gRPC-Java - An RPC library and framework

gRPC-Java works with JDK 8. gRPC-Java clients are supported on Android API levels 19 and up (KitKat 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.

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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>1.47.0</version>
  <scope>runtime</scope>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.47.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.47.0</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:1.47.0'
implementation 'io.grpc:grpc-protobuf:1.47.0'
implementation 'io.grpc:grpc-stub:1.47.0'
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:1.47.0'
implementation 'io.grpc:grpc-protobuf-lite:1.47.0'
implementation 'io.grpc:grpc-stub:1.47.0'
compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+

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:3.19.2:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.47.0:exe:${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 '0.8.18'
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.19.2"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.47.0'
    }
  }
  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 '0.8.18'
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.19.2"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.47.0'
    }
  }
  generateProtoTasks {
    all().each { task ->
      task.builtins {
        java { option 'lite' }
      }
      task.plugins {
        grpc { option 'lite' }
      }
    }
  }
}

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.