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 JARs. Or for Maven with non-Android, add to your pom.xml:

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-netty</artifactId>
  <version>1.4.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.4.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.4.0</version>
</dependency>

Or for Gradle with non-Android, add to your dependencies:

compile 'io.grpc:grpc-netty:1.4.0'
compile 'io.grpc:grpc-protobuf:1.4.0'
compile 'io.grpc:grpc-stub:1.4.0'

For Android client, use grpc-okhttp instead of grpc-netty and
grpc-protobuf-lite or grpc-protobuf-nano instead of grpc-protobuf:

compile 'io.grpc:grpc-okhttp:1.4.0'
compile 'io.grpc:grpc-protobuf-lite:1.4.0'
compile 'io.grpc:grpc-stub:1.4.0'

Development snapshots are available in Sonatypes's snapshot
repository.

For protobuf-based codegen, you can put your proto files in the src/main/proto
and src/test/proto directories along with an appropriate plugin.

For protobuf-based codegen integrated with the Maven build system, you can use
protobuf-maven-plugin (Eclipse and NetBeans users should also look at
os-maven-plugin's
IDE documentation):

<build>
  <extensions>
    <extension>
      <groupId>kr.motd.maven</groupId>
      <artifactId>os-maven-plugin</artifactId>
      <version>1.4.1.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>org.xolstice.maven.plugins</groupId>
      <artifactId>protobuf-maven-plugin</artifactId>
      <version>0.5.0</version>
      <configuration>
        <protocArtifact>com.google.protobuf:protoc:3.3.0:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.4.0:exe:${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 {
    // ASSUMES GRADLE 2.12 OR HIGHER. Use plugin version 0.7.5 with earlier
    // gradle versions
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.0'
  }
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.2.0"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.4.0'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}

How to Build

If you are making changes to gRPC-Java, see the compiling
instructions.

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

The examples
and the
Android example are standalone projects that
showcase the usage of gRPC.