mirror of https://github.com/grpc/grpc-java.git
254 lines
8.3 KiB
Markdown
254 lines
8.3 KiB
Markdown
gRPC-Java - An RPC library and framework
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========================================
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gRPC-Java works with JDK 7. gRPC-Java clients are supported on Android API
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levels 19 and up (KitKat and later). Deploying gRPC servers on an Android
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device is not supported.
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TLS usage typically requires using Java 8, or Play Services Dynamic Security
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Provider on Android. Please see the [Security Readme](SECURITY.md).
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<table>
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<tr>
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<td><b>Homepage:</b></td>
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<td><a href="https://grpc.io/">grpc.io</a></td>
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</tr>
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<tr>
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<td><b>Mailing List:</b></td>
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<td><a href="https://groups.google.com/forum/#!forum/grpc-io">grpc-io@googlegroups.com</a></td>
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</tr>
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</table>
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[](https://gitter.im/grpc/grpc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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[](https://travis-ci.org/grpc/grpc-java)
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[](https://coveralls.io/github/grpc/grpc-java?branch=master)
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[](https://codecov.io/gh/grpc/grpc-java)
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Getting Started
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---------------
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For a guided tour, take a look at the [quick start
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guide](https://grpc.io/docs/languages/java/quickstart) or the more explanatory [gRPC
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basics](https://grpc.io/docs/languages/java/basics).
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The [examples](https://github.com/grpc/grpc-java/tree/v1.42.1/examples) and the
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[Android example](https://github.com/grpc/grpc-java/tree/v1.42.1/examples/android)
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are standalone projects that showcase the usage of gRPC.
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Download
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--------
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Download [the JARs][]. Or for Maven with non-Android, add to your `pom.xml`:
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```xml
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-netty-shaded</artifactId>
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<version>1.42.1</version>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-protobuf</artifactId>
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<version>1.42.1</version>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-stub</artifactId>
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<version>1.42.1</version>
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</dependency>
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<dependency> <!-- necessary for Java 9+ -->
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<groupId>org.apache.tomcat</groupId>
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<artifactId>annotations-api</artifactId>
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<version>6.0.53</version>
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<scope>provided</scope>
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</dependency>
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```
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Or for Gradle with non-Android, add to your dependencies:
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```gradle
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implementation 'io.grpc:grpc-netty-shaded:1.42.1'
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implementation 'io.grpc:grpc-protobuf:1.42.1'
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implementation 'io.grpc:grpc-stub:1.42.1'
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compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+
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```
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For Android client, use `grpc-okhttp` instead of `grpc-netty-shaded` and
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`grpc-protobuf-lite` instead of `grpc-protobuf`:
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```gradle
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implementation 'io.grpc:grpc-okhttp:1.42.1'
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implementation 'io.grpc:grpc-protobuf-lite:1.42.1'
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implementation 'io.grpc:grpc-stub:1.42.1'
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compileOnly 'org.apache.tomcat:annotations-api:6.0.53' // necessary for Java 9+
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```
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[the JARs]:
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https://search.maven.org/search?q=g:io.grpc%20AND%20v:1.42.1
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Development snapshots are available in [Sonatypes's snapshot
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repository](https://oss.sonatype.org/content/repositories/snapshots/).
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Generated Code
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--------------
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For protobuf-based codegen, you can put your proto files in the `src/main/proto`
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and `src/test/proto` directories along with an appropriate plugin.
