Java SPI (Service Provider Interface)
插件式架构(Plug-in architecture)
Dubbo 的插件式设计
Dubbo SPI 约定
adaptive=com.alibaba.dubbo.common.extension.factory.AdaptiveExtensionFactory
spi=com.alibaba.dubbo.common.extension.factory.SpiExtensionFactory
spring=com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory
@SPI 、@Adaptive 、@Activate 作用
@SPI (注解在类上) : @SPI 注解标识了接口是一个扩展点 , 属性 value 用来指定默认适配扩展点的名称。
@Activate (注解在类型和方法上) : @Activate 注解在扩展点的实现类上 ,表示了一个扩展类被获取到的的条件,符合条件就被获取,不符合条件就不获取 ,根据 @Activate 中的 group 、 value 属性来过滤 。具体参考 ExtensionLoader 中的 getActivateExtension 函数。
@Adaptive (注解在类型和方法上) : @Adaptive 注解在类上 , 这个类就是缺省的适配扩展。@Adaptive 注解在扩展点 Interface 的方法上时 , dubbo 动态的生成一个这个扩展点的适配扩展类(生成代码 ,动态编译实例化 Class ),名称为 扩展点 Interface 的简单类名 + $Adaptive ,例如 :ProxyFactory$Adpative 。这么做的目的是为了在运行时去适配不同的扩展实例 , 在运行时通过传入的 URL 类型的参数或者内部含有获取 URL 方法的参数 ,从 URL 中获取到要使用的扩展类的名称 ,再去根据名称加载对应的扩展实例 ,用这个扩展实例对象调用相同的方法 。如果运行时没有适配到运行的扩展实例 , 那么就使用 @SPI 注解缺省指定的扩展。通过这种方式就实现了运行时去适配到对应的扩展。运行时动态生成的适配扩展类代码 :
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.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws java.lang.Class {
if (arg1 == null) throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg1;
// 从 URL 中获取扩展名称 , "dubbo" 是从 ExtensionLoader 对象中的 cachedDefaultName
// 属性获取到的 , cachedDefaultName 是扩展点上 @SPI 注解中 value 属性指定的
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])");
// 通过扩展名称获取扩展实例对象 , 调用扩展实例对象的相同方法
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);
}
public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.Invoker {
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();
// 从 URL 中获取扩展名称
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])");
// 通过扩展名称获取扩展实例对象 , 调用扩展实例对象的相同方法
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);
}
}
package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class ProxyFactory$Adpative implements com.alibaba.dubbo.rpc.ProxyFactory {
public java.lang.Object getProxy(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.Invoker {
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();
// 从 URL 中获取扩展名称
String extName = url.getParameter("proxy", "javassist");
if (extName == null)
throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.ProxyFactory) name from url(" + url.toString() + ") use keys([proxy])");
// 通过扩展名称获取扩展实例对象 , 调用扩展实例对象的相同方法
com.alibaba.dubbo.rpc.ProxyFactory extension = (com.alibaba.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.ProxyFactory.class).getExtension(extName);
return extension.getProxy(arg0);
}
public com.alibaba.dubbo.rpc.Invoker getInvoker(java.lang.Object arg0, java.lang.Class arg1, com.alibaba.dubbo.common.URL arg2) throws java.lang.Object {
if (arg2 == null) throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg2;
// 从 URL 中获取扩展名称
String extName = url.getParameter("proxy", "javassist");
if (extName == null)
throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.ProxyFactory) name from url(" + url.toString() + ") use keys([proxy])");
// 通过扩展名称获取扩展实例对象 , 调用扩展实例对象的相同方法
com.alibaba.dubbo.rpc.ProxyFactory extension = (com.alibaba.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.ProxyFactory.class).getExtension(extName);
return extension.getInvoker(arg0, arg1, arg2);
}
}
ExtensionLoader.getExtensionLoader(Xxx.class).getExtension(extName);
扩展加载器 ExtensionLoader
Class<?> type;
ExtensionFactory objectFactory;
ConcurrentMap<Class<?>, String> cachedNames;
Holder<Map<String, Class<?>>> cachedClasses;
Map<String, Activate> cachedActivates;
Class<?> cachedAdaptiveClass;
ConcurrentMap<String, Holder<Object>> cachedInstances;
String cachedDefaultName;
Holder<Object> cachedAdaptiveInstance;
Throwable createAdaptiveInstanceError;
Set<Class<?>> cachedWrapperClasses;
Map<String, IllegalStateException> exceptions;
com.alibaba.dubbo.cache.CacheFactory
com.alibaba.dubbo.common.compiler.Compiler
com.alibaba.dubbo.common.extension.ExtensionFactory
com.alibaba.dubbo.common.logger.LoggerAdapter
com.alibaba.dubbo.common.serialize.Serialization
com.alibaba.dubbo.common.status.StatusChecker
com.alibaba.dubbo.common.store.DataStore
com.alibaba.dubbo.common.threadpool.ThreadPool
com.alibaba.dubbo.container.Container
com.alibaba.dubbo.container.page.PageHandler
com.alibaba.dubbo.monitor.MonitorFactory
com.alibaba.dubbo.registry.RegistryFactory
com.alibaba.dubbo.remoting.Codec2
com.alibaba.dubbo.remoting.Dispatcher
com.alibaba.dubbo.remoting.exchange.Exchanger
com.alibaba.dubbo.remoting.http.HttpBinder
com.alibaba.dubbo.remoting.p2p.Networker
com.alibaba.dubbo.remoting.telnet.TelnetHandler
com.alibaba.dubbo.remoting.Transporter
com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter
com.alibaba.dubbo.rpc.cluster.Cluster
com.alibaba.dubbo.rpc.cluster.ConfiguratorFactory
com.alibaba.dubbo.rpc.cluster.LoadBalance
com.alibaba.dubbo.rpc.cluster.Merger
com.alibaba.dubbo.rpc.cluster.RouterFactory
com.alibaba.dubbo.rpc.Filter
com.alibaba.dubbo.rpc.InvokerListener
com.alibaba.dubbo.rpc.Protocol
com.alibaba.dubbo.rpc.protocol.thrift.ClassNameGenerator
com.alibaba.dubbo.rpc.ProxyFactory
com.alibaba.dubbo.validation.Validation
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