上一篇講到了Dubbo中不得不說的SPI機制，鏈接爲 Dubbo源碼解析 一、Dubbo的SPI機制 ，這一節將會講到Dubbo中Consumer的啓動過程。
下面以xxxxConsumer啓動的過程爲例。
我認爲Consumer的啓動主要分爲兩個方面：
1、如何根據要實現的接口注入到Spring服務中
2、如何根據實現的consumer接口、調用的方法、調用的參數值來實現代理
下面以DemoService爲例：
public interface DemoService {
String sayHello(String name);
}
對應xml文件爲：
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
xmlns="http://www.springframework.org/schema/beans"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd">
<!-- consumer's application name, used for tracing dependency relationship (not a matching criterion),
don't set it same as provider -->
<dubbo:application name="demo-consumer"/>
<!-- use multicast registry center to discover service -->
<!--<dubbo:registry address="multicast://224.5.6.7:1234"/>-->
<dubbo:registry group="providertest" protocol="zookeeper" address="127.0.0.1:2181" />
<!-- generate proxy for the remote service, then demoService can be used in the same way as the
local regular interface -->
<dubbo:reference id="demoService" check="false" interface="com.alibaba.dubbo.demo.DemoService"/>
</beans>
在xml中，我們主要看 <dubbo:reference> 這個節點的實現，我們第一步關注的即爲如何生成demoService的代理對象，有了這個代理對象，我們就可以像使用本地實現一樣，使用demoService。
我們之前解析過Spring啓動代碼，知道Spring啓動時會先獲取到bean的定義，之後在根據bean的定義去生成bean。鏈接爲 Spring 源碼剖析 二、主要邏輯代碼賞析之獲取bean的定義。dubbo也不例外，<dubbo:reference>肯定會生成對應的一個對應的beanDefinition，我們看一下其源碼：
public class DubboNamespaceHandler extends NamespaceHandlerSupport {
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("monitor", new DubboBeanDefinitionParser(MonitorConfig.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, false));
registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
}
}
可以看到reference對應的節點解析類型爲 DubboBeanDefinitionParser ，且傳入了ReferenceBean這個class，DubboBeanDefinitionParser我們都知道是用來解析xml節點並獲取到beanDefinition的，那ReferenceBean呢？我們看一下DubboBeanDefinitionParser解析的源碼：
public class DubboBeanDefinitionParser implements BeanDefinitionParser {
private static final Logger logger = LoggerFactory.getLogger(DubboBeanDefinitionParser.class);
private static final Pattern GROUP_AND_VERION = Pattern.compile("^[\\-.0-9_a-zA-Z]+(\\:[\\-.0-9_a-zA-Z]+)?$");
private final Class<?> beanClass;
private final boolean required;
public DubboBeanDefinitionParser(Class<?> beanClass, boolean required) {
this.beanClass = beanClass;
this.required = required;
}
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
return parse(element, parserContext, beanClass, required);
}
@SuppressWarnings("unchecked")
private static BeanDefinition parse(Element element, ParserContext parserContext, Class<?> beanClass, boolean required) {
RootBeanDefinition beanDefinition = new RootBeanDefinition();
// beanDefinition對應的beanClass則爲初始化DubboBeanDefinitionParser傳入的beanClass
beanDefinition.setBeanClass(beanClass);
beanDefinition.setLazyInit(false);
// 獲取到beanDefinition的id
String id = element.getAttribute("id");
if ((id == null || id.length() == 0) && required) {
String generatedBeanName = element.getAttribute("name");
if (generatedBeanName == null || generatedBeanName.length() == 0) {
if (ProtocolConfig.class.equals(beanClass)) {
generatedBeanName = "dubbo";
} else {
generatedBeanName = element.getAttribute("interface");
}
}
if (generatedBeanName == null || generatedBeanName.length() == 0) {
generatedBeanName = beanClass.getName();
}
id = generatedBeanName;
int counter = 2;
while (parserContext.getRegistry().containsBeanDefinition(id)) {
id = generatedBeanName + (counter++);
}
}
. . .
