Spring Cloud Gateway重试机制原理解析

spring:
 cloud:
  gateway:
   routes:
   - id: fsh-house
    uri: lb://fsh-house
    predicates:
    - Path=/house/**
    filters:
    - name: Retry
     args:
      retries: 3
      series:
      - SERVER_ERROR
      statuses:
      - OK
      methods:
      - GET
      - POST
      exceptions:
      - java.io.IOException

public static class RetryConfig {
  private int retries = 3;

  private List<Series> series = toList(Series.SERVER_ERROR);

  private List<HttpStatus> statuses = new ArrayList<>();

  private List<HttpMethod> methods = toList(HttpMethod.GET);

  private List<Class<? extends Throwable>> exceptions = toList(IOException.class);

  // .....
}

public enum Series {
  INFORMATIONAL(1),
  SUCCESSFUL(2),
  REDIRECTION(3),
  CLIENT_ERROR(4),
  SERVER_ERROR(5);
}

public enum HttpMethod {
  GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;
}

AtomicInteger ac = new AtomicInteger();

@GetMapping("/data")
public HouseInfo getData(@RequestParam("name") String name) {
  if (StringUtils.isBlank(name)) {
    throw new RuntimeException("error");
  }
  System.err.println(ac.addAndGet(1));
  return new HouseInfo(1L, "上海", "虹口", "XX小区");
}

@Override
public GatewayFilter apply(RetryConfig retryConfig) {
  // 验证重试配置格式是否正确
  retryConfig.validate();

  Repeat<ServerWebExchange> statusCodeRepeat = null;
  if (!retryConfig.getStatuses().isEmpty() || !retryConfig.getSeries().isEmpty()) {
    Predicate<RepeatContext<ServerWebExchange>> repeatPredicate = context -> {
      ServerWebExchange exchange = context.applicationContext();
      // 判断重试次数是否已经达到了配置的最大值
      if (exceedsMaxIterations(exchange, retryConfig)) {
        return false;
      }
      // 获取响应的状态码
      HttpStatus statusCode = exchange.getResponse().getStatusCode();
      // 获取请求方法类型
      HttpMethod httpMethod = exchange.getRequest().getMethod();
      // 判断响应状态码是否在配置中存在
      boolean retryableStatusCode = retryConfig.getStatuses().contains(statusCode);

      if (!retryableStatusCode && statusCode != null) { // null status code might mean a network exception?
        // try the series
        retryableStatusCode = retryConfig.getSeries().stream()
            .anyMatch(series -> statusCode.series().equals(series));
      }
      // 判断方法是否包含在配置中
      boolean retryableMethod = retryConfig.getMethods().contains(httpMethod);
      // 决定是否要进行重试
      return retryableMethod && retryableStatusCode;
    };

    statusCodeRepeat = Repeat.onlyIf(repeatPredicate)
        .doOnRepeat(context -> reset(context.applicationContext()));
  }

  //TODO: support timeout, backoff, jitter, etc... in Builder

  Retry<ServerWebExchange> exceptionRetry = null;
  if (!retryConfig.getExceptions().isEmpty()) {
    Predicate<RetryContext<ServerWebExchange>> retryContextPredicate = context -> {
      if (exceedsMaxIterations(context.applicationContext(), retryConfig)) {
        return false;
      }
      // 异常判断
      for (Class<? extends Throwable> clazz : retryConfig.getExceptions()) {       
        if (clazz.isInstance(context.exception())) {
          return true;
        }
      }
      return false;
    };
    // 使用reactor extra的retry组件
    exceptionRetry = Retry.onlyIf(retryContextPredicate)
        .doOnRetry(context -> reset(context.applicationContext()))
        .retryMax(retryConfig.getRetries());
   }

   return apply(statusCodeRepeat, exceptionRetry);
}

public boolean exceedsMaxIterations(ServerWebExchange exchange, RetryConfig retryConfig) {
  Integer iteration = exchange.getAttribute(RETRY_ITERATION_KEY);

  //TODO: deal with null iteration
  return iteration != null && iteration >= retryConfig.getRetries();
}

public void reset(ServerWebExchange exchange) {
  //TODO: what else to do to reset SWE?
  exchange.getAttributes().remove(ServerWebExchangeUtils.GATEWAY_ALREADY_ROUTED_ATTR);
}

public GatewayFilter apply(Repeat<ServerWebExchange> repeat, Retry<ServerWebExchange> retry) {
  return (exchange, chain) -> {
    if (log.isTraceEnabled()) {
      log.trace("Entering retry-filter");
    }

    // chain.filter returns a Mono<Void>
    Publisher<Void> publisher = chain.filter(exchange)
        //.log("retry-filter", Level.INFO)
        .doOnSuccessOrError((aVoid, throwable) -> {
          // 获取已经重试的次数，默认值为-1
          int iteration = exchange.getAttributeOrDefault(RETRY_ITERATION_KEY, -1);
          // 增加重试次数
          exchange.getAttributes().put(RETRY_ITERATION_KEY, iteration + 1);
        });

    if (retry != null) {
      // retryWhen returns a Mono<Void>
      // retry needs to go before repeat
      publisher = ((Mono<Void>)publisher).retryWhen(retry.withApplicationContext(exchange));
    }
    if (repeat != null) {
      // repeatWhen returns a Flux<Void>
      // so this needs to be last and the variable a Publisher<Void>
      publisher = ((Mono<Void>)publisher).repeatWhen(repeat.withApplicationContext(exchange));
    }

    return Mono.fromDirect(publisher);
  };
}