SpringBoot 返回 BigDecimal ，数值太小导致返回科学计数法

针对使用 Jackson 返回

1、自定义ObjectMapper替换 或 自定义 MappingJackson2HttpMessageConverter 或 便利现有 messageConverters 进行 objectMapper 配置

2、配置 objectMapper

configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN,true);

3、针对替换不生效可自行搜索类似文章或关键字

springboot - Spring Boot ObjectMapper 配置不生效问题 - 个人文章 - SegmentFault 思否
https://segmentfault.com/a/1190000041997183

针对使用 Fastjson返回

1、自定义 FastJsonHttpMessageConverter ，放置list首位或，移除其他 json messageConverter

2、配置 fastJsonConfig

SerializerFeature.WriteBigDecimalAsPlain //防止科学计数法

```

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.collections.CollectionUtils;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.math.BigDecimal;
import java.util.List;

/**
*
*/
@Slf4j
@Configuration
public class WebAppConfig implements WebMvcConfigurer {

//    @Bean
//    @Primary
//    public ObjectMapper objectMapper() {
//        ObjectMapper objectMapper = new ObjectMapper();
//        objectMapper.configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN,true);
//        //objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
//        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//        objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
//        return objectMapper;
//    }

/**

* 更改全局fastjson配置
* @param converters
  */
  @Override
  public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
  // 清除默认json转换器
  //converters.removeIf(converter -> converter instanceof MappingJackson2HttpMessageConverter);

//        MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessageConverter();
//        ObjectMapper objectMapper = new ObjectMapper();
//        objectMapper.configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN,true);
//        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//        objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
//        mappingJackson2HttpMessageConverter.setObjectMapper(objectMapper);
//        converters.clear();
//        converters.add(mappingJackson2HttpMessageConverter);

if(CollectionUtils.isNotEmpty(converters)){
converters.stream().filter(e->e instanceof AbstractJackson2HttpMessageConverter).forEach(m->{
((AbstractJackson2HttpMessageConverter) m).getObjectMapper().
configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN,true);
});
}

//        //1.需要定义一个convert转换消息的对象;
//        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
//        //2:添加fastJson的配置信息;
//        FastJsonConfig fastJsonConfig = new FastJsonConfig();
//        fastJsonConfig.setSerializerFeatures(
//                SerializerFeature.WriteDateUseDateFormat,
//                SerializerFeature.WriteMapNullValue,//输出值为null的字段
//                SerializerFeature.WriteNullStringAsEmpty,//字符类型字段如果为null,输出为”“,而非null
//                SerializerFeature.WriteNullListAsEmpty,//List字段如果为null,输出为[],而非null
//                SerializerFeature.DisableCircularReferenceDetect,
//                SerializerFeature.WriteBigDecimalAsPlain //防止科学计数法
//        );
//        //3处理中文乱码问题
//        List<MediaType> fastMediaTypes = new ArrayList<>();
//        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
//        //4.在convert中添加配置信息.
//        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);
//        fastJsonHttpMessageConverter.setObjectMapper(fastJsonConfig);
//        converters.add(fastJsonHttpMessageConverter);
converters.forEach(e->{
log.info("HttpMessageConverter e = {}",e.getClass().getName());
});
}

public static void main(String[] args) throws JsonProcessingException {
ObjectMapper om = new ObjectMapper();
om.configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN,true);
BigDecimal b = new BigDecimal("0.0000000000123");
String result = om.writeValueAsString(b);
System.out.println();
}

}

```