// 將節點中內容設置到類的setter方法中，來完成屬性的注入
Set<String> props = new HashSet<String>();
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 property = StringUtils.camelToSplitName(name.substring(3, 4).toLowerCase() + name.substring(4), "-");
props.add(property);
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) {
}
}
if (getter == null
|| !Modifier.isPublic(getter.getModifiers())
|| !type.equals(getter.getReturnType())) {
continue;
}
if ("parameters".equals(property)) {
parameters = parseParameters(element.getChildNodes(), beanDefinition);
} 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 = element.getAttribute(property);
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(property, registryConfig);
} else if ("registry".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("registries", value, beanDefinition, parserContext);
} else if ("provider".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("providers", value, beanDefinition, parserContext);
} else if ("protocol".equals(property) && value.indexOf(',') != -1) {
parseMultiRef("protocols", value, beanDefinition, parserContext);
} 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 ("protocol".equals(property)
&& ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(value)
&& (!parserContext.getRegistry().containsBeanDefinition(value)
|| !ProtocolConfig.class.getName().equals(parserContext.getRegistry().getBeanDefinition(value).getBeanClassName()))) {
if ("dubbo:provider".equals(element.getTagName())) {
logger.warn("Recommended replace <dubbo:provider protocol=\"" + value + "\" ... /> to <dubbo:protocol name=\"" + value + "\" ... />");
}
// backward compatibility
ProtocolConfig protocol = new ProtocolConfig();
protocol.setName(value);
reference = protocol;
} else if ("onreturn".equals(property)) {
int index = value.lastIndexOf(".");
String returnRef = value.substring(0, index);
String returnMethod = value.substring(index + 1);
reference = new RuntimeBeanReference(returnRef);
beanDefinition.getPropertyValues().addPropertyValue("onreturnMethod", returnMethod);
} else if ("onthrow".equals(property)) {
int index = value.lastIndexOf(".");
String throwRef = value.substring(0, index);
String throwMethod = value.substring(index + 1);
reference = new RuntimeBeanReference(throwRef);
beanDefinition.getPropertyValues().addPropertyValue("onthrowMethod", throwMethod);
} else if ("oninvoke".equals(property)) {
int index = value.lastIndexOf(".");
String invokeRef = value.substring(0, index);
String invokeRefMethod = value.substring(index + 1);
reference = new RuntimeBeanReference(invokeRef);
beanDefinition.getPropertyValues().addPropertyValue("oninvokeMethod", invokeRefMethod);
}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(property, reference);
}
}
}
}
}
}
. . .
return beanDefinition;
}
}
可以看到最後是解析成了一個beanClass爲ReferenceBean的beanDefinition，所以最後生成的一定是ReferenceBean這個類，我們看一下ReferenceBean的源碼：
// ReferenceBean 繼承自FactoryBean，這樣，當getObjectType()方法爲代理接口Class時，Spring就會調用其getObject()獲取到代理接口的實現對象，這樣就完成了對Spring中代理接口的注入
public class ReferenceBean<T> extends ReferenceConfig<T> implements FactoryBean, ApplicationContextAware, InitializingBean, DisposableBean {
. . .
@Override
public Object getObject() throws Exception {
return get();
}
public synchronized T get() {
if (destroyed) {
throw new IllegalStateException("Already destroyed!");
}
if (ref == null) {
init();
}
return ref;
}
@Override
public Class<?> getObjectType() {
return getInterfaceClass();
}
@Override
@Parameter(excluded = true)
public boolean isSingleton() {
return true;
}
. . .
}
知道如何注入對象後，我們來看一下如何生成這個對象的代理，即 init() 方法：
private void init() {
if (initialized) {
return;
}
. . .
// 得到dubbo中的各個組件，比將其組合到map中
checkApplication();
checkStubAndMock(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.getVersion());
map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
. . .
map.put(Constants.INTERFACE_KEY, interfaceName);
appendParameters(map, application);
appendParameters(map, module);
appendParameters(map, consumer, Constants.DEFAULT_KEY);
appendParameters(map, this);
// 最後使用組成的map數據來生成代理對象
ref = createProxy(map);
ConsumerModel consumerModel = new ConsumerModel(getUniqueServiceName(), this, ref, interfaceClass.getMethods());
ApplicationModel.initConsumerModel(getUniqueServiceName(), consumerModel);
}
@SuppressWarnings({"unchecked", "rawtypes", "deprecation"})
private T createProxy(Map<String, String> map) {
. . .
// 加載註冊中心，每個註冊中心都得到一個URL
List<URL> us = loadRegistries(false);
if (us != null && !us.isEmpty()) {
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.isEmpty()) {
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) {
// 如果只有一個註冊中心，調用refprotocol.refer(interfaceClass, url)來得到最終執行的invoker，即MergeableClusterInvoker
invoker = refprotocol.refer(interfaceClass, urls.get(0));
} else {
. . .
}
}
// invoker可以執行invocation，但是Spring中要求獲取到的是接口的實現對象，所以要使用動態代理（可以參考jdk的java.lang.reflect.Proxy），並實現其InvocationHandler接口
// proxyFactory.getProxy的作用就是根據invoker生成最終的動態代理對象，當InvocationHandler方法被調用時，生成invocation供invoker來調用
return (T) proxyFactory.getProxy(invoker);
}