gRPC-Java - An RPC library and framework ========================================
Homepage: grpc.io
Mailing List: grpc-io@googlegroups.com
[![Join the chat at https://gitter.im/grpc/grpc](https://badges.gitter.im/grpc/grpc.svg)](https://gitter.im/grpc/grpc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) [![GitHub Actions Linux Testing](https://github.com/grpc/grpc-java/actions/workflows/testing.yml/badge.svg?branch=master)](https://github.com/grpc/grpc-java/actions/workflows/testing.yml?branch=master) [![Line Coverage Status](https://coveralls.io/repos/grpc/grpc-java/badge.svg?branch=master&service=github)](https://coveralls.io/github/grpc/grpc-java?branch=master) [![Branch-adjusted Line Coverage Status](https://codecov.io/gh/grpc/grpc-java/branch/master/graph/badge.svg)](https://codecov.io/gh/grpc/grpc-java) Supported Platforms ------------------- gRPC-Java supports Java 8 and later. Android minSdkVersion 21 (Lollipop) and later are supported with [Java 8 language desugaring][android-java-8]. TLS usage on Android typically requires Play Services Dynamic Security Provider. Please see the [Security Readme](SECURITY.md). Older Java versions are not directly supported, but a branch remains available for fixes and releases. See [gRFC P5 JDK Version Support Policy][P5-jdk-version-support]. Java version | gRPC Branch ------------ | ----------- 7 | 1.41.x [android-java-8]: https://developer.android.com/studio/write/java8-support#supported_features [P5-jdk-version-support]: https://github.com/grpc/proposal/blob/master/P5-jdk-version-support.md#proposal Getting Started --------------- For a guided tour, take a look at the [quick start guide](https://grpc.io/docs/languages/java/quickstart) or the more explanatory [gRPC basics](https://grpc.io/docs/languages/java/basics). The [examples](https://github.com/grpc/grpc-java/tree/v1.66.0/examples) and the [Android example](https://github.com/grpc/grpc-java/tree/v1.66.0/examples/android) are standalone projects that showcase the usage of gRPC. Download -------- Download [the JARs][]. Or for Maven with non-Android, add to your `pom.xml`: ```xml io.grpc grpc-netty-shaded 1.67.0 runtime io.grpc grpc-protobuf 1.67.0 io.grpc grpc-stub 1.67.0 org.apache.tomcat annotations-api 6.0.53 provided ``` Or for Gradle with non-Android, add to your dependencies: ```gradle runtimeOnly 'io.grpc:grpc-netty-shaded:1.67.0' implementation 'io.grpc:grpc-protobuf:1.67.0' implementation 'io.grpc:grpc-stub:1.67.0' 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`: ```gradle implementation 'io.grpc:grpc-okhttp:1.67.0' implementation 'io.grpc:grpc-protobuf-lite:1.67.0' implementation 'io.grpc:grpc-stub:1.67.0' compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+ ``` For [Bazel](https://bazel.build), you can either [use Maven](https://github.com/bazelbuild/rules_jvm_external) (with the GAVs from above), or use `@io_grpc_grpc_java//api` et al (see below). [the JARs]: https://search.maven.org/search?q=g:io.grpc%20AND%20v:1.66.0 Development snapshots are available in [Sonatypes's snapshot repository](https://oss.sonatype.org/content/repositories/snapshots/). 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](https://github.com/trustin/os-maven-plugin#issues-with-eclipse-m2e-or-other-ides)): ```xml kr.motd.maven os-maven-plugin 1.7.1 org.xolstice.maven.plugins protobuf-maven-plugin 0.6.1 com.google.protobuf:protoc:3.25.3:exe:${os.detected.classifier} grpc-java io.grpc:protoc-gen-grpc-java:1.67.0:exe:${os.detected.classifier} compile compile-custom ``` [protobuf-maven-plugin]: https://www.xolstice.org/protobuf-maven-plugin/ For non-Android protobuf-based codegen integrated with the Gradle build system, you can use [protobuf-gradle-plugin][]: ```gradle plugins { id 'com.google.protobuf' version '0.9.4' } protobuf { protoc { artifact = "com.google.protobuf:protoc:3.25.3" } plugins { grpc { artifact = 'io.grpc:protoc-gen-grpc-java:1.67.0' } } generateProtoTasks { all()*.plugins { grpc {} } } } ``` [protobuf-gradle-plugin]: https://github.com/google/protobuf-gradle-plugin 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. [Alpine grpc-java package]: https://pkgs.alpinelinux.org/package/edge/community/x86_64/grpc-java For Android protobuf-based codegen integrated with the Gradle build system, also use protobuf-gradle-plugin but specify the 'lite' options: ```gradle plugins { id 'com.google.protobuf' version '0.9.4' } protobuf { protoc { artifact = "com.google.protobuf:protoc:3.25.3" } plugins { grpc { artifact = 'io.grpc:protoc-gen-grpc-java:1.67.0' } } generateProtoTasks { all().each { task -> task.builtins { java { option 'lite' } } task.plugins { grpc { option 'lite' } } } } } ``` For [Bazel](https://bazel.build), use the [`proto_library`](https://github.com/bazelbuild/rules_proto) and the [`java_proto_library`](https://bazel.build/reference/be/java#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`](https://github.com/grpc/grpc-java/blob/master/examples/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](https://github.com/grpc/grpc-java-api-checker) (an [Error Prone](https://github.com/google/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](COMPILING.md). 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](https://github.com/google/grpc-java/blob/master/compiler) 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](https://netty.io). It is not officially supported on Android. There is a "grpc-netty-shaded" version of this transport. It is generally preferred over using the Netty-based transport directly as it requires less dependency management and is easier to upgrade within many applications. 2. The OkHttp-based HTTP/2 transport is a lightweight transport based on [Okio](https://square.github.io/okio/) and forked low-level parts of [OkHttp](https://square.github.io/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.