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-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);
// .....
}
●
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);
}
● 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;
}
●
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");
}
更多Spring Cloud代码尽在:
https://github.com/yinjihuan/spring-cloud
源码欣赏
@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);
};
}
原文发布时间为:2018-09-17
本文作者:尹吉欢