重試，我相信大家并不陌生。在我們調(diào)用Http接口的時(shí)候，總會因?yàn)槟撤N原因調(diào)用失敗，這個(gè)時(shí)候我們可以通過重試的方式，來重新請求接口。

生活中這樣的事例很多，比如打電話，對方正在通話中啊，信號不好啊等等原因，你總會打不通，當(dāng)你第一次沒打通之后，你會打第二次，第三次…第四次就通了。

重試也要注意應(yīng)用場景，讀數(shù)據(jù)的接口比較適合重試的場景，寫數(shù)據(jù)的接口就需要注意接口的冪等性了。還有就是重試次數(shù)如果太多的話會導(dǎo)致請求量加倍，給后端造成更大的壓力，設(shè)置合理的重試機(jī)制才是最關(guān)鍵的。今天我們來簡單的了解下Spring Cloud Gateway中的重試機(jī)制和使用。

使用講解

RetryGatewayFilter是Spring Cloud Gateway對請求重試提供的一個(gè)GatewayFilter Factory。

配置方式：

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

配置講解

配置類源碼：org.springframework.cloud.gateway.filter.factory.RetryGatewayFilterFactory.RetryConfig：

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); // .....}

retries：重試次數(shù)，默認(rèn)值是3次

series：狀態(tài)碼配置（分段），符合的某段狀態(tài)碼才會進(jìn)行重試邏輯，默認(rèn)值是SERVER_ERROR，值是5，也就是5XX(5開頭的狀態(tài)碼)，共有5個(gè)值：

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

statuses：狀態(tài)碼配置，和series不同的是這邊是具體狀態(tài)碼的配置，取值請參考：org.springframework.http.HttpStatus

methods：指定哪些方法的請求需要進(jìn)行重試邏輯，默認(rèn)值是GET方法，取值如下：

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

exceptions：指定哪些異常需要進(jìn)行重試邏輯，默認(rèn)值是java.io.IOException

代碼測試

就寫個(gè)接口，在接口中記錄請求次數(shù)，然后拋出一個(gè)異常模擬500，通過網(wǎng)關(guān)訪問這個(gè)接口，如果你配置了重試次數(shù)是3，那么接口中會輸出4次結(jié)果才是對的，證明重試生效了。

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小區(qū)');}

源碼欣賞

@Overridepublic GatewayFilter apply(RetryConfig retryConfig) { // 驗(yàn)證重試配置格式是否正確 retryConfig.validate(); Repeat<ServerWebExchange> statusCodeRepeat = null; if (!retryConfig.getStatuses().isEmpty() || !retryConfig.getSeries().isEmpty()) { Predicate<RepeatContext<ServerWebExchange>> repeatPredicate = context -> { ServerWebExchange exchange = context.applicationContext(); // 判斷重試次數(shù)是否已經(jīng)達(dá)到了配置的最大值 if (exceedsMaxIterations(exchange, retryConfig)) {return false; } // 獲取響應(yīng)的狀態(tài)碼 HttpStatus statusCode = exchange.getResponse().getStatusCode(); // 獲取請求方法類型 HttpMethod httpMethod = exchange.getRequest().getMethod(); // 判斷響應(yīng)狀態(tài)碼是否在配置中存在 boolean retryableStatusCode = retryConfig.getStatuses().contains(statusCode); if (!retryableStatusCode && statusCode != null) { // null status code might mean a network exception?// try the seriesretryableStatusCode = retryConfig.getSeries().stream() .anyMatch(series -> statusCode.series().equals(series)); } // 判斷方法是否包含在配置中 boolean retryableMethod = retryConfig.getMethods().contains(httpMethod); // 決定是否要進(jìn)行重試 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; } // 異常判斷 for (Class<? extends Throwable> clazz : retryConfig.getExceptions()) { if (clazz.isInstance(context.exception())) { return true;} } return false; }; // 使用reactor extra的retry組件 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) -> { // 獲取已經(jīng)重試的次數(shù)，默認(rèn)值為-1 int iteration = exchange.getAttributeOrDefault(RETRY_ITERATION_KEY, -1); // 增加重試次數(shù) 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); };}

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持好吧啦網(wǎng)。