Main Portal page for Jackson project
Latest commit a5025f4 Jan 16, 2017 @cowtowncoder cowtowncoder committed on GitHub Merge pull request #57 from dadoonet/patch-1
Update to 2.8.6

README.md

Jackson Project Home @github

This is the home page of the Jackson Project, formerly known as the standard JSON library for Java (or JVM platform in general), or, as the "best JSON parser for Java." Or simply as "JSON for Java." More than that, Jackson is a suite of data-processing tools for Java (and the JVM platform), including the flagship streaming JSON parser / generator library, matching data-binding library (POJOs to and from JSON) and additional data format modules to process data encoded in Avro, BSON, CBOR, CSV, Smile, (Java) Properties, Protobuf, XML or YAML; and even the large set of data format modules to support data types of widely used data types such as Guava, Joda, PCollections and many, many more (see below).

While the actual core components live under their own projects -- including the three core packages (streaming, databind, annotations; data format libraries; data type libraries; JAX-RS provider; and a miscellaneous set of other extension modules -- this project act as the central hub for linking all the pieces together.

A good companion to this README is the Jackson Project FAQ.

On reporting issues

First things first: unless you know what you are doing, DO NOT FILE ISSUES ON THE ISSUE TRACKER OF THIS REPO.

Instead, do one of the following:

  • For Jackson usage questions (for core components or modules), please use the Jackson-user Google group
  • For reporting issues on Jackson implementation, report it against one of the components
  • For suggestions and new ideas, try Jackson Future Ideas

Actively developed versions

Jackson suite has two major branches: 1.x is in maintenance mode, and only bug-fix versions are released; 2.x is the actively developed version. These two major versions use different Java packages and Maven artifact ids, so they are not mutually compatible, but can peacefully co-exist: a project can depend on both Jackson 1.x and 2.x, without conflicts. This is by design and was chosen as the strategy to allow smoother migration from 1.x to 2.x.

The latest stable versions from these branches are:

  • 2.8.6, released 12-Jan-2017
  • 1.9.13, released 14-Jul-2013

Recommended way to use Jackson is through Maven repositories; releases are made to Central Maven Repository (CMR). Individual project pages typically contain download links, leading to CMR.

Release notes found from Jackson Releases page.

Active Jackson projects

Most projects listed below are lead by Jackson development team; but some by other at-large Jackson community members. We try to keep versioning of modules compatible to reduce confusion regarding which versions work together.

Core modules

Core modules are the foundation on which extensions (modules) build upon. There are 3 such modules currently (as of Jackson 2.6):

  • Streaming (docs) ("jackson-core") defines low-level streaming API, and includes JSON-specific implementations
  • Annotations (docs) ("jackson-annotations") contains standard Jackson annotations
  • Databind (docs) ("jackson-databind") implements data-binding (and object serialization) support on streaming package; it depends both on streaming and annotations packages

Third-party datatype modules

These extensions are plug-in Jackson Modules (registered with ObjectMapper.registerModule()), and add support for datatypes of various commonly used Java libraries, by adding serializers and deserializers so that Jackson databind package (ObjectMapper / ObjectReader / ObjectWriter) can read and write these types.

Datatype modules directly maintained by Jackson team are:

In addition, we are aware of additional modules that are not directly maintained by core Jackson team:

Providers for JAX-RS

Jackson JAX-RS Providers has handlers to add dataformat support for JAX-RS implementations (like Jersey, RESTeasy, CXF). Providers implement MessageBodyReader and MessageBodyWriter. Supported formats currently include JSON, Smile, XML, YAML and CBOR.

Data format modules

Data format modules offer support for data formats other than JSON. Most of them simply implement streaming API abstractions, so that databinding component can be used as is; some offer (and few require) additional databind level functionality for handling things like schemas.

Currently following data format modules are fully usable and supported:

  • Avro: supports Avro data format, with streaming implementation plus additional databind-level support for Avro Schemas
  • CBOR: supports CBOR data format (a binary JSON variant).
  • CSV: supports Comma-separated values format -- streaming api, with optional convenience databind additions
  • (Java) Properties (NEW with Jackson 2.7.2!): creating nested structure out of implied notation (dotted by default, configurable), flattening similarly on serialization
  • Protobuf (NEW with Jackson 2.6): supported similar to Avro
  • Smile: supports Smile (binary JSON) -- 100% API/logical model compatible via streaming API, no changes for databind
  • XML: supports XML; provides both streaming and databind implementations. Similar to JAXB' "code-first" mode (no support for "XML Schema first", but can use JAXB beans)
  • YAML: supports YAML, which being similar to JSON is fully supported with simple streaming implementation

There are also other data format modules, provided by developers outside Jackson core team:

