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

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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 HandlerMapping s:

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 HandlerAdapter s:

RequestMappingHandlerAdapter for processing requests with annotated controller methods.
HttpRequestHandlerAdapter for processing requests with HttpRequestHandler s.
SimpleControllerHandlerAdapter for processing requests with interface-based Controller s.

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 HttpMessageConverter s depending on the third-party libraries available on the classpath.