feign返回null_聊聊feign的Retryer

最新推荐文章于 2025-03-16 22:25:01 发布

最新推荐文章于 2025-03-16 22:25:01 发布 · 285 阅读

文章标签：

本文详细介绍了Feign中Retryer接口的功能，Retryer.Default类的实现，包括最大尝试次数、重试间隔计算等。当请求失败时，Retryer.Default会根据重试策略进行休眠并重新尝试，直到达到最大尝试次数。同时，Retryer.NEVER_RETRY则不执行任何重试操作，直接抛出异常。SynchronousMethodHandler类在捕获RetryableException时，会利用Retryer进行重试控制。

序

本文主要研究一下feign的Retryer

Retryer

feign-core-10.2.3-sources.jar!/feign/Retryer.java

public interface Retryer extends Cloneable { /** * if retry is permitted, return (possibly after sleeping). Otherwise propagate the exception. */ void continueOrPropagate(RetryableException e); Retryer clone(); class Default implements Retryer { private final int maxAttempts; private final long period; private final long maxPeriod; int attempt; long sleptForMillis; public Default() { this(100, SECONDS.toMillis(1), 5); } public Default(long period, long maxPeriod, int maxAttempts) { this.period = period; this.maxPeriod = maxPeriod; this.maxAttempts = maxAttempts; this.attempt = 1; } // visible for testing; protected long currentTimeMillis() { return System.currentTimeMillis(); } public void continueOrPropagate(RetryableException e) { if (attempt++ >= maxAttempts) { throw e; } long interval; if (e.retryAfter() != null) { interval = e.retryAfter().getTime() - currentTimeMillis(); if (interval > maxPeriod) { interval = maxPeriod; } if (interval < 0) { return; } } else { interval = nextMaxInterval(); } try { Thread.sleep(interval); } catch (InterruptedException ignored) { Thread.currentThread().interrupt(); throw e; } sleptForMillis += interval; } /** * Calculates the time interval to a retry attempt. 
 * 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() { long interval = (long) (period * Math.pow(1.5, attempt - 1)); return interval > maxPeriod ? maxPeriod : interval; } @Override public Retryer clone() { return new Default(period, maxPeriod, maxAttempts); } } /** * Implementation that never retries request. It propagates the RetryableException. */ Retryer NEVER_RETRY = new Retryer() { @Override public void continueOrPropagate(RetryableException e) { throw e; } @Override public Retryer clone() { return this; } };}

Retryer继承了Cloneable接口，它定义了continueOrPropagate、clone方法；它内置了一个名为Default以及名为NEVER_RETRY的实现
Default有period、maxPeriod、maxAttempts参数可以设置，默认构造器使用的period为100，maxPeriod为1000，maxAttempts为5；continueOrPropagate方法首先判断attempt是否达到阈值，达到则抛出异常，否则进一步计算interval，然后进行sleep
NEVER_RETRY的continueOrPropagate直接抛出异常，而clone方法直接返回当前实例

SynchronousMethodHandler

feign-core-10.2.3-sources.jar!/feign/SynchronousMethodHandler.java

final class SynchronousMethodHandler implements MethodHandler { //...... public Object invoke(Object[] argv) throws Throwable { RequestTemplate template = buildTemplateFromArgs.create(argv); Retryer retryer = this.retryer.clone(); while (true) { try { return executeAndDecode(template); } catch (RetryableException e) { try { retryer.continueOrPropagate(e); } catch (RetryableException th) { Throwable cause = th.getCause(); if (propagationPolicy == UNWRAP && cause != null) { throw cause; } else { throw th; } } if (logLevel != Logger.Level.NONE) { logger.logRetry(metadata.configKey(), logLevel); } continue; } } } //......}

SynchronousMethodHandler的invoke的方法首先使用retryer.clone()创建一个retryer，然后在捕获到RetryableException的时候，会执行retryer.continueOrPropagate(e)

RetryableException

feign-core-10.2.3-sources.jar!/feign/RetryableException.java

public class RetryableException extends FeignException { private static final long serialVersionUID = 1L; private final Long retryAfter; private final HttpMethod httpMethod; /** * @param retryAfter usually corresponds to the {@link feign.Util#RETRY_AFTER} header. */ public RetryableException(int status, String message, HttpMethod httpMethod, Throwable cause, Date retryAfter) { super(status, message, cause); this.httpMethod = httpMethod; this.retryAfter = retryAfter != null ? retryAfter.getTime() : null; } /** * @param retryAfter usually corresponds to the {@link feign.Util#RETRY_AFTER} header. */ public RetryableException(int status, String message, HttpMethod httpMethod, Date retryAfter) { super(status, message); this.httpMethod = httpMethod; this.retryAfter = retryAfter != null ? retryAfter.getTime() : null; } /** * Sometimes corresponds to the {@link feign.Util#RETRY_AFTER} header present in {@code 503} * status. Other times parsed from an application-specific response. Null if unknown. */ public Date retryAfter() { return retryAfter != null ? new Date(retryAfter) : null; } public HttpMethod method() { return this.httpMethod; }}

RetryableException继承了FeignException，它的构造器会接收retryAfter，该参数可以为null

FeignException

feign-core-10.2.3-sources.jar!/feign/FeignException.java

public class FeignException extends RuntimeException { //...... static FeignException errorReading(Request request, Response response, IOException cause) { return new FeignException( response.status(), format("%s reading %s %s