Java SPI (Service Provider Interface)
插件式架構(Plug-in architecture)
Dubbo 的插件式設計
Dubbo SPI 約定
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 (註解在類上) : @SPI 註解標識了接口是一個擴展點 , 屬性 value 用來指定默認適配擴展點的名稱。
@Activate (註解在類型和方法上) : @Activate 註解在擴展點的實現類上 ,表示了一個擴展類被獲取到的的條件,符合條件就被獲取,不符合條件就不獲取 ,根據 @Activate 中的 group 、 value 屬性來過濾 。具體參考 ExtensionLoader 中的 getActivateExtension 函數。
@Adaptive (註解在類型和方法上) : @Adaptive 註解在類上 , 這個類就是缺省的適配擴展。@Adaptive 註解在擴展點 Interface 的方法上時 , dubbo 動態的生成一個這個擴展點的適配擴展類(生成代碼 ,動態編譯實例化 Class ),名稱爲 擴展點 Interface 的簡單類名 + $Adaptive ,例如 :ProxyFactory$Adpative 。這麼做的目的是爲了在運行時去適配不同的擴展實例 , 在運行時通過傳入的 URL 類型的參數或者內部含有獲取 URL 方法的參數 ,從 URL 中獲取到要使用的擴展類的名稱 ,再去根據名稱加載對應的擴展實例 ,用這個擴展實例對象調用相同的方法 。如果運行時沒有適配到運行的擴展實例 , 那麼就使用 @SPI 註解缺省指定的擴展。通過這種方式就實現了運行時去適配到對應的擴展。運行時動態生成的適配擴展類代碼 :
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;
// 從 URL 中獲取擴展名稱 , "dubbo" 是從 ExtensionLoader 對象中的 cachedDefaultName
// 屬性獲取到的 , cachedDefaultName 是擴展點上 @SPI 註解中 value 屬性指定的
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])");
// 通過擴展名稱獲取擴展實例對象 , 調用擴展實例對象的相同方法
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();
// 從 URL 中獲取擴展名稱
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])");
// 通過擴展名稱獲取擴展實例對象 , 調用擴展實例對象的相同方法
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();
// 從 URL 中獲取擴展名稱
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])");
// 通過擴展名稱獲取擴展實例對象 , 調用擴展實例對象的相同方法
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;
// 從 URL 中獲取擴展名稱
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])");
// 通過擴展名稱獲取擴展實例對象 , 調用擴展實例對象的相同方法
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);
擴展加載器 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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