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本篇内容介绍了“feign中的Retryer有什么作用”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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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", cause.getMessage(), request.httpMethod(), request.url()),
cause,
request.requestBody().asBytes());
}
//......
}FeignException定义了errorReading静态方法，它创建的是FeignException
ErrorDecoder
feign-core-10.2.3-sources.jar!/feign/codec/ErrorDecoder.java
public interface ErrorDecoder {
//......
public static class Default implements ErrorDecoder {
private final RetryAfterDecoder retryAfterDecoder = new RetryAfterDecoder();
@Override
public Exception decode(String methodKey, Response response) {
FeignException exception = errorStatus(methodKey, response);
Date retryAfter = retryAfterDecoder.apply(firstOrNull(response.headers(), RETRY_AFTER));
if (retryAfter != null) {
return new RetryableException(
response.status(),
exception.getMessage(),
response.request().httpMethod(),
exception,
retryAfter);
}
return exception;
}
private T firstOrNull(Map> map, String key) {
if (map.containsKey(key) && !map.get(key).isEmpty()) {
return map.get(key).iterator().next();
}
return null;
}
}
static class RetryAfterDecoder {
static final DateFormat RFC822_FORMAT =
new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss 'GMT'", US);
private final DateFormat rfc822Format;
RetryAfterDecoder() {
this(RFC822_FORMAT);
}
RetryAfterDecoder(DateFormat rfc822Format) {
this.rfc822Format = checkNotNull(rfc822Format, "rfc822Format");
}
protected long currentTimeMillis() {
return System.currentTimeMillis();
}
/**
* returns a date that corresponds to the first time a request can be retried.
*
* @param retryAfter String in
* Retry-After format
*/
public Date apply(String retryAfter) {
if (retryAfter == null) {
return null;
}
if (retryAfter.matches("^[0-9]+$")) {
long deltaMillis = SECONDS.toMillis(Long.parseLong(retryAfter));
return new Date(currentTimeMillis() + deltaMillis);
}
synchronized (rfc822Format) {
try {
return rfc822Format.parse(retryAfter);
} catch (ParseException ignored) {
return null;
}
}
}
}
//......
} ErrorDecoder提供了Default的默认实现，其decode方法会使用RetryAfterDecoder来计算retryAfter值，在该值不为null时会返回RetryableException；RetryAfterDecoder的apply方法会根据retryAfter来计算retryAfter日期，该retryAfter参数是从response的名为Retry-After的header读取而来
小结
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
“feign中的Retryer有什么作用”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注创新互联网站，小编将为大家输出更多高质量的实用文章！
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