目录
- 前言
- 一、Retryer
- 二、Default
前言
请求远程接口失败时，会进入到重试策略。
一、Retryer
1、 Retryer接口；
public interface Retryer extends Cloneable {
/**
* if retry is permitted, return (possibly after sleeping). Otherwise propagate the exception.
* 在休眠后执行重试，或抛出异常
*/
void continueOrPropagate(RetryableException e);
Retryer clone();
}
2、 默认不进行重试NEVER_RETRY；
Retryer NEVER_RETRY = new Retryer() {
@Override
public void continueOrPropagate(RetryableException e) {
//直接抛出异常
throw e;
}
@Override
public Retryer clone() {
return this;
}
};
在FeignClientsConfiguration 中 定义了默认的重试策略
@Bean
@ConditionalOnMissingBean
public Retryer feignRetryer() {
return Retryer.NEVER_RETRY;
}
二、Default
feign 里定义的默认重试策略
class Default implements Retryer {
//最大重试次数
private final int maxAttempts;
//重试周期
private final long period;
//重试最大周期
private final long maxPeriod;
//当前重试次数
int attempt;
//休眠总时间
long sleptForMillis;
public void continueOrPropagate(RetryableException e) {
//达到了最大重试次数，抛异常
if (attempt++ >= maxAttempts) {
throw e;
}
long interval;
if (e.retryAfter() != null) {
//根据 RetryableException 里 retryAfter 计算时间间隔
interval = e.retryAfter().getTime() - currentTimeMillis();
//不能超过 maxPeriod
if (interval > maxPeriod) {
interval = maxPeriod;
}
//时间到了，直接返回进行重试
if (interval < 0) {
return;
}
} else {
//计算时间间隔
interval = nextMaxInterval();
}
try {
//休眠
Thread.sleep(interval);
} catch (InterruptedException ignored) {
Thread.currentThread().interrupt();
throw e;
}
sleptForMillis += interval;
}
/**
* Calculates the time interval to a retry attempt. <br>
* The interval increases exponentially with each attempt, at a rate of nextInterval *= 1.5
* (where 1.5 is the backoff factor), to the maximum interval.
*
* @return time in nanoseconds from now until the next attempt.
*/
long nextMaxInterval() {
//根据当前重试次数和重试周期计算时间间隔，重试次数越多，周期越长
long interval = (long) (period * Math.pow(1.5, attempt - 1));
//时间间隔不能超过最大重试周期
return interval > maxPeriod ? maxPeriod : interval;
}
}
注册Default
@Configuration
public class CustomFeignClientsConfiguration {
@Bean
public Retryer feignRetryer() {
return new Retryer.Default();
}
}