Maven

To get started with Akka gRPC read the client or server introductions.

Configuring what to generate

The plugin can be configured to generate either Java or Scala classes, and then server and or client for the chosen language. By default both client and server in Java are generated.

Java

<plugin>
    <groupId>com.lightbend.akka.grpc</groupId>
    <artifactId>akka-grpc-maven-plugin</artifactId>
    <version>${akka.grpc.version}</version>
    <configuration>
      <language>Java</language>
      <generateClient>false</generateClient>
      <generateServer>true</generateServer>
    </configuration>
</plugin>

Scala

<plugin>
    <groupId>com.lightbend.akka.grpc</groupId>
    <artifactId>akka-grpc-maven-plugin</artifactId>
    <version>${akka.grpc.version}</version>
    <configuration>
      <language>Scala</language>
      <generateClient>false</generateClient>
      <generateServer>true</generateServer>
    </configuration>
</plugin>

Generating server “power APIs”

To additionally generate server “power APIs” that have access to request metadata, as described here, set the serverPowerApis tag as true:

pom.xml

<plugin>
    ...
    <configuration>
      ...
      <generatorSettings>
        <serverPowerApis>true</serverPowerApis>
      </generatorSettings>
    </configuration>
</plugin>

Proto source directory

By default the plugin looks for .proto-files under src/main/protobuf (and src/main/proto). This can be changed with the protoPaths setting, which is a relative path to the project basedir. The below configuration overrides the proto path to be only src/main/protobuf:

pom.xml

<plugin>
    <groupId>com.lightbend.akka.grpc</groupId>
    <artifactId>akka-grpc-maven-plugin</artifactId>
    <version>${akka.grpc.version}</version>
    <configuration>
      <protoPaths>
        <protoPath>src/main/protobuf</protoPath>
      </protoPaths>
    </configuration>
</plugin>

Loading proto files from artifacts

Instead of duplicating the .proto definitions between server and client projects, you can add artifacts that contain proto definitions to your build.

A full example of a maven build definition can be found here which allows to import external protos like this:

Java

copysourceimport "google/api/annotations.proto";
import "google/api/httpbody.proto";

The pom.xml has to be adjusted as follows. As a first step in the <build>, the maven-dependency-plugin needs to pull in the artifacts containing the protobuf file. The <outputDirectory> is the place where the protos from the dependencies are getting placed into (target):

Java

copysource<execution>
  <id>unpack</id>
  <phase>generate-sources</phase>
  <goals>
    <goal>unpack</goal>
  </goals>
  <configuration>
    <artifactItems>
      <artifactItem>
        <groupId>com.google.protobuf</groupId>
        <artifactId>protobuf-java</artifactId>
        <version>${protobuf-java.version}</version>
        <type>jar</type>
        <overWrite>true</overWrite>
        <outputDirectory>${project.build.directory}/proto</outputDirectory>
        <includes>**/*.proto</includes>
      </artifactItem>
      <artifactItem>
        <groupId>com.google.api.grpc</groupId>
        <artifactId>proto-google-common-protos</artifactId>
        <version>${proto-google-common-protos.version}</version>
        <type>jar</type>
        <overWrite>true</overWrite>
        <outputDirectory>${project.build.directory}/proto</outputDirectory>
        <includes>**/*.proto</includes>
      </artifactItem>
    </artifactItems>
    <overWriteReleases>false</overWriteReleases>
    <overWriteSnapshots>true</overWriteSnapshots>
  </configuration>
</execution>

Finally, the target/proto directory has to be introduced to the akka-grpc-maven-plugin to be picket up during protoc compilation. Make sure to include all other folders from the project as well, since the definition of <protoPaths> overrides the default:

Java

copysource<protoPaths>
  <protoPath>target/proto</protoPath>
  <protoPath>src/main/proto</protoPath>
  <protoPath>src/main/protobuf</protoPath>
</protoPaths>

JDK 8 support

If you want to use TLS-based negotiation on JDK 8, Akka gRPC requires JDK 8 update 252 or later. JVM support for ALPN has been backported to JDK 8u252 which is now widely available. Support for using the Jetty ALPN agent has been dropped in Akka HTTP 10.2.0, and therefore is not supported by Akka gRPC.

Starting your Akka gRPC server from Maven

You can start your gRPC application as usual with:

mvn compile exec:exec