README.md

Protocol Buffers - Google's data interchange format

Copyright 2008 Google Inc.

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

Use Java 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>3.5.1</version>
</dependency>

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>3.5.1</version>
</dependency>

Use Java Protocol Buffers on Android

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.

Use Java Protocol Buffers with Bazel

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.

Build from Source

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 folllow the instructions below to build protobuf from source code.

Build from Source - With Maven

  1. Install Apache Maven if you don't have it:

    http://maven.apache.org/

  2. 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

    You will need to place the protoc executable in ../src. (If you built it yourself, it should already be there.)

  3. Run the tests:

    $ mvn test

    If some tests fail, this library may not work correctly on your system. Continue at your own risk.

  4. Install the library into your Maven repository:

    $ mvn install

  5. If you do not use Maven to manage your own build, you can build a .jar file to use:

    $ mvn package

    The .jar will be placed in the "target" directory.

The above instructions will install 2 maven artifacts:

  • protobuf-java: The core Java Protocol Buffers library. Most users only need this artifact.
  • protobuf-java-util: Utilities to work with protos. It contains JSON support as well as utilities to work with proto3 well-known types.

Build from Source - Without Maven

If you would rather not install Maven to build the library, you may follow these instructions instead. 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. 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.

Compatibility Notice

  • 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-compatbile 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.

Documentation

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

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