gRPC-Java - An RPC library and framework

gRPC-Java works with JDK 6. gRPC-Java clients are supported on Android API levels 14 and up (Ice Cream Sandwich and later). Deploying gRPC servers on an Android device is not supported.

TLS usage typically requires using Java 8, or Play Services Dynamic Security Provider on Android. Please see the Security Readme.

Homepage:	grpc.io
Mailing List:	grpc-io@googlegroups.com

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>1.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.14.0</version>
</dependency>

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

compile 'io.grpc:grpc-netty:1.14.0'
compile 'io.grpc:grpc-protobuf:1.14.0'
compile 'io.grpc:grpc-stub:1.14.0'

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:1.14.0'
compile 'io.grpc:grpc-protobuf-lite:1.14.0'
compile 'io.grpc:grpc-stub:1.14.0'

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>1.5.0.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>org.xolstice.maven.plugins</groupId>
      <artifactId>protobuf-maven-plugin</artifactId>
      <version>0.5.1</version>
      <configuration>
        <protocArtifact>com.google.protobuf:protoc:3.5.1-1:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.14.0:exe:${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:0.8.3'
  }
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.5.1-1"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.14.0'
    }
  }
  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.

Tools

APIs annotated with @Internal are for internal use by the gRPC library and should not be used by gRPC users. APIs annotated with @ExperimentalApi are subject to change in future releases, and library code that other projects may depend on should not use these APIs. We recommend using the grpc-java-api-checker (an Error Prone plugin) to check for usages of @ExperimentalApi and @Internal in any library code that depends on gRPC. It may also be used to check for @Internal usage or unintended @ExperimentalApi consumption in non-library code.