1、前言
使用spring框架来整合Dubbo服务，Dubbo中的各项配置最终都会成为spring中的Bean对象，并遵循spring bean的整个生命周期管理。本文使用xml配置文件的方式来配置Dubbo服务来分析下整个过程。
如果是spring项目，在启动时会加载并解析resources目录下的xml，然后将xml配置文件中的配置加载成spring容器的bean，dubbo需要定义dubbo_provider.xml或consumer_provider.xml并加入到applicationContext.xml中。
如果是springboot项目，则通过配置类的注解来导入
@SpringBootApplication
@ImportResource(locations = {"classpath:dubbo-provider.xml"})
public class DubboProviderApplication {
下面给出provider.xml和consumer.xml简单示例，他们分别为服务提供者和服务消费者配置文件
provider.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd">
<!--配置应用名-->
<dubbo:application name="dubbo-provider">
<dubbo:parameter key="qos.enable" value="false"/>
</dubbo:application>
<!--配置注册中心-->
<dubbo:registry address="zookeeper://localhost:2181" file="${ZOOKEEPER_CACHE_FILE:/tmp/test/dubbo.cache}"/>
<!--配置服务协议-->
<dubbo:protocol name="dubbo" port="20880"/>
<!--配置服务暴露，暴露一个服务-->
<bean id="userService" class="com.example.springboot.dubbo.dubboprovider.service.UserServiceImpl"/>
<dubbo:service interface="com.example.springboot.dubbo.dubboapi.service.UserService" ref="userService"/>
</beans>
consumer.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd">
<!--配置应用名-->
<dubbo:application name="dubbo-customer">
<dubbo:parameter key="qos.enable" value="false"/>
</dubbo:application>
<dubbo:consumer timeout="50000" filter="">
</dubbo:consumer>
<!--配置注册中心-->
<dubbo:registry address="zookeeper://localhost:2181"/>
<!--配置代理-->
<dubbo:reference id="userService" check="false" interface="com.example.springboot.dubbo.dubboapi.service.UserService"/>
</beans>
2、dubbo框架与spring整合过程
如果是通过xml的方式来配置dubbo服务，无论是spring还是springboot，最终都是通过xml标签解析器来读取xml中的配置信息，将其转化为dubbo框架中对应的配置类对象。整合过程如下:
1、定义xsd标签定义META-INF/dubbo.xsd
2、在META-INF/spring.schemas文件中，定义xsd文件全限定名与一个在spring的xml配置文件中可以配置的命名空间url的映射；
3、定义一个实现了BeanDefinitionParser接口的实现类DubboBeanDefinitionParser，定义标签的处理逻辑；
public class DubboBeanDefinitionParser implements BeanDefinitionParser {
private static RootBeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
//省略...
if (ProtocolConfig.class.equals(beanClass)) {
for (String name : parserContext.getRegistry().getBeanDefinitionNames()) {
BeanDefinition definition = parserContext.getRegistry().getBeanDefinition(name);
PropertyValue property = definition.getPropertyValues().getPropertyValue("protocol");
if (property != null) {
Object value = property.getValue();
if (value instanceof ProtocolConfig && id.equals(((ProtocolConfig) value).getName())) {
definition.getPropertyValues().addPropertyValue("protocol", new RuntimeBeanReference(id));
}
}
}
} else if (ServiceBean.class.equals(beanClass)) {
String className = resolveAttribute(element, "class", parserContext);
if (StringUtils.isNotEmpty(className)) {
RootBeanDefinition classDefinition = new RootBeanDefinition();
classDefinition.setBeanClass(ReflectUtils.forName(className));
classDefinition.setLazyInit(false);
parseProperties(element.getChildNodes(), classDefinition, parserContext);
beanDefinition.getPropertyValues().addPropertyValue("ref", new BeanDefinitionHolder(classDefinition, id + "Impl"));
}
} else if (ProviderConfig.class.equals(beanClass)) {
parseNested(element, parserContext, ServiceBean.class, true, "service", "provider", id, beanDefinition);
} else if (ConsumerConfig.class.equals(beanClass)) {
parseNested(element, parserContext, ReferenceBean.class, false, "reference", "consumer", id, beanDefinition);
}
Set<String> props = new HashSet<>();
ManagedMap parameters = null;
for (Method setter : beanClass.getMethods()) {
String name = setter.getName();
if (name.length() > 3 && name.startsWith("set")
&& Modifier.isPublic(setter.getModifiers())
&& setter.getParameterTypes().length == 1) {
Class<?> type = setter.getParameterTypes()[0];
String beanProperty = name.substring(3, 4).toLowerCase() + name.substring(4);
String property = StringUtils.camelToSplitName(beanProperty, "-");
props.add(property);
// check the setter/getter whether match
Method getter = null;
try {
getter = beanClass.getMethod("get" + name.substring(3), new Class<?>[0]);
} catch (NoSuchMethodException e) {
try {
getter = beanClass.getMethod("is" + name.substring(3), new Class<?>[0]);
} catch (NoSuchMethodException e2) {
// ignore, there is no need any log here since some class implement the interface: EnvironmentAware,
// ApplicationAware, etc. They only have setter method, otherwise will cause the error log during application start up.
