dubbo擴(kuò)展點(diǎn)AOP切面功能擴(kuò)展示例詳解

更新時(shí)間：2023年08月16日 10:45:52 作者：包月星

這篇文章主要為大家介紹了dubbo擴(kuò)展點(diǎn)AOP切面功能擴(kuò)展示例詳解,有需要的朋友可以借鑒參考下,希望能夠有所幫助,祝大家多多進(jìn)步,早日升職加薪

dubbo擴(kuò)展點(diǎn)的AOP

對(duì)dubbo的擴(kuò)展點(diǎn)做一些切面功能的擴(kuò)展

ExtensionLoader createExtension

從ExtensionLoader的createExtension代碼說(shuō)起

@SuppressWarnings("unchecked")
    private T createExtension(String name) {
        Class<?> clazz = getExtensionClasses().get(name);
        if (clazz == null) {
            throw findException(name);
        }
        try {
            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;
            //begin 
            if (wrapperClasses != null && wrapperClasses.size() > 0) {
                for (Class<?> wrapperClass : wrapperClasses) {
                    instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
                }
            }
            //end 
            return instance;
        } catch (Throwable t) {
            throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
                    type + ")  could not be instantiated: " + t.getMessage(), t);
        }
    }

關(guān)鍵說(shuō)明

cachedWrapperClasses是在loadFile里面加載的，"WrapperClass"是符合某種特征的擴(kuò)展接口實(shí)現(xiàn)類(lèi)的稱(chēng)呼。例如ProtocolFilterWrapper

和ProtocolListenerWrapper。他們共同特征就是帶有Protocol接口的構(gòu)造函數(shù)。

/**
 * ListenerProtocol
 *
 * @author william.liangf
 */
public class ProtocolFilterWrapper implements Protocol {
    private final Protocol protocol;
    public ProtocolFilterWrapper(Protocol protocol) {
        if (protocol == null) {
            throw new IllegalArgumentException("protocol == null");
        }
        this.protocol = protocol;
    }
    private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {
        Invoker<T> last = invoker;
        List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
        if (filters.size() > 0) {
            for (int i = filters.size() - 1; i >= 0; i--) {
                final Filter filter = filters.get(i);
                final Invoker<T> next = last;
                last = new Invoker<T>() {
                    public Class<T> getInterface() {
                        return invoker.getInterface();
                    }
                    public URL getUrl() {
                        return invoker.getUrl();
                    }
                    public boolean isAvailable() {
                        return invoker.isAvailable();
                    }
                    public Result invoke(Invocation invocation) throws RpcException {
                        return filter.invoke(next, invocation);
                    }
                    public void destroy() {
                        invoker.destroy();
                    }
                    @Override
                    public String toString() {
                        return invoker.toString();
                    }
                };
            }
        }
        return last;
    }
    public int getDefaultPort() {
        return protocol.getDefaultPort();
    }
    public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
            return protocol.export(invoker);
        }
        return protocol.export(buildInvokerChain(invoker, Constants.SERVICE_FILTER_KEY, Constants.PROVIDER));
    }
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
            return protocol.refer(type, url);
        }
        return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
    }
    public void destroy() {
        protocol.destroy();
    }
}

instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance)); 就是將拿到的instance放到一個(gè)包裝類(lèi)中，然后經(jīng)過(guò)一層包裝之后，在放到另外一個(gè)包裝類(lèi)中，

通過(guò)這種方式dubbo實(shí)現(xiàn)了擴(kuò)展點(diǎn)的AOP