dubbo源码版本：2.5.4
经统计，dubbo一共有31个扩展，如下：
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META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler
META-INF/dubbo/internal/com.alibaba.dubbo.common.extension.ExtensionFactory
META-INF/dubbo/internal/com.alibaba.dubbo.common.serialize.Serialization
META-INF/dubbo/internal/com.alibaba.dubbo.common.status.StatusChecker
META-INF/dubbo/internal/com.alibaba.dubbo.common.threadpool.ThreadPool
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Dispatcher
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Codec2
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Transporter
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.exchange.Exchanger
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.http.HttpBinder
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.p2p.Networker
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.telnet.TelnetHandler
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Filter
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.InvokerListener
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.ExporterListener
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.ProxyFactory
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.Cluster
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.LoadBalance
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.Merger
META-INF/dubbo/internal/com.alibaba.dubbo.common.extension.ExtensionFactory
META-INF/dubbo/internal/com.alibaba.dubbo.common.serialize.Serialization
META-INF/dubbo/internal/com.alibaba.dubbo.common.status.StatusChecker
META-INF/dubbo/internal/com.alibaba.dubbo.common.threadpool.ThreadPool
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Dispatcher
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Codec2
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Transporter
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.exchange.Exchanger
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.http.HttpBinder
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.p2p.Networker
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.telnet.TelnetHandler
META-INF/dubbo/internal/com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Filter
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.InvokerListener
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.ExporterListener
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.ProxyFactory
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.Cluster
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.LoadBalance
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.Merger
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.RouterFactory
META-INF/dubbo/internal/com.alibaba.dubbo.rpc.cluster.ConfiguratorFactory
META-INF/dubbo/internal/com.alibaba.dubbo.container.Container
META-INF/dubbo/internal/com.alibaba.dubbo.container.page.PageHandler
META-INF/dubbo/internal/com.alibaba.dubbo.monitor.MonitorFactory
META-INF/dubbo/internal/com.alibaba.dubbo.registry.RegistryFactory
META-INF/dubbo/internal/com.alibaba.dubbo.validation.Validation
META-INF/dubbo/internal/com.alibaba.dubbo.cache.CacheFactory
META-INF/dubbo/internal/com.alibaba.dubbo.common.store.DataStore
META-INF/dubbo/internal/com.alibaba.dubbo.common.logger.LoggerAdapter