Maven and Tycho

The IBEX GUI is built using Tycho, which is a Maven plugin used for building Eclipse RCP products.

This document provides a brief overview of both Maven and Tycho.

Maven

The official description:

Apache Maven is a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project’s build, reporting and documentation from a central piece of information.

In simple terms, Maven is a build automation tool used primarily for Java projects.

See the getting started guide in the Maven documentation for more information about what Maven is.

POM files

POM files are XML files, called pom.xml, that describes the software project being built, its dependencies on other external modules and components, the build order, directories, and required plug-ins. In many ways, it can be considered the equivalent of a C-style Makefile as it defines how the project is built.

See the Maven documentation for detailed information on the various sections of a pom.xml in a pure Maven project.

Building a Maven project

Maven uses multiple build phases - for example, compile, test, package. If you are really unsure, a good default is to run mvn clean verify to build a project; this will clean the project (deleting any old build files), and then run compilation, unit tests, packaging, and verification (e.g. checkstyle) phases.

For more information, see the Maven build lifecycle documentation.

Tycho

Tycho is a set of Maven plugins and extensions for building Eclipse-based applications with Maven. Tycho allows Maven to support building bundles, fragments, features, P2 repositories, RCP applications etc.

Tycho is used to build the IBEX GUI application.

Parent POM

Maven allows a parent POM to be defined which contains references to the other POM files for the other projects that make up an application. This is used in the IBEX GUI because it allows the centralisation of the settings for building the application.

The IBEX GUI parent pom.xml contains a lot of information, so here is a stripped down version to show the key points:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>CSS_ISIS</groupId>
    <artifactId>uk.ac.stfc.isis.ibex.client.tycho.parent</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <properties>
        <tycho.version>4.0.9</tycho.version>
        <tycho-repo.url>https://oss.sonatype.org/content/groups/public/</tycho-repo.url>
        <photon-repo.url>http://download.eclipse.org/releases/2024-09</photon-repo.url>
        <photon-updates-repo.url>http://download.eclipse.org/eclipse/updates/4.33</photon-updates-repo.url>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <repositories>
        <repository>
            <id>photon-updates</id>
            <layout>p2</layout>
            <url>${photon-updates-repo.url}</url>
        </repository>
    </repositories>

    <build>
        <plugins>
            <plugin>
                <groupId>org.eclipse.tycho</groupId>
                <artifactId>tycho-maven-plugin</artifactId>
                <version>${tycho.version}</version>
                <extensions>true</extensions>
            </plugin>
            <!-- Other maven plugins omitted such as unit testing and checkstyle -->
        </plugins>
    </build>

    <modules>
        <module>../uk.ac.stfc.isis.ibex.client.product</module>
        <module>../uk.ac.stfc.isis.ibex.feature.base</module>
        <!-- Other modules that make up IBEX would be listed here -->
        <module>../uk.ac.stfc.isis.ibex.ui.mainmenu.tests</module>
    </modules>
</project>

Let’s explain the various parts shown:

At the top we have the standard Maven metadata: groupId, artifactId, version.
The properties section is used to define URLs for the Tycho plugin and the Eclipse RCP framework. The versions here are updated periodically during dependency updates
The repositories section tells Maven to look for a repository for the Eclipse RCP framework version specified above
The build section defines the Maven plugins necessary to build the application. The Tycho plugin entry tells Maven to download Tycho and use it as part of the build process
The modules section lists the locations of the POM files for the various modules that make up the application. When a new module is added to IBEX, it will need to be added to this list.

Child POM

A typical child POM look like this. It is very simple - it points at the parent POM to get most of its information. These is one of these pom.xml files for each module that makes up the IBEX client.

The packaging type is defined as eclipse-plugin; this is a packaging type defined by Tycho. Other Tycho types used in IBEX are eclipse-feature for features, eclipse-test-plugin for fragment projects that define unit tests and eclipse-repository for configuring builds.

Application POM

In IBEX we define a separate project called uk.ac.stfc.isis.ibex.e4.client.product which defines how the product is built. It has a POM file of packaging type eclipse-repository.

The key area is the materialize-products section, this tells Tycho to actually create the product. Without this Maven will compile & unit test the code, but will not produce an executable.