Springboot：统一处理null数据类型默认值

因为服务端经常定义字段大部分是封装类型，在返回给前端时没有值的时候一般直接返回的null，但是有的时候由于增加了前端的处理或者业务的需要,需要把值为null的设置成""或者[]亦或者{}，此时我们可以配置返回值为null的统一处理：

@Configuration
public class MyWebmvcConfiguration implements WebMvcConfigurer {

	@Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		registry.addResourceHandler("/statics/**").addResourceLocations("classpath:/statics/");
	}

	public HttpMessageConverter stringConverter() {
		StringHttpMessageConverter converter = new StringHttpMessageConverter(
				Charset.forName("UTF-8"));
		return converter;
	}

	public HttpMessageConverter fastConverter() {
		// 定义一个convert转换消息的对象
		FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();
		// 添加Fast Json的配置信息
		FastJsonConfig fastJsonConfig = new FastJsonConfig();
		fastJsonConfig.setSerializerFeatures(SerializerFeature.PrettyFormat,
				SerializerFeature.WriteNullStringAsEmpty, //字符串null返回空字符串
				SerializerFeature.WriteNullNumberAsZero, //数值类型为0
				SerializerFeature.WriteNullListAsEmpty, //空字段保留
				SerializerFeature.WriteMapNullValue);
		fastJsonConfig.setCharset(Charset.forName("UTF-8"));
		fastJsonConfig.setDateFormat("yyyy-MM-dd hh:mm:ss");
		// 处理中文乱码问题
		List fastMediaTypes = new ArrayList<>();
		fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
		fastConverter.setSupportedMediaTypes(fastMediaTypes);
		// 在convert中添加配置信息
		fastConverter.setFastJsonConfig(fastJsonConfig);
		return fastConverter;
	}

	@Override
	public void extendMessageConverters(List> converters) {
		converters.clear();
		converters.add(fastConverter());
		converters.add(stringConverter());
		for (HttpMessageConverter messageConverter : converters) {
			System.out.println(messageConverter);
		}
	}

	@Bean
	public WebMvcConfigurer corsConfigurer() {
		return new WebMvcConfigurer() {
			@Override
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/**").allowedOrigins("*").allowedMethods("*").allowCredentials(true).maxAge(3600);
			}
		};
	}
}