gRPC-Java - An RPC library and framework

gRPC-Java works with JDK 7. 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.

Getting Started

For a guided tour, take a look at the quick start
guide or the more explanatory gRPC
basics.

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

Download

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

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-netty-shaded</artifactId>
  <version>1.27.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.27.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.27.0</version>
</dependency>

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

implementation 'io.grpc:grpc-netty-shaded:1.27.0'
implementation 'io.grpc:grpc-protobuf:1.27.0'
implementation 'io.grpc:grpc-stub:1.27.0'

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

implementation 'io.grpc:grpc-okhttp:1.27.0'
implementation 'io.grpc:grpc-protobuf-lite:1.27.0'
implementation 'io.grpc:grpc-stub:1.27.0'

Development snapshots are available in Sonatypes's snapshot
repository.

Generated Code

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>1.6.2</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>org.xolstice.maven.plugins</groupId>
      <artifactId>protobuf-maven-plugin</artifactId>
      <version>0.6.1</version>
      <configuration>
        <protocArtifact>com.google.protobuf:protoc:3.11.0:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.27.0:exe:${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:

plugins {
    id 'com.google.protobuf' version '0.8.8'
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.11.0"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.27.0'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}

The prebuilt protoc-gen-grpc-java binary uses glibc on Linux. If you are
compiling on Alpine Linux, you may want to use the Alpine grpc-java package
which uses musl instead.

API Stability

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.

How to Build

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

High-level Components

At a high level there are three distinct layers to the library: Stub,
Channel, and 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 are easy and encouraged.

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.

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. 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 in-process transport is for when a server is in the same process as the
   client. It is useful for testing, while also being safe for production use.