Selectively build maven modules based on the changes in the git workspace.

build-changed-modules.sh

git status --porcelain | ExtractMavenModules.java | xargs mvn clean install -pl 

ExtractMavenModules.java

/*bin/echo Running $0 > /dev/null
filename=`basename "$0"`
mytmpdir=/tmp/$filename
classname=${filename%.*}
if [ $0 -nt $mytmpdir/$classname.class ]
then
  echo Compiling $0 > /dev/null
  mkdir $mytmpdir 2> /dev/null
  javac -d $mytmpdir $0 || exit
fi
java -cp $mytmpdir $classname "$@"
exit
 */
import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

public class ExtractMavenModules {
  public static void main(String[] args) throws Exception {
    if (args.length != 0 || System.console() != null) {
      System.out.println();
      System.out.println("Description: reads filenames from stdin, writes the pom module names to");
      System.out
          .println(" stdout in a format compatable with mvn's -pl flag, :module1,:module2...");
      System.out.println("Suppoorts git short / porcelain format");
      System.out.println();
      System.out.println("Error: Arguments specified, or stdin not redirected");
      System.exit(1);
    }

    // Read from stdin line-by-line.
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in, "UTF-8"));

    while (true) {
      String line = in.readLine();
      if (line == null) break;

      String[] filenames = getFileNames(line);
      for (String filename : filenames) {
        File file = new File(filename);
        File pomFile = findPom(file);
        if (pomFile != null) {
          String moduleName = readArtifactId(pomFile);
          System.out.print(":" + moduleName + ",");
        }
      }
    }
  }

  private static String readArtifactId(File pomFile) throws JAXBException {
    // JAXB trivia:
    JAXBContext jc = JAXBContext.newInstance(Pom.class);
    Unmarshaller ju = jc.createUnmarshaller();

    Pom pom = (Pom) ju.unmarshal(pomFile);

    return pom.artifactId;
  }

  /** Given a file, finds the nearest pom.xml file. */
  private static File findPom(File file) {
    while (file != null) {
      File parent = file.getParentFile();
      File maybePom = new File(parent, "pom.xml");
      if (maybePom.canRead()) return maybePom;
      file = parent;
    }

    return null;
  }

  /**
   * Parses lines in one of these formats. Leading, trailing spaces are ignored. Status code may be
   * multiple characters but is ignored.
   *
   * <pre>
   * filename
   * c filename (status code, space, filename)
   * c filename -> newfilename (status code, space, filename, renamed filename)
   * </pre>
   */
  private static String[] getFileNames(String line) {
    String[] split = line.trim().split(" ");
    switch (split.length) {
      case 1: // Just a filename.
        return new String[] { split[0] };

      case 2: // status-filename
        return new String[] { split[1] };

      case 4: // status-filename-renamed
        return new String[] { split[1], split[3] };

      case 5: // status-space-filename-renamed
        return new String[] { split[2], split[4] };

      default:
        throw new IllegalArgumentException("Could not parse line: '" + line + "'");
    }
  }

  @XmlRootElement(name = "project", namespace = "http://maven.apache.org/POM/4.0.0")
  public static class Pom {
    @XmlElement(name = "artifactId", namespace = "http://maven.apache.org/POM/4.0.0")
    public String artifactId;
  }
}