Using Protobuf Toolchain

Defining Toolchains

Toolchains are declared in a toolchains.xml file, which is by default expected to reside in ~/.m2 directory (however, in Maven3 it is possible to override the default location with -t or --toolchains command line parameter).

A sample toolchains.xml file with a protobuf toolchain definition:

<?xml version="1.0" encoding="UTF-8"?>
<toolchains>
  <toolchain>
    <type>protobuf</type>
    <provides>
      <version>2.4.1</version>
    </provides>
    <configuration>
      <protocExecutable>C:/Java/protobuf-2.4.1/bin/protoc.exe</protocExecutable>
    </configuration>
  </toolchain>
  ...
</toolchains>

Using Protobuf Toolchain In Standalone Project

A sample configuration is provided below:

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-toolchains-plugin</artifactId>
        <version>1.0</version>
        <executions>
          <execution>
            <phase>validate</phase>
            <goals>
              <goal>toolchain</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <toolchains>
            <protobuf>
              <version>[2.4,2.5)</version>
            </protobuf>
          </toolchains>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.xolstice.maven.plugins</groupId>
        <artifactId>protobuf-maven-plugin</artifactId>
        <version>0.6.1</version>
        <extensions>true</extensions>
        <executions>
          <execution>
            <goals>
              <goal>compile</goal>
              <goal>test-compile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

Reusing Protobuf Toolchain From Parent Project

Suppose that there is a common parent for a number of child projects, which may also be contained as modules in the parent project. In that case it makes sense to enforce the toolchain once in the parent project and let the children inherit it.

Parent project is configured as in the example below. Note that only extensions are required from protobuf-maven-plugin; all the executions will be declared in the child projects.

<project>
  ...
  <packaging>pom</packaging>
  <groupId>com.yourcompany</groupId>
  <artifactId>parent</artifactId>
  <version>1.0</version>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-toolchains-plugin</artifactId>
        <version>1.0</version>
        <executions>
          <execution>
            <phase>validate</phase>
            <goals>
              <goal>toolchain</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <toolchains>
            <protobuf>
              <version>[2.4,2.5)</version>
            </protobuf>
          </toolchains>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.xolstice.maven.plugins</groupId>
        <artifactId>protobuf-maven-plugin</artifactId>
        <version>0.6.1</version>
        <extensions>true</extensions>
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

Child project is configured as in the example below. Note that there is no need to load protobuf-maven-plugin extensions in the child project, and neither there is any need to load toolchains again: this is all handled by the parent project.

<project>
  ...
  <parent>
    <groupId>com.yourcompany</groupId>
    <artifactId>parent</artifactId>
    <version>1.0</version>
  </parent>
  <groupId>com.yourcompany</groupId>
  <artifactId>child</artifactId>
  <version>1.0</version>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.xolstice.maven.plugins</groupId>
        <artifactId>protobuf-maven-plugin</artifactId>
        <version>0.6.1</version>
        <executions>
          <execution>
            <goals>
              <goal>compile</goal>
              <goal>test-compile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

References