前言
前面解析过很多@EnableXXX注解开启某个功能的原理，其注解内部都是通过@Import注解，来引入一个类，通过这个类，将开启功能的核心类引入spring容器，并进行一系列初始化操作。@EnableDubbo注解也不例外，还是这个套路，下面看其详细实现。
@EnableDubbo原理解析
点进去，看其源码:
@Target({
ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@EnableDubboConfig
@DubboComponentScan
public @interface EnableDubbo {
/**
* Base packages to scan for annotated @Service classes.
* <p>
* Use {@link #scanBasePackageClasses()} for a type-safe alternative to String-based
* package names.
*
* @return the base packages to scan
* @see DubboComponentScan#basePackages()
*/
@AliasFor(annotation = DubboComponentScan.class, attribute = "basePackages")
String[] scanBasePackages() default {
};
/**
* Type-safe alternative to {@link #scanBasePackages()} for specifying the packages to
* scan for annotated @Service classes. The package of each class specified will be
* scanned.
*
* @return classes from the base packages to scan
* @see DubboComponentScan#basePackageClasses
*/
@AliasFor(annotation = DubboComponentScan.class, attribute = "basePackageClasses")
Class<?>[] scanBasePackageClasses() default {
};
/**
* It indicates whether {@link AbstractConfig} binding to multiple Spring Beans.
*
* @return the default value is <code>false</code>
* @see EnableDubboConfig#multiple()
*/
@AliasFor(annotation = EnableDubboConfig.class, attribute = "multiple")
boolean multipleConfig() default true;
}
核心是@EnableDubboConfig注解和@DubboComponentScan。先看@EnableDubboConfig注解源码:
@Target({
ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@Import(DubboConfigConfigurationRegistrar.class)
public @interface EnableDubboConfig {
/**
* It indicates whether binding to multiple Spring Beans.
* <p>
* Please note that if {@link #multiple()} is <code>true</code> since 2.6.6, the multiple bean bindings will be
* enabled, works with single bean bindings, rather than they are mutually exclusive before.
*
* @return the default value is <code>true</code> since 2.6.6, the value is inverse earlier.
* @revised 2.5.9
*/
boolean multiple() default true;
}
找到了熟悉的@Import注解，那么就看Import进来的这个类：
public class DubboConfigConfigurationRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AnnotationAttributes attributes = AnnotationAttributes.fromMap(
importingClassMetadata.getAnnotationAttributes(EnableDubboConfig.class.getName()));
boolean multiple = attributes.getBoolean("multiple");
// Single Config Bindings
registerBeans(registry, DubboConfigConfiguration.Single.class);
if (multiple) {
// Since 2.6.6 https://github.com/apache/incubator-dubbo/issues/3193
registerBeans(registry, DubboConfigConfiguration.Multiple.class);
}
}
}
可以看出，是一个BeanDefinitionRegistrar，是可以将bean注册到spring容器的，那么它将什么注册进了spring容器呢？核心代码如下：
registerBeans(registry, DubboConfigConfiguration.Single.class);
看DubboConfigConfiguration源码:
public class DubboConfigConfiguration {
/**
* Single Dubbo {@link AbstractConfig Config} Bean Binding
*/
@EnableDubboConfigBindings({
@EnableDubboConfigBinding(prefix = "dubbo.application", type = ApplicationConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.module", type = ModuleConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.registry", type = RegistryConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.protocol", type = ProtocolConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.monitor", type = MonitorConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.provider", type = ProviderConfig.class),
@EnableDubboConfigBinding(prefix = "dubbo.consumer", type = ConsumerConfig.class)
})
public static class Single {
}
/**
* Multiple Dubbo {@link AbstractConfig Config} Bean Binding
*/
@EnableDubboConfigBindings({
@EnableDubboConfigBinding(prefix = "dubbo.applications", type = ApplicationConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.modules", type = ModuleConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.registries", type = RegistryConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.protocols", type = ProtocolConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.monitors", type = MonitorConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.providers", type = ProviderConfig.class, multiple = true),
@EnableDubboConfigBinding(prefix = "dubbo.consumers", type = ConsumerConfig.class, multiple = true)
})
public static class Multiple {
}
}
可以看出，这里是将xml里的一些配置信息，绑定到了类里，加入到了Spring缓存。
下面再看另一个核心注解@DubboComponentScan源码:
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(DubboComponentScanRegistrar.class)
public @interface DubboComponentScan {
/**
* Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
* declarations e.g.: {@code @DubboComponentScan("org.my.pkg")} instead of
* {@code @DubboComponentScan(basePackages="org.my.pkg")}.
