@Configuration
public class ApplicationContextConfig {
  @Bean
  @LoadBalanced
  public RestTemplate restTemplate() {
    return new RestTemplate();
  }
}

@Slf4j
@RestController
@RequestMapping("/order")
public class OrderController {
  @Autowired
  RestTemplate restTemplate;  // 在ioc容器中獲取
  @Value("${payment.url}")
  String paymentUrl;  // 遠(yuǎn)程調(diào)用的URL，保存在配置文件中，解耦

  @GetMapping("/payment/get/{id}")
  public CommonResult<Payment> getPaymentById(@PathVariable("id") Long id) {
    CommonResult<Payment> result = restTemplate.getForObject(paymentUrl + "/payment/get/" + id, CommonResult.class);  // get方法調(diào)用，并且返回封裝成 CommonResult 類型
    log.info("Order 查詢 Payment，id：" + id);
    return result;
  }
}

  @GetMapping("/payment/getEntity/{id}")
  public CommonResult<Payment> getPaymentEntityById(@PathVariable("id") Long id) {
    ResponseEntity<CommonResult> entity = restTemplate.getForEntity(paymentUrl + "/payment/get/" + id, CommonResult.class);
    log.info("獲取到的信息是：" + entity.toString());
    log.info("獲取到的StatusCode是：" + entity.getStatusCode());
    log.info("獲取到的StatusCodeValue是：" + entity.getStatusCodeValue());
    log.info("獲取到的Headers是：" + entity.getHeaders());

    if (entity.getStatusCode().is2xxSuccessful()) {
      log.info("查詢成功：" + id);
      return entity.getBody();
    } else {
      log.info("查詢失?。? + id);
      return new CommonResult<>(CommonResult.FAIlURE, "查詢失敗");
    }
  }

payment:
  url: "http://CLOUD-PAYMENT-SERVICE"

@Configuration
public class MyRule {
  @Bean
  public IRule rule() {
    return new RandomRule();
  }
}

@SpringBootApplication
@EnableEurekaClient
@RibbonClient(name = "CLOUD-PAYMENT-SERVICE", configuration = MyRule.class)
public class OrderApplication80 {
  public static void main(String[] args) {
    SpringApplication.run(OrderApplication80.class, args);
  }
}

CLOUD-PAYMENT-SERVICE:  # 服務(wù)名稱
  ribbon:
    NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule  # 算法選擇

public interface IRule {
  Server choose(Object var1);  // 選擇服務(wù)器，最重要的方法

  void setLoadBalancer(ILoadBalancer var1);

  ILoadBalancer getLoadBalancer();
}

public abstract class AbstractLoadBalancerRule implements IRule, IClientConfigAware {
  private ILoadBalancer lb;  // ILoadBalancer接口，主要的功能就是獲取當(dāng)前服務(wù)器的狀態(tài)、數(shù)量等，為負(fù)載均衡算法提供計(jì)算的參數(shù)

  public AbstractLoadBalancerRule() {
  }

  public void setLoadBalancer(ILoadBalancer lb) {
    this.lb = lb;
  }

  public ILoadBalancer getLoadBalancer() {
    return this.lb;
  }
}

public class RoundRobinRule extends AbstractLoadBalancerRule {
  private AtomicInteger nextServerCyclicCounter;  // 原子類，用來保存一個計(jì)數(shù)，記錄現(xiàn)在輪詢到哪了
  private static final boolean AVAILABLE_ONLY_SERVERS = true;
  private static final boolean ALL_SERVERS = false;
  private static Logger log = LoggerFactory.getLogger(RoundRobinRule.class);

  public RoundRobinRule() {
    this.nextServerCyclicCounter = new AtomicInteger(0);  // 初始化
  }

  public RoundRobinRule(ILoadBalancer lb) {  // 設(shè)置LoadBalancer
    this();
    this.setLoadBalancer(lb);
  }

  public Server choose(ILoadBalancer lb, Object key) {  // 最重要的方法，選擇服務(wù)器并返回
  // 下面貼出來
  }
 
  private int incrementAndGetModulo(int modulo) {  // 對計(jì)數(shù)器進(jìn)行修改，并返回一個選擇值，是輪詢算法的實(shí)現(xiàn)
  // 下面貼出來
  }

  public Server choose(Object key) {   // 接口的方法，在該類中調(diào)用了另一個方法實(shí)現(xiàn)
    return this.choose(this.getLoadBalancer(), key);
  }

  public void initWithNiwsConfig(IClientConfig clientConfig) {}
}

public Server choose(ILoadBalancer lb, Object key) {
    if (lb == null) {  // 如果沒有LoadBalancer，那就不白費(fèi)功夫了
      log.warn("no load balancer");
      return null;
    } else {
      Server server = null;
      int count = 0;

      while(true) {  
        if (server == null && count++ < 10) {  // 嘗試十次，如果還找不到server就放棄了
          List<Server> reachableServers = lb.getReachableServers();  // 通過LB獲取目前所有可獲取的服務(wù)器
          List<Server> allServers = lb.getAllServers();  // 獲取實(shí)際上的所有服務(wù)器
          int upCount = reachableServers.size();  // 獲取目前可獲得的服務(wù)器數(shù)量
          int serverCount = allServers.size();  // 所有服務(wù)器的數(shù)量，這是取余的除數(shù)
          if (upCount != 0 && serverCount != 0) {  // 如果目前有服務(wù)器且服務(wù)器可用
            int nextServerIndex = this.incrementAndGetModulo(serverCount);  // 最關(guān)鍵的選擇算法，將目前的的服務(wù)器數(shù)量放進(jìn)去，返回一個選擇的號碼
            server = (Server)allServers.get(nextServerIndex);   // 根據(jù)下標(biāo)將服務(wù)器取出來
            if (server == null) {  // 如果取出來為空，表示目前不可用，則進(jìn)入下一個循環(huán)
              Thread.yield(); 
            } else {
              if (server.isAlive() && server.isReadyToServe()) {  // 如果該服務(wù)器活著且可以被使用，則直接將其返回
                return server;
              }

              server = null;
            }
            continue;
          }

          log.warn("No up servers available from load balancer: " + lb);
          return null;
        }

        if (count >= 10) {
          log.warn("No available alive servers after 10 tries from load balancer: " + lb);
        }

        return server;
      }
    }
  }

  private int incrementAndGetModulo(int modulo) {
    int current;
    int next;
    do {
      current = this.nextServerCyclicCounter.get();  // 獲取當(dāng)前值
      next = (current + 1) % modulo;  // +1取余
    } while(!this.nextServerCyclicCounter.compareAndSet(current, next));  // CAS，如果成功就返回，失敗就再來

    return next;
  }