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springboot-8-async

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Async 原理

##Async

待续

EnableAsync注解

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@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {
	Class<? extends Annotation> annotation() default Annotation.class;
	boolean proxyTargetClass() default false;
	AdviceMode mode() default AdviceMode.PROXY;
	int order() default Ordered.LOWEST_PRECEDENCE;
}

使能注解中包含一个至关重要的@Import。

还是以@EnableAsync为例。

从EnableAsync注解源码中可以看到

  • @EnableAsync的@Import会将AsyncConfigurationSelector注入到spring容器中
  • AsyncConfigurationSelector又是ImportSelector的子类，其会根据 selectImports()的返回值注入指定类。
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public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {
	private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME =
			"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";
  // 根据 @EnableAsync 的 AdviceMode 字段返回指定的全类名。
	@Override
	public String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
				return new String[] { ProxyAsyncConfiguration.class.getName() };
			case ASPECTJ:
				return new String[] { ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME };
			default:
				return null;
		}
	}
}
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public abstract class AdviceModeImportSelector<A extends Annotation> implements ImportSelector {

	public static final String DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME = "mode";
	protected String getAdviceModeAttributeName() {
		return DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME;
	}

	@Override
	public final String[] selectImports(AnnotationMetadata importingClassMetadata) {
		Class<?> annoType = GenericTypeResolver.resolveTypeArgument(getClass(), AdviceModeImportSelector.class);
		AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType);
		if (attributes == null) {
			throw new IllegalArgumentException(String.format(
				"@%s is not present on importing class '%s' as expected",
				annoType.getSimpleName(), importingClassMetadata.getClassName()));
		}

		AdviceMode adviceMode = attributes.getEnum(this.getAdviceModeAttributeName());
		String[] imports = selectImports(adviceMode);
		if (imports == null) {
			throw new IllegalArgumentException(String.format("Unknown AdviceMode: '%s'", adviceMode));
		}
		return imports;
	}
  // 子类实现：根据配置，导入指定的类
	protected abstract String[] selectImports(AdviceMode adviceMode);
}

##参考