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For protobuf-based codegen integrated with the Maven build system, you can use
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[protobuf-maven-plugin][] (Eclipse and NetBeans users should also look at
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`os-maven-plugin`'s
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[IDE documentation](https://github.com/trustin/os-maven-plugin#issues-with-eclipse-m2e-or-other-ides)):
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```xml
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<build>
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<extensions>
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<extension>
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<groupId>kr.motd.maven</groupId>
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<artifactId>os-maven-plugin</artifactId>
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<version>1.6.2</version>
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</extension>
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</extensions>
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<plugins>
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<plugin>
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<groupId>org.xolstice.maven.plugins</groupId>
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<artifactId>protobuf-maven-plugin</artifactId>
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<version>0.6.1</version>
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<configuration>
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<protocArtifact>com.google.protobuf:protoc:3.17.2:exe:${os.detected.classifier}</protocArtifact>
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<pluginId>grpc-java</pluginId>
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<pluginArtifact>io.grpc:protoc-gen-grpc-java:1.42.1:exe:${os.detected.classifier}</pluginArtifact>
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</configuration>
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<executions>
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<execution>
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<goals>
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<goal>compile</goal>
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<goal>compile-custom</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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```
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[protobuf-maven-plugin]: https://www.xolstice.org/protobuf-maven-plugin/
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For non-Android protobuf-based codegen integrated with the Gradle build system,
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you can use [protobuf-gradle-plugin][]:
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```gradle
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plugins {
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id 'com.google.protobuf' version '0.8.17'
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}
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protobuf {
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protoc {
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artifact = "com.google.protobuf:protoc:3.17.2"
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}
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plugins {
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grpc {
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artifact = 'io.grpc:protoc-gen-grpc-java:1.42.1'
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}
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}
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generateProtoTasks {
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all()*.plugins {
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grpc {}
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}
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}
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}
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```
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[protobuf-gradle-plugin]: https://github.com/google/protobuf-gradle-plugin
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The prebuilt protoc-gen-grpc-java binary uses glibc on Linux. If you are
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compiling on Alpine Linux, you may want to use the [Alpine grpc-java package][]
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which uses musl instead.
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[Alpine grpc-java package]: https://pkgs.alpinelinux.org/package/edge/testing/x86_64/grpc-java
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For Android protobuf-based codegen integrated with the Gradle build system, also
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use protobuf-gradle-plugin but specify the 'lite' options:
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```gradle
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plugins {
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id 'com.google.protobuf' version '0.8.17'
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}
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protobuf {
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protoc {
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artifact = "com.google.protobuf:protoc:3.17.2"
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}
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plugins {
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grpc {
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artifact = 'io.grpc:protoc-gen-grpc-java:1.42.1'
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}
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}
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generateProtoTasks {
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all().each { task ->
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task.builtins {
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java { option 'lite' }
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}
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task.plugins {
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grpc { option 'lite' }
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}
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}
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}
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}
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```
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API Stability
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-------------
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APIs annotated with `@Internal` are for internal use by the gRPC library and
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should not be used by gRPC users. APIs annotated with `@ExperimentalApi` are
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subject to change in future releases, and library code that other projects
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may depend on should not use these APIs.
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We recommend using the
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[grpc-java-api-checker](https://github.com/grpc/grpc-java-api-checker)
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(an [Error Prone](https://github.com/google/error-prone) plugin)
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to check for usages of `@ExperimentalApi` and `@Internal` in any library code
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that depends on gRPC. It may also be used to check for `@Internal` usage or
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unintended `@ExperimentalApi` consumption in non-library code.
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How to Build
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------------
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If you are making changes to gRPC-Java, see the [compiling
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instructions](COMPILING.md).
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High-level Components
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---------------------
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At a high level there are three distinct layers to the library: *Stub*,
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*Channel*, and *Transport*.
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### Stub
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The Stub layer is what is exposed to most developers and provides type-safe
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bindings to whatever datamodel/IDL/interface you are adapting. gRPC comes with
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a [plugin](https://github.com/google/grpc-java/blob/master/compiler) to the
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protocol-buffers compiler that generates Stub interfaces out of `.proto` files,
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but bindings to other datamodel/IDL are easy and encouraged.
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### Channel
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The Channel layer is an abstraction over Transport handling that is suitable for
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interception/decoration and exposes more behavior to the application than the
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Stub layer. It is intended to be easy for application frameworks to use this
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layer to address cross-cutting concerns such as logging, monitoring, auth, etc.
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### Transport
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The Transport layer does the heavy lifting of putting and taking bytes off the
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wire. The interfaces to it are abstract just enough to allow plugging in of
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different implementations. Note the transport layer API is considered internal
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to gRPC and has weaker API guarantees than the core API under package `io.grpc`.
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gRPC comes with three Transport implementations:
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1. The Netty-based transport is the main transport implementation based on
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[Netty](https://netty.io). It is for both the client and the server.
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2. The OkHttp-based transport is a lightweight transport based on
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[OkHttp](https://square.github.io/okhttp/). It is mainly for use on Android
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and is for client only.
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3. The in-process transport is for when a server is in the same process as the
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client. It is useful for testing, while also being safe for production use.
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