之前的文章用到了一些Enable*开头的注解，比如EnableAsync、EnableScheduling、EnableAspectJAutoProxy、EnableCaching等，Enable表示开启/允许一项功能。
我们只需要几个很简单的注解就能开启一个复杂的功能，这是多么简易的用法，这是怎么办到的？
首先来看看计划任务@EnableScheduling的源代码
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {
}
主要核心的配置就是导入了一个配置文件，所以谜底也就接开了。
@Import(SchedulingConfiguration.class)
来看看Import的源码
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
/**
* {@link Configuration}, {@link ImportSelector}, {@link ImportBeanDefinitionRegistrar}
* or regular component classes to import.
*/
Class<?>[] value();
}
即上面的用法，直接导入Configuration配置类。
根据条件选择导入不同的配置类，参考@EnableAsync
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {
public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {
private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME =
"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";
/**
* {@inheritDoc}
* @return {@link ProxyAsyncConfiguration} or {@code AspectJAsyncConfiguration} for
* {@code PROXY} and {@code ASPECTJ} values of {@link EnableAsync#mode()}, respectively
*/
@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;
}
}
}
动态注册Bean，参考@EnableAspectJAutoProxy
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {
class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
/**
* Register, escalate, and configure the AspectJ auto proxy creator based on the value
* of the @{@link EnableAspectJAutoProxy#proxyTargetClass()} attribute on the importing
* {@code @Configuration} class.
*/
@Override
public void registerBeanDefinitions(
AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
AnnotationAttributes enableAspectJAutoProxy =
AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
}
if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
}
}
}