feign.codec.DecodeException: No qualifying bean of type HttpMessageConverters

现象

在spring cloud gateway中使用fegin调用服务时，返回时报错。

feign.codec.DecodeException: No qualifying bean of type 'org.springframework.boot.autoconfigure.http.HttpMessageConverters' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
	at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:182)

原因分析

feign中对返回的数据进行解析时，缺少依赖对象导致。

• feign对返回信息response解析

package org.springframework.cloud.openfeign.support;
...
public class SpringDecoder implements Decoder {
...
    public Object decode(final Response response, Type type) throws IOException, FeignException {
        if (!(type instanceof Class) && !(type instanceof ParameterizedType) && !(type instanceof WildcardType)) {
            throw new DecodeException(response.status(), "type is not an instance of Class or ParameterizedType: " + type, response.request());
        } else {
//异常处
            HttpMessageConverterExtractor extractor = new HttpMessageConverterExtractor(type, ((HttpMessageConverters)this.messageConverters.getObject()).getConverters());
            return extractor.extractData(new SpringDecoder.FeignResponseAdapter(response));
        }
    }

...
}

• Spring内部方法验证

package org.springframework.beans.factory.support;
...
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
...
    @Nullable
    public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName, @Nullable Set autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
//此处判断HttpMessageConverters未加载导致异常
            if (this.isRequired(descriptor)) {
                this.raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
            }

...
        return autowiredBeanName;
    }
...
}

处理办法

feign配置中增加HttpMessageConverters即可。

import feign.codec.Decoder;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.cloud.openfeign.support.ResponseEntityDecoder;
import org.springframework.cloud.openfeign.support.SpringDecoder;
import org.springframework.context.annotation.Bean;
import org.springframework.http.MediaType;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;

import java.util.ArrayList;
import java.util.List;

/**
 * @description: feign配置
 * @author: lizz
 * @date: 2020/4/23 2:32 下午
 */
@SpringBootConfiguration
public class FeignConfig {
    @Bean
    public Decoder feignDecoder() {
        return new ResponseEntityDecoder(new SpringDecoder(feignHttpMessageConverter()));
    }

    public ObjectFactory feignHttpMessageConverter() {
        final HttpMessageConverters httpMessageConverters = new HttpMessageConverters(new GateWayMappingJackson2HttpMessageConverter());
        return new ObjectFactory() {
            @Override
            public HttpMessageConverters getObject() throws BeansException {
                return httpMessageConverters;
            }
        };
    }

    public class GateWayMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
        GateWayMappingJackson2HttpMessageConverter(){
            List mediaTypes = new ArrayList<>();
            mediaTypes.add(MediaType.valueOf(MediaType.TEXT_HTML_VALUE + ";charset=UTF-8")); 
            setSupportedMediaTypes(mediaTypes);
        }
    }
}

参考：https://springboot.io/t/topic/1361