}
}
if (getter == null
|| !Modifier.isPublic(getter.getModifiers())
|| !type.equals(getter.getReturnType())) {
continue;
}
if ("parameters".equals(property)) {
parameters = parseParameters(element.getChildNodes(), beanDefinition, parserContext);
} else if ("methods".equals(property)) {
parseMethods(id, element.getChildNodes(), beanDefinition, parserContext);
} else if ("arguments".equals(property)) {
parseArguments(id, element.getChildNodes(), beanDefinition, parserContext);
} else {
String value = resolveAttribute(element, property, parserContext);
if (value != null) {
value = value.trim();
if (value.length() > 0) {
if ("registry".equals(property) && RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(value)) {
RegistryConfig registryConfig = new RegistryConfig();
registryConfig.setAddress(RegistryConfig.NO_AVAILABLE);
beanDefinition.getPropertyValues().addPropertyValue(beanProperty, registryConfig);
} else if ("provider".equals(property) || "registry".equals(property) || ("protocol".equals(property) && AbstractServiceConfig.class.isAssignableFrom(beanClass))) {
beanDefinition.getPropertyValues().addPropertyValue(beanProperty + "Ids", value);
} else {
Object reference;
if (isPrimitive(type)) {
if ("async".equals(property) && "false".equals(value)
|| "timeout".equals(property) && "0".equals(value)
|| "delay".equals(property) && "0".equals(value)
|| "version".equals(property) && "0.0.0".equals(value)
|| "stat".equals(property) && "-1".equals(value)
|| "reliable".equals(property) && "false".equals(value)) {
// backward compatibility for the default value in old version's xsd
value = null;
}
reference = value;
} else if (ONRETURN.equals(property) || ONTHROW.equals(property) || ONINVOKE.equals(property)) {
int index = value.lastIndexOf(".");
String ref = value.substring(0, index);
String method = value.substring(index + 1);
reference = new RuntimeBeanReference(ref);
beanDefinition.getPropertyValues().addPropertyValue(property + METHOD, method);
} else {
if ("ref".equals(property) && parserContext.getRegistry().containsBeanDefinition(value)) {
BeanDefinition refBean = parserContext.getRegistry().getBeanDefinition(value);
if (!refBean.isSingleton()) {
throw new IllegalStateException("The exported service ref " + value + " must be singleton! Please set the " + value + " bean scope to singleton, eg: <bean id=\"" + value + "\" scope=\"singleton\" ...>");
}
}
reference = new RuntimeBeanReference(value);
}
beanDefinition.getPropertyValues().addPropertyValue(beanProperty, reference);
}
}
}
}
}
}
NamedNodeMap attributes = element.getAttributes();
int len = attributes.getLength();
for (int i = 0; i < len; i++) {
Node node = attributes.item(i);
String name = node.getLocalName();
if (!props.contains(name)) {
if (parameters == null) {
parameters = new ManagedMap();
}
String value = node.getNodeValue();
parameters.put(name, new TypedStringValue(value, String.class));
}
}
if (parameters != null) {
beanDefinition.getPropertyValues().addPropertyValue("parameters", parameters);
