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本文主要研究一下spring cloud gateway的RetryGatewayFilter

GatewayAutoConfiguration

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@Configuration@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)@EnableConfigurationProperties@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})@ConditionalOnClass(DispatcherHandler.class)public class GatewayAutoConfiguration {    //......	@Bean	public RetryGatewayFilterFactory retryGatewayFilterFactory() {		return new RetryGatewayFilterFactory();	}    //......}

默认启用了RetryGatewayFilterFactory

RetryGatewayFilterFactory

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/filter/factory/RetryGatewayFilterFactory.java

public class RetryGatewayFilterFactory extends AbstractGatewayFilterFactory
    
      {	private static final Log log = LogFactory.getLog(RetryGatewayFilterFactory.class);	public RetryGatewayFilterFactory() {		super(RetryConfig.class);	}	@Override	public GatewayFilter apply(RetryConfig retryConfig) {		retryConfig.validate();		Predicate
     > predicate = context -> {			ServerWebExchange exchange = context.applicationContext();			if (exceedsMaxIterations(exchange, retryConfig)) {				return false;			}			HttpStatus statusCode = exchange.getResponse().getStatusCode();			HttpMethod httpMethod = exchange.getRequest().getMethod();			boolean retryableStatusCode = retryConfig.getStatuses().contains(statusCode);			if (!retryableStatusCode && statusCode != null) { // null status code might mean a network exception?				// try the series				retryableStatusCode = retryConfig.getSeries().stream()						.anyMatch(series -> statusCode.series().equals(series));			}			boolean retryableMethod = retryConfig.getMethods().contains(httpMethod);			return retryableMethod && retryableStatusCode;		};		Repeat
     
       repeat = Repeat.onlyIf(predicate)				.doOnRepeat(context -> reset(context.applicationContext()));		//TODO: support timeout, backoff, jitter, etc... in Builder		Predicate
      
       
        > retryContextPredicate = context -> {			if (exceedsMaxIterations(context.applicationContext(), retryConfig)) {				return false;			}			for (Class
         clazz : retryConfig.getExceptions()) {				if (clazz.isInstance(context.exception())) {					return true;				}			}            return false;		};		Retry
        
          reactorRetry = Retry.onlyIf(retryContextPredicate)				.doOnRetry(context -> reset(context.applicationContext()))				.retryMax(retryConfig.getRetries());		return apply(repeat, reactorRetry);	}	public boolean exceedsMaxIterations(ServerWebExchange exchange, RetryConfig retryConfig) {		Integer iteration = exchange.getAttribute("retry_iteration");		//TODO: deal with null iteration		return iteration != null && iteration >= retryConfig.getRetries();	}	public void reset(ServerWebExchange exchange) {		//TODO: what else to do to reset SWE?		exchange.getAttributes().remove(ServerWebExchangeUtils.GATEWAY_ALREADY_ROUTED_ATTR);	}	@Deprecated	public GatewayFilter apply(Repeat
         
           repeat) { return apply(repeat, Retry.onlyIf(ctxt -> false)); } public GatewayFilter apply(Repeat
          
            repeat, Retry
           
             retry) { return (exchange, chain) -> { log.trace("Entering retry-filter"); int iteration = exchange.getAttributeOrDefault("retry_iteration", -1); exchange.getAttributes().put("retry_iteration", iteration + 1); return Mono.fromDirect(chain.filter(exchange) .log("retry-filter", Level.INFO) .retryWhen(retry.withApplicationContext(exchange)) .repeatWhen(repeat.withApplicationContext(exchange))); }; } //......}
           
          
         
        
       
      
     
    

• 可以看到这个filter使用了reactor的Retry组件，同时往exchange的attribues添加retry_iteration，用来记录重试次数，该值默认从-1开始，第一次执行的时候，retry_iteration+1为0。之后每重试一次，就添加1。
• filter的apply接收两个参数，一个是Repeat<ServerWebExchange>，一个是Retry<ServerWebExchange>。
• repeat与retry的区别是repeat是在onCompleted的时候会重试，而retry是在onError的时候会重试。这里由于不一定是异常的时候才可能重试，所以加了repeat。

RetryConfig

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/filter/factory/RetryGatewayFilterFactory.java

public static class RetryConfig {		private int retries = 3;				private List
    
      series = toList(Series.SERVER_ERROR);				private List
     
       statuses = new ArrayList<>();				private List
      
        methods = toList(HttpMethod.GET);		private List
       
        > exceptions = toList(IOException.class);		//......		public void validate() {			Assert.isTrue(this.retries > 0, "retries must be greater than 0");			Assert.isTrue(!this.series.isEmpty() || !this.statuses.isEmpty(),					"series and status may not both be empty");			Assert.notEmpty(this.methods, "methods may not be empty");		}        //......	}
       
      
     
    

可以看到配置文件有5个属性，如下：

• retries，默认为3，用来标识重试次数
• series，用来指定哪些段的状态码需要重试，默认SERVER_ERROR即5xx
• statuses，用于指定哪些状态需要重试，默认为空，它跟series至少得指定一个
• methods，用于指定那些方法的请求需要重试，默认为GET
• exceptions，用于指定哪些异常需要重试，默认为java.io.IOException

实例

spring:  cloud:    gateway:      routes:      - id: retry-demo        uri: http://localhost:9090        predicates:        - Path=/retry/**        filters:        - name: Retry          args:           retries: 15           series:            - SERVER_ERROR            - CLIENT_ERROR           methods:            - GET            - POST           exceptions:            - java.io.IOException            - java.util.concurrent.TimeoutException

这里指定了针对4xx及5xx的GET或POST方法或者IOException或TimeoutException的时候进行重试，重试次数为15次。

小结

RetryGatewayFilter借助了reactor-addons的retry组件进行了重试，主要使用了Mono的repeatWhen及retryWhen方法，前者在onCompleted的时候触发，后者在onError的时候触发。

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