SpringCloud Alibaba Sentinel整合SpringCloud OpenFeign，启动报错。

Caused by: java.lang.AbstractMethodError: com.alibaba.cloud.sentinel.feign.SentinelContractHolder.parseAndValidatateMetadata(Ljava/lang/Class;)Ljava/util/List;at feign.ReflectiveFeign$ParseHandlersByName.apply(ReflectiveFeign.java:154)at feign.ReflectiveFeign.newInstance(ReflectiveFeign.java:52)at feign.Feign$Builder.target(Feign.java:251)at org.springframework.cloud.openfeign.HystrixTargeter.target(HystrixTargeter.java:38)at org.springframework.cloud.openfeign.FeignClientFactoryBean.loadBalance(FeignClientFactoryBean.java:242)at org.springframework.cloud.openfeign.FeignClientFactoryBean.getTarget(FeignClientFactoryBean.java:271)at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:251)at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:169)... 39 common frames omitted

报错原因：

       Sentinel框架SentinelContractHolder类中找不到parseAndValidatateMetadata这个方法，是因为这个方法拼写有错误，在Sentinel和OpenFeign新版本中已经修正parseAndValidateMetadata。

Sentinel（2.2.1.RELEASE）中的SentinelContractHolder类调用的是新版本的OpenFeign（2.2.2.RELEASE）方法

而Spring Cloud Alibaba（2.2.1.RELEASE）引入的是旧版本的OpenFeign（2.2.1.RELEASE）方法。

两种解决办法：

1.解决版本问题

在父工程引入2.2.0.release版本，一定要在spring-cloud-dependencies前面，因为依赖从上到下有优先级。

 org.springframework.cloudspring-cloud-openfeign-dependencies2.2.0.RELEASEpomimportorg.springframework.cloudspring-cloud-dependenciesHoxton.SR3pomimport

2.新建一个com.alibaba.cloud.sentinel.feign.SentinelContractHolder

import feign.Contract;
import feign.MethodMetadata;
import java.util.HashMap;
import java.util.List;
import java.util.Map;public class SentinelContractHolder implements Contract {private final Contract delegate;public static final Map METADATA_MAP = new HashMap();public SentinelContractHolder(Contract delegate) {this.delegate = delegate;}@Overridepublic List parseAndValidatateMetadata(Class targetType) {List metadatas = this.delegate.parseAndValidatateMetadata(targetType);metadatas.forEach((metadata) -> {MethodMetadata var10000 = (MethodMetadata)METADATA_MAP.put(targetType.getName() + metadata.configKey(), metadata);});return metadatas;}
}