SpringCloud升级之路2020.0.x版-39. 改造 resilience4j 粘合 WebClient

本系列代码地址：https://github.com/JoJoTec/spring-cloud-parent

要想实现我们上一节中提到的：

• 需要在重试以及断路中加一些日志，便于日后的优化
• 需要定义重试的 Exception，并且与断路器相结合，将非 2xx 的响应码也封装成特定的异常
• 需要在断路器相关的 Operator 中增加类似于 FeignClient 中的负载均衡的数据更新，使得负载均衡更加智能

我们需要将 resilience4j 本身提供的粘合库做一些改造，其实主要就是对 resilience4j 实现的 project reactor 的 Operator 进行改造。

关于断路器的改造

首先，WebClient 的返回对象只可能是

ClientResponse

类型，所以我们这里改造出来的 Operator 不必带上形参，只需要针对 ClientResponse 即可，即：

public class ClientResponseCircuitBreakerOperator implements UnaryOperator<Publisher<ClientResponse>> {
...
}

在原有的断路器逻辑中，我们需要加入针对 GET 方法以及之前定义的可以重试的路径匹配配置可以重试的逻辑，这需要我们拿到原有请求的 URL 信息。但是 ClientResponse 中并没有暴露这些信息的接口，其默认实现 DefaultClientResponse（我们只要没有自己给 WebClient 加入特殊的改造逻辑，实现都是 DefaultClientResponse） 中的

request()

方法可以获取请求 HttpRequest，其中包含 url 信息。但是这个类还有方法都是 package-private 的，我们需要反射出来：

ClientResponseCircuitBreakerSubscriber

private static final Class<?> aClass;
private static final Method request;

static {
try {
aClass = Class.forName("org.springframework.web.reactive.function.client.DefaultClientResponse");
request = ReflectionUtils.findMethod(aClass, "request");
request.setAccessible(true);
} catch (Exception e) {
throw new RuntimeException(e);
}
}

之后，在获取到 ClientResponse 之后记录断路器的逻辑中，需要加入上面提到的关于重试的改造，以及负载均衡器的记录：

ClientResponseCircuitBreakerSubscriber

protected void hookOnNext(ClientResponse clientResponse) {
if (!isDisposed()) {
if (singleProducer && successSignaled.compareAndSet(false, true)) {
int rawStatusCode = clientResponse.rawStatusCode();
HttpStatus httpStatus = HttpStatus.resolve(rawStatusCode);
try {
HttpRequest httpRequest = (HttpRequest) request.invoke(clientResponse);
//判断方法是否为 GET，以及是否在可重试路径配置中，从而得出是否可以重试
if (httpRequest.getMethod() != HttpMethod.GET && !webClientProperties.retryablePathsMatch(httpRequest.getURI().getPath())) {
//如果不能重试，则直接返回结果
circuitBreaker.onResult(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit(), clientResponse);
} else {
if (httpStatus != null && httpStatus.is2xxSuccessful()) {
//如果成功，则直接返回结果
circuitBreaker.onResult(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit(), clientResponse);
} else {
/**
* 如果异常，参考 DefaultClientResponse 的代码进行异常封装
* @see org.springframework.web.reactive.function.client.DefaultClientResponse#createException
*/
Exception exception;
if (httpStatus != null) {
exception = WebClientResponseException.create(rawStatusCode, httpStatus.getReasonPhrase(), clientResponse.headers().asHttpHeaders(), EMPTY, null, null);
} else {
exception = new UnknownHttpStatusCodeException(rawStatusCode, clientResponse.headers().asHttpHeaders(), EMPTY, null, null);
}
circuitBreaker.onError(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit(), exception);
downstreamSubscriber.onError(exception);
return;
}
}
} catch (Exception e) {
log.fatal("judge request method in circuit breaker error! the resilience4j feature would not be enabled: {}", e.getMessage(), e);
circuitBreaker.onResult(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit(), clientResponse);
}
}
eventWasEmitted.set(true);
downstreamSubscriber.onNext(clientResponse);
}
}

