandidates();
		Assert.notEmpty(configurations,
				"No auto configuration classes found in "
						+ "META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you "
						+ "are using a custom packaging, make sure that file is correct.");
		return configurations;
	}

protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return EMPTY_ENTRY;
		}
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
		// 这一步获取所有的需要自动装配的类名
		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
		// 去重
		configurations = removeDuplicates(configurations);
		// 需要排除的类
		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, exclusions);
		configurations.removeAll(exclusions);
		// 过滤掉条件不存在的配置类。如图BatchAutoConfiguration会被过滤掉，不会出现在configurations中
		// 如图MybatisPlusInnerInterceptorAutoConfiguration则依然保留在configurations中
		configurations = getConfigurationClassFilter().filter(configurations);
		fireAutoConfigurationImportEvents(configurations, exclusions);
		return new AutoConfigurationEntry(configurations, exclusions);
	}

}

图AutoConfiguration.imports-1

图AutoConfiguration.imports-2

图BatchAutoConfiguration

图MybatisPlusInnerInterceptorAutoConfiguration

总结

版权声明：本文为CSDN博主「CodeAmaz」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。

原文链接：https://blog.csdn.net/zhiyuanit/article/details/155698485