本文的代码例子来自：https://github.com/grpc/grpc-java
定义服务
这一步与其他语言完全一样，需要定义gRPC的服务、方法、request和response的类型。
完整的proto定义代码在：grpc-java/examples/src/main/proto/route_guide.proto
在proto中，下面几个定义是为我们生成 Java 类所特有的定义。
option java_multiple_files = true;
option java_package = "io.grpc.examples.routeguide";
option java_outer_classname = "RouteGuideProto";
如果在 .proto 文件中没有显示的 java_package 参数，
那么就会使用缺省的 proto 包（通过 "package" 关键字指定）。但是，因为 proto 包一般不是以域名
翻转的格式命名，所以它不是好的 Java 包。 如果我们用其它语言通过 .proto 文件生成代码，java_package 是不起任何作用的。
定义四种方法（简单RPC、服务器端流式RPC、客户端流式RPC、双向流式RPC）的细节就不在重复，跟其他语言完全一样。
生成客户端和服务器端代码
从 .proto 的服务定义中生成 gRPC 客户端和服务器端的接口。我们通过 protocol buffer 的编译器 protoc 以及一个特殊的 gRPC Java 插件来完成。
这个工具请在 https://github.com/google/protobuf/releases 这里下载。
具体编译的方法，请参考： http://www.cnblogs.com/ghj1976/p/5391205.html
完整的生产内容如下：
编译执行客户端和服务器代码
https://github.com/grpc/grpc-java 例子的编译方法在：
https://github.com/grpc/grpc-java/blob/master/examples/README.md
编译例子，我们需要在 examples 目录运行下面命令:
$ ../gradlew installDist -PskipCodegen=true
执行的结果如下：
pwd
/Users/ghj1976/project/github/grpc/grpc-java/examples
localhost:examples ghj1976$
localhost:examples ghj1976$ ls
README.md android build.gradle src
localhost:examples ghj1976$
localhost:examples ghj1976$ ../gradlew installDist -PskipCodegen=true
Downloading https://services.gradle.org/distributions/gradle-2.11-bin.zip
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Unzipping /Users/ghj1976/.gradle/wrapper/dists/gradle-2.11-bin/452syho4l32rlk2s8ivdjogs8/gradle-2.11-bin.zip to /Users/ghj1976/.gradle/wrapper/dists/gradle-2.11-bin/452syho4l32rlk2s8ivdjogs8
Set executable permissions for: /Users/ghj1976/.gradle/wrapper/dists/gradle-2.11-bin/452syho4l32rlk2s8ivdjogs8/gradle-2.11/bin/gradle
*** Skipping the build of codegen and compilation of proto files because skipCodegen=true
Download https://repo1.maven.org/maven2/com/google/gradle/osdetector-gradle-plugin/1.4.0/osdetector-gradle-plugin-1.4.0.pom
Download https://repo1.maven.org/maven2/kr/motd/maven/os-maven-plugin/1.4.0.Final/os-maven-plugin-1.4.0.Final.pom
Download https://repo1.maven.org/maven2/com/google/gradle/osdetector-gradle-plugin/1.4.0/osdetector-gradle-plugin-1.4.0.jar
Download https://repo1.maven.org/maven2/kr/motd/maven/os-maven-plugin/1.4.0.Final/os-maven-plugin-1.4.0.Final.jar
Download https://repo1.maven.org/maven2/org/apache/maven/maven-plugin-api/3.2.1/maven-plugin-api-3.2.1.jar
Download https://repo1.maven.org/maven2/org/apache/maven/maven-model/3.2.1/maven-model-3.2.1.jar
Download https://repo1.maven.org/maven2/org/apache/maven/maven-artifact/3.2.1/maven-artifact-3.2.1.jar
Download https://repo1.maven.org/maven2/org/codehaus/plexus/plexus-classworlds/2.4/plexus-classworlds-2.4.jar
Download https://repo1.maven.org/maven2/org/kt3k/gradle/plugin/coveralls-gradle-plugin/2.0.1/coveralls-gradle-plugin-2.0.1.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpmime/4.3/httpmime-4.3.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpcomponents-client/4.3/httpcomponents-client-4.3.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/project/7/project-7.pom
Download https://repo1.maven.org/maven2/org/codehaus/groovy/modules/http-builder/http-builder/0.7.1/http-builder-0.7.1.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpclient/4.3/httpclient-4.3.pom
Download https://repo1.maven.org/maven2/net/sf/json-lib/json-lib/2.3/json-lib-2.3.pom
Download https://repo1.maven.org/maven2/net/sourceforge/nekohtml/nekohtml/1.9.16/nekohtml-1.9.16.pom
Download https://repo1.maven.org/maven2/xml-resolver/xml-resolver/1.2/xml-resolver-1.2.pom
Download https://repo1.maven.org/maven2/commons-beanutils/commons-beanutils/1.8.0/commons-beanutils-1.8.0.pom