*
* @return the base packages to scan
*/
String[] value() default {
};
/**
* Base packages to scan for annotated @Service classes. {@link #value()} is an
* alias for (and mutually exclusive with) this attribute.
* <p>
* Use {@link #basePackageClasses()} for a type-safe alternative to String-based
* package names.
*
* @return the base packages to scan
*/
String[] basePackages() default {
};
/**
* Type-safe alternative to {@link #basePackages()} for specifying the packages to
* scan for annotated @Service classes. The package of each class specified will be
* scanned.
*
* @return classes from the base packages to scan
*/
Class<?>[] basePackageClasses() default {
};
}
可以看到@Import进来了DubboComponentScanRegistrar类，看其源码:
public class DubboComponentScanRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);
registerServiceAnnotationBeanPostProcessor(packagesToScan, registry);
registerReferenceAnnotationBeanPostProcessor(registry);
}
/**
* Registers {@link ServiceAnnotationBeanPostProcessor}
*
* @param packagesToScan packages to scan without resolving placeholders
* @param registry {@link BeanDefinitionRegistry}
* @since 2.5.8
*/
private void registerServiceAnnotationBeanPostProcessor(Set<String> packagesToScan, BeanDefinitionRegistry registry) {
BeanDefinitionBuilder builder = rootBeanDefinition(ServiceAnnotationBeanPostProcessor.class);
builder.addConstructorArgValue(packagesToScan);
builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
BeanDefinitionReaderUtils.registerWithGeneratedName(beanDefinition, registry);
}
/**
* Registers {@link ReferenceAnnotationBeanPostProcessor} into {@link BeanFactory}
*
* @param registry {@link BeanDefinitionRegistry}
*/
private void registerReferenceAnnotationBeanPostProcessor(BeanDefinitionRegistry registry) {
// Register @Reference Annotation Bean Processor
BeanRegistrar.registerInfrastructureBean(registry,
ReferenceAnnotationBeanPostProcessor.BEAN_NAME, ReferenceAnnotationBeanPostProcessor.class);
}
private Set<String> getPackagesToScan(AnnotationMetadata metadata) {
AnnotationAttributes attributes = AnnotationAttributes.fromMap(
metadata.getAnnotationAttributes(DubboComponentScan.class.getName()));
String[] basePackages = attributes.getStringArray("basePackages");
Class<?>[] basePackageClasses = attributes.getClassArray("basePackageClasses");
String[] value = attributes.getStringArray("value");
// Appends value array attributes
Set<String> packagesToScan = new LinkedHashSet<String>(Arrays.asList(value));
packagesToScan.addAll(Arrays.asList(basePackages));
for (Class<?> basePackageClass : basePackageClasses) {
packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
}
if (packagesToScan.isEmpty()) {
return Collections.singleton(ClassUtils.getPackageName(metadata.getClassName()));
}
return packagesToScan;
}
}
可以看到里面有registerServiceAnnotationBeanPostProcessor方法和registerReferenceAnnotationBeanPostProcessor方法。这里注册进来两个BeanPostProcessor，一个用于扫描@Service注解，一个用于扫描@Reference注解。
总结
@EnableDubbo做了两件事，一个是初始化Dubbo核心组件，加载Dubbo配置到内存。另一个是注册BeanPostProcessor，用来扫描@Service和@Reference注解。