07_dubbo_compiler

【开始解析最后一行代码 ExtensionLoader.getAdaptiveExtension()】

ExtensionLoader<Protocol> loader = ExtensionLoader.getExtensionLoader(Protocol.class);
final Protocol dubboProtocol = loader.getExtension("dubbo");
final Protocol adaptiveExtension = loader.getAdaptiveExtension();

【getAdaptiveExtension()调用结果】

ExtesionLoader.getAdaptiveExtension()
--createAdaptiveExtension()
----getAdaptiveExtensionClass()
//从spi文件中查找实现类上有@Adaptive注解的类
------getExtensionClasses()
--------loadExtensionClasses()
----------loadFile(Map<String, Class<?>> extensionClasses, String dir)
//第三行代码的重点,如果从spi文件中没找到实现类上有@Adaptive的类，则动态创建类
------createAdaptiveExtensionClass()

【 createAdaptiveExtensionClass()源码】

private Class<?> createAdaptiveExtensionClass() {
    String code = createAdaptiveExtensionClassCode();
    ClassLoader classLoader = findClassLoader();
    com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
    return compiler.compile(code, classLoader);
}

【createAdaptiveExtensionClassCode()方法】

createAdaptiveExtensionClassCode()方法中会判断：如果一个类中没有@Adaptive注解，直接抛出IllegalStateException异常；如果类有含@Adaptive注解的方法，则为其构造代码；如果类没有含@Adaptive注解的方法的，直接抛出UnsupportedOperationException异常，见下图

【含有@Adaptive注解的方法构造的Protocol$Adaptive对象如下】

package com.alibaba.dubbo.rpc;

import com.alibaba.dubbo.common.extension.ExtensionLoader;

public class Protocol$Adaptive 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 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);
    }
    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);
    }
}

【获取Compiler装饰类】

com.alibaba.dubbo.common.compiler.Compiler compiler = 
ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();

【com.alibaba.dubbo.common.compiler.Compiler 接口】

@SPI 注解的默认值为"javassist"，根据上一节的经验，默认获取的Compiler接口的实现类是META-INF/dubbo/internal/com.alibaba.dubbo.common.compiler.Compiler文件中的key为javassist的实现类，如下：

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adaptive=com.alibaba.dubbo.common.compiler.support.AdaptiveCompiler
jdk=com.alibaba.dubbo.common.compiler.support.JdkCompiler
javassist=com.alibaba.dubbo.common.compiler.support.JavassistCompiler

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