Gson

Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Gson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of.

There are a few open-source projects that can convert Java objects to JSON. However, most of them require that you place Java annotations in your classes; something that you can not do if you do not have access to the source-code. Most also do not fully support the use of Java Generics. Gson considers both of these as very important design goals.

[!NOTE]
Gson is currently in maintenance mode; existing bugs will be fixed, but large new features will likely not be added. If you want to add a new feature, please first search for existing GitHub issues, or create a new one to discuss the feature and get feedback.

[!IMPORTANT]
Gson’s main focus is on Java. Using it with other JVM languages such as Kotlin or Scala might work fine in many cases, but language-specific features such as Kotlin’s non-null types or constructors with default arguments are not supported. This can lead to confusing and incorrect behavior.
When using languages other than Java, prefer a JSON library with explicit support for that language.

Goals

Provide simple toJson() and fromJson() methods to convert Java objects to JSON and vice-versa
Allow pre-existing unmodifiable objects to be converted to and from JSON
Extensive support of Java Generics
Allow custom representations for objects
Support arbitrarily complex objects (with deep inheritance hierarchies and extensive use of generic types)

Download

Gradle:

dependencies {
  implementation 'com.google.code.gson:gson:2.11.0'
}

Maven:

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.11.0</version>
</dependency>

Gson jar downloads are available from Maven Central.

Requirements

Minimum Java version

Gson 2.9.0 and newer: Java 7
Gson 2.8.9 and older: Java 6

Despite supporting older Java versions, Gson also provides a JPMS module descriptor (module name com.google.gson) for users of Java 9 or newer.

JPMS dependencies (Java 9+)

These are the optional Java Platform Module System (JPMS) JDK modules which Gson depends on. This only applies when running Java 9 or newer.

java.sql (optional since Gson 2.8.9)
When this module is present, Gson provides default adapters for some SQL date and time classes.
jdk.unsupported, respectively class sun.misc.Unsafe (optional)
When this module is present, Gson can use the Unsafe class to create instances of classes without no-args constructor. However, care should be taken when relying on this. Unsafe is not available in all environments and its usage has some pitfalls, see GsonBuilder.disableJdkUnsafe().

Minimum Android API level

Gson 2.11.0 and newer: API level 21
Gson 2.10.1 and older: API level 19

Older Gson versions may also support lower API levels, however this has not been verified.

Documentation

API Javadoc: Documentation for the current release
User guide: This guide contains examples on how to use Gson in your code
Troubleshooting guide: Describes how to solve common issues when using Gson
Releases and change log: Latest releases and changes in these versions; for older releases see CHANGELOG.md
Design document: This document discusses issues we faced while designing Gson. It also includes a comparison of Gson with other Java libraries that can be used for Json conversion

Please use the ‘gson’ tag on StackOverflow, GitHub Discussions or the google-gson Google group to discuss Gson or to post questions.

Building

Gson uses Maven to build the project:

mvn clean verify

JDK 11 or newer is required for building, JDK 17 is recommended. Newer JDKs are currently not supported for building (but are supported when using Gson).

Contributing

See the contributing guide.
Please perform a quick search to check if there are already existing issues or pull requests related to your contribution.

Keep in mind that Gson is in maintenance mode. If you want to add a new feature, please first search for existing GitHub issues, or create a new one to discuss the feature and get feedback.

License

Gson is released under the Apache 2.0 license.

Copyright 2008 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Disclaimer

This is not an officially supported Google product.