Copyright 2008 Google Inc.

https://developers.google.com/protocol-buffers/

To use protobuf in Java, first obtain the protocol compiler (a.k.a., protoc, see instructions in the toplevel README.md) and use it to generate Java code for your .proto files:

$ protoc --java_out=${OUTPUT_DIR} path/to/your/proto/file

Include the generated Java files in your project and add a dependency on the protobuf Java runtime.

If you are using Maven, use the following:

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
  <version><!--version--></version>
</dependency>

And replace <!--version--> with a version from the Maven Protocol Buffers Repository. For example, 4.28.2.

Make sure the version number of the runtime matches (or is newer than) the version number of the protoc.

If you want to use features like protobuf JsonFormat, add a dependency on the protobuf-java-util package:

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java-util</artifactId>
  <version><!--version--></version>
</dependency>

For Android users, it's recommended to use protobuf Java Lite runtime because of its smaller code size. Java Lite runtime also works better with Proguard because it doesn't rely on Java reflection and is optimized to allow as much code stripping as possible. You can following these instructions to use Java Lite runtime.

Bazel has native build rules to work with protobuf. For Java, you can use the java_proto_library rule for server and the java_lite_proto_library rule for Android. Check out our build files examples to learn how to use them.

Most users should follow the instructions above to use protobuf Java runtime. If you are contributing code to protobuf or want to use a protobuf version that hasn't been officially released yet, you can follow the instructions below to build protobuf from source code.

You may follow these instructions to build from source. This does not require Maven to be installed. Note that these instructions skip running unit tests and only describes how to install the core protobuf library (without the util package).

1. Build the C++ code, or obtain a binary distribution of protoc (see the toplevel README.md). If you install a binary distribution, make sure that it is the same version as this package. If in doubt, run:

   $ protoc --version

   If you built the C++ code without installing, the compiler binary should be located in ../src.

2. Invoke protoc to build DescriptorProtos.java:

   $ protoc --java_out=core/src/main/java -I../src
   ../src/google/protobuf/descriptor.proto

3. Compile the code in core/src/main/java using whatever means you prefer.

4. Install the classes wherever you prefer.

This directory also provides support for Kotlin protocol buffers, which are built on top of Java protocol buffers. Kotlin protocol buffers require a dependency on Java protocol buffers, and both Java and Kotlin protocol buffer code must be generated for every proto file.

The main goal of Kotlin protobuf is to provide idiomatic ways to build and read protocol buffers in Kotlin. Learn more about Kotlin protobufs in our documentation.

To use protobuf in Kotlin, first install the protocol compiler (protoc -- instructions for installing are in the top-level README.md) and use it to generate Java and Kotlin code for your .proto files:

$ protoc --java_out=${OUTPUT_DIR} --kotlin_out=${OUTPUT_DIR} path/to/your/proto/file

Include the generated Java and Kotlin files in your project and add a dependency on the protobuf Java and Kotlin runtime.

If you are using Maven, use the following:

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
  <version><!--version--></version>
</dependency>

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-kotlin</artifactId>
  <version><!--version--></version>
</dependency>

Replace <!--version--> with a version from the Maven Protocol Buffers Repository, such as 4.28.2.

Make sure the version number of the runtimes match each other and match (or are newer than) the version number of the protoc.

For Android users, it's recommended to use the Java Lite runtime for its smaller code size. We provide a protobuf-kotlin-lite package in Maven and Bazel to pair with the Java Lite runtime. Use these if you want to use Kotlin on Android or in another context where you want to use Java Lite. Similar to the full runtime, protobuf-kotlin-lite requires a dependency on protobuf-java-lite.

• Protobuf minor version releases are backwards-compatible. If your code can build/run against the old version, it's expected to build/run against the new version as well. Both binary compatibility and source compatibility are guaranteed for minor version releases if the user follows the guideline described in this section.

• Protobuf major version releases may also be backwards-compatible with the last release of the previous major version. See the release notice for more details.

• APIs marked with the @ExperimentalApi annotation are subject to change. They can be modified in any way, or even removed, at any time. Don't use them if compatibility is needed. If your code is a library itself (i.e. it is used on the CLASSPATH of users outside your own control), you should not use experimental APIs, unless you repackage them (e.g. using ProGuard).

• Deprecated non-experimental APIs will be removed two years after the release in which they are first deprecated. You must fix your references before this time. If you don't, any manner of breakage could result (you are not guaranteed a compilation error).

• Protobuf message interfaces/classes are designed to be subclassed by protobuf generated code only. Do not subclass these message interfaces/classes yourself. We may add new methods to the message interfaces/classes which will break your own subclasses.

• Don't use any method/class that is marked as "used by generated code only". Such methods/classes are subject to change.

• Protobuf LITE runtime APIs are not stable yet. They are subject to change even in minor version releases.

The complete documentation for Protocol Buffers is available via the web at:

https://developers.google.com/protocol-buffers/