Download https://repo1.maven.org/maven2/net/sf/ezmorph/ezmorph/1.0.6/ezmorph-1.0.6.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpcore/4.3/httpcore-4.3.pom
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpcomponents-core/4.3/httpcomponents-core-4.3.pom
Download https://repo1.maven.org/maven2/org/kt3k/gradle/plugin/coveralls-gradle-plugin/2.0.1/coveralls-gradle-plugin-2.0.1.jar
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpmime/4.3/httpmime-4.3.jar
Download https://repo1.maven.org/maven2/org/codehaus/groovy/modules/http-builder/http-builder/0.7.1/http-builder-0.7.1.jar
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpclient/4.3/httpclient-4.3.jar
Download https://repo1.maven.org/maven2/net/sf/json-lib/json-lib/2.3/json-lib-2.3-jdk15.jar
Download https://repo1.maven.org/maven2/net/sourceforge/nekohtml/nekohtml/1.9.16/nekohtml-1.9.16.jar
Download https://repo1.maven.org/maven2/xml-resolver/xml-resolver/1.2/xml-resolver-1.2.jar
Download https://repo1.maven.org/maven2/commons-beanutils/commons-beanutils/1.8.0/commons-beanutils-1.8.0.jar
Download https://repo1.maven.org/maven2/net/sf/ezmorph/ezmorph/1.0.6/ezmorph-1.0.6.jar
Download https://repo1.maven.org/maven2/org/apache/httpcomponents/httpcore/4.3/httpcore-4.3.jar
Download https://plugins.gradle.org/m2/be/insaneprogramming/gradle/animalsniffer-gradle-plugin/1.4.0/animalsniffer-gradle-plugin-1.4.0.pom
FAILURE: Build failed with an exception.
* Where:
Build file '/Users/ghj1976/project/github/grpc/grpc-java/all/build.gradle' line: 32
* What went wrong:
A problem occurred evaluating project ':grpc-all'.
> A problem occurred configuring project ':grpc-auth'.
> Could not resolve all dependencies for configuration ':grpc-auth:classpath'.
> Could not download animalsniffer-gradle-plugin.jar (be.insaneprogramming.gradle:animalsniffer-gradle-plugin:1.4.0)
> Could not get resource 'https://plugins.gradle.org/m2/be/insaneprogramming/gradle/animalsniffer-gradle-plugin/1.4.0/animalsniffer-gradle-plugin-1.4.0.jar'.
> Could not GET 'https://plugins.gradle.org/m2/be/insaneprogramming/gradle/animalsniffer-gradle-plugin/1.4.0/animalsniffer-gradle-plugin-1.4.0.jar'.
> gradleware-plugins.s3.amazonaws.com:443 failed to respond
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
BUILD FAILED
Total time: 16 mins 47.903 secs
localhost:examples ghj1976$
这个build错误，是因为下载https://plugins.gradle.org时需要翻墙才能下载。设置翻墙后，设置本机代理：
export http_proxy=http://127.0.0.1:8787
既可以正常下载了。
localhost:examples ghj1976$
localhost:examples ghj1976$ export http_proxy=http://127.0.0.1:8787
localhost:examples ghj1976$
localhost:examples ghj1976$ ../gradlew installDist -PskipCodegen=true
*** Skipping the build of codegen and compilation of proto files because skipCodegen=true
Download https://plugins.gradle.org/m2/gradle/plugin/me/champeau/gradle/jmh-gradle-plugin/0.3.0/jmh-gradle-plugin-0.3.0.jar
Download https://repo1.maven.org/maven2/com/google/gradle/osdetector-gradle-plugin/1.2.1/osdetector-gradle-plugin-1.2.1.jar
Download https://repo1.maven.org/maven2/kr/motd/maven/os-maven-plugin/1.2.3.Final/os-maven-plugin-1.2.3.Final.jar
Download https://repo1.maven.org/maven2/org/mortbay/jetty/alpn/alpn-boot/8.1.2.v20141202/alpn-boot-8.1.2.v20141202.pom
Download https://repo1.maven.org/maven2/org/mortbay/jetty/alpn/alpn-project/8.1.2.v20141202/alpn-project-8.1.2.v20141202.pom
Download https://repo1.maven.org/maven2/org/eclipse/jetty/jetty-parent/23/jetty-parent-23.pom
Download https://repo1.maven.org/maven2/org/mortbay/jetty/alpn/alpn-boot/8.1.2.v20141202/alpn-boot-8.1.2.v20141202.jar
:grpc-core:compileJava
Download https://repo1.maven.org/maven2/com/google/guava/guava/19.0/guava-19.0.pom
Download https://repo1.maven.org/maven2/com/google/guava/guava-parent/19.0/guava-parent-19.0.pom
Download https://repo1.maven.org/maven2/com/google/guava/guava/19.0/guava-19.0.jar
