in Tutorials |

Maven – Tycho, Java, Scala and APT

This tutorial shows a small project which is build with maven-tycho and the following requirements:

  • Mixed Java / Scala project
  • Eclipse plugin deployment
  • Eclipse Annotation Processing (APT)
  • Manifest-first approach
  • Java 7 / Scala 2.9.2
That doesn’t sound too hard. In fact it isn’t, if you are familiar with maven and how tycho works. 

Setting up maven

First download maven 3 and configure it.
I created two profiles in my settings.xml and added some repositories.
My two profiles are tycho-build and scala-build which are activated with
the corresponding property present.
<settings>
 <profiles>
  <profile>
   <id>tycho</id>
   <activation>
    <activeByDefault>false</activeByDefault>
    <property>
     <name>tycho-build</name>
    </property>
  </activation>
  <repositories>
   <repository>
    <id>eclipse-indigo</id>
    <layout>p2</layout>
    <url>http://download.eclipse.org/releases/indigo</url>
   </repository>
   <repository>
    <id>eclipse-sapphire</id>
    <layout>p2</layout>
    <url>http://download.eclipse.org/sapphire/0.4.1/repository</url>
   </repository>
   <repository>
    <id>eclipse-scala-ide</id>
    <layout>p2</layout>
   <url>http://download.scala-ide.org/releases-29/milestone/site</url>
  </repository>
  <repository>
   <id>eclipse-gemini-dbaccess</id>
   <layout>p2</layout>
   <url>http://download.eclipse.org/gemini/dbaccess/updates/1.0</url>
   </repository>
  </repositories>
 </profile>
 
 <profile>
  <id>scala</id>
  <activation>
   <activeByDefault>false</activeByDefault>
    <property>
     <name>scala-build</name>
    </property>
   </activation>
  <repositories>
   <repository>
    <id>scala-tools.org</id>
    <name>Scala-tools Maven2 Repository</name>
    <url>http://scala-tools.org/repo-releases</url>
   </repository>
   <repository>
    <id>typesafe</id>
    <name>Typesafe Repository</name>
    <url>http://repo.typesafe.com/typesafe/releases/</url>
   </repository>
  </repositories>
 <pluginRepositories>
  <pluginRepository>
    <id>scala-tools.org</id>
    <name>Scala-tools Maven2 Repository</name>
    <url>http://scala-tools.org/repo-releases</url>
   </pluginRepository>
  </pluginRepositories>
 </profile>
</profiles>
</settings>

Setting up the project – The tycho build

For my project I just used two simple plugins. Nothing fancy here.
  1. Create plugin-project
  2. Add some dependencies
  3. Write some classes in Java
I recommend the following project structure
root-project/
 plugin.core
 plugin.ui
 plugin.xy
go to your root-project folder in your favorite console and use the following command to generate pom.xml with tycho.
mvn org.sonatype.tycho:maven-tycho-plugin:generate-poms -DgroupId=de.mukis -Dtycho.targetPlatform=path/to/target/platform/
which generates a first project for you. A few things to „tweak“ as I saw it as a best-practice in most of the other tutorials:
  • Replace all concrete version numbers with property placeholders, e.g 0.12.0 with ${tycho.version}
  • Remove all groupId and version tags in the pom.xml. The parent pom.xml will generate these.
  • Check your folder structure. Tycho infers AND changes your source directory according to your build.properties.
Next add the p2 repositories needed to resolve all dependencies. This is done via the <repository> tag. The full pom.xml is at the end.
Sometimes you have existing OSGi bundles but no p2 repository you can use it. Eclipse PDE has a nice extra feature for you. Features and bundles publisher application. Note: It’s very important that your repository folder has two folder plugins and features.
Now you can run your maven build with
mvn clean package
and you will get a nice packaged osgi bundle.

