通观全部Dubbo代码，有两个很重要的对象就是Invoker和Exporter，Dubbo会根据用户配置的协议调用不同协议的Invoker，再通过ReferenceFonfig将Invoker的引用关联到Reference的ref属性上提供给消费端调用。当用户调用一个Service接口的一个方法后由于Dubbo使用javassist动态代理，会调用Invoker的Invoke方法从而初始化一个RPC调用访问请求访问服务端的Service返回结果。下面我们就从Comsumer端开始逐步解析这个框架。
Dubbo首先使用com.alibaba.dubbo.config.spring.schema.NamespaceHandler注册解析器，当spring解析xml配置文件时就会调用这些解析器生成对应的BeanDefinition交给spring管理：
public class DubboNamespaceHandler extends NamespaceHandlerSupport {
static {
Version.checkDuplicate(DubboNamespaceHandler.class);
}
public void init() {
//配置<dubbo:application>标签解析器
registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
//配置<dubbo:module>标签解析器
registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
//配置<dubbo:registry>标签解析器
registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
//配置<dubbo:monitor>标签解析器
registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
//配置<dubbo:provider>标签解析器
registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
//配置<dubbo:consumer>标签解析器
registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
//配置<dubbo:protocol>标签解析器
registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
//配置<dubbo:service>标签解析器
registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
//配置<dubbo:refenrence>标签解析器
registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
//配置<dubbo:annotation>标签解析器
registerBeanDefinitionParser("annotation", new DubboBeanDefinitionParser(AnnotationBean.class, true));
}
}
Spring在初始化IOC容器时会利用这里注册的BeanDefinitionParser的parse方法获取对应的ReferenceBean的BeanDefinition实例，由于ReferenceBean实现了InitializingBean接口，在设置了bean的所有属性后会调用afterPropertiesSet方法：
public void afterPropertiesSet() throws Exception {
//如果Consumer还未注册
if (getConsumer() == null) {
//获取applicationContext这个IOC容器实例中的所有ConsumerConfig
Map<String, ConsumerConfig> consumerConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ConsumerConfig.class, false, false);
//如果IOC容器中存在这样的ConsumerConfig
if (consumerConfigMap != null && consumerConfigMap.size() > 0) {
ConsumerConfig consumerConfig = null;
//遍历这些ConsumerConfig
for (ConsumerConfig config : consumerConfigMap.values()) {
//如果用户没配置Consumer系统会生成一个默认Consumer，且它的isDefault返回ture
//这里是说要么是Consumer是默认的要么是用户配置的Consumer并且没设置isDefault属性
if (config.isDefault() == null || config.isDefault().booleanValue()) {
//防止存在两个默认Consumer
if (consumerConfig != null) {
throw new IllegalStateException("Duplicate consumer configs: " + consumerConfig + " and " + config);
}
//获取默认Consumer
consumerConfig = config;
}
}
if (consumerConfig != null) {
//设置默认Consumer
setConsumer(consumerConfig);
}
}
}
//如果reference未绑定application且（reference未绑定consumer或referenc绑定的consumer没绑定application
if (getApplication() == null
&& (getConsumer() == null || getConsumer().getApplication() == null)) {
//获取IOC中所有application的实例
Map<String, ApplicationConfig> applicationConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ApplicationConfig.class, false, false);
if (applicationConfigMap != null && applicationConfigMap.size() > 0) {
//如果IOC中存在application
ApplicationConfig applicationConfig = null;
//遍历这些application
for (ApplicationConfig config : applicationConfigMap.values()) {
//如果application是默认创建或者被指定成默认
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (applicationConfig != null) {
throw new IllegalStateException("Duplicate application configs: " + applicationConfig + " and " + config);
}
//获取application
applicationConfig = config;
}
}
if (applicationConfig != null) {
//关联到reference
setApplication(applicationConfig);
}
}
}
//如果reference未绑定module且（reference未绑定consumer或referenc绑定的consumer没绑定module
if (getModule() == null
&& (getConsumer() == null || getConsumer().getModule() == null)) {
//获取IOC中所有module的实例
Map<String, ModuleConfig> moduleConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ModuleConfig.class, false, false);