:grpc-core:animalSniffer
Download https://repo1.maven.org/maven2/org/codehaus/mojo/signature/java16/1.1/java16-1.1.pom
Download https://repo1.maven.org/maven2/org/codehaus/mojo/signature/signatures-parent/1.1/signatures-parent-1.1.pom
Download https://repo1.maven.org/maven2/org/codehaus/mojo/mojo-parent/23/mojo-parent-23.pom
Download https://repo1.maven.org/maven2/org/codehaus/mojo/signature/java16/1.1/java16-1.1.signature
:grpc-core:processResources UP-TO-DATE
:grpc-core:classes
:grpc-core:jar
:grpc-netty:compileJava
Download https://repo1.maven.org/maven2/io/netty/netty-codec-http2/4.1.0.CR7/netty-codec-http2-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-parent/4.1.0.CR7/netty-parent-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-codec-http/4.1.0.CR7/netty-codec-http-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-handler/4.1.0.CR7/netty-handler-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-codec/4.1.0.CR7/netty-codec-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-buffer/4.1.0.CR7/netty-buffer-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-transport/4.1.0.CR7/netty-transport-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-common/4.1.0.CR7/netty-common-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-resolver/4.1.0.CR7/netty-resolver-4.1.0.CR7.pom
Download https://repo1.maven.org/maven2/io/netty/netty-codec-http2/4.1.0.CR7/netty-codec-http2-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-codec-http/4.1.0.CR7/netty-codec-http-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-handler/4.1.0.CR7/netty-handler-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-codec/4.1.0.CR7/netty-codec-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-buffer/4.1.0.CR7/netty-buffer-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-transport/4.1.0.CR7/netty-transport-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-common/4.1.0.CR7/netty-common-4.1.0.CR7.jar
Download https://repo1.maven.org/maven2/io/netty/netty-resolver/4.1.0.CR7/netty-resolver-4.1.0.CR7.jar
:grpc-netty:processResources
:grpc-netty:classes
:grpc-netty:jar
:grpc-protobuf-lite:compileJava
:grpc-protobuf-lite:animalSniffer
:grpc-protobuf-lite:processResources UP-TO-DATE
:grpc-protobuf-lite:classes
:grpc-protobuf-lite:jar
:grpc-protobuf:compileJava
Download https://repo1.maven.org/maven2/com/google/protobuf/protobuf-java-util/3.0.0-beta-2/protobuf-java-util-3.0.0-beta-2.pom
Download https://repo1.maven.org/maven2/com/google/code/gson/gson/2.3/gson-2.3.pom
Download https://repo1.maven.org/maven2/com/google/protobuf/protobuf-java-util/3.0.0-beta-2/protobuf-java-util-3.0.0-beta-2.jar
Download https://repo1.maven.org/maven2/com/google/code/gson/gson/2.3/gson-2.3.jar
:grpc-protobuf:animalSniffer
:grpc-protobuf:processResources UP-TO-DATE
:grpc-protobuf:classes
:grpc-protobuf:jar
:grpc-stub:compileJava
:grpc-stub:animalSniffer
:grpc-stub:processResources UP-TO-DATE
:grpc-stub:classes
:grpc-stub:jar
:grpc-examples:compileJava
:grpc-examples:processResources
:grpc-examples:classes
:grpc-examples:jar
:grpc-examples:compressingHelloWorldClient
:grpc-examples:helloWorldClient
:grpc-examples:helloWorldServer
:grpc-examples:routeGuideClient
:grpc-examples:routeGuideServer
:grpc-examples:startScripts SKIPPED
:grpc-examples:installDist
BUILD SUCCESSFUL
Total time: 1 mins 44.412 secs
This build could be faster, please consider using the Gradle Daemon: https://docs.gradle.org/2.11/userguide/gradle_daemon.html
localhost:examples ghj1976$
命令执行完毕后，会在 build/install/grpc-examples/bin/ 目录下产生编译好的文件。
运行服务器端：
$ ./build/install/grpc-examples/bin/hello-world-server
在另外一个终端窗口运行客户端：
$ ./build/install/grpc-examples/bin/hello-world-client
参考资料：