FasterXML/jackson-modules-java8

Overview

This is a multi-module umbrella project for Jackson modules needed to support Java 8 features, especially with Jackson 2.x that only requires Java 7 for running (and until 2.7 only Java 6).

Jackson 2.x

When used with Jackson 2.x, Java 8 support is provided via 3 separate modules:

• Parameter names: support for detecting constructor and factory method ("creator") parameters without having to use @JsonProperty annotation
  • provides com.fasterxml.jackson.module.paramnames.ParameterNamesModule
• Java 8 Date/time: support for Java 8 date/time types (specified in JSR-310 specification)
  • provides com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
  • ALSO provides legacy variant com.fasterxml.jackson.datatype.jsr310.JSR310TimeModule
  • difference between 2 modules is that of configuration defaults: use of JavaTimeModule strongly recommended for new code
• Java 8 Datatypes: support for other new Java 8 datatypes outside of date/time: most notably Optional, OptionalLong, OptionalDouble
  • provides com.fasterxml.jackson.datatype.jdk8.Jdk8Module

all of which are built from this repository, and accessed and used as separate Jackson modules (with separate Maven artifacts).

Jackson 3.x

Jackson 3.0 changes things as it requires Java 17 to work and can thereby directly supported features.

Because of this, all 3 modules are merged into jackson-databind and need not be registered (as of Jackson 3.0.0)

License

All modules are licensed under Apache License 2.0.

Status

Usage

Maven dependencies

To include modules, you use some or all of:

<!-- parameter names -->
<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-parameter-names</artifactId>
</dependency>

<!-- Java 8 Date/time -->
<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
</dependency>

<!-- Java 8 Datatypes -->
<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jdk8</artifactId>
</dependency>

and either include versions directly, OR, preferably, import Jackson BOM that will specify consistent version set.

Note that the parent project -- jackson-modules-java8 -- is ONLY used as parent pom by individual "child" modules, and DOES NOT have dependencies on them. This means that you should not depend on it as that will not include child modules.

Registering modules

The most common mechanism (and one recommended by Jackson team) is to explicitly register modules you want. This is done by code like:

// Up to Jackson 2.9: (but not with 3.0)
ObjectMapper mapper = new ObjectMapper()
   .registerModule(new ParameterNamesModule())
   .registerModule(new Jdk8Module())
   .registerModule(new JavaTimeModule()); // new module, NOT JSR310Module

// with 3.0 (or with 2.10 as alternative)
ObjectMapper mapper = JsonMapper.builder() // or different mapper for other format
   .addModule(new ParameterNamesModule())
   .addModule(new Jdk8Module())
   .addModule(new JavaTimeModule())
   // and possibly other configuration, modules, then:
   .build();

Alternatively, you can also auto-discover these modules with:

ObjectMapper mapper = new ObjectMapper();
mapper.findAndRegisterModules();

Regardless of registration mechanism, after registration all functionality is available for all normal Jackson operations.

Notes on Registration

But do note that you should only either explicit OR automatic registration: DO NOT combine explicit and auto-registration. If you use both, only one of registrations will have effect. And selection of which one varies by module and settings:

• If MapperFeature.IGNORE_DUPLICATE_MODULE_REGISTRATIONS is defined, the FIRST registration succeeds, rest ignored
  • Duplicates are detected using id provided by Module.getTypeId(); duplicate-detection requires that Module provides same for all instances (true for Modules provided by this repo)
• Otherwise all registrations are processed by the LAST one has effect as it has precedence over earlier registrations.

Also note that before Jackson 2.10, auto-registration would only register older JSR310Module, and not newer JavaTimeModule -- this is due to backwards compatibility. This was changed in Jackson 2.10.

If you want "the other" version of the module but also use auto-registration, make sure to register "other" module explicitly AFTER calling mapper.findAndRegisterModules(). Call after works because getTypeId() provided by modules differs so they are not considered duplicates.

Development

Maintainers

Following developers have committer access to this project.

• Authors
  • Nick Williams (beamerblvd@github) contributed Java 8 date/time module; still helps issues from time to time
  • Tatu Saloranta (@cowtowncoder) wrote the other 2 modules and maintains them for 2.x (in 3.0, integrated into core jackson-databind)
• Maintainers:
  • Michael O'Keeffe (kupci@github) is the current maintainer of Java 8 date/time module

More

See Wiki for more information.