SpringBoot自定义序列化的使用方式--WebMvcConfigurationSupport

场景及需求： 项目接入了SpringBoot开发，现在需求是服务端接口返回的字段如果为空，那么自动转为空字符串。

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

如上，格式化后的返回内容应该为：
[
     {
         "id": 1,
         "name": ""
     },
     {
         "id": 2,
         "name": "xiaohong"
     }
]

这里直接给出解决方案代码，这里支持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);

        //这里是fastJSON的配置方式，更多的内容可以查看SerializerFeature
//        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
//        converter.setFeatures(SerializerFeature.WriteNullStringAsEmpty, SerializerFeature.WriteNullNumberAsZero,
//                SerializerFeature.WriteNullBooleanAsFalse, SerializerFeature.WriteNullListAsEmpty);
        converters.add(converter);
    }

}

最后我们也可以了解一下：WebMvcConfigurationSupport类
下面是它的官方文档描述：

public class WebMvcConfigurationSupport
extends Object
implements ApplicationContextAware, ServletContextAware

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.

Registers these HandlerAdapters:

• RequestMappingHandlerAdapter for processing requests with annotated controller methods.
• HttpRequestHandlerAdapter for processing requests with HttpRequestHandlers.
• SimpleControllerHandlerAdapter for processing requests with interface-based Controllers.

Registers a HandlerExceptionResolverComposite with this chain of exception resolvers:

• ExceptionHandlerExceptionResolver for handling exceptions through @ExceptionHandler methods.
• ResponseStatusExceptionResolver for exceptions annotated with @ResponseStatus.
• DefaultHandlerExceptionResolver for resolving known Spring exception types

Registers an AntPathMatcher and a UrlPathHelper to be used by:

• the RequestMappingHandlerMapping,
• the HandlerMapping for ViewControllers
• and the HandlerMapping for serving resources

Note that those beans can be configured with a PathMatchConfigurer.

Both the RequestMappingHandlerAdapter and the ExceptionHandlerExceptionResolver are configured with default instances of the following by default:

• a ContentNegotiationManager
• a DefaultFormattingConversionService
• a OptionalValidatorFactoryBean if a JSR-303 implementation is available on the classpath
• a range of HttpMessageConverters depending on the third-party libraries available on the classpath.