}
return beanDefinition;
}
}
4、定义一个实现了NamespaceHandler接口或者继承Spring的NamespaceHandlerSupport的实现类DubboNamespaceHandler。在init方法中，使用registerBeanDefinitionParser方法配置标签名称和BeanDefinitionParser实现类的映射关系。
public class DubboNamespaceHandler extends NamespaceHandlerSupport implements ConfigurableSourceBeanMetadataElement {
static {
Version.checkDuplicate(DubboNamespaceHandler.class);
}
@Override
public void init() {
registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
registerBeanDefinitionParser("config-center", new DubboBeanDefinitionParser(ConfigCenterBean.class, true));
registerBeanDefinitionParser("metadata-report", new DubboBeanDefinitionParser(MetadataReportConfig.class, true));
registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
registerBeanDefinitionParser("metrics", new DubboBeanDefinitionParser(MetricsConfig.class, true));
registerBeanDefinitionParser("ssl", new DubboBeanDefinitionParser(SslConfig.class, true));
registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, true));
registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
}
......
}
5、在META-INF/spring.handlers文件中，定义以上命名空间url和该NamespaceHandler实现类的映射。
3、实现原理剖析
springboot项目在启动的核心流程refresh方法中执行一个类名为ConfigurationClassPostProcessor的BeanFactoryPostProcessor，主要是调用postProcessBeanDefinitionRegistry方法，用于通过解析配置类加载bean definition, 我们最终关注的逻辑是通过ConfigurationClassBeanDefinitionReader来处理loadBeanDefinitionsFromImportedResources，即配置文件上通过@ImportResource导入的xml配置文件中的配置信息，通过解析配置标签来转成相应的Bean对象，后续的处理与spring项目基本一致，
核心流程在DefaultNamespaceHandlerResolver.resolve方法中调用NamespaceHandler.init()方法来注册所支持的标签解析处理器BeanDefinitionParser，即DubboBeanDefinitionParser，每个标签的解析过程主要在parse方法中执行。最终，xml中所有配置标签转换为dubbo中的config配置对象。
核心的几个配置类如下图
3.1 服务端暴露服务入口
通过上图可知，这些配置类都共同继承于顶层抽象类AbstractConfig，在AbstractConfig类内部有一个使用@PostConstruct注解的方法addIntoConfigManager，将所有配置统一添加到dubbo的配置管理器ConfigManager中
@PostConstruct
public void addIntoConfigManager() {
ApplicationModel.getConfigManager().addConfig(this);
}
这个addconfig方法是线程安全的，所有配置类保存在内部的一个缓存Map中
final Map<String, Map<String, AbstractConfig>> configsCache = newMap();
此外，Dubbo内部定义了一个事件监听器DubboBootstrapApplicationListener，继承OnceApplicationContextEventListener，在ApplicationContext执行refresh的最后阶段finishRefresh方法中会调用publishEvent来通知事件监听器，我们看下DubboBootstrapApplicationListener的源码
public class DubboBootstrapApplicationListener extends OnceApplicationContextEventListener implements Ordered {
//...省略...
@Override
public void onApplicationContextEvent(ApplicationContextEvent event) {
if (DubboBootstrapStartStopListenerSpringAdapter.applicationContext == null) {
DubboBootstrapStartStopListenerSpringAdapter.applicationContext = event.getApplicationContext();
}
if (event instanceof ContextRefreshedEvent) {
onContextRefreshedEvent((ContextRefreshedEvent) event);
} else if (event instanceof ContextClosedEvent) {
onContextClosedEvent((ContextClosedEvent) event);
}
}
private void onContextRefreshedEvent(ContextRefreshedEvent event) {
dubboBootstrap.start();
}
//...省略...