  • BEncode: support for reading/writing BEncode (BitTorrent format) encoded data
  • bson4jackson: adds support for BSON data format (by Mongo project).
    • Implemented as full streaming implementation, which allows full access (streaming, data-binding, tree-model)
    • Also see [MongoJack] library below; while not a dataformat module, it allows access to BSON data as well.
  • jackson-dataformat-msgpack adds support MessagePack (aka MsgPack) format
    • Implemented as full streaming implementation, which allows full access (streaming, data-binding, tree-model)
  • HOCON: experimental, partial implementation to support HOCON format -- work in progress
  • Rison: Jackson backend to support Rison)

JVM Language modules

  • Kotlin to handle native types of Kotlin
  • Scala to handle native Scala types (including but not limited to Scala collection/map types, case classes)
    • Currently (December 2015) Scala 2.10 and 2.11 supported (2.9 was supported up to Jackson 2.3)

Support for Schemas

Jackson annotations define intended properties and expected handling for POJOs, and in addition to Jackson itself using this for reading/writing JSON and other formats, it also allows generation of external schemas. Some of this functionality is included in above-mentioned data-format extensions; but there are also many stand-alone Schema tools, such as:

JSON Schema

Other schema languages

Other modules, stable

Other fully usable modules by FasterXML team include:

  • JAXB Annotations: allow use of JAXB annotations as an alternative (in addition to or instead of) standard Jackson annotations
  • JDK 8 Parameter names: Module that adds support for using a new JDK8 feature: ability to access names of constructor and method parameters.
  • Base modules:
    • Afterburner: speed up databinding by 30-40% with bytecode generation to replace use of Reflection for field access, method/constructor calls
    • Guice: extension that allows injection values from Guice injectors (and basic Guice annotations), instead of standard @JacksonInject (or in addition to)
    • Mr Bean: "type materialization" -- let Mr Bean generate implementation classes on-the-fly (NO source code generation), to avoid monkey code
    • OSGi: allows injection of values from OSGi registry, via standard Jackson @JacksonInject annotation
    • Paranamer: tiny extension for automatically figuring out creator (constructor, factory method) parameter names, to avoid having to specify @JsonProperty.

Jackson jr

While Jackson databind is a good choice for general-purpose data-binding, its footprint and startup overhead may be problematic in some domains, such as mobile phones; and especially for light usage (couple of reads or writes). In addition, some developers find full Jackson API overwhelming.

For all these reasons, we decided to create a much simpler, smaller library, which supports a subset of functionality, called Jackson jr. It builds on Jackson Streaming API, but does not depend on databind. As a result its size (both jar, and runtime memory usage) is considerably smaller; and its API is very compact.

Third-party non-module libraries based on Jackson

Jackson helper libraries

  • Jackson Ant path filter adds powerful filtering of properties to serialize, using Ant Path notation for hierarchic filtering

Support for datatypes

Participation

The easiest ways to participate beyond using Jackson is to join one of Jackson mailing lists (Jackson google groups):

  • Jackson Announce: Announcement-only list for new Jackson releases, meetups and other events related to Jackson
  • Jackson User: List dedicated for discussion on Jackson usage
  • Jackson Dev: List for developers of Jackson core components and modules, discussing implementation details, API changes.

There are other related lists and forums as well:

Other things related to or inspired by Jackson

  • Pyckson is a Python library that aims for same goals as Java Jackson, such as Convention over Configuration
  • Rackson is a Ruby library that offers Jackson-like functionality on Ruby platform

Documentation

Web sites

  • jackson-docs is our Github Jackson documentation hub
  • Jackson Wiki contains older documentation (some 1.x specific; but mostly relevant for both 1.x and 2.x)
  • CowTalk -- Blog with lots of Jackson-specific content

Note on reporting Bugs

Jackson bugs need to be reported against component they affect: for this reason, issue tracker is not enabled for this project. If you are unsure which specific project issue affects, the most likely component is jackson-databind, so you would use Jackson Databind Issue Tracker.

Paperwork

  • Contributor License Agreement, needed by core team to accept contributions. There are 2 options:
    • Standard Jackson Contributor License Agreement (CLA) is a one-page document we need from every contributor of code (we will request it for pull requests), used mostly by individual contributors
    • Corporate CLA is used by Corporations to avoid individual employees from having to send separate CLAs; it is also favored by corporate IP lawyers.

Note that the first option is available for corporations as well, but most companies have opted to use the second option instead. Core team has no preference over which one gets used; both work; we care more about actual contributions.

Java JSON library comparisons

Since you probably want opinions by Java developers NOT related to Jackson project, regarding which library to use, here are links to some of existing independent comparisons: