gRPC-Java - An RPC library and framework

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

Supported Platforms

gRPC-Java supports Java 8 and later. Android minSdkVersion 19 (KitKat) and later are supported with Java 8 language desugaring.

TLS usage on Android typically requires Play Services Dynamic Security Provider. Please see the Security Readme.

Older Java versions are not directly supported, but a branch remains available for fixes and releases. See gRFC P5 JDK Version Support Policy.

Java version	gRPC Branch
7	1.41.x

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>1.56.0</version>
  <scope>runtime</scope>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.56.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.56.0</version>
</dependency>
<dependency> <!-- necessary for Java 9+ -->
  <groupId>org.apache.tomcat</groupId>
  <artifactId>annotations-api</artifactId>
  <version>6.0.53</version>
  <scope>provided</scope>
</dependency>

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

runtimeOnly 'io.grpc:grpc-netty-shaded:1.56.0'
implementation 'io.grpc:grpc-protobuf:1.56.0'
implementation 'io.grpc:grpc-stub:1.56.0'
compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+

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

implementation 'io.grpc:grpc-okhttp:1.56.0'
implementation 'io.grpc:grpc-protobuf-lite:1.56.0'
implementation 'io.grpc:grpc-stub:1.56.0'
compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+

For Bazel, you can either use Maven (with the GAVs from above), or use @io_grpc_grpc_java//api et al (see below).

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>1.7.1</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:3.22.3:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.56.0:exe:${os.detected.classifier}</pluginArtifact>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>compile-custom</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

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

plugins {
    id 'com.google.protobuf' version '0.9.1'
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.22.3"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.56.0'
    }
  }
  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.

For Android protobuf-based codegen integrated with the Gradle build system, also use protobuf-gradle-plugin but specify the 'lite' options:

plugins {
    id 'com.google.protobuf' version '0.9.1'
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.22.3"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.56.0'
    }
  }
  generateProtoTasks {
    all().each { task ->
      task.builtins {
        java { option 'lite' }
      }
      task.plugins {
        grpc { option 'lite' }
      }
    }
  }
}

For Bazel, use the proto_library and the java_proto_library (no load() required) and load("@io_grpc_grpc_java//:java_grpc_library.bzl", "java_grpc_library") (from this project), as in this example BUILD.bazel.

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 multiple Transport implementations:

1. The Netty-based HTTP/2 transport is the main transport implementation based on Netty. It is not officially supported on Android.
2. The OkHttp-based HTTP/2 transport is a lightweight transport based on Okio and forked low-level parts of OkHttp. It is mainly for use on Android.
3. The in-process transport is for when a server is in the same process as the client. It is used frequently for testing, while also being safe for production use.
4. The Binder transport is for Android cross-process communication on a single device.