SpringRetry

RetryTemplate

提供给外部调用的重试执行器

class RetryTemplate{
	BackOffPolicy backOffPolicy
	RetryPolicy retryPolicy
	public final <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback,
			RecoveryCallback<T> recoveryCallback) throws E {
		return doExecute(retryCallback, recoveryCallback, null);
	}
}
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执行流程：

1. 使用重试策略(RetryPolicy)创建重试上下文，org.springframework.retry.RetryPolicy#open(RetryContext parent)
2. 使用退避策略(BackOffPolicy)创建退避上下文，org.springframework.retry.backoff.BackOffPolicy#start(RetryContext context)
3. 执行org.springframework.retry.RetryPolicy#canRetry判断是否应该重试，并且重试上下文的强制结束标志(org.springframework.retry.RetryContext#isExhaustedOnly)为false，如果不应该重试，执行兜底方案org.springframework.retry.RecoveryCallback#recover
4. 执行重试逻辑，也就是业务逻辑，org.springframework.retry.RetryCallback#doWithRetry
5. 如果抛异常了，先执行org.springframework.retry.RetryPolicy#registerThrowable，再执行退避策略org.springframework.retry.backoff.BackOffPolicy#backOff，跳到第3步

• RetryPolicy：重试策略，用来控制是否应该重试，比如抛出了指定异常或达到最大重试次数时停止重试
• BackOffPolicy：退避策略，用来控制重试的时间间隔，比如按照指数增长的间隔和最大时间间隔来重试
• RetryCallback：重试的具体逻辑
• RecoveryCallback：重试策略判断不再继续重试时的兜底逻辑，比如返回一个错误信息

RetryTemplate retryTemplate = new RetryTemplate();
//指数退避策略
ExponentialBackOffPolicy backOffPolicy = new ExponentialBackOffPolicy();
backOffPolicy.setInitialInterval(3000);
backOffPolicy.setMultiplier(2);
backOffPolicy.setMaxInterval(15000);

retryTemplate.setBackOffPolicy(backOffPolicy);

CircuitBreakerRetryPolicy retryPolicy = new CircuitBreakerRetryPolicy();
retryPolicy.setOpenTimeout(3000);
retryPolicy.setResetTimeout(6000);
retryTemplate.setRetryPolicy(retryPolicy);
String result = retryTemplate.execute(context -> {
    int i = new Random().nextInt(10);
    if (i < 7) {
        throw new RuntimeException("fail");
    }
    return "success" + i;
}, context -> {
    return "兜底";
});
System.out.println(result);
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