Return ISO-8601 dates with custom ObjectMapper in Spring Boot 2

Question

I want my LocalDateTimes to be returned as ISO-8601 strings (e.g. "2020-10-12T10:57:15Z") from my Spring REST Controllers. This has worked previously, but now that I'm using a custom Jackson2 ObjectMapper these dates are instead being returned as arrays: [2020, 10, 12, 10, 57, 15, 200000000].

Why is this happening and how can I customize the ObjectMapper while still returning ISO-8601 dates?

Answer 1

JacksonAutoConfiguration creates an ObjectMapper with the WRITE_DATES_AS_TIMESTAMPS feature turned off, which returns LocalDateTimes as ISO-8601 strings. When you provide a custom ObjectMapper this default auto-configuration is turned off.

This can be solved by, instead of providing a custom ObjectMapper, providing a Jackson2ObjectMapperBuilderCustomizer. This bean will be used by JacksonAutoConfiguration to customize the ObjectMapper while maintaining the auto-configured behaviour such as turning off the WRITE_DATES_AS_TIMESTAMPS feature.

@Configuration
public class Config {
    @Bean
    public Jackson2ObjectMapperBuilderCustomizer objectMapperBuilderCustomizer() {
        return jacksonObjectMapperBuilder -> {
            // Customize the ObjectMapper while maintaining the auto-configuration
        };
    }
}