同样的，在原有的完成，取消还有失败的记录逻辑中，也加上记录负载均衡数据：

ClientResponseCircuitBreakerSubscriber

@Override
protected void hookOnComplete() {
if (successSignaled.compareAndSet(false, true)) {
serviceInstanceMetrics.recordServiceInstanceCalled(serviceInstance, true);
circuitBreaker.onSuccess(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit());
}

downstreamSubscriber.onComplete();
}

@Override
public void hookOnCancel() {
if (!successSignaled.get()) {
serviceInstanceMetrics.recordServiceInstanceCalled(serviceInstance, true);
if (eventWasEmitted.get()) {
circuitBreaker.onSuccess(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit());
} else {
circuitBreaker.releasePermission();
}
}
}

@Override
protected void hookOnError(Throwable e) {
serviceInstanceMetrics.recordServiceInstanceCalled(serviceInstance, false);
circuitBreaker.onError(circuitBreaker.getCurrentTimestamp() - start, circuitBreaker.getTimestampUnit(), e);
downstreamSubscriber.onError(e);
}

粘合 WebClient 与 resilience4j 的同时覆盖重试逻辑

由于前面的断路器中，我们针对可以重试的非 2XX 响应封装成为 WebClientResponseException。所以在重试器中，我们需要加上针对这个异常的重试。

同时，需要将重试器放在负载均衡器之前，因为每次重试，都要从负载均衡器中获取一个新的实例。同时，断路器需要放在负载均衡器之后，因为只有在这个之后，才能获取到本次调用的实例，我们的的断路器是针对实例方法级别的：

WebClientDefaultConfiguration.java

@Bean
public WebClient getWebClient(
ReactorLoadBalancerExchangeFilterFunction lbFunction,
WebClientConfigurationProperties webClientConfigurationProperties,
Environment environment,
RetryRegistry retryRegistry,
CircuitBreakerRegistry circuitBreakerRegistry,
ServiceInstanceMetrics serviceInstanceMetrics
) {
String name = environment.getProperty(WebClientNamedContextFactory.PROPERTY_NAME);
Map<String, WebClientConfigurationProperties.WebClientProperties> configs = webClientConfigurationProperties.getConfigs();
if (configs == null || configs.size() == 0) {
throw new BeanCreationException("Failed to create webClient, please provide configurations under namespace: webclient.configs");
}
WebClientConfigurationProperties.WebClientProperties webClientProperties = configs.get(name);
if (webClientProperties == null) {
throw new BeanCreationException("Failed to create webClient, please provide configurations under namespace: webclient.configs." + name);
}
String serviceName = webClientProperties.getServiceName();
//如果没填写微服务名称，就使用配置 key 作为微服务名称
if (StringUtils.isBlank(serviceName)) {
serviceName = name;
}
String baseUrl = webClientProperties.getBaseUrl();
//如果没填写 baseUrl，就使用微服务名称填充
if (StringUtils.isBlank(baseUrl)) {
baseUrl = "http://" + serviceName;
}

Retry retry = null;
try {
retry = retryRegistry.retry(serviceName, serviceName);
} catch (ConfigurationNotFoundException e) {
retry = retryRegistry.retry(serviceName);
}
//覆盖其中的异常判断
retry = Retry.of(serviceName, RetryConfig.from(retry.getRetryConfig()).retryOnException(throwable -> {
//WebClientResponseException 会重试，因为在这里能 catch 的 WebClientResponseException 只对可以重试的请求封装了 WebClientResponseException
//参考 ClientResponseCircuitBreakerSubscriber 的代码
if (throwable instanceof WebClientResponseException) {
log.info("should retry on {}", throwable.toString());
return true;
}
//断路器异常重试，因为请求没有发出去
if (throwable instanceof CallNotPermittedException) {
log.info("should retry on {}", throwable.toString());
return true;
}
if (throwable instanceof WebClientRequestException) {
WebClientRequestException webClientRequestException = (WebClientRequestException) throwable;
HttpMethod method = webClientRequestException.getMethod();
URI uri = webClientRequestException.getUri();
//判断是否为响应超时，响应超时代表请求已经发出去了，对于非 GET 并且没有标注可以重试的请求则不能重试
boolean isResponseTimeout = false;
Throwable cause = throwable.getCause();
//netty 的读取超时一般是 ReadTimeoutException
if (cause instanceof ReadTimeoutException) {
log.info("Cause is a ReadTimeoutException which indicates it is a response time out");
isResponseTimeout = true;
} else {
//对于其他一些框架，使用了 java 底层 nio 的一般是 SocketTimeoutException，message 为 read time out
//还有一些其他异常，但是 message 都会有 read time out 字段，所以通过 message 判断
String message = throwable.getMessage();
if (StringUtils.isNotBlank(message) && StringUtils.containsIgnoreCase(message.replace(" ", ""), "readtimeout")) {
log.info("Throwable message contains readtimeout which indicates it is a response time out");
isResponseTimeout = true;
}
}
//如果请求是 GET 或者标注了重试，则直接判断可以重试
if (method == HttpMethod.GET || webClientProperties.retryablePathsMatch(uri.getPath())) {
log.info("should retry on {}-{}, {}", method, uri, throwable.toString());
return true;
} else {
//否则，只针对请求还没有发出去的异常进行重试
if (isResponseTimeout) {
log.info("should not retry on {}-{}, {}", method, uri, throwable.toString());
} else {
log.info("should retry on {}-{}, {}", method, uri, throwable.toString());
return true;
}
}
}
return false;
}).build());

