feign改写默认编码器

背景：项目中遇到一个坑，用feign调用其他服务在编码json的时候，会把数值类型的null转成0。

解决：feign默认的编码器是ResponseEntityDecoder，改成fastjson解决这个问题。

直接上代码：

package com.gtmc.agg.dms.wty.core.config;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import com.alibaba.fastjson.support.springfox.SwaggerJsonSerializer;
import feign.codec.Decoder;
import feign.codec.Encoder;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.cloud.openfeign.support.SpringDecoder;
import org.springframework.cloud.openfeign.support.SpringEncoder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;

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

/**
 * @author ：TianYuan
 * @date ：Created in 2022/3/22 18:10
 * @description：
 * @modified By：
 */
@Configuration
public class FeignConfig {

    @Bean
    public Encoder feignEncoder() {
        return new SpringEncoder(feignHttpMessageConverter());
    }

    @Bean
    public Decoder feignDecoder() {
        return new SpringDecoder(feignHttpMessageConverter());
    }

    /**
     * 设置解码器为fastjson
     *
     * @return
     */
    private ObjectFactory<HttpMessageConverters> feignHttpMessageConverter() {
        final HttpMessageConverters httpMessageConverters = new HttpMessageConverters(this.getFastJsonConverter());
        return () -> httpMessageConverters;
    }

    private FastJsonHttpMessageConverter getFastJsonConverter() {
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();

        List<MediaType> supportedMediaTypes = new ArrayList<>();
        MediaType mediaTypeJson = MediaType.valueOf(MediaType.APPLICATION_JSON_UTF8_VALUE);
        supportedMediaTypes.add(mediaTypeJson);
        converter.setSupportedMediaTypes(supportedMediaTypes);
        FastJsonConfig config = new FastJsonConfig();
        config.getSerializeConfig().put(JSON.class, new SwaggerJsonSerializer());
        config.setSerializerFeatures(SerializerFeature.WriteMapNullValue);
        converter.setFastJsonConfig(config);

        return converter;
    }
}

SerializerFeature.WriteMapNullValue可以根据自己的要求来设置