dubbo源码——Aop

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：

• Class<?> type = interface com.alibaba.dubbo.rpc.Protocol
• ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）
  • factories = [SpringExtensionFactory实例, SpiExtensionFactory实例]
• cachedWrapperClasses = [class ProtocolListenerWrapper, class ProtocolFilterWrapper]

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。