dubbo是如何“暗度陈仓”调用的？
是通过@adaptive注解。
dubbo中 @adaptive 的具体作用
1、注解在类上：代表人工实现的自适应的装饰类
2、注解在方法上：代表自动生成和编译一个动态的adaptive类
@adaptive 自适应性是指在调用的时候根据URL中的参数动态的获取实现类。
例如：
protocol实现类有如下：
registry=com.alibaba.dubbo.registry.integration.RegistryProtocolfilter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapperlistener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrappermock=com.alibaba.dubbo.rpc.support.MockProtocolinjvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocoldubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocolrmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocolhessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocolcom.alibaba.dubbo.rpc.protocol.http.HttpProtocolcom.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocolthrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocolmemcached=memcom.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocolredis=com.alibaba.dubbo.rpc.protocol.redis.RedisProtocol
再看下protocol 动态生成的adaptive类
package com.alibaba.dubbo.rpc;import com.alibaba.dubbo.common.extension.ExtensionLoader;public class Protocol$Adaptive implements com.alibaba.dubbo.rpc.Protocol {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 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 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);}}
你会发现每次在调用的时候，先从URL中获取当前参数的值来获取具体的实现类。这就是dubbo的自适应性。