Dubbo服务发现
Dubbo 提供的是一种 Client-Based 的服务发现机制，依赖第三方注册中心组件来协调服务发现过程，支持常用的注册中心如 Nacos、Consul、Zookeeper 等。
以下是 Dubbo 服务发现机制的基本工作原理图：

服务发现包含提供者、消费者和注册中心三个参与角色，其中，Dubbo 提供者实例注册 URL 地址到注册中心，注册中心负责对数据进行聚合，Dubbo 消费者从注册中心读取地址列表并订阅变更，每当地址列表发生变化，注册中心将最新的列表通知到所有订阅的消费者实例。

Dubbo与Nacos整合
前置条件
● 当Dubbo使用3.0.0及以上版本时，需要使用Nacos 2.0.0及以上版本。
● 注意：目前最新版本Dubbo 3.1.8不支持Spring Boot 3，因此开发环境必须基于Spring Boot 2.x + JDK17/8，对应的Spring Cloud与Spring Cloud Alibaba也要调整为2021.x

<properties>
    <java.version>17</java.version>
    <spring-cloud.version>2021.0.3</spring-cloud.version>
    <spring-cloud-alibaba.version>2021.0.4.0</spring-cloud-alibaba.version>
</properties>

生产者服务provider-service-dubbo

<dependency>
  <groupId>org.apache.dubbo</groupId>
  <artifactId>dubbo-spring-boot-starter</artifactId>
  <version>3.1.8</version>
</dependency>

配置文件application.yaml

server:
  port: 8001
spring:
  application:
    name: provider-service
  cloud:
    nacos:
      server-addr: 192.168.31.231:8848
      username: nacos
      password: nacos
dubbo:
  application:
    name: provider-service-dubbo
  registry:
    address: nacos://192.168.31.231:8848
    username: nacos
    password: nacos
  protocol:
    name: dubbo
    port: 20880
logging:
  level:
    root: info

应用入口增加两个注解，启用Dubbo
● @EnableDubbo
@EnableDubbo是一个注解，用于启用Dubbo的自动配置，将Dubbo服务注册到注册中心。它可以放置在Spring Boot应用程序的主类上。通过使用@EnableDubbo注解，可以避免手动配置Dubbo服务的繁琐工作，只需添加相应的注解和配置参数即可自动配置Dubbo。
● @DubboComponentScan
@DubboComponentScan是一个注解，用于扫描Dubbo服务的实现类。它可以放置在Spring Boot应用程序的主类上。通过使用@DubboComponentScan注解，可以自动扫描指定包及其子包中的Dubbo服务实现类，将它们注册为Dubbo服务。这样，Dubbo框架就能够自动发现和管理Dubbo服务，方便使用和维护。

package com.itlaoqi.providerservicedubbo;

import org.apache.dubbo.config.spring.context.annotation.DubboComponentScan;
import org.apache.dubbo.config.spring.context.annotation.EnableDubbo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@EnableDubbo
@DubboComponentScan
public class ProviderServiceDubboApplication {

    public static void main(String[] args) {
        SpringApplication.run(ProviderServiceDubboApplication.class, args);
    }

}

实现业务接口
接口

package com.itlaoqi.providerservicedubbo.dubbo;

import com.itlaoqi.providerservicedubbo.entity.User;
import org.springframework.http.ResponseEntity;

import java.util.List;
import java.util.Map;

public interface ProviderService {
    public Map hello();

    public User createUser(String uid, String username, String password, String nickname);

    public ResponseEntity<List<User>> query(int page, int rows);
}

实现
@DubboService是一个注解，用于标注Dubbo服务的实现类。在Dubbo框架中，服务提供者需要将服务注册到注册中心，以便服务消费者能够发现和调用服务。@DubboService注解可以将标注的服务实现类注册为Dubbo服务，使其能够被Dubbo框架自动管理和发布。

package com.itlaoqi.providerservicedubbo.dubbo.impl;

import com.itlaoqi.providerservicedubbo.dubbo.ProviderService;
import com.itlaoqi.providerservicedubbo.dto.User;
import org.apache.dubbo.config.annotation.DubboService;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@DubboService
public class ProviderServiceImpl implements ProviderService {
    public Map hello() {
        Map result = new HashMap();
        result.put("code", "0");
        result.put("message", "hello world~");
        return result;
    }

    public User createUser(String uid, String username , String password , String nickname) {
        return new User(uid,username,password,nickname);
    }

    public ResponseEntity<List<User>> query(int page, int rows) {
        List<User> users = new ArrayList<>();
        for (int i = rows * (page - 1); i < rows * page; i++) {
            String uid = "uid:" + i;
            String username = "username-" + i;
            String password = "password-" + i;
            String nickname = "nickname-" + i;
            User user = new User(uid, username, password, nickname);
            users.add(user);
        }
        return new ResponseEntity<>(users, HttpStatus.OK);
    }
}

