com.alibaba.dubbo.demo.provider.DemoProvider#main
com.alibaba.dubbo.container.Main.main(args);
com.alibaba.dubbo.container.Main#main
//初始化com.alibaba.dubbo.container.Main#loader静态变量
private static final ExtensionLoader<Container> loader = ExtensionLoader.getExtensionLoader(Container.class);
com.alibaba.dubbo.common.extension.ExtensionLoader#getExtensionLoader
//获取ExtensionLoader并缓存到com.alibaba.dubbo.common.extension.ExtensionLoader#EXTENSION_LOADERS
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
//ExtensionLoader包含两个属性
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
//关于objectFactory的细节：它就是为dubbo的IOC提供所有对象。
到这里获取到了
Container.class类型的ExtensionLoader（包含一个不为空的objectFactory）
ExtensionFactory.class类型的ExtensionLoader
并缓存到了类变量EXTENSION_LOADERS中
@Adaptive注解
注解在类上：代表人工实现编码，即实现一个装饰类（装饰模式），如：ExtensionFactory
注解在方法上：代表自动生成和编译一个动态的adaptive类，如：Protocol$Adaptive
@Adaptive注解在方法上(以Protocol为例)
com.alibaba.dubbo.config.spring.ServiceBean
com.alibaba.dubbo.config.ServiceConfig
//初始化类变量
private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
com.alibaba.dubbo.common.extension.ExtensionLoader#getAdaptiveExtension
//创建并缓存到成员变量cachedAdaptiveInstance中
instance = createAdaptiveExtension();
cachedAdaptiveInstance.set(instance);
com.alibaba.dubbo.common.extension.ExtensionLoader#getAdaptiveExtensionClass
com.alibaba.dubbo.common.extension.ExtensionLoader#getExtensionClasses
classes = loadExtensionClasses();
cachedClasses.set(classes);
com.alibaba.dubbo.common.extension.ExtensionLoader#loadExtensionClasses
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
//这个loadFile方法很复杂
//DUBBO_INTERNAL_DIRECTORY = META-INF\dubbo\internal
//DUBBO_DIRECTORY = META-INF/dubbo/
//SERVICES_DIRECTORY = META-INF/services/
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
loadFile(extensionClasses, DUBBO_DIRECTORY);
loadFile(extensionClasses, SERVICES_DIRECTORY);
com.alibaba.dubbo.common.extension.ExtensionLoader#loadFile
//fileName = META-INF\dubbo\internal\com.alibaba.dubbo.rpc.Protocol这个文件下有很多相关的实现类
String fileName = dir + type.getName();
image.png
关于loadFile的细节：
目的：通过把配置文件META-INF\dubbo\internal\com.alibaba.dubbo.rpc.Protocol的内容，储存在缓存变量里面
cachedAdaptiveClass:如果这个class含有adaptive注解就赋值，例如ExtensionFatory，而例如Protocol在这个环节是没有的。
cachedWrapperClasses：只有当该class没有adaptive注解，并且该class目标函数包含目标接口（type）类型，例如protocol里的spi就只有ProtocolFilterWrapper和ProtocolListenerWrapper能命中。
image.png
cachedActivates：class包含Activate注解
cachedNames：返回该实现类与对应的前缀命名。
image.png
最后的extensionClasses值为：
image.png
因为是已Protocol这个类为例，这个类没有@Adaptive注解标注，所以成员变量cachedAdaptiveClass在这里肯定是为null的，即通过下面方法createAdaptiveExtensionClass去动态生成一个动态类Protocol$Adaptive。
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
动态生成的代码：
package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adpative 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);
}
}
最后回到com.alibaba.dubbo.common.extension.ExtensionLoader#injectExtension ，这个方法的作用，IOC控制反转，实现动态注入。
image.png
最后：
com.alibaba.dubbo.common.extension.ExtensionLoader#getExtensionLoader 通过这个方法得到了对应实现类的具体对象Protocol$Adaptive,而生成此对象的ExtensionLoader的各个成员变量的值对应如下：
image.png
image.png
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