It's time for the interview again to prepare some dry goods for the interview.

provider example

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
    xsi:schemaLocation="http://www.springframework.org/schema/beans  
        http://www.springframework.org/schema/beans/spring-beans.xsd  
        http://code.alibabatech.com/schema/dubbo  
        http://code.alibabatech.com/schema/dubbo/dubbo.xsd  
        ">

    <!-- use dubbo Protocol Exposure Service at Port 20880 -->
    <dubbo:protocol name="dubbo" port="20952"/>

    <!-- Declare service interfaces that need to be exposed -->
    <dubbo:service interface="com.***.workorder.facade.exports.ApplyTaskFacade" ref="applyTaskFacadeImpl" version="1.0.0" delay="-1"/>
    <dubbo:service interface="com.***.workorder.facade.exports.TaskFacade" ref="taskFacadeImpl" version="1.0.0" delay="-1"/>
</beans> 

These are the basic provider configurations

dubbo seamlessly plugged into spring. Let's see how it works.

From the configuration file above, you can see that dubbo uses custom tags, so you must have implemented Namespace Handler Support to parse your tags.
You can find the implementation of Namespace Handler SupportDubbo Namespace Handler

DubboNamespaceHandler

Here, Dubbo Namespace Handler delegates parsing to DubboBean Definition Parser, but there's not much to say here.

DubboBean Definition Parser can see that dubbo collates the classes used for each custom tag parsing

Here the specific tag attribute parsing process is not analyzed for the time being. If you are interested, you can view the original tag by yourself.
DubboBean Definition Parser completes the process of parsing the xml configuration and loading it into the spring container

When the provider object is parsed and loaded, the service is naturally generated according to configuration.
Let's look at the implementation of ServiceBean code

public class ServiceBean<T> extends ServiceConfig<T> implements 
InitializingBean, DisposableBean, ApplicationContextAware, ApplicationListener, BeanNameAware 

Service exposure

Service service exposure process

You can see that the export() method that eventually calls to the Protocol object exposes the service.
At this point, service exposures on the process are completed. The details of the exposures are implemented by the protocols themselves.

Service Citation

Service Reference Process

An Invoker object is obtained by refer() of Protocol, and then the proxy object of interface is generated by dynamic proxy to realize rpc communication.

dubbo calling procedure

Introduction of dubbo-protocol layer

Protocol interface belongs to Protocol layer in dubbo. There are three main objects in Protocol layer: Exporter, Invoker and Protocol.

• Exporter: Exporter through which Invoker objects can be obtained
• Invoker:(Communication) Actuator to communicate with the remote end
• Protocol: An Abstract protocol that exposes and references services

Look at Protocol,Exporter,Invoker interface definitions

@SPI("dubbo")
public interface Protocol {
    
    /**
     * Gets the default port, which is used when the user does not configure the port.
     * 
     * @return Default port
     */
    int getDefaultPort();

    /**
     * Exposure to remote services: <br>
     * 1. When receiving a request, the protocol should record the address information of the requester's source: RpcContext. getContext (). setRemoteAddress (); < br >
     * 2. export()It must be idempotent, that is, the Invoker that exposes the same URL twice is no different from the Invoker that exposes the same URL once. <br>
     * 3. export()The incoming Invoker is implemented by the framework and passed in. The protocol does not need to be concerned. <br>
     * 
     * @param <T> Types of services
     * @param invoker Executives of services
     * @return exporter Exposure service references for eliminating exposure
     * @throws RpcException Thrown when exposing service errors, such as port occupancy
     */
    @Adaptive
    <T> Exporter<T> export(Invoker<T> invoker) throws RpcException;

    /**
     * Reference to remote services: <br>
     * 1. When the user calls the invoke() method of the Invoker object returned by refer(), the protocol needs to execute the invoke() method of the Invoker object passed in with the remote export() of the URL. <br>
     * 2. refer()The returned Invoker is implemented by a protocol in which remote requests are usually sent. <br>
     * 3. When check=false is set in the url, the connection failure cannot throw an exception, and the internal recovery is automatic. <br>
     * 
     * @param <T> Types of services
     * @param type Types of services
     * @param url URL address of remote service
     * @return invoker Local Agent for Services
     * @throws RpcException Thrown when the connection service provider fails
     */
    @Adaptive
    <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;

    /**
     * Release agreement: <br>
     * 1. Cancel all exposed and referenced services of the protocol. <br>
     * 2. Release all resources occupied by the protocol, such as connections and ports. <br>
     * 3. After release, the protocol can still expose and refer to new services. <br>
     */
    void destroy();
}

public interface Exporter<T> {
    Invoker<T> getInvoker();
    
    void unexport();
}

**
 * Invoker. (API/SPI, Prototype, ThreadSafe)
 * There are three kinds.:
 * 1.AbstractInvoker      Calling remote services over the network (Client side)
 * 2.AbstractProxyInvoker Call local implementation (Server side)
 * 3.ClusterInvoker       Providing Cluster Services (Client side)
 */
public interface Invoker<T> extends Node {


    Class<T> getInterface();

    Result invoke(Invocation invocation) throws RpcException;

}