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This document, together with the hello-world plugin, shows you how to get started with the plugin development.

Table of Contents

What Can Plugins Do?

Jenkins defines extensibility points, which are interfaces or abstract classes that model an aspect of a build system. Those interfaces define contracts of what need to be implemented, and Jenkins allows plugins to contribute those implementations. See this document for more about extension points.

In this document, we'll be implementing a Builder that says hello. (built-in builders include Ant, Maven, and shell script. Builders build a project.)

Setting Up Environment

To develop a plugin, you need Maven 2 (why?) and JDK 6.0 or later. If this is the first time you use Maven, make sure Maven can download stuff over the internet.

Nexus Users

If you are using the Nexus Maven Repository Manager, you can ignore these instructions, and instead, click here for instructions on how to add Jenkins build prerequisites and the proper settings.xml entries.

With a fairly recent version of Maven (ie. 2.0.9 or newer) you should only need to add the following to your ~/.m2/settings.xml (Windows users will find them in %USERPROFILE%\.m2\settings.xml):

<settings>
  <pluginGroups>
    <pluginGroup>org.jenkins-ci.tools</pluginGroup>
  </pluginGroups>

  <profiles>
    <!-- Give access to Jenkins plugins -->
    <profile>
      <id>jenkins</id>
      <activation>
        <activeByDefault>true</activeByDefault> <!-- change this to false, if you don't like to have it on per default -->
      </activation>
      <repositories>
        <repository>
          <id>repo.jenkins-ci.org</id>
          <url>http://repo.jenkins-ci.org/public/</url>
        </repository>
      </repositories>
      <pluginRepositories>
        <pluginRepository>
          <id>repo.jenkins-ci.org</id>
          <url>http://repo.jenkins-ci.org/public/</url>
        </pluginRepository>
      </pluginRepositories>
    </profile>
  </profiles>
</settings>

This will let you use short names for Jenkins Maven plugins (i.e. hpi:create instead of org.jenkins-ci.tools:maven-hpi-plugin:1.61:create).

If you are using Maven version earlier than 2.0.9, you'll need to follow additional steps.

Creating a New Plugin

To start a new plugin, run the following Maven command:

$ mvn -cpu hpi:create

This will ask you a few questions, like the groupId (the Maven jargon for the package name) and the artifactId (the Maven jargon for your project name), then create a skeleton plugin from which you can start with. Make sure you can build this:

$ cd newly-created-directory
$ mvn package

Explanations:

-cpu means that Maven should update all relevant Maven plugins (check for plugin updates)
hpi: this prefix specifies that the Jenkins HPI Plugin is being invoked, a plugin that supports development of Jenkins plugins
create is the goal which creates the directory layout and the POM for your new Jenkins plugin and it adds it to the module list
package is a standard phase which compiles all sources, runs the tests and creates a package - when used by the HPI plugin it will create an *.hpi file

Building a Plugin

To build a plugin, run mvn install. This will create the file ./target/pluginname.hpi that you can deploy to Jenkins.

$ mvn install

Setting up a productive environment with your IDE

NetBeans

NetBeans users can use the IDE's Maven support to open the project directly. (Bundled in 6.7 and up; available from Plugin Manager for 6.5.) The archetype may also be available right from the New Project dialog.

As you navigate through the code, you can tell NetBeans to attach source code jar files by clicking "Attach" button that appears in the top of the main content window. This allows you to read the Jenkins core source code as you develop plugins.

IntelliJ IDEA

IntelliJ 7.0 (or later) users can load pom.xml directly from IDE, and you should see all the source code of libraries and Jenkins core all the way to the bottom.

IntelliJ defaults to downloading sources and JavaDocs on demand. So, to see the source, you may need to click the Download artifacts button in the Maven Projects tab.

Eclipse

Use Eclipse 3.3 or later to avoid a bug in Eclipse 3.2.
Eclipse users can run the following Maven command to generate Eclipse project files (the custom outputDirectory parameter is used to work around the lack of JSR-269 annotation processor support in Eclipse:)

$ mvn -DdownloadSources=true -DdownloadJavadocs=true -DoutputDirectory=target/eclipse-classes eclipse:eclipse

Alternatively, Eclipse users can install m2eclipse to open a Maven project directly in IDE.

