gRPC-Java - An RPC library and framework

gRPC-Java works with JDK 6. TLS usage typically requires using Java 8, or Play Services Dynamic Security Provider on Android. Please see the Security Readme.

Download

Download the JAR. Or for Maven, add to your pom.xml:

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-all</artifactId>
  <version>0.7.1</version>
</dependency>

Or for Gradle, add to your dependencies:

compile 'io.grpc:grpc-all:0.7.1'

Development snapshots are available in Sonatypes's snapshot repository.

For protobuf-based codegen integrated with the Maven build system, you can use maven-protoc-plugin:

<pluginRepositories>
  <pluginRepository>
    <releases>
      <updatePolicy>never</updatePolicy>
    </releases>
    <snapshots>
      <enabled>false</enabled>
    </snapshots>
    <id>central</id>
    <name>Central Repository</name>
    <url>https://repo.maven.apache.org/maven2</url>
  </pluginRepository>
  <pluginRepository>
    <id>protoc-plugin</id>
    <url>https://dl.bintray.com/sergei-ivanov/maven/</url>
  </pluginRepository>
</pluginRepositories>
<build>
  <extensions>
    <extension>
      <groupId>kr.motd.maven</groupId>
      <artifactId>os-maven-plugin</artifactId>
      <version>1.2.3.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>com.google.protobuf.tools</groupId>
      <artifactId>maven-protoc-plugin</artifactId>
      <version>0.4.2</version>
      <configuration>
        <!--
          The version of protoc must match protobuf-java. If you don't depend on
          protobuf-java directly, you will be transitively depending on the
          protobuf-java version that grpc depends on.
        -->
        <protocArtifact>com.google.protobuf:protoc:3.0.0-alpha-2:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:0.7.1:exe:${os.detected.classifier}</pluginArtifact>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>compile-custom</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

For protobuf-based codegen integrated with the Gradle build system, you can use protobuf-gradle-plugin:

apply plugin: 'java'
apply plugin: 'com.google.protobuf'

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.6.1'
  }
}

protobuf {
  protoc {
    // The version of protoc must match protobuf-java. If you don't depend on
    // protobuf-java directly, you will be transitively depending on the
    // protobuf-java version that grpc depends on.
    artifact = "com.google.protobuf:protoc:3.0.0-alpha-2"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:0.7.1'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}

How to Build

This section is only necessary if you are making changes to gRPC-Java.

Building requires JDK 8, as our tests use TLS.

grpc-java has a C++ code generation plugin for protoc. Since many Java developers don't have C compilers installed and don't need to modify the codegen, the build can skip it. To skip, create the file <project-root>/gradle.properties and add skipCodegen=true.

Then, to build, run:

$ ./gradlew build

To install the artifacts to your Maven local repository for use in your own project, run:

$ ./gradlew install

How to Build Code Generation Plugin

This section is only necessary if you are making changes to the code generation. Most users only need to use skipCodegen=true as discussed above.

Build Protobuf

The codegen plugin is C++ code and requires protobuf 3.0.0-alpha-3.1.

For Linux, Mac and MinGW:

$ git clone https://github.com/google/protobuf.git
$ cd protobuf
$ git checkout v3.0.0-alpha-3.1
$ ./autogen.sh
$ ./configure
$ make
$ make check
$ sudo make install

If you are comfortable with C++ compilation and autotools, you can specify a --prefix for Protobuf and use -I in CXXFLAGS, -L in LDFLAGS, LD_LIBRARY_PATH, and PATH to reference it. The environment variables will be used when building grpc-java.

Protobuf installs to /usr/local by default.

For Visual C++, please refer to the Protobuf README for how to compile Protobuf.

Linux and MinGW

If /usr/local/lib is not in your library search path, you can add it by running:

$ sudo sh -c 'echo /usr/local/lib >> /etc/ld.so.conf'
$ sudo ldconfig

Mac

Some versions of Mac OS X (e.g., 10.10) doesn't have /usr/local in the default search paths for header files and libraries. It will fail the build of the codegen. To work around this, you will need to set environment variables:

$ export CXXFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib"

Notes for Visual C++

When building on Windows and VC++, you need to specify project properties for Gradle to find protobuf:

.\gradlew install ^
    -PvcProtobufInclude=C:\path\to\protobuf-3.0.0-alpha-3.1\src ^
    -PvcProtobufLibs=C:\path\to\protobuf-3.0.0-alpha-3.1\vsprojects\Release

Since specifying those properties every build is bothersome, you can instead create <project-root>\gradle.properties with contents like:

vcProtobufInclude=C:\\path\\to\\protobuf-3.0.0-alpha-3.1\\src
vcProtobufLibs=C:\\path\\to\\protobuf-3.0.0-alpha-3.1\\vsprojects\\Release

The build script will build the codegen for the same architecture as the Java runtime installed on your system. If you are using 64-bit JVM, the codegen will be compiled for 64-bit, that means you must have compiled Protobuf in 64-bit.

Notes for MinGW on Windows

If you have both MinGW and VC++ installed on Windows, VC++ will be used by default. To override this default and use MinGW, add -PvcDisable=true to your Gradle command line or add vcDisable=true to your <project-root>\gradle.properties.

Notes for Unsupported Operating Systems

The build script pulls pre-compiled protoc from Maven Central by default. We have built protoc binaries for popular systems, but they may not work for your system. If protoc cannot be downloaded or would not run, you can use the one that has been built by your own, by adding this property to <project-root>/gradle.properties:

protoc=/path/to/protoc

Navigating Around the Source

Here's a quick readers' guide to the code to help folks get started. At a high level there are three distinct layers to the library: Stub, Channel & Transport.

Stub

The Stub layer is what is exposed to most developers and provides type-safe bindings to whatever datamodel/IDL/interface you are adapting. gRPC comes with a plugin to the protocol-buffers compiler that generates Stub interfaces out of .proto files, but bindings to other datamodel/IDL should be trivial to add and are welcome.

Key Interfaces

Stream Observer

Channel

The Channel layer is an abstraction over Transport handling that is suitable for interception/decoration and exposes more behavior to the application than the Stub layer. It is intended to be easy for application frameworks to use this layer to address cross-cutting concerns such as logging, monitoring, auth etc. Flow-control is also exposed at this layer to allow more sophisticated applications to interact with it directly.

Common

• Metadata - headers & trailers
• Status - error code namespace & handling

Client

• Channel - client side binding
• Client Call
• Client Interceptor

Server

• Server call handler - analog to Channel on server
• Server Call

Transport

The Transport layer does the heavy lifting of putting and taking bytes off the wire. The interfaces to it are abstract just enough to allow plugging in of different implementations. Transports are modeled as Stream factories. The variation in interface between a server Stream and a client Stream exists to codify their differing semantics for cancellation and error reporting.

Note the transport layer API is considered internal to gRPC and has weaker API guarantees than the core API under package io.grpc.

gRPC comes with three Transport implementations:

1. The Netty-based transport is the main transport implementation based on Netty. It is for both the client and the server.
2. The OkHttp-based transport is a lightweight transport based on OkHttp. It is mainly for use on Android and is for client only.
3. The inProcess transport is for when a server is in the same process as the client. It is useful for testing.

Common

• Stream
• Stream Listener

Client

• Client Stream
• Client Stream Listener

Server

• Server Stream
• Server Stream Listener

Examples

Tests showing how these layers are composed to execute calls using protobuf messages can be found here https://github.com/google/grpc-java/tree/master/interop-testing/src/main/java/io/grpc/testing/integration