if (moduleConfigMap != null && moduleConfigMap.size() > 0) {
ModuleConfig moduleConfig = null;
//遍历这些module
for (ModuleConfig config : moduleConfigMap.values()) {
//如果module是默认创建或者被指定成默认
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (moduleConfig != null) {
throw new IllegalStateException("Duplicate module configs: " + moduleConfig + " and " + config);
}
//获取module
moduleConfig = config;
}
}
if (moduleConfig != null) {
//关联到reference
setModule(moduleConfig);
}
}
}
//如果reference未绑定注册中心（Register）且（reference未绑定consumer或referenc绑定的consumer没绑定注册中心（Register）
if ((getRegistries() == null || getRegistries().size() == 0)
&& (getConsumer() == null || getConsumer().getRegistries() == null || getConsumer().getRegistries().size() == 0)
&& (getApplication() == null || getApplication().getRegistries() == null || getApplication().getRegistries().size() == 0)) {
//获取IOC中所有的注册中心（Register）实例
Map<String, RegistryConfig> registryConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, RegistryConfig.class, false, false);
if (registryConfigMap != null && registryConfigMap.size() > 0) {
List<RegistryConfig> registryConfigs = new ArrayList<RegistryConfig>();
//遍历这些registry
for (RegistryConfig config : registryConfigMap.values()) {
//如果registry是默认创建或者被指定成默认
if (config.isDefault() == null || config.isDefault().booleanValue()) {
registryConfigs.add(config);
}
}
if (registryConfigs != null && registryConfigs.size() > 0) {
//关联到reference，此处可以看出一个consumer可以绑定多个registry（注册中心）
super.setRegistries(registryConfigs);
}
}
}
//如果reference未绑定监控中心（Monitor）且（reference未绑定consumer或reference绑定的consumer没绑定监控中心（Monitor）
if (getMonitor() == null
&& (getConsumer() == null || getConsumer().getMonitor() == null)
&& (getApplication() == null || getApplication().getMonitor() == null)) {
//获取IOC中所有的监控中心（Monitor）实例
Map<String, MonitorConfig> monitorConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, MonitorConfig.class, false, false);
if (monitorConfigMap != null && monitorConfigMap.size() > 0) {
MonitorConfig monitorConfig = null;
//遍历这些监控中心（Monitor）
for (MonitorConfig config : monitorConfigMap.values()) {
//如果monitor是默认创建或者被指定成默认
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (monitorConfig != null) {
throw new IllegalStateException("Duplicate monitor configs: " + monitorConfig + " and " + config);
}
monitorConfig = config;
}
}
if (monitorConfig != null) {
//关联到reference,一个consumer绑定到一个监控中心（monitor）
setMonitor(monitorConfig);
}
}
}
Boolean b = isInit();
if (b == null && getConsumer() != null) {
b = getConsumer().isInit();
}
if (b != null && b.booleanValue()) {
//如果consumer已经被关联则组装Reference
getObject();
}
}
}这步其实是Reference确认生成Invoker所需要的组件是否已经准备好，都准备好后我们进入生成Invoker的部分。这里的getObject会调用父类ReferenceConfig的init方法完成组装：
private void init() {
//避免重复初始化
if (initialized) {
return;
}
//置为已经初始化
initialized = true;
//如果interfaceName不存在
if (interfaceName == null || interfaceName.length() == 0) {
throw new IllegalStateException("<dubbo:reference interface=\"\" /> interface not allow null!");
}
// 获取消费者
checkDefault();
appendProperties(this);
//如果未使用泛接口并且consumer已经准备好的情况下，reference使用和consumer一样的泛接口
if (getGeneric() == null && getConsumer() != null) {
setGeneric(getConsumer().getGeneric());
}
//如果是泛接口那么interface的类型是GenericService
if (ProtocolUtils.isGeneric(getGeneric())) {
interfaceClass = GenericService.class;
} else {
//如果不是泛接口使用interfaceName指定的泛接口
try {
interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
.getContextClassLoader());
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e.getMessage(), e);
}
//检查接口以及接口中的方法都是否配置齐全
checkInterfaceAndMethods(interfaceClass, methods);
}
//如果服务比较多可以指定dubbo-resolve.properties文件配置service（service集中配置文件）
String resolve = System.getProperty(interfaceName);
String resolveFile = null;