Setting up the project – The scala build

So now we want to add some Scala classes. Create new source folder src/main/scala and create some classes. Don’t forget to import Scala packages. So your MANIFEST.MF contains something like:
Import-Package: org.osgi.framework;version="1.6.0",
 scala;version="[2.9.0.1,2.9.3.0]",
 scala.collection;version="[2.9.0.1,2.9.3.0]",
 scala.collection.generic;version="[2.9.0.1,2.9.3.0]",
 scala.collection.immutable;version="[2.9.0.1,2.9.3.0]",
 scala.collection.interfaces;version="[2.9.0.1,2.9.3.0]",
 scala.collection.mutable;version="[2.9.0.1,2.9.3.0]",
 scala.collection.parallel;version="[2.9.0.1,2.9.3.0]",
 scala.collection.parallel.immutable;version="[2.9.0.1,2.9.3.0]",
 scala.collection.parallel.mutable;version="[2.9.0.1,2.9.3.0]",
 scala.concurrent;version="[2.9.0.1,2.9.3.0]",
 scala.concurrent.forkjoin;version="[2.9.0.1,2.9.3.0]",
 scala.io;version="[2.9.0.1,2.9.3.0]",
 scala.math;version="[2.9.0.1,2.9.3.0]",
 scala.parallel;version="[2.9.0.1,2.9.3.0]",
 scala.ref;version="[2.9.0.1,2.9.3.0]",
 scala.reflect,
 scala.reflect.generic;version="[2.9.0.1,2.9.3.0]",
 scala.runtime;version="[2.9.0.1,2.9.3.0]",
 scala.text;version="[2.9.0.1,2.9.3.0]",
 scala.util;version="[2.9.0.1,2.9.3.0]",
No there are, too alternatives to build. I choose to add the source folder in my build.properties and exclude the .scala files in my maven pom. The alternative is described here.
We need the maven scala plugin. Add the repository
...
 <repository>
  <id>scala-tools.org</id>
  <name>Scala-tools Maven2 Repository</name>
  <url>http://scala-tools.org/repo-releases</url>
 </repository>
...
 <pluginRepository>
  <id>scala-tools.org</id>
  <name>Scala-tools Maven2 Repository</name>
  <url>http://scala-tools.org/repo-releases</url>
 </pluginRepository>
and to our root pom.xml we add the maven-scala-plugin
<plugin>
 <groupId>org.scala-tools</groupId>
 <artifactId>maven-scala-plugin</artifactId>
 <version>2.15.0</version>
 <executions>
  <execution>
   <id>compile</id>
   <goals>
    <goal>compile</goal>
   </goals>
   <phase>compile</phase>
  </execution>
 
  <execution>
   <id>test-compile</id>
   <goals>
    <goal>testCompile</goal>
   </goals>
   <phase>test-compile</phase>
  </execution>
 
  <execution>
   <phase>process-resources</phase>
   <goals>
    <goal>compile</goal>
   </goals>
  </execution>
 </executions>
</plugin>
There is actually an easier version, but which doesn’t work with circular dependencies.
If you have added the src/main/scala folder in your build.properties, than you have to add another plugin, to prevent tycho from exporting all scala source files.
<plugin>
 <groupId>org.eclipse.tycho</groupId>
 <artifactId>tycho-compiler-plugin</artifactId>
 <version>${tycho.version}</version>
 <configuration>
  <excludeResources>
   <excludeResource>**/*.scala</excludeResource>
  </excludeResources>
 </configuration>
</plugin>
Now the build should work with scala, too.

Setting up the project – APT code generation with Eclipse Sapphire

I’m creating some models with Eclipse Sapphire which uses Java Annotation Processing (APT) to generate the models. Apt-maven-plugin is a maven allows us to trigger a processing factory during the build process. The current version alpha-04 has a bug which leads to an error with java 7. So, before we can use this plugin you have to checkout the source code and build the latest alpha-05 version as it’s not released at the moment. Install it in your local maven repository.
Now you can add the apt-maven-plugin to your plugin which needs apt. This could look like
<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
 
<parent>
 <groupId>de.lmu.ifi.dbs.knowing</groupId>
 <artifactId>Knowing</artifactId>
 <version>0.1.4-SNAPSHOT</version>
</parent>
 
<artifactId>de.lmu.ifi.dbs.knowing.core</artifactId>
<packaging>eclipse-plugin</packaging>
 
<build>
 <plugins>
  <plugin>
   <groupId>org.codehaus.mojo</groupId>
   <artifactId>apt-maven-plugin</artifactId>
   <version>1.0-alpha-5-SNAPSHOT</version>
   <executions>
    <execution>
     <goals>
      <goal>process</goal>
     </goals>
    </execution>
   </executions>
   <configuration>
  <factory>org.eclipse.sapphire.sdk.build.processor.internal.APFactory</factory>
   </configuration>
  </plugin>
 </plugins>
</build>
</project>
At last you have  to add the factory as optional dependencies to your MANIFEST.MF of your plugin using apt.
org.eclipse.sapphire.sdk;bundle-version="[0.4.0,0.5.0)";resolution:=optional,
org.eclipse.sapphire.sdk.build.processor;bundle-version="[0.4.0,0.5.0)";resolution:=optional
I you trigger the build, you will see that your apt sources are generated in target/generated-sources/apt. However the files are not compiled. At first I tried the maven-build-helper, but tycho seems to override these settings. So i added target/generated-sources/apt to the build.properties of the plugin using apt, which seems for my as a bad work-around. However it works fine.

Source Code

You can find the code in my github repository.

Conclusion

For a beginner it was not that easy to avoid all little traps with tycho, scala, maven apt. But in the end I hope to safe a lot of time when building and testing.

Things to add

The tutorial doesn’t include any testing.

Links

https://github.com/muuki88/tycho
http://wiki.eclipse.org/Tycho/Reference_Card
http://mattiasholmqvist.se/2010/02/building-with-tycho-part-1-osgi-bundles/
https://github.com/misto/Scala-Hello-World-Plug-in
Compiling circular dependent java-scala classes
Eclipse sapphire and tycho
compile generated sources
http://mojo.codehaus.org/apt-maven-plugin/
APT M2E Connector
Publish pre-compiled bundles in p2 repository

Veröffentlicht