Unexpected behavior with custom Jackson serializer for LocalDateTime in Java 17
Hey everyone, I'm running into an issue that's driving me crazy. I'm converting an old project and I'm dealing with I've searched everywhere and can't find a clear answer... I'm stuck on something that should probably be simple. I'm working with a Spring Boot 2.6 application and I've implemented a custom Jackson serializer for `LocalDateTime`. The goal is to serialize `LocalDateTime` objects into a specific string format (e.g., `yyyy-MM-dd'T'HH:mm:ss.SSSZ`) for our API responses. However, I'm encountering issues where some `LocalDateTime` objects are serialized correctly while others are not, leading to inconsistent API responses. Here’s the code I’ve written for the custom serializer: ```java import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; import java.io.IOException; import java.time.LocalDateTime; import java.time.format.DateTimeFormatter; public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> { private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ"); @Override public void serialize(LocalDateTime dateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeString(dateTime.format(formatter)); } } ``` To apply this serializer, I annotated my `LocalDateTime` field in the DTO class like this: ```java import com.fasterxml.jackson.databind.annotation.JsonSerialize; import java.time.LocalDateTime; public class MyDTO { @JsonSerialize(using = LocalDateTimeSerializer.class) private LocalDateTime timestamp; // getters and setters } ``` What’s strange is that when I return DTOs that contain `LocalDateTime` values created in different time zones, the formatted strings vary unexpectedly. For instance, a timestamp from `UTC` ends up formatted correctly, but a timestamp from `PST` shows a different output: ``` {"timestamp":"2023-10-01T15:00:00.000-0700"} {"timestamp":"2023-10-01T22:00:00.000+0000"} ``` I’ve also tried configuring the `ObjectMapper` to use my custom serializer globally but it didn’t change the outcome: ```java import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class JacksonConfig { @Bean public ObjectMapper objectMapper() { ObjectMapper mapper = new ObjectMapper(); mapper.findAndRegisterModules(); // This should register my serializers return mapper; } } ``` I’m not sure why the serialization is inconsistent across different time zones. Are there best practices or configurations I might be missing when using `LocalDateTime` with Jackson? Any insights would be greatly appreciated! This is part of a larger web app I'm building. Am I missing something obvious? This is my first time working with Java 3.10. I'm using Java stable in this project. How would you solve this?