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 。
首先参考下https://blog.csdn.net/qq_27529917/article/details/78454912学习 @Autowired 工作原理 ，可跳过。
@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<String, ReferenceBean<?>> referenceBeanCache =
new ConcurrentHashMap<>(CACHE_SIZE);
private final ConcurrentHashMap<String, ReferenceBeanInvocationHandler> localReferenceBeanInvocationHandlerCache =
new ConcurrentHashMap<>(CACHE_SIZE);
private final ConcurrentMap<InjectionMetadata.InjectedElement, ReferenceBean<?>> injectedFieldReferenceBeanCache =
new ConcurrentHashMap<>(CACHE_SIZE);
private final ConcurrentMap<InjectionMetadata.InjectedElement, ReferenceBean<?>> 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<ReferenceAnnotationBeanPostProcessor.ReferenceFieldElement> findFieldReferenceMetadata(Class<?> beanClass) {
final List<ReferenceAnnotationBeanPostProcessor.ReferenceFieldElement> 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<InjectionMetadata.InjectedElement> 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<InjectionMetadata.InjectedElement> checkedElements = this.checkedElements;
Collection<InjectionMetadata.InjectedElement> 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<T> extends ReferenceConfig<T>
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。