If you get the error message Unable to find a plugin class. Did you put @plugin in javadoc? this maybe caused by Eclipse and Maven both using the target folder for build output.
Run mvn clean before building with Maven or change the output path.

Plugin Workspace Layout

The plugin workspace consists of the following major pieces:

pom.xml

Maven uses it for building your plugin.

src/main/java

Java source files of the plugin.

src/main/resources

Jelly/Groovy views of the plugin. See this document for more about it.

src/main/webapp

Static resources of the plugin, such as images and HTML files.

Source Code

Let's take a look at the source code. A plugin's main entry point is a PluginImpl class that extends from Plugin. Once Jenkins detects your plugin class (via its inheritance relationship from Plugin), it will create an instance, and invoke methods. A Plugin class is optional; a plugin may simply implement extensions:

Most of the time, a plugin class just registers extension points, and your main work involves implementing those extension points. See the source code for more about how a Builder is implemented and what it does.

Debugging a Plugin

NetBeans 6.7+ users can just hit Debug. For all others, run the following command to launch Jenkins with your plugin:
Convenient:

mvnDebug hpi:run

Unix:

$ export MAVEN_OPTS="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n"
$ mvn hpi:run

Windows:

> set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n
> mvn hpi:run

If you open http://localhost:8080/ in your browser, you should see the Jenkins page running in Jetty. The MAVEN_OPTS portion launches this whole thing with the debugger port 8000, so you should be able to start a debug session to this port from your IDE.

Once this starts running, keep it running. Jetty will pick up all the changes automatically.

  1. When you make changes to view files in src/main/resources or resource files in src/main/webapp, just hit F5 in your browser to see the changes.
  2. When you change Java source files, compile them in your IDE (NetBeans 6.7+: Debug > Apply Code Changes) and Jetty should automatically redeploy Jenkins to pick up those changes. There is no need to run mvn at all.

    MAVEN_OPTS can be used to specify all sorts of other JVM parameters, like -Xmx

Changing port

If you need to launch the Jenkins on a different port than 8080, set the port through the system property jetty.port.

$ mvn hpi:run -Djetty.port=8090

Setting context path

maven-hpi-plugin 1.65 or later (used by parent POM 1.401 or later) can set the context path by using a system property.

$ mvn hpi:run -Dhpi.prefix=/jenkins

Distributing a Plugin

To create a distribution image of your plugin, run the following Maven command:

$ mvn package

This should create target/*.hpi file. Other users can use Jenkins' web UI to upload this plugin to Jenkins (or place it in $JENKINS_HOME/plugins.)

Hosting a Plugin on jenkins-ci.org

If you got to this point, you should definitely consider hosting your plugin on jenkins-ci.org. Move on to this document for how to do that.

Using custom builds of plugins included in the Jenkins WAR

If you are building a patched version of one of the plugins in the Jenkins core, the deployment process is a bit different. This is because Jenkins will itself manage these plugins unless you tell it not to.

Deploying a custom build of a core plugin

  1. Stop Jenkins
  2. Copy the custom HPI file to $JENKINS_HOME/plugins
  3. Remove the previously expanded plugin directory
  4. Create an empty file called <plugin>.hpi.pinned - e.g. maven-plugin.hpi.pinned
  5. Start Jenkins

Other tips

  1. Consider running Maven like this mvn -o ... to avoid hitting repositories every time. This will make various operations considerably faster.
  2. Subscribe to the users' alias from here so that we can get in touch with you.
  3. When you bump up the version of Jenkins you depend on, make sure to run mvn clean once, in particular to delete target/work that Jetty uses. Newer versions may just use work, not target/work. Otherwise your Jetty may continue to pick up old left-over JAR files.

Other resources

Besides this tutorial, there are other tutorials and examples available on line:

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