OpenCms is written in Java and uses the Gradle build tool for building the sources. Eclipse with Gradle is the recommended environment for OpenCms core development.
You need a Java Development Kit (JDK) of version 8 or higher installed, but it is not necessary to install Gradle because it's bundled with the OpenCms source code project.
Although a server-side Java application, OpenCms uses some UI-related libraries for its image processing functionalities. Standard JDK distributions contain all the UI-related packages needed. There are "slim" JDKs available for headless systems, though, that cannot be used.
You can download the latest Eclipse IDE at www.eclipse.org.
For OpenCms development, the Eclipse IDE for Java Developers is most suitable since this distribution by default ships with a Gradle integration.
Other Eclipse versions can be used as well. If you use an older version of Eclipse or another distribution, make sure that the Gradle integration is installed.
The source code of OpenCms is available on GitHub.
Development takes place in the master branch: https://github.com/alkacon/opencms-core.
The latest release and former releases are available here: https://github.com/alkacon/opencms-core/releases.
