java/README.md

Protocol Buffers - Google's data interchange format
===================================================

[![Build Status](https://travis-ci.org/google/protobuf.svg?branch=master)](https://travis-ci.org/google/protobuf)

Copyright 2008 Google Inc.

This directory contains the Java Protocol Buffers runtime library.

Installation - With Maven
=========================

The Protocol Buffers build is managed using Maven.  If you would
rather build without Maven, see below.

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](../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 3 maven artifacts:

  * protobuf-java: The core Java Protocol Buffers library. Most users only
                   need this artifact.
  * protobuf-lite: The lite version of core Java Protobuf Buffers library. It
                   is a subset of the core library and is used together with
                   the 'lite' code generator flag to reduce generated code size
                   for mobile.
  * protobuf-java-util: Utilities to work with protos. It contains JSON support
                        as well as utilities to work with proto3 well-known
                        types.

Installation - 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/