05_dubbo_aop

时间：2018-09-08 21:05:49 阅读：189 评论：0 收藏：0 [点我收藏+]

标签：mem load png pie 分享图片 ssi 文件内容 rpc ice

【对这行代码进行源码分析】

ExtensionLoader<Protocol> loader = ExtensionLoader.getExtensionLoader(Protocol.class);
final Protocol dubboProtocol = loader.getExtension("dubbo");  //要分析的源码
final Protocol adaptiveExtension = loader.getAdaptiveExtension();

【对上面第二行代码进行源码分析】

先看下第一行代码执行后的ExtensionLoader实例化的结果

技术分享图片

其中

* type =interface com.alibaba.dubbo.rpc.Protocol

* ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）

* AdaptiveExtensionFactory成员变量factories = [ SpringExtensionFactory实例，SpiExtensionFactory实例 ]

【 getExtension(String name)源码】

ExtensionLoader<Protocol> loader = ExtensionLoader.getExtensionLoader(Protocol.class);
final Protocol dubboProtocol = loader.getExtension("dubbo");
--createExtension(name);
----getExtensionClasses() //获取扩展类
------loadExtensionClasses()
--------loadFile(Map<String, Class<?>> extensionClasses, String dir)
//ioc属性注入
----injectExtension(instance);   
//aop+ioc属性注入  aop获得一个wrapper装饰类
----instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));

【】

private T createExtension(String name) {
    /**
     * 从Holder<Map<String, Class<?>>>cachedClasses缓存中获取所有的实现类map，
     * 然后通过name获取到对应的实现类（此时只是一个对象实例，还没有属性注入）
     */
    Class<?> clazz = getExtensionClasses().get(name);
    if (clazz == null) {
        throw findException(name);
    }
    try {
        /**
         * 从 ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES 类缓存中获取到对应的实现类的Class对象，
         * 如果没有，直接创建，之后放入缓存
         */
        T instance = (T) EXTENSION_INSTANCES.get(clazz);
        if (instance == null) {
            EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
            instance = (T) EXTENSION_INSTANCES.get(clazz);
        }
        injectExtension(instance);
        Set<Class<?>> wrapperClasses = cachedWrapperClasses;
        if (wrapperClasses != null && wrapperClasses.size() > 0) {
            for (Class<?> wrapperClass : wrapperClasses) {
                instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
            }
        }
        return instance;
    } catch (Throwable t) {
        throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
                type + ")  could not be instantiated: " + t.getMessage(), t);
    }
}

回头看下META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol文件内容

registry=com.alibaba.dubbo.registry.integration.RegistryProtocol
dubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol
filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper
listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper
mock=com.alibaba.dubbo.rpc.support.MockProtocol
injvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocol
rmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocol
hessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocol
com.alibaba.dubbo.rpc.protocol.http.HttpProtocol
com.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocol
thrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocol
memcached=com.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocol

redis=com.alibaba.dubbo.rpc.protocol.redis.RedisProtocol

com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper和com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper，这两个类不含有@Adaptive注解且含有Protocol的单参数构造方法，符合这2个条件的类会被列入AOP增强类，会被防止在ExtensionLoader的实例缓存Set<Class<?>> cachedWrapperClasses;中。

此时的loader：

* type =interface com.alibaba.dubbo.rpc.Protocol

* ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）

* AdaptiveExtensionFactory成员变量factories = [ SpringExtensionFactory实例，SpiExtensionFactory实例 ]

* cachedWrapperClasses = [ class ProtocolListenerWrapper, class ProtocolFilterWrapper ]

技术分享图片