[FIXED] Null values returned using WebMvcConfigurationSupport instead of WebMvcConfigurerAdapter

Issue

As WebMvcConfigurerAdapter is deprecated as of Spring 5.0, I have changed it to WebMvcConfigurationSupport, but I get null values in response.

{
"key": null,
"value": null,
"name":"test"
}

If I change it back to WebMvcConfigurerAdapter, I get the expected response:

{
"name":"test"
}

Spring version: 5.7.0 Jackson Version: 2.9.7

I have googled a lot of things but still no luck. I don't want to use the deprecated class. Tried removing @EnableWebMvc annotation after adding WebMvcConfigurationSupport as it's not required.

I have overridden configureMessageConverters where I setup MappingJackson2HttpMessageConverter with the inclusion NOT_NULL

@Configuration
@EnableAspectJAutoProxy
@EnableSwagger2
@PropertySource("classpath:test.properties")
@ComponentScan(basePackages = {"com.test.web"})
public class UmwWebConfig extends WebMvcConfigurationSupport {

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        ByteArrayHttpMessageConverter bahHumbug = new ByteArrayHttpMessageConverter();
        bahHumbug.setSupportedMediaTypes(Collections.singletonList(MediaType.parseMediaType("application/pdf")));
        converters.add(bahHumbug);

        final MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        final ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        objectMapper.getFactory().configure(JsonGenerator.Feature.ESCAPE_NON_ASCII, true);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        converter.setObjectMapper(objectMapper);
        converters.add(converter);
        super.configureMessageConverters(converters);
    }

Want to remove the null fields from the response. Please let me know if anything is wrong in the configuration.

Solution

Don't extend WebMvcConfigurationSupport as that is not equivalent to extending the deprecated WebMvcConfigurerAdapter.

Instead implement WebMvcConfigurer which is also what is suggested in the deprecation documentation in the javadoc of `WebMvcConfigurerAdapter.

Deprecated. as of 5.0 WebMvcConfigurer has default methods (made possible by a Java 8 baseline) and can be implemented directly without the need for this adapter

So your configuration class header should look something like this

@Configuration
@EnableAspectJAutoProxy
@EnableSwagger2
@EnableWebMvc
@PropertySource("classpath:test.properties")
@ComponentScan(basePackages = {"com.test.web"})
public class UmwWebConfig implements WebMvcConfigurer { ... }

You need to add @EnableWebMvc again (as it should` and override/implement the interface method you need to use. In thise case probably only a single one.

PRO-TIP: Use the Jackson2ObjectMapperBuilder to build the ObjectMapper and use the constructor of the MappingJackson2HttpMessageConverter. This saves creating an additional ObjectMapper (which happens in the default constructor).

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        ByteArrayHttpMessageConverter bahHumbug = new ByteArrayHttpMessageConverter();
        bahHumbug.setSupportedMediaTypes(Collections.singletonList(MediaType.parseMediaType("application/pdf")));
        converters.add(bahHumbug);

        final ObjectMapper objectMapper = 
          Jackson2ObjectMapperBuilder.json()
            .serializationInclusion(JsonInclude.Include.NON_NULL)
            .failOnUnknownProperties(true)
            .featuresToEnable(JsonGenerator.Feature.ESCAPE_NON_ASCII)
            .build();       

        converters.add(new MappingJackson2HttpMessageConverter(objectMapper);
        super.configureMessageConverters(converters);
    }

Answered By - M. Deinum