在dubbo里面比较复杂的是dubbo服务的refer过程。对dubbo service服务的引用都封装在ReferenceBean的实现里面。其继承关系如下
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可以看到ReferenceBean实现了FactoryBean，所以会调用其 getObject()方法，如下
Class ReferenceBean
public Object getObject() throws Exception {
return get();
}
其实现在父类ReferenceConfig里面
Class ReferenceConfig
public synchronized T get() {
if (destroyed) {
throw new IllegalStateException("Already destroyed!");
}
if (ref == null) {
init();
}
return ref;
}
看源码，其实就是如何init ref的过程
Class ReferenceConfig
private void init() {
//如果已经initialized，直接的return
if (initialized) {
return;
}
initialized = true;
//实现的interfaceName不能为空
if (interfaceName == null || interfaceName.length() == 0) {
throw new IllegalStateException("<dubbo:reference interface=\"\" /> interface not allow null!");
}
// get consumer's global configuration
//根据系统配置，给ConsumerConfig设置相关的值（如果有配置）
checkDefault();
// //根据系统配置，给ReferenceConfig设置相关的值（如果有配置）
appendProperties(this);
//设置是否是泛化调用（一般在搭建通用框架的时候使用）
if (getGeneric() == null && getConsumer() != null) {
setGeneric(getConsumer().getGeneric());
}
if (ProtocolUtils.isGeneric(getGeneric())) {
interfaceClass = GenericService.class;
} else {
try {
//加载interfaceClass 的Class
interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
.getContextClassLoader());
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e.getMessage(), e);
}
//检查interfaceClass和其方法是否合法
checkInterfaceAndMethods(interfaceClass, methods);
}
//检查是否有用户的自定义的配置，主要是可以配置直连的url
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) {
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.");
}
}
}
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();
}
}
if (module != null) {
if (registries == null) {
registries = module.getRegistries();
}
if (monitor == null) {
monitor = module.getMonitor();
}
}
if (application != null) {
if (registries == null) {
registries = application.getRegistries();
}
if (monitor == null) {
monitor = application.getMonitor();
}
}
checkApplication();
checkStub(interfaceClass);
checkMock(interfaceClass);
Map<String, String> map = new HashMap<String, String>();
Map<Object, Object> attributes = new HashMap<Object, Object>();
map.put(Constants.SIDE_KEY, Constants.CONSUMER_SIDE);
map.put(Constants.DUBBO_VERSION_KEY, Version.getProtocolVersion());
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);
appendParameters(map, application);
appendParameters(map, module);
appendParameters(map, consumer, Constants.DEFAULT_KEY);
appendParameters(map, this);
String prefix = StringUtils.getServiceKey(map);
if (methods != null && !methods.isEmpty()) {
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, prefix + "." + method.getName());
checkAndConvertImplicitConfig(method, map, attributes);
}
}
String hostToRegistry = ConfigUtils.getSystemProperty(Constants.DUBBO_IP_TO_REGISTRY);
if (hostToRegistry == null || hostToRegistry.length() == 0) {
hostToRegistry = NetUtils.getLocalHost();
} else if (isInvalidLocalHost(hostToRegistry)) {
throw new IllegalArgumentException("Specified invalid registry ip from property:" + Constants.DUBBO_IP_TO_REGISTRY + ", value:" + hostToRegistry);
}
map.put(Constants.REGISTER_IP_KEY, hostToRegistry);
//attributes are stored by system context.
