Dubbo自定义扩展filter

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DUBBO版本：2.7.0

Dubbo的扩展点是带@SPI注解的，比如：

@SPI
public interface Filter {

    /**
     * do invoke filter.
     * 

     * 
     * // before filter
     * Result result = invoker.invoke(invocation);
     * // after filter
     * return result;
     * 
     *
     * @param invoker    service
     * @param invocation invocation.
     * @return invoke result.
     * @throws RpcException
     * @see org.apache.dubbo.rpc.Invoker#invoke(Invocation)
     */
    Result invoke(Invoker invoker, Invocation invocation) throws RpcException;

    default Result onResponse(Result result, Invoker invoker, Invocation invocation) {
        return result;
    }

}

@SPI("dubbo")
public interface Protocol {

    /**
     * Get default port when user doesn't config the port.
     *
     * @return default port
     */
    int getDefaultPort();

    /**
     * Export service for remote invocation: 

     * 1. Protocol should record request source address after receive a request:
     * RpcContext.getContext().setRemoteAddress();

     * 2. export() must be idempotent, that is, there's no difference between invoking once and invoking twice when
     * export the same URL

     * 3. Invoker instance is passed in by the framework, protocol needs not to care 

     *
     * @param      Service type
     * @param invoker Service invoker
     * @return exporter reference for exported service, useful for unexport the service later
     * @throws RpcException thrown when error occurs during export the service, for example: port is occupied
     */
    @Adaptive
     Exporter export(Invoker invoker) throws RpcException;

    /**
     * Refer a remote service: 

     * 1. When user calls `invoke()` method of `Invoker` object which's returned from `refer()` call, the protocol
     * needs to correspondingly execute `invoke()` method of `Invoker` object 

     * 2. It's protocol's responsibility to implement `Invoker` which's returned from `refer()`. Generally speaking,
     * protocol sends remote request in the `Invoker` implementation. 

     * 3. When there's check=false set in URL, the implementation must not throw exception but try to recover when
     * connection fails.
     *
     * @param   Service type
     * @param type Service class
     * @param url  URL address for the remote service
     * @return invoker service's local proxy
     * @throws RpcException when there's any error while connecting to the service provider
     */
    @Adaptive
     Invoker refer(Class type, URL url) throws RpcException;

    /**
     * Destroy protocol: 

     * 1. Cancel all services this protocol exports and refers 

     * 2. Release all occupied resources, for example: connection, port, etc. 

     * 3. Protocol can continue to export and refer new service even after it's destroyed.
     */
    void destroy();

}

只是DUBOO增强的SPI机制，按需加载

配置方式和JDK原生的差不太多。在META-INF包下dubbo目录下：

注意：老版本可能是com.alibaba的包名，移交到apache后都要用新的包名了

xxxFilter=com.wm.test.xxxFilter

这就可以实现Filter的扩展了。并不需要注入到spring容器中。这点注意一下。