}
DubboBootstrapApplicationListener接收到spring容器的事件通知后会调用 dubboBootstrap.start()，至此进入dubbo的世界。
我们看下dubboBootstrap的start方式做了什么
public DubboBootstrap start() {
if (started.compareAndSet(false, true)) {
destroyed.set(false);
ready.set(false);
//一系列初始化
initialize();
if (logger.isInfoEnabled()) {
logger.info(NAME + " is starting...");
}
// 1. 导出provider服务
exportServices();
// Not only provider register
if (!isOnlyRegisterProvider() || hasExportedServices()) {
// 2. export MetadataService
exportMetadataService();
//3. Register the local ServiceInstance if required
registerServiceInstance();
}
referServices();
if (asyncExportingFutures.size() > 0) {
new Thread(() -> {
try {
this.awaitFinish();
} catch (Exception e) {
logger.warn(NAME + " exportAsync occurred an exception.");
}
ready.set(true);
if (logger.isInfoEnabled()) {
logger.info(NAME + " is ready.");
}
ExtensionLoader<DubboBootstrapStartStopListener> exts = getExtensionLoader(DubboBootstrapStartStopListener.class);
exts.getSupportedExtensionInstances().forEach(ext -> ext.onStart(this));
}).start();
} else {
ready.set(true);
if (logger.isInfoEnabled()) {
logger.info(NAME + " is ready.");
}
ExtensionLoader<DubboBootstrapStartStopListener> exts = getExtensionLoader(DubboBootstrapStartStopListener.class);
exts.getSupportedExtensionInstances().forEach(ext -> ext.onStart(this));
}
if (logger.isInfoEnabled()) {
logger.info(NAME + " has started.");
}
}
return this;
}
我们想探寻Dubbo是如何将服务端的服务导出供客户端调用的话，重点看上面的exportServices方法，这里是服务导出的入口。
主要过程是先在配置中心中获取所有的ServiceBean配置类，然后遍历每个serviceBean，通过其父类ServiceConfig的export方法来进行真正的服务暴露流程，这个后面单独拿出一篇来讲。
private void exportServices() {
configManager.getServices().forEach(sc -> {
// TODO, compatible with ServiceConfig.export()
ServiceConfig serviceConfig = (ServiceConfig) sc;
serviceConfig.setBootstrap(this);
if (exportAsync) {
ExecutorService executor = executorRepository.getServiceExporterExecutor();
Future<?> future = executor.submit(() -> {
try {
exportService(serviceConfig);
} catch (Throwable t) {
logger.error("export async catch error : " + t.getMessage(), t);
}
});
asyncExportingFutures.add(future);
} else {
exportService(serviceConfig);
}
});
}
3.2 消费端引用服务入口
服务消费端的引用过程与服务提供者的暴露过程有点区别，由于在消费端是对服务端的Service的引用reference，不是真实的service bean，故获取这个reference时，其实是获取了一个到服务端Service的proxy。故通过spring容器获取这个Service的bean时，需要返回一个proxy。
为了之后客户端调用的性能考虑，在spring启动时，dubbo提前初始化好refer代理，之后spring容器获取该bean，而不是等到调用时再初始化生成refer代理。
消费端通过ReferenceBean来开启整个引用的过程，看下类的定义：
public class ReferenceBean<T> extends ReferenceConfig<T> implements FactoryBean,
ApplicationContextAware, InitializingBean, DisposableBean {
}
RefrenceBean实现了FactoryBean说明他是一个工厂Bean，在spring容器中获取Bean实例时得到的并不是ReferenceBean的自身实例，而是getObject方法返回的对象。
此外，它还是实现了InitializingBean接口，在bean的所有属性都设好值后，调用afterPropertiesSet方法来执行自定义bean的实例化过程。
真正的过程在其父类ReferenceConfig中的get方法中执行，具体过程后面再细说。
public void afterPropertiesSet() throws Exception {
// Initializes Dubbo's Config Beans before @Reference bean autowiring
prepareDubboConfigBeans();
// lazy init by default.
if (init == null) {
init = false;
}
// eager init if necessary.
if (shouldInit()) {
getObject();
}
}
@Override
public Object getObject() {
return get();
}