場景及需求： 專案接入了SpringBoot開發，現在需求是服務端介面返回的欄位如果為空，那麼自動轉為空字串。

例如：
[
     {
         "id": 1,
         "name": null
     },
     {
         "id": 2,
         "name": "xiaohong"
     }
]

如上，格式化後的返回內容應該為：
[
     {
         "id": 1,
         "name": ""
     },
     {
         "id": 2,
         "name": "xiaohong"
     }
]

這裡直接給出解決方案程式碼，這裡支援FastJson和Jackson配置序列化的方式：

@Configuration
public class WebCatMvcConfiguration extends WebMvcConfigurationSupport {

    @Override
    protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        ObjectMapper objectMapper = new ObjectMapper();
        SimpleModule module = new SimpleModule();
        module.addSerializer(new ToStringSerializer(Long.TYPE));
        module.addSerializer(new ToStringSerializer(Long.class));
        module.addSerializer(new ToStringSerializer(BigInteger.class));
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
            @Override
            public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
                jsonGenerator.writeString("");
            }
        });
        objectMapper.registerModule(module);
        converter.setObjectMapper(objectMapper);

        //這裡是fastJSON的配置方式，更多的內容可以檢視SerializerFeature
//        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
//        converter.setFeatures(SerializerFeature.WriteNullStringAsEmpty, SerializerFeature.WriteNullNumberAsZero,
//                SerializerFeature.WriteNullBooleanAsFalse, SerializerFeature.WriteNullListAsEmpty);
        converters.add(converter);
    }

}

最後我們也可以瞭解一下：WebMvcConfigurationSupport類
下面是它的官方文件描述：

This is the main class providing the configuration behind the MVC Java config. It is typically imported by adding @EnableWebMvc to an application@Configuration class. An alternative more advanced option is to extend directly from this class and override methods as necessary remembering to add@Configuration

to the subclass and @Bean to overridden @Bean methods. For more details see the Javadoc of @EnableWebMvc.

This class registers the following HandlerMappings:

• RequestMappingHandlerMapping ordered at 0 for mapping requests to annotated controller methods.
• HandlerMapping ordered at 1 to map URL paths directly to view names.
• BeanNameUrlHandlerMapping ordered at 2 to map URL paths to controller bean names.
• HandlerMapping ordered at Integer.MAX_VALUE-1 to serve static resource requests.
• HandlerMapping ordered at Integer.MAX_VALUE to forward requests to the default servlet.

Note that those beans can be configured with a PathMatchConfigurer.