if (resolve == null || resolve.length() == 0) {
resolveFile = System.getProperty("dubbo.resolve.file");
if (resolveFile == null || resolveFile.length() == 0) {
File userResolveFile = new File(new File(System.getProperty("user.home")), "dubbo-resolve.properties");
if (userResolveFile.exists()) {
resolveFile = userResolveFile.getAbsolutePath();
}
}
if (resolveFile != null && resolveFile.length() > 0) {
Properties properties = new Properties();
FileInputStream fis = null;
try {
fis = new FileInputStream(new File(resolveFile));
properties.load(fis);
} catch (IOException e) {
throw new IllegalStateException("Unload " + resolveFile + ", cause: " + e.getMessage(), e);
} finally {
try {
if(null != fis) fis.close();
} catch (IOException e) {
logger.warn(e.getMessage(), e);
}
}
resolve = properties.getProperty(interfaceName);
}
}
if (resolve != null && resolve.length() > 0) {
url = resolve;
if (logger.isWarnEnabled()) {
if (resolveFile != null && resolveFile.length() > 0) {
logger.warn("Using default dubbo resolve file " + resolveFile + " replace " + interfaceName + "" + resolve + " to p2p invoke remote service.");
} else {
logger.warn("Using -D" + interfaceName + "=" + resolve + " to p2p invoke remote service.");
}
}
}
//如果application、module、registries、monitor未配置则使用consumer的
if (consumer != null) {
if (application == null) {
application = consumer.getApplication();
}
if (module == null) {
module = consumer.getModule();
}
if (registries == null) {
registries = consumer.getRegistries();
}
if (monitor == null) {
monitor = consumer.getMonitor();
}
}
//如果module已关联则关联module的registries和monitor
if (module != null) {
if (registries == null) {
registries = module.getRegistries();
}
if (monitor == null) {
monitor = module.getMonitor();
}
}
//如果application已关联则关联application的registries和monitor
if (application != null) {
if (registries == null) {
registries = application.getRegistries();
}
if (monitor == null) {
monitor = application.getMonitor();
}
}
//检查application
checkApplication();
//检查远端和本地服务接口真实存在（是否可load）
checkStubAndMock(interfaceClass);
Map<String, String> map = new HashMap<String, String>();
//配置dubbo的端属性（是consumer还是provider）、版本属性、创建时间、进程号
Map<Object, Object> attributes = new HashMap<Object, Object>();
map.put(Constants.SIDE_KEY, Constants.CONSUMER_SIDE);
map.put(Constants.DUBBO_VERSION_KEY, Version.getVersion());
map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
if (ConfigUtils.getPid() > 0) {
map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));
}
if (! isGeneric()) {
String revision = Version.getVersion(interfaceClass, version);
if (revision != null && revision.length() > 0) {
map.put("revision", revision);
}
String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
if(methods.length == 0) {
logger.warn("NO method found in service interface " + interfaceClass.getName());
map.put("methods", Constants.ANY_VALUE);
}
else {
map.put("methods", StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));
}
}
map.put(Constants.INTERFACE_KEY, interfaceName);
//调用application、module、consumer的get方法将属性设置到map中
appendParameters(map, application);
appendParameters(map, module);
appendParameters(map, consumer, Constants.DEFAULT_KEY);
appendParameters(map, this);
String prifix = StringUtils.getServiceKey(map);
if (methods != null && methods.size() > 0) {
for (MethodConfig method : methods) {
appendParameters(map, method, method.getName());
String retryKey = method.getName() + ".retry";
if (map.containsKey(retryKey)) {
String retryValue = map.remove(retryKey);
if ("false".equals(retryValue)) {
map.put(method.getName() + ".retries", "0");
}
}
appendAttributes(attributes, method, prifix + "." + method.getName());
checkAndConvertImplicitConfig(method, map, attributes);
}
}
//attributes通过系统context进行存储.
