dubbo源码——Aop

秒速五厘米 2022-05-22 10:18 285阅读 0赞

**一、获取一个ExtensionLoader**

第一行代码后获得的loader：

*  Class<?> type = interface com.alibaba.dubbo.rpc.Protocol
 *  ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）
    
     *  factories = \[SpringExtensionFactory实例, SpiExtensionFactory实例\]

**二、getExtension("dubbo")**

调用层级：

1 ExtensionLoader<T>.getExtension()
    2 --createExtension(String name)
    3 ----getExtensionClasses().get(name)//获取扩展类
    4 ------loadExtensionClasses()
    5 --------loadFile(Map<String, Class<?>> extensionClasses, String dir)
    6 ----injectExtension(instance);//ioc
    7 ----wrapper包装;//aop

createExtension(String name)，该方法源码如下：

1     private T createExtension(String name) {
     2         /** 从cachedClasses缓存中获取所有的实现类map,之后通过name获取到对应的实现类的Class对象 */
     3         Class<?> clazz = getExtensionClasses().get(name);
     4         if (clazz == null) {
     5             throw findException(name);
     6         }
     7         try {
     8             /** 从EXTENSION_INSTANCES缓存中获取对应的实现类的Class对象,如果没有,直接创建,之后放入缓存 */
     9             T instance = (T) EXTENSION_INSTANCES.get(clazz);
    10             if (instance == null) {
    11                 EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
    12                 instance = (T) EXTENSION_INSTANCES.get(clazz);
    13             }
    14             injectExtension(instance);
    15             Set<Class<?>> wrapperClasses = cachedWrapperClasses;
    16             if (wrapperClasses != null && wrapperClasses.size() > 0) {
    17                 for (Class<?> wrapperClass : wrapperClasses) {
    18                     instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
    19                 }
    20             }
    21             return instance;
    22         } catch (Throwable t) {
    23             throw new IllegalStateException("Extension instance(name: " + name + ", class: " + type
    24                                             + ")  could not be instantiated: " + t.getMessage(),
    25                 t);
    26         }
    27     }

这里，先给出META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol内容：

1 registry=com.alibaba.dubbo.registry.integration.RegistryProtocol
     2 dubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol
     3 filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper
     4 listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper
     5 mock=com.alibaba.dubbo.rpc.support.MockProtocol
     6 injvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocol
     7 rmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocol
     8 hessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocol
     9 com.alibaba.dubbo.rpc.protocol.http.HttpProtocol
    10 com.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocol
    11 thrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocol
    12 memcached=com.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocol
    13 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注解且具有含有Protocol的单参构造器，符合这样条件的会被列入**AOP增强类**。放置在loader的私有属性cachedWrapperClasses中。

此时的loader：

再来看createExtension(String name)中的红色部分，就是今天的重点AOP。如上所讲，我在cachedWrapperClasses中缓存了两个AOP增强类：class ProtocolListenerWrapper和class ProtocolFilterWrapper。