Upgrading to Jackson 3 with Spring Boot 4

December 21st, 2025

2 minute read

Spring Spring boot Advent of Spring

Introduction

Spring Boot 4 has been released last month! Considering all the new features it has, I decided to write about these features throughout the month of December. It will be an advent of Spring Boot 4 related tips!

I’ve mentioned it a few times before, but whenever you upgrade your Spring Boot application to the latest Spring Boot version, you’re not only upgrading the Spring framework version you use, but also countless other libraries. One of those libraries is Jackson. When you switch to Spring Boot 4, you’ll see that you’re no longer using Jackson v2, but the new Jackson v3!

Package rename

One of the big changes within Jackson 3 is that components such as ObjectMapper now sit within the tools.jackson package and no longer in the com.fasterxml package. In fact, the dependencies themselves now have a group ID starting with tools.jackson (e.g. tools.jackson.core:jackson-core).

Be aware, the annotations such as @JsonProperty still come from com.fasterxml for backwards compatibility.

A new mapper

The biggest change (in my opinion) is that you should no longer use ObjectMapper directly, but use the new JsonMapper instead. This new JsonMapper extends ObjectMapper, but provides a fluent, immutable API for configuring.

The new mapper is also automatically configured to map things like Optional, LocalDateTime and so on. This means that you no longer need to work with modules such as jackson-datatype-jsr310.

Due to that, the new JsonMapper is more aligned with Spring, and thus the Spring team deprecated the Jackson2ObjectMapperBuilder class and recommends using the JsonMapper.Builder instead. For example:

@Bean
JsonMapper jsonMapper(JsonMapper.Builder builder) {
    return builder
        .enable(SerializationFeature.INDENT_OUTPUT)
        .build();
}

An even better solution is to use the new JsonMapperBuilderCustomizer, which essentially is the same as Jackson2ObjectMapperBuilderCustomizer, but for the new JsonMapper:

@Bean
JsonMapperBuilderCustomizer jacksonCustomizer() {
    return builder -> builder.enable(SerializationFeature.INDENT_OUTPUT);
}

Another big difference is that the JsonMapper no longer throws checked exceptions such as JsonProcessingException. Instead, it will now throw unchecked exceptions (JacksonException). This makes it easier to use JsonMapper within lambdas, for example.

Different feature toggles

Jackson always worked with all kinds of feature toggles (e.g. SerializationFeature, MappingFeature, …). Some of the defaults have also changed in Jackson 3.

For example:

• DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES is now true by default
• SerializationFeature.WRITE_DATES_AS_TIMESTAMPS is now true by default, meaning that you no longer get these Unix timestamps when serializing dates
• MapperFeature.SORT_PROPERTIES_ALPHABETICALLY is now true by default. This could impact some tests that rely on the order of JSON properties as they’re now alphabetically sorted.
• …

A full list of these changes can be found on the wiki of Jackson.

Conclusion

The release of Jackson 3 introduces some very logical defaults (immutability, some logical feature toggle changes, unchecked exceptions, …). With this, I think Jackson became even easier to use for both Spring- and non-Spring users.

This blogpost is a part of the Advent of Spring Boot 2025 series.