## File: README.md # 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](https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/basic-serialization.md#basics), > 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](Troubleshooting.md#proguard-r8). ### 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: ```gradle dependencies { implementation 'com.google.code.gson:gson:2.14.0' } ``` Maven: ```xml com.google.code.gson gson 2.14.0 ``` [Gson jar downloads](https://central.sonatype.com/artifact/com.google.code.gson/gson) 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()`](https://javadoc.io/doc/com.google.code.gson/gson/latest/com.google.gson/com/google/gson/GsonBuilder.html#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](https://www.javadoc.io/doc/com.google.code.gson/gson): Documentation for the current release * [User guide](UserGuide.md): This guide contains examples on how to use Gson in your code * [Troubleshooting guide](Troubleshooting.md): Describes how to solve common issues when using Gson * [Releases and change log](https://github.com/google/gson/releases): Latest releases and changes in these versions; for older releases see [`CHANGELOG.md`](CHANGELOG.md) * [Design document](GsonDesignDocument.md): 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](https://stackoverflow.com/questions/tagged/gson), [GitHub Discussions](https://github.com/google/gson/discussions) or the [google-gson Google group](https://groups.google.com/group/google-gson) to discuss Gson or to post questions. ### ProGuard / R8 See the details in the related section in the [Troubleshooting guide](Troubleshooting.md#proguard-r8). ### Building Gson uses Maven to build the project: ``` mvn clean verify ``` JDK 17 or newer is required for building, JDK 21 is recommended. Newer JDKs are currently not supported for building (but are supported when _using_ Gson). ### Contributing See the [contributing guide](https://github.com/google/.github/blob/master/CONTRIBUTING.md).\ 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](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. --- ## File: extras/README.md # extras This Maven module contains the source code for supplementary Gson features which are not included by default. The artifacts created by this module are currently not deployed to Maven Central. --- ## File: gson/README.md # gson This Maven module contains the Gson source code. The artifacts created by this module are deployed to Maven Central under the coordinates `com.google.code.gson:gson`. --- ## File: metrics/README.md # metrics This Maven module contains the source code for running internal benchmark tests against Gson. --- ## File: proto/README.md # proto This Maven module contains the source code for a JSON serializer and deserializer for [Protocol Buffers (protobuf)](https://developers.google.com/protocol-buffers/docs/javatutorial) messages. The artifacts created by this module are currently not deployed to Maven Central. --- ## File: test-graal-native-image/README.md # test-graal-native-image This Maven module contains integration tests for using Gson in a GraalVM Native Image. Execution requires using GraalVM as JDK, and can be quite resource intensive. Native Image tests are therefore not enabled by default and the tests are only executed as regular unit tests. To run Native Image tests, make sure your `PATH` and `JAVA_HOME` environment variables point to GraalVM and then run: ``` mvn clean test --activate-profiles native-image-test ``` Technically it would also be possible to directly configure Native Image test execution for the `gson` module instead of having this separate Maven module. However, maintaining the reflection metadata for the unit tests would be quite cumbersome and would hinder future changes to the `gson` unit tests because many of them just happen to use reflection, without all of them being relevant for Native Image testing. ## Reflection metadata Native Image creation requires configuring which class members are accessed using reflection, see the [GraalVM documentation](https://www.graalvm.org/jdk21/reference-manual/native-image/metadata/#specifying-reflection-metadata-in-json). The file [`reflect-config.json`](./src/test/resources/META-INF/native-image/reflect-config.json) contains this reflection metadata. You can also run with `-Dagent=true` to let the Maven plugin automatically generate a metadata file, see the [plugin documentation](https://graalvm.github.io/native-build-tools/latest/maven-plugin.html#agent-support-running-tests). --- ## File: test-jpms/README.md # test-jpms This Maven module contains tests to verify that Gson's `module-info.class` which is used by the Java Platform Module System (JPMS) works properly and can be used by other projects. The module declaration file `src/test/java/module-info.java` uses Gson's module. This is a separate Maven module to test Gson's final JAR instead of just the compiled classes. --- ## File: test-shrinker/README.md # test-shrinker This Maven module contains integration tests which check the behavior of Gson when used in combination with code shrinking and obfuscation tools, such as ProGuard or R8. The code which is shrunken is under `src/main/java`; it should not contain any important assertions in case the code shrinking tools affect these assertions in any way. The test code under `src/test/java` executes the shrunken and obfuscated JAR and verifies that it behaves as expected. The tests might be a bit brittle, especially the R8 test setup. Future ProGuard and R8 versions might cause the tests to behave differently. In case tests fail the ProGuard and R8 mapping files created in the `target` directory can help with debugging. If necessary rewrite tests or even remove them if they cannot be implemented anymore for newer ProGuard or R8 versions. **Important:** Because execution of the code shrinking tools is performed during the Maven build, trying to directly run the integration tests from the IDE might not work, or might use stale results if you changed the configuration in between. Run `mvn clean verify` before trying to run the integration tests from the IDE.