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.
[!IMPORTANT]
Gson is not a recommended library for interacting with JSON on Android. The open-ended reflection in the Gson runtime doesn't play nicely with shrinking/optimization/obfuscation passes that Android release apps should perform.
If your app or library may be running on Android, consider using Kotlin Serialization,
which uses code generation instead of reflection. This avoids Gson's runtime crashes when optimizations are applied (usually due to the fields missing or being obfuscated), and results in faster performance on Android devices.
If you still want to use Gson and attempt to avoid these crashes, you can see how to do so here.
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:2.14.0'
}
Maven:
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.14.0</version>
</dependency>
Gson jar downloads are available from Maven Central.
Requirements
Minimum Java version
- Gson 2.12.0 and newer: Java 8
- Gson 2.9.0 to 2.11.0: 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 a 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 2.15.0 and newer: API level 24
- 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.
ProGuard / R8
See the details in the related section in the Troubleshooting guide.
Building
Gson uses Maven to build the project:
mvn clean verify
JDK 17 or newer is required for building, JDK 21 is recommended. JDK 25 is supported, but only runs a subset of all tests if JDK jmod files are missing. 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.
Gson 是一个 Java 库，可以把 Java 对象序列化成 JSON，也能把 JSON 反序列化回 Java 对象，而且适用于任意类——哪怕你没有源代码的类也行。