一. 使用注解

在dubbo springboot 使用时，在需要调用的服务接口上使用 @Reference 即可直接调用远程服务

@Reference(version = "1.0.0",

application = "${dubbo.application.id}")

private HelloService helloService;

比如上述样式 调试发现调用时 helloSevice为一个生产的代理对象如下图:

二.分析原理

@Reference 的行为跟 @Autowired 类似 均实现了自动注入的过程 。

@Reference 的注解处理依赖于 ReferenceAnnotationBeanPostProcessor 类 该类的定义如下:

public class ReferenceAnnotationBeanPostProcessor extends AnnotationInjectedBeanPostProcessor implements

ApplicationContextAware, ApplicationListener {

/**

* The bean name of {@link ReferenceAnnotationBeanPostProcessor}

*/

public static final String BEAN_NAME = "referenceAnnotationBeanPostProcessor";

/**

* Cache size

*/

private static final int CACHE_SIZE = Integer.getInteger(BEAN_NAME + ".cache.size", 32);

private final ConcurrentMap> referenceBeanCache =

new ConcurrentHashMap<>(CACHE_SIZE);

private final ConcurrentHashMap localReferenceBeanInvocationHandlerCache =

new ConcurrentHashMap<>(CACHE_SIZE);

private final ConcurrentMap> injectedFieldReferenceBeanCache =

new ConcurrentHashMap<>(CACHE_SIZE);

private final ConcurrentMap> injectedMethodReferenceBeanCache =

new ConcurrentHashMap<>(CACHE_SIZE);

private ApplicationContext applicationContext;

其中 referenceBeanCache缓存了接口对应bean的定义 localReferenceBeanInvocationHandlerCache缓存了接口对应InvocationHandler的定义。

参考 autowired的解析过程 分析首先找到 (2.63定义在当前类 原理一致)

class AnnotationInjectedBeanPostProcessor{

@Override

public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class> beanType, String beanName) {

if (beanType != null) {

InjectionMetadata metadata = findInjectionMetadata(beanName, beanType, null);

metadata.checkConfigMembers(beanDefinition);

}

}

}

执行的时间节点是bean刚刚初始化完 但在属性填充之前， spring会为每个beanDefinition依次调用实现了 MergedBeanDefinitionPostProcessor接口的PostProcessor的改方法(注册过程单独放在spring boot 自动配置章节)

该函数依次处理spring传来的beanClass 并解析class field method尝试找到

private List findFieldReferenceMetadata(Class> beanClass) {

final List elements = new LinkedList();

ReflectionUtils.doWithFields(beanClass, new FieldCallback() {

public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {

Reference reference = (Reference)AnnotationUtils.getAnnotation(field, Reference.class);

if (reference != null) {

if (Modifier.isStatic(field.getModifiers())) {

if (ReferenceAnnotationBeanPostProcessor.this.logger.isWarnEnabled()) {

ReferenceAnnotationBeanPostProcessor.this.logger.warn("@Reference annotation is not supported on static fields: " + field);

}

return;

}

elements.add(ReferenceAnnotationBeanPostProcessor.this.new ReferenceFieldElement(field, reference));

}

}

});

return elements;

}

有这个定义的filed或者method 如果存在的话 就建立类定义中对应field method的缓存。同时加入到beanclass/beanname对应该meta信息的缓存 以便同样的请求过来不在解析。

之后 处理调用该函数

public void checkConfigMembers(RootBeanDefinition beanDefinition) {

Set checkedElements = new LinkedHashSet(this.injectedElements.size());

Iterator var3 = this.injectedElements.iterator();

while(var3.hasNext()) {

InjectionMetadata.InjectedElement element = (InjectionMetadata.InjectedElement)var3.next();

Member member = element.getMember();

if (!beanDefinition.isExternallyManagedConfigMember(member)) {

beanDefinition.registerExternallyManagedConfigMember(member);

checkedElements.add(element);

if (logger.isDebugEnabled()) {

logger.debug("Registered injected element on class [" + this.targetClass.getName() + "]: " + element);

}

}

}

this.checkedElements = checkedElements;

}

这个函数会将上个函数标注出来需要被注入的域标注为"外部管理"，只有被标注为外部管理的成员 在后续才会在当前bean实例化调用postProcessPropertyValues来处理外部注入

最后一步 postProcessPropertyValues 注入属性

public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

InjectionMetadata metadata = this.findReferenceMetadata(beanName, bean.getClass(), pvs);

try {

metadata.inject(bean, beanName, pvs);

return pvs;

} catch (BeanCreationException var7) {

throw var7;

} catch (Throwable var8) {

throw new BeanCreationException(beanName, "Injection of @Reference dependencies failed", var8);

}

}

public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {

Collection checkedElements = this.checkedElements;

Collection elementsToIterate = checkedElements != null ? checkedElements : this.injectedElements;

if (!((Collection)elementsToIterate).isEmpty()) {

boolean debug = logger.isDebugEnabled();

InjectionMetadata.InjectedElement element;

for(Iterator var7 = ((Collection)elementsToIterate).iterator(); var7.hasNext(); element.inject(target, beanName, pvs)) {

element = (InjectionMetadata.InjectedElement)var7.next();

if (debug) {

logger.debug("Processing injected element of bean '" + beanName + "': " + element);

}

}

}

}

具体过程为判断当前bean 是否需要当前的processor注入 如果需要的话 即执行注入

protected void inject(Object target, @Nullable String requestingBeanName, @Nullable PropertyValues pvs) throws Throwable {

if (this.isField) {

Field field = (Field)this.member;

ReflectionUtils.makeAccessible(field);

field.set(target, this.getResourceToInject(target, requestingBeanName));

} else {

if (this.checkPropertySkipping(pvs)) {

return;

}

try {

Method method = (Method)this.member;

ReflectionUtils.makeAccessible(method);

method.invoke(target, this.getResourceToInject(target, requestingBeanName));

} catch (InvocationTargetException var5) {

throw var5.getTargetException();

}

}

}

其中 本实例中实际处理inject动作的为

private class ReferenceFieldElement extends InjectedElement

protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {

Class> referenceClass = this.field.getType();

this.referenceBean = ReferenceAnnotationBeanPostProcessor.this.buildReferenceBean(this.reference, referenceClass);

ReflectionUtils.makeAccessible(this.field);

this.field.set(bean, this.referenceBean.getObject());

}

其中具体的创建代码为

private ReferenceBean> buildReferenceBean(Reference reference, Class> referenceClass) throws Exception {

String referenceBeanCacheKey = this.generateReferenceBeanCacheKey(reference, referenceClass);

ReferenceBean> referenceBean = (ReferenceBean)this.referenceBeansCache.get(referenceBeanCacheKey);

if (referenceBean == null) {

ReferenceBeanBuilder beanBuilder = (ReferenceBeanBuilder)ReferenceBeanBuilder.create(reference, this.classLoader, this.applicationContext).interfaceClass(referenceClass);

referenceBean = (ReferenceBean)beanBuilder.build();

this.referenceBeansCache.putIfAbsent(referenceBeanCacheKey, referenceBean);

}

return referenceBean;

}

该过程生成了一个referencebean的实例 并根据注解参数配置了

public class ReferenceBean extends ReferenceConfig

ReferenceConfig的参数。

此时执行最后一步

this.field.set(bean, this.referenceBean.getObject());

此时尝试去当前referenceBean去除绑定的 dubbo调用invoke对象 如果不存在则创建一个

具体创建过程比较长

private void init() {

// 构建参数map

this.ref = this.createProxy(map);

}

最终创建动态代理 并将ref对象赋值给@Reference注解的成员 。

完。