Spring Boot 项目中如何实现服务发现与负载均衡？请结合Eureka 或 Consul 以及 Ribbon 或 Spring Cloud LoadBalancer进行说明？

在Spring Boot项目中实现服务发现与负载均衡，可以使用Spring Cloud的Eureka和Ribbon。以下是一个简单的例子：

1. 添加依赖到pom.xml：

<!-- Eureka Discovery Client -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
<!-- Ribbon -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
</dependency>

2. 配置application.properties或application.yml：

spring:
  application:
    name: service-consumer
 
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

3. 启动类添加@EnableDiscoveryClient注解：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
 
@EnableDiscoveryClient
@SpringBootApplication
public class ServiceConsumerApplication {
 
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
 
    public static void main(String[] args) {
        SpringApplication.run(ServiceConsumerApplication.class, args);
    }
}

4. 使用Ribbon进行服务调用：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
 
@RestController
public class ConsumerController {
 
    private final RestTemplate restTemplate;
 
    @Autowired
    public ConsumerController(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }
 
    @GetMapping("/call-service")
    public String callService() {
        return restTemplate.getForObject("http://SERVICE-PROVIDER/greeting", String.class);
    }
}

在上述代码中，RestTemplate已被标记为@LoadBalanced，这意味着Ribbon会用来处理服务调用，并且Eureka Client会用来发现服务提供者。调用\`http://SERVICE-PROVIDER