StaticContext.getSystemContext().putAll(attributes);
//在map装载了application、module、consumer、reference的所有属性信息后创建代理
ref = createProxy(map);
}
private T createProxy(Map<String, String> map) {
URL tmpUrl = new URL("temp", "localhost", 0, map);
final boolean isJvmRefer;
if (isInjvm() == null) {
if (url != null && url.length() > 0) { //指定URL的情况下，不做本地引用
isJvmRefer = false;
} else if (InjvmProtocol.getInjvmProtocol().isInjvmRefer(tmpUrl)) {
//默认情况下如果本地有服务暴露，则引用本地服务.
isJvmRefer = true;
} else {
isJvmRefer = false;
}
} else {
isJvmRefer = isInjvm().booleanValue();
}
if (isJvmRefer) {
URL url = new URL(Constants.LOCAL_PROTOCOL, NetUtils.LOCALHOST, 0, interfaceClass.getName()).addParameters(map);
invoker = refprotocol.refer(interfaceClass, url);
if (logger.isInfoEnabled()) {
logger.info("Using injvm service " + interfaceClass.getName());
}
} else {
if (url != null && url.length() > 0) { // 用户指定URL，指定的URL可能是对点对直连地址，也可能是注册中心URL
String[] us = Constants.SEMICOLON_SPLIT_PATTERN.split(url);
if (us != null && us.length > 0) {
for (String u : us) {
URL url = URL.valueOf(u);
if (url.getPath() == null || url.getPath().length() == 0) {
url = url.setPath(interfaceName);
}
if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
urls.add(url.addParameterAndEncoded(Constants.REFER_KEY, StringUtils.toQueryString(map)));
} else {
urls.add(ClusterUtils.mergeUrl(url, map));
}
}
}
} else { // 通过注册中心配置拼装URL
List<URL> us = loadRegistries(false);
if (us != null && us.size() > 0) {
for (URL u : us) {
URL monitorUrl = loadMonitor(u);
if (monitorUrl != null) {
map.put(Constants.MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
}
urls.add(u.addParameterAndEncoded(Constants.REFER_KEY, StringUtils.toQueryString(map)));
}
}
if (urls == null || urls.size() == 0) {
throw new IllegalStateException("No such any registry to reference " + interfaceName + " on the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", please config <dubbo:registry address=\"...\" /> to your spring config.");
}
}
if (urls.size() == 1) {
//此处举例说明如果是Dubbo协议则调用DubboProtocol的refer方法生成invoker，当用户调用service接口实际调用的是invoker的invoke方法
invoker = refprotocol.refer(interfaceClass, urls.get(0));
} else {
//多个service生成多个invoker
List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();
URL registryURL = null;
for (URL url : urls) {
invokers.add(refprotocol.refer(interfaceClass, url));
if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
registryURL = url; // 用了最后一个registry url
}
}
if (registryURL != null) { // 有 注册中心协议的URL
// 对有注册中心的Cluster 只用 AvailableCluster
URL u = registryURL.addParameter(Constants.CLUSTER_KEY, AvailableCluster.NAME);
invoker = cluster.join(new StaticDirectory(u, invokers));
} else { // 不是 注册中心的URL
invoker = cluster.join(new StaticDirectory(invokers));
}
}
}
Boolean c = check;
if (c == null && consumer != null) {
c = consumer.isCheck();
}
if (c == null) {
c = true; // default true
}
if (c && ! invoker.isAvailable()) {
throw new IllegalStateException("Failed to check the status of the service " + interfaceName + ". No provider available for the service " + (group == null ? "" : group + "/") + interfaceName + (version == null ? "" : ":" + version) + " from the url " + invoker.getUrl() + " to the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion());
}
if (logger.isInfoEnabled()) {
logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
}
// 创建服务代理
return (T) proxyFactory.getProxy(invoker);
}
至此Reference在关联了所有application、module、consumer、registry、monitor、service、protocol后调用对应Protocol类的refer方法生成InvokerProxy。当用户调用service时dubbo会通过InvokerProxy调用Invoker的invoke的方法向服务端发起请求。客户端就这样完成了自己的初始化。
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