Integrate Protocol Buffers into Maven2 build

Question

I'm experimenting with Protocol Buffers in an existing, fairly vanilla Maven 2 project. Currently, I invoke a shell script every time I need to update my generated sources. This is obviously a hassle, as I would like the sources to be generated automatically before each build. Hopefully without resorting to shameful hackery.

So, my question is two-fold:

1. Long shot: is there a "Protocol Buffers plugin" for Maven 2 that can achieve the above in an automagic way? There's a branch on Google Code whose author appears to have taken a shot at implementing such a plugin. Unfortunately, it hasn't passed code review or been merged into protobuf trunk. The status of that plugin is thus unknown.

2. Probably more realistic: lacking an actual plugin, how else might I go about invoking protoc from my Maven 2 build? I suppose I may be able to wire up my existing shell script into an antrun invocation or something similar.

Personal experiences are most appreciated.

Answer 1

You'll find some information about the plugin available in the Protocol Buffers repository in the Protocol Buffers Compiler Maven Plug-In thread on the Protocol Buffers discussion group. My understanding is that it's usable but lacking tests. I'd give it a try.

Or you could just use the antrun plugin (snipet pasted from the thread mentioned above):

 <build>
   <plugins>
     <plugin>
       <artifactId>maven-antrun-plugin</artifactId>
       <executions>
         <execution>
           <id>generate-sources</id>
           <phase>generate-sources</phase>
           <configuration>
             <tasks>
               <mkdir dir="target/generated-sources"/>
               <exec executable="protoc">
                 <arg value="--java_out=target/generated-sources"/>
                 <arg value="src/main/protobuf/test.proto"/>
               </exec>
             </tasks>
             <sourceRoot>target/generated-sources</sourceRoot>
           </configuration>
           <goals>
             <goal>run</goal>
           </goals>
         </execution>
       </executions>
     </plugin>
   </plugins>
 </build>

 <dependencies>
   <dependency>
     <groupId>com.google.protobuf</groupId>
     <artifactId>protobuf-java</artifactId>
     <version>2.0.3</version>
   </dependency>
 </dependencies>

Answer 2

The accepted answer encouraged me to get the Google-provided plugin to work. I merged the branch mentioned in my question into a checkout of 2.2.0 source code, built and installed/deployed the plugin, and was able to use it in my project as follows:

  <build>
    <plugins>
      <plugin>
        <groupId>com.google.protobuf.tools</groupId>
        <artifactId>maven-protoc-plugin</artifactId>
        <version>0.0.1</version>
        <executions>
          <execution>
            <id>generate-sources</id>
            <goals>
              <goal>compile</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <protoSourceRoot>${basedir}/src/main/protobuf/</protoSourceRoot>
              <includes>
                <param>**/*.proto</param>
              </includes>
            </configuration>
          </execution>
        </executions>
        <configuration>
          <protocExecutable>/usr/local/bin/protoc</protocExecutable>
        </configuration>
      </plugin>
    </plugins>
  </build>

Note that I changed the plugin's version to 0.0.1 (no -SNAPSHOT) in order to make it go into my non-snapshot thirdparty Nexus repository. YMMV. The takeaway is that this plugin will be usable once it's no longer necessary to jump through hoops in order to get it going.

Answer 3

The accepted solution does not scale for multiple proto files. I had to come up with my own:

<build>
    <plugins>
        <plugin>
            <artifactId>maven-antrun-plugin</artifactId>
            <executions>
                <execution>
                    <id>compile-protoc</id>
                    <phase>generate-sources</phase>
                    <configuration>
                        <tasks>
                            <mkdir dir="${generated.sourceDirectory}" />
                            <path id="proto.path">
                                <fileset dir="src/main/proto">
                                    <include name="**/*.proto" />
                                </fileset>
                            </path>
                            <pathconvert pathsep=" " property="proto.files" refid="proto.path" />
                            <exec executable="protoc" failonerror="true">
                                <arg value="--java_out=${generated.sourceDirectory}" />
                                <arg value="-I${project.basedir}/src/main/proto" />
                                <arg line="${proto.files}" />
                            </exec>
                        </tasks>
                    </configuration>
                    <goals>
                        <goal>run</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
</build>

Answer 4

There's also great plugin by Igor Petruk named protobuf-maven-plugin. It's in central repo now and plays nicely with eclipse (m2e-1.1 is recommended).