title: protoc-jar-maven-plugin: Not generating grpc service stubs
body: <p>I have added maven configuration as follows.</p>
  
  <pre><code>        &lt;plugin&gt;
                &lt;groupId&gt;com.github.os72&lt;/groupId&gt;
                &lt;artifactId&gt;protoc-jar-maven-plugin&lt;/artifactId&gt;
                &lt;version&gt;3.5.1&lt;/version&gt;
                &lt;executions&gt;
                    &lt;execution&gt;
                        &lt;phase&gt;generate-sources&lt;/phase&gt;
                        &lt;goals&gt;
                            &lt;goal&gt;run&lt;/goal&gt;
                        &lt;/goals&gt;
                        &lt;configuration&gt;
                            &lt;protocArtifact&gt;com.google.protobuf:protoc:3.0.0&lt;/protocArtifact&gt;
                            &lt;inputDirectories&gt;
                                &lt;include&gt;src/main/protobuf&lt;/include&gt;
                            &lt;/inputDirectories&gt;
                           &lt;outputTargets&gt;
                                &lt;outputTarget&gt;
                                    &lt;type&gt;java&lt;/type&gt;
                                    &lt;outputDirectory&gt;src/main/java&lt;/outputDirectory&gt;
                                &lt;/outputTarget&gt;
                                &lt;outputTarget&gt;
                                    &lt;type&gt;grpc-java&lt;/type&gt;
                                    &lt;outputDirectory&gt;src/main/java&lt;/outputDirectory&gt;
                                    &lt;pluginArtifact&gt;io.grpc:protoc-gen-grpc-java:1.0.1&lt;/pluginArtifact&gt;
                                &lt;/outputTarget&gt;
                            &lt;/outputTargets&gt;
                        &lt;/configuration&gt;
                    &lt;/execution&gt;
                &lt;/executions&gt;
         &lt;/plugin&gt;
  </code></pre>
  
  <p>I am executing it by "mvn protoc-jar:run", however it skips the grpc service stubs, only coverts "messages" to java code.</p>
  
  <p>output is</p>
  
  <pre><code>[INFO] Protoc version: 3.5.1
  protoc-jar: protoc version: 3.5.1, detected platform: osx-x86_64 (mac os x/x86_64)
  protoc-jar: embedded: bin/3.5.1/protoc-3.5.1-osx-x86_64.exe
  protoc-jar: executing: [/var/folders/9y/w8qrc__9513dv57323sjdlmw0000gn/T/protocjar320569499467403052/bin/protoc.exe, --version]
  libprotoc 3.5.1
  [INFO] Protoc command: /var/folders/9y/w8qrc__9513dv57323sjdlmw0000gn/T/protocjar320569499467403052/bin/protoc.exe
  [INFO] Input directories:
  [INFO]     /Users/dev/learn/proto-java/src/main/protobuf
  [INFO] Output targets:
  [INFO]     java: /Users/dev/learn/proto-java/target/generated-sources (add: main, clean: false, plugin: null, outputOptions: null)
  [INFO]     Processing (java): helloworld.proto
  protoc-jar: executing: [/var/folders/9y/w8qrc__9513dv57323sjdlmw0000gn/T/protocjar320569499467403052/bin/protoc.exe, -I/Users/dev/learn/proto-java/src/main/protobuf, --java_out=/Users/dev/learn/proto-java/target/generated-sources, /Users/dev/learn/proto-java/src/main/protobuf/helloworld.proto]
  [INFO] Adding generated classes to classpath
  </code></pre>
  
  <p>I've a simple proto file defined as</p>
  
  <pre><code>syntax = "proto3";
  
  option java_multiple_files = true;
  option java_package = "-.-.-.helloworld";
  option java_outer_classname = "HelloWorldProto";
  option objc_class_prefix = "HLW";
  
  package helloworld;
  
  // The greeting service definition.
  service Greeter {
      // Sends a greeting
      rpc SayHello (HelloRequest) returns (HelloReply) {}
      rpc SayHelloAgain (HelloRequest) returns (HelloReply) {}
  }
  
  // The request message containing the user's name.
  message HelloRequest {
      string name = 1;
  }
  
  // The response message containing the greetings
  message HelloReply {
      string message = 1;
  }
  </code></pre>
  
  <p>I only output files generated as HelloReply, HelloReplyOrBuilder, HelloRequest, HelloRequestOrBuilder, HelloWorldProto. The Greeter Grpc service stub is missing. I am new to maven, am I missing something.</p>