前言

重试，我相信大家并不陌生。在我们调用Http接口的时候，总会因为某种原因调用失败，这个时候我们可以通过重试的方式，来重新请求接口。

生活中这样的事例很多，比如打电话，对方正在通话中啊，信号不好啊等等原因，你总会打不通，当你第一次没打通之后，你会打第二次，第三次...第四次就通了。

重试也要注意应用场景，读数据的接口比较适合重试的场景，写数据的接口就需要注意接口的幂等性了。还有就是重试次数如果太多的话会导致请求量加倍，给后端造成更大的压力，设置合理的重试机制才是最关键的。

今天我们来简单的了解下Spring Cloud Gateway中的重试机制和使用。

使用讲解

RetryGatewayFilter是Spring Cloud Gateway对请求重试提供的一个GatewayFilter Factory。

配置方式：

spring:cloud:gateway:routes:- id: fsh-houseuri: lb://fsh-housepredicates:- Path=/house/**filters:- name: Retryargs:retries: 3series:- SERVER_ERRORstatuses:- OKmethods:- GET- POSTexceptions:- java.io.IOException
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配置讲解

配置类源码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);// .....
}
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• retries：重试次数，默认值是3次
• series：状态码配置（分段），符合的某段状态码才会进行重试逻辑，默认值是SERVER_ERROR，值是5，也就是5XX(5开头的状态码)，共有5个值：

public enum Series {INFORMATIONAL(1),SUCCESSFUL(2),REDIRECTION(3),CLIENT_ERROR(4),SERVER_ERROR(5);
}
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• statuses：状态码配置，和series不同的是这边是具体状态码的配置，取值请参考：org.springframework.http.HttpStatus
• methods：指定哪些方法的请求需要进行重试逻辑，默认值是GET方法，取值如下：

public enum HttpMethod {GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;
}
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• exceptions：指定哪些异常需要进行重试逻辑，默认值是java.io.IOException

代码测试

就写个接口，在接口中记录请求次数，然后抛出一个异常模拟500，通过网关访问这个接口，如果你配置了重试次数是3，那么接口中会输出4次结果才是对的，证明重试生效了。

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小区");
}
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更多Spring Cloud代码尽在：github.com/yinjihuan/s…

源码欣赏

    @Overridepublic 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 seriesretryableStatusCode = 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 BuilderRetry<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 iterationreturn 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-1int 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 repeatpublisher = ((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);};}复制代码