注意，需要依赖的DTO对象，必须实现序列化接口Serializable

package com.itlaoqi.providerservicedubbo.dto;

import lombok.AllArgsConstructor;
import lombok.Data;

import java.io.Serializable;

@Data
@AllArgsConstructor
public class User implements Serializable {

    private String uid;
    private String username;
    private String password;
    private String nickname;
}

启动时要万分注意，JDK17与Dubbo 3.1.8有兼容问题，需要在启动项增加，官方说3.2版本会修正这个问题

--add-opens java.base/java.lang=ALL-UNNAMED

消费者服务consumer-service-dubbo

  <dependency>
      <groupId>org.apache.dubbo</groupId>
      <artifactId>dubbo-spring-boot-starter</artifactId>
      <version>3.1.8</version>
  </dependency>

配置消费者接口

server:
  port: 8002
spring:
  application:
    name: consumer-service
  cloud:
    nacos:
      server-addr: 192.168.31.231:8848
      username: nacos
      password: nacos
dubbo:
  application:
    name: consumer-service-dubbo
  registry:
    address: nacos://192.168.31.231:8848
    username: nacos
    password: nacos
logging:
  level:
    root: info

启用Dubbo

package com.itlaoqi.consumerservicedubbo;

import org.apache.dubbo.config.spring.context.annotation.EnableDubbo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@EnableDubbo
public class ConsumerServiceDubboApplication {

    public static void main(String[] args) {
        SpringApplication.run(ConsumerServiceDubboApplication.class, args);
    }

}

将服务端接口与依赖的类加载到本地
● 复制源代码
● Maven依赖
注意包名是com.itlaoqi.providerservicedubbo.dubbo

package com.itlaoqi.providerservicedubbo.dubbo;

import com.itlaoqi.providerservicedubbo.dto.User;

import java.util.List;
import java.util.Map;

public interface ProviderService {
    public Map hello();

    public User createUser(String uid, String username, String password, String nickname);

    public List<User> query(int page, int rows);
}

package com.itlaoqi.providerservicedubbo.dto;

import lombok.AllArgsConstructor;
import lombok.Data;

import java.io.Serializable;

@Data
@AllArgsConstructor
public class User implements Serializable {

    private String uid;
    private String username;
    private String password;
    private String nickname;
}

依赖并远程访问
● @DubboReference
通过在 Spring 容器中标记 @DubboReference 注解，可以让 Dubbo 自动为该属性注入一个代理对象，该对象可以调用远程 Dubbo 服务的方法，使得在使用 Dubbo 服务时可以像调用本地服务一样方便。

package com.itlaoqi.consumerservicedubbo.controller;

import com.itlaoqi.providerservicedubbo.dubbo.ProviderService;
import com.itlaoqi.providerservicedubbo.dto.User;
import org.apache.dubbo.config.annotation.DubboReference;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class ConsumerController {
    @DubboReference
    private ProviderService providerService;
    @GetMapping("/list")
    public List<User> list(int page, int rows) {
        return providerService.query(page, rows);
    }
}

执行结果

###
GET http://localhost:8002/list?page=2&rows=10

[
  {
    "uid": "uid:10",
    "username": "username-10",
    "password": "password-10",
    "nickname": "nickname-10"
  },
  {
    "uid": "uid:11",
    "username": "username-11",
    "password": "password-11",
    "nickname": "nickname-11"
  },
  {
    "uid": "uid:12",
    "username": "username-12",
    "password": "password-12",
    "nickname": "nickname-12"
  },
  {
    "uid": "uid:13",
    "username": "username-13",
    "password": "password-13",
    "nickname": "nickname-13"
  },
  {
    "uid": "uid:14",
    "username": "username-14",
    "password": "password-14",
    "nickname": "nickname-14"
  },
  {
    "uid": "uid:15",
    "username": "username-15",
    "password": "password-15",
    "nickname": "nickname-15"
  },
  {
    "uid": "uid:16",
    "username": "username-16",
    "password": "password-16",
    "nickname": "nickname-16"
  },
  {
    "uid": "uid:17",
    "username": "username-17",
    "password": "password-17",
    "nickname": "nickname-17"
  },
  {
    "uid": "uid:18",
    "username": "username-18",
    "password": "password-18",
    "nickname": "nickname-18"
  },
  {
    "uid": "uid:19",
    "username": "username-19",
    "password": "password-19",
    "nickname": "nickname-19"
  }
]

启动时要万分注意，JDK17与Dubbo 3.1.8有兼容问题，需要在启动项增加，官方说3.2版本会修正这个问题

--add-opens java.base/java.lang=ALL-UNNAMED