基本概念

HttpMessageConverter：

org.springframework.http.converter.HttpMessageConverter 是一个策略接口

接口说明如下：

Strategy interface that specifies a converter that can convert from and to HTTP requests and responses.

简单说就是 HTTP request (请求)和response (响应)的转换器。

API

public class MappingJackson2HttpMessageConverter
extends AbstractJackson2HttpMessageConverter

Implementation of HttpMessageConverter that can read and write JSON using Jackson 2.x's ObjectMapper.

This converter can be used to bind to typed beans, or untyped HashMap instances.

By default, this converter supports application/json and application/*+json with UTF-8 character set. This can be overridden by setting the supportedMediaTypes property.

The default constructor uses the default configuration provided by Jackson2ObjectMapperBuilder.

Compatible with Jackson 2.9 and higher, as of Spring 5.0.

解决方案 

@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurationSupport {

	/**
	 * 统一输出风格
	 * See {@link com.fasterxml.jackson.databind.PropertyNamingStrategy.SnakeCaseStrategy} for details.
	 * @param converters
	 */
	@Override
	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
		for (int i = 0; i < converters.size(); i++) {
			if (converters.get(i) instanceof MappingJackson2HttpMessageConverter) {
				ObjectMapper objectMapper = new ObjectMapper();
				// 统一返回数据的输出风格
				objectMapper.setPropertyNamingStrategy(new PropertyNamingStrategy.SnakeCaseStrategy());
				objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
				objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
				objectMapper.setTimeZone(TimeZone.getTimeZone("GMT+8"));
				MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
				converter.setObjectMapper(objectMapper);
				converters.set(i, converter);
				break;
			}
		}
	}
}

运行结果

参考文章

https://blog.csdn.net/limenghua9112/article/details/84976621

https://www.jianshu.com/p/3e1de3d02dd8