HttpClient httpClient = HttpClient
.create()
.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, (int) webClientProperties.getConnectTimeout().toMillis())
.doOnConnected(connection ->
connection
.addHandlerLast(new ReadTimeoutHandler((int) webClientProperties.getResponseTimeout().toSeconds()))
.addHandlerLast(new WriteTimeoutHandler((int) webClientProperties.getResponseTimeout().toSeconds()))
);

Retry finalRetry = retry;
String finalServiceName = serviceName;
return WebClient.builder()
.exchangeStrategies(ExchangeStrategies.builder()
.codecs(configurer -> configurer
.defaultCodecs()
//最大 body 占用 16m 内存
.maxInMemorySize(16 * 1024 * 1024))
.build())
.clientConnector(new ReactorClientHttpConnector(httpClient))
//Retry在负载均衡前
.filter((clientRequest, exchangeFunction) -> {
return exchangeFunction
.exchange(clientRequest)
.transform(ClientResponseRetryOperator.of(finalRetry));
})
//负载均衡器，改写url
.filter(lbFunction)
//实例级别的断路器需要在负载均衡获取真正地址之后
.filter((clientRequest, exchangeFunction) -> {
ServiceInstance serviceInstance = getServiceInstance(clientRequest);
serviceInstanceMetrics.recordServiceInstanceCall(serviceInstance);
CircuitBreaker circuitBreaker;
//这时候的url是经过负载均衡器的，是实例的url
//需要注意的一点是，使用异步 client 的时候，最好不要带路径参数，否则这里的断路器效果不好
//断路器是每个实例每个路径一个断路器
String instancId = clientRequest.url().getHost() + ":" + clientRequest.url().getPort() + clientRequest.url().getPath();
try {
//使用实例id新建或者获取现有的CircuitBreaker,使用serviceName获取配置
circuitBreaker = circuitBreakerRegistry.circuitBreaker(instancId, finalServiceName);
} catch (ConfigurationNotFoundException e) {
circuitBreaker = circuitBreakerRegistry.circuitBreaker(instancId);
}
log.info("webclient circuit breaker [{}-{}] status: {}, data: {}", finalServiceName, instancId, circuitBreaker.getState(), JSON.toJSONString(circuitBreaker.getMetrics()));
return exchangeFunction.exchange(clientRequest).transform(ClientResponseCircuitBreakerOperator.of(circuitBreaker, serviceInstance, serviceInstanceMetrics, webClientProperties));
}).baseUrl(baseUrl)
.build();
}

private ServiceInstance getServiceInstance(ClientRequest clientRequest) {
URI url = clientRequest.url();
DefaultServiceInstance defaultServiceInstance = new DefaultServiceInstance();
defaultServiceInstance.setHost(url.getHost());
defaultServiceInstance.setPort(url.getPort());
return defaultServiceInstance;
}

这样，我们就实现了我们封装的基于配置的 WebClient

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