jackson core

Core part of Jackson that defines Streaming API as well as basic shared abstractions

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Java

Overview

This project contains core low-level incremental (“streaming”) parser and generator abstractions used by
Jackson Data Processor.
It also includes the default implementation of handler types (parser, generator) that handle JSON format.
The core abstractions are not JSON specific, although naming does contain ‘JSON’ in many places, due to historical reasons. Only packages that specifically contain word ‘json’ are JSON-specific.

This package is the base on which Jackson data-binding package builds on.
It is licensed under Apache License 2.0.

Alternate data format implementations (like
Smile (binary JSON),
XML,
CSV,
Protobuf,
and CBOR)
also build on this base package, implementing the core interfaces,
making it possible to use standard data-binding package regardless of underlying data format.

Project contains versions 2.0 and above: source code for earlier (1.x) versions can be found from
Jackson-1 github repo.

Status

Type	Status
Build (CI)
Artifact
OSS Sponsorship
Javadocs
Code coverage (2.18)
CodeQ (ClusterFuzz)
OpenSSF Score

Get it!

Maven

Functionality of this package is contained in
Java package com.fasterxml.jackson.core.

To use the package, you need to use following Maven dependency:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>${jackson.version.core}</version>
</dependency>

or download jars from Maven repository or links on Wiki.
Core jar is a functional OSGi bundle, with proper import/export declarations.

Package has no external dependencies, except for testing (which uses JUnit).

Non-Maven

For non-Maven use cases, you download jars from Central Maven repository.

Core jar is also a functional OSGi bundle, with proper import/export declarations, so it can be use on OSGi container as is.

Jackson 2.10 and above include module-info.class definitions so the jar is also a proper Java module (JPMS).

Jackson 2.12 and above include additional Gradle 6 Module Metadata for version alignment with Gradle.

Use it!

General

Usage typically starts with creation of a reusable (and thread-safe, once configured) JsonFactory instance:

// Builder-style since 2.10:
JsonFactory factory = JsonFactory.builder()
// configure, if necessary:
     .enable(JsonReadFeature.ALLOW_JAVA_COMMENTS)
     .build();

// older 2.x mechanism, still supported for 2.x
JsonFactory factory = new JsonFactory();
// configure, if necessary:
factory.enable(JsonReadFeature.ALLOW_JAVA_COMMENTS);

Alternatively, you have an ObjectMapper (from Jackson Databind package) handy; if so, you can do:

JsonFactory factory = objectMapper.getFactory();

Usage, simple reading

All reading is by using JsonParser (or its sub-classes, in case of data formats other than JSON),
instance of which is constructed by JsonFactory.

An example can be found from Reading and Writing Event Streams

Usage, simple writing

All writing is by using JsonGenerator (or its sub-classes, in case of data formats other than JSON),
instance of which is constructed by JsonFactory:

An example can be found from Reading and Writing Event Streams

Processing limits

Starting with Jackson 2.15, Jackson has configurable limits for some aspects of input decoding and output generation.

Implemented limits are:

Length are expressed in input/output units – bytes or chars – depending on input source
Defined as longest allowed length, but not necessarily imposed at 100% accuracy: that is, if maximum allowed length is specified as 1000 units, something with length of, say 1003 may not cause exception (but 1500 would typically do)
Defined using new StreamReadConstraints / StreamWriteConstraints classes, configurable on per-JsonFactory basis
Main focus is to reduce likelihood of excessive memory usage/retention and/or processing costs; not validation

Input parsing limits

Maximum Number token length (2.15+): (see https://github.com/FasterXML/jackson-core/issues/815)
- Default: Maximum 1000 for both integral and floating-point numbers.
Maximum String value length (2.15+): (see https://github.com/FasterXML/jackson-core/issues/863)
- Default: 20_000_000 (20 million) (since 2.15.1; 2.15.0 had lower limit, 5 million)
Maximum Input nesting depth (2.15+): (see https://github.com/FasterXML/jackson-core/pull/943)
- Default: 1000 levels
Maximum Property name length (2.16+): (see https://github.com/FasterXML/jackson-core/issues/1047)
- Default: 50,000
Maximum Document length (2.16+): (see https://github.com/FasterXML/jackson-core/issues/1046)
- Default: Unlimited (-1)

Output generation limits

Maximum Output nesting depth (2.16+): (see https://github.com/FasterXML/jackson-core/pull/1055)
- Default: 1000 levels

Re-configuring limits

You can change per-factory limits as follows:

JsonFactory f = JsonFactory.builder()
  .streamReadConstraints(StreamReadConstraints.builder().maxDocumentLength(10_000_000L).build())
  .streamReadConstraints(StreamReadConstraints.builder().maxNumberLength(250).build())
  .streamWriteConstraints(StreamWriteConstraints.builder().maxNestingDepth(2000).build())
  .build();

Error Report Configuration

Starting with Jackson 2.16, Jackson offers configurable
behavior around error-reporting.

Currently supported configuration options are:

maxErrorTokenLength : Maximum length of token to include in error messages (2.16+): (see #1066)
maxRawContentLength : Maximum length of raw content to include in error messages (2.16+): (see #1066)

… see Example section below.

Example

JsonFactory f = JsonFactory.builder()
 .errorReportConfiguration(ErrorReportConfiguration.builder()
   .maxErrorTokenLength(1004)
   .maxRawContentLength(2008)
   .build()
 ).build();

Compatibility

JDK

Jackson-core package baseline JDK requirement:

Versions 2.0 - 2.13 require JDK 6
Versions 2.14 and above require JDK 8

Android

List is incomplete due to recent addition of compatibility checker.

2.13: Android SDK 19+
2.14 and above: Android SDK 26+

for information on Android SDK versions to Android Release names see Android version history

Release Process

Starting with Jackson 2.15, releases of this module will be SLSA compliant: see issue #844 for details.

Release process is triggered by

./release.sh

script which uses Maven Release plug-in under the hood (earlier release plug-in was directly invoked).

Support

Community support

Jackson components are supported by the Jackson community through mailing lists, Gitter forum, Github issues. See Participation, Contributing for full details.

Enterprise support

Available as part of the Tidelift Subscription.

The maintainers of jackson-core and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.