StaticContext.getSystemContext().putAll(attributes);
//最重要的是这句，通过收集的一系列的信息到map里面，然后根据map来生成我们的代理对象
ref = createProxy(map);
ConsumerModel consumerModel = new ConsumerModel(getUniqueServiceName(), this, ref, interfaceClass.getMethods());
ApplicationModel.initConsumerModel(getUniqueServiceName(), consumerModel);
}
如上可以看出，在调用 ref = createProxy(map);
之前，就是一些列的校验和收集map信息，然后根据map的信息，来生成代理对象，我们接下来看最重要的createProxy(map);方法
private T createProxy(Map<String, String> map) {
//***
//上面的代码主要是判断是否是jvm引用，或者是用户是否有自定义url
else { // assemble URL from register center's configuration
List<URL> us = loadRegistries(false);
//如果是单注册中心，这是我们常用的
if (urls.size() == 1) {
invoker = refprotocol.refer(interfaceClass, urls.get(0));
//如果是多注册中心
} else {
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; // use last registry url
}
}
if (registryURL != null) { // registry url is available
// use AvailableCluster only when register's cluster is available
URL u = registryURL.addParameterIfAbsent(Constants.CLUSTER_KEY, AvailableCluster.NAME);
invoker = cluster.join(new StaticDirectory(u, invokers));
} else { // not a registry url
invoker = cluster.join(new StaticDirectory(invokers));
}
}
}
// create service proxy
return (T) proxyFactory.getProxy(invoker);
}
由上可以看到就是如何初始化ReferenceBean里面的invoker对象，然后根据invoke对象生成代理对象。其实核心的就两句
invoker = refprotocol.refer(interfaceClass, urls.get(0));
return (T) proxyFactory.getProxy(invoker);
由于refprotocol是通过动态生成java代码生成的，我们看下我本机具体生成的代码，如下
package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adaptive implements com.alibaba.dubbo.rpc.Protocol {
public void destroy() {throw new UnsupportedOperationException("method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {throw new UnsupportedOperationException("method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");com.alibaba.dubbo.common.URL url = arg0.getUrl();
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])");
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.export(arg0);
}
public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws com.alibaba.dubbo.rpc.RpcException {
if (arg1 == null) throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg1;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])");
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.refer(arg0, arg1);
}
}
由于 urls.get(0).getProtocol()返回registry，所以会调用RegistryProtocol类的refer方法。
源码如下
Class RegistryProtocol
public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
//默认是zk的地址
url = url.setProtocol(url.getParameter(Constants.REGISTRY_KEY, Constants.DEFAULT_REGISTRY)).removeParameter(Constants.REGISTRY_KEY);
//默认是ZookeeperRegistry的Wrapper类
Registry registry = registryFactory.getRegistry(url);
if (RegistryService.class.equals(type)) {
return proxyFactory.getInvoker((T) registry, type, url);
}
//是否有分组控制
// group="a,b" or group="*"
Map<String, String> qs = StringUtils.parseQueryString(url.getParameterAndDecoded(Constants.REFER_KEY));
String group = qs.get(Constants.GROUP_KEY);
if (group != null && group.length() > 0) {
if ((Constants.COMMA_SPLIT_PATTERN.split(group)).length > 1
|| "*".equals(group)) {
return doRefer(getMergeableCluster(), registry, type, url);
}
}
return doRefer(cluster, registry, type, url);
}
最终我们进入了doRefer(cluster, registry, type, url);方法，
整个refer最核心的方法如下
private <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url) {
RegistryDirectory<T> directory = new RegistryDirectory<T>(type, url);
directory.setRegistry(registry);
directory.setProtocol(protocol);
// all attributes of REFER_KEY
Map<String, String> parameters = new HashMap<String, String>(directory.getUrl().getParameters());
URL subscribeUrl = new URL(Constants.CONSUMER_PROTOCOL, parameters.remove(Constants.REGISTER_IP_KEY), 0, type.getName(), parameters);
if (!Constants.ANY_VALUE.equals(url.getServiceInterface())
&& url.getParameter(Constants.REGISTER_KEY, true)) {
URL registeredConsumerUrl = getRegisteredConsumerUrl(subscribeUrl, url);
registry.register(registeredConsumerUrl);
directory.setRegisteredConsumerUrl(registeredConsumerUrl);
}
directory.subscribe(subscribeUrl.addParameter(Constants.CATEGORY_KEY,
Constants.PROVIDERS_CATEGORY
+ "," + Constants.CONFIGURATORS_CATEGORY
+ "," + Constants.ROUTERS_CATEGORY));
Invoker invoker = cluster.join(directory);
ProviderConsumerRegTable.registerConsumer(invoker, url, subscribeUrl, directory);
return invoker;
}
如上可以看到基本都是围绕directory在操作。
第一步订阅，第二步就是通过cluster.join(directory)封装成了Invoker返回。
最后通过 return (T) proxyFactory.getProxy(invoker);生成代理直接的返回即可。
cluster.join(directory)的作用可以认为是将多个Invoke封装成一个Invoke给上层调用，屏蔽底层的细节和路由规则，由于dubbo的rpc模块较复杂，后面我们对里面的每个组件从源码的角度做一一的分析。
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