dubbo复读_1:入口怎么找

前言

本系列的文章纯属自己看dubbo源码的心得

入口寻找：

dubbo作为一个框架，我们使用的时候，首先会去引包，然后再spring的配置文件里配置dubbo的自定义标签，可能还需要引入dubbo的schema文件。所以入口是从dubbo的schema文件入手。

1 先熟悉下 spring自定义文件的方法

2 寻找dubbo的schema文件

image.png

http://code.alibabatech.com/schema/dubbo 是位于名为spring.handlers文件中，

http\://code.alibabatech.com/schema/dubbo=com.alibaba.dubbo.config.spring.schema.DubboNamespaceHandler

=左边是key，右边是解析dubbo自定义标签的handler类
http://code.alibabatech.com/schema/dubbo/dubbo.xsd 是位于spring.schemas文件中，

http\://code.alibabatech.com/schema/dubbo/dubbo.xsd=META-INF/dubbo.xsd

左边是key 右边是 dubbo自定义标签的定义文件是dubbo.xsd

3 看DubboNamespaceHandler类

public void init() {
        registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
        registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
        registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
        registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
        registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
        registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
        registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
        registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
        registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
        registerBeanDefinitionParser("annotation", new DubboBeanDefinitionParser(AnnotationBean.class, true));
    }

会看到<dubbo:service interface="com.alibaba.dubbo.demo.DemoService" ref="demoService" /> 这个标签最终被解析成ServiceBean.class

4 看ServiceBean.class

会看到

public class ServiceBean<T> extends ServiceConfig<T> 
                    implements InitializingBean, 
                                       DisposableBean,
                                       ApplicationContextAware, 
                                       ApplicationListener,
                                       BeanNameAware 

可以看到ServiceBean实现了这么多的spring的接口，
InitializingBean：初始化时的回调 afterPropertiesSet
DisposableBean：销毁时的回调 destroy()
ApplicationContextAware：通过 setApplicationContext（）可以获取spring容器ApplicationContext
ApplicationListener：spring的监听器接口，可以实现bean与bean之间的通信，不熟悉用法的可以看 https://blog.csdn.net/sinat_33625560/article/details/78605367，
BeanNameAware ：获取该bean的name的接口。不熟悉的可以看看https://www.jianshu.com/writer#/notebooks/28099010/notes/32861542/preview

5 看ServiceConfig

ServiceBean继承了ServiceConfig
就可以找到spi的入口了

public class ServiceConfig<T> extends AbstractServiceConfig {

    private static final long   serialVersionUID = 3033787999037024738L;

    private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
    
    private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();

6 看Protocol$Adpative的作用

从下面代码可以看出Protocol$Adpative的作用是 根据url得到 具体实现类来实现接下来的 export和refer

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.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();

        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 java.lang.Class {
        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);
    }
}