1. Extending Eclipse Kai-Uwe Mätzel IBM OTI Labs Zurich kai-uwe_maetzel@ch.ibm.com www.eclipse.org

2. Overview Eclipse is more than a Java IDE Eclipse is more than a Java IDE –it has an open, extensible architecture –built out of layers of plug-ins everybody can contribute plug-ins everybody can contribute plug-ins in many ways Eclipse is the Emacs for the 21st century – Martin Fowler in many ways Eclipse is the Emacs for the 21st century – Martin Fowler Social implications: Social implications: –every programmer can be a tool smith –creating opportunities for further extension makes it possible for the tool smith to benefit from the work of others it has to be easy to install and manage plug-ins it has to be easy to install and manage plug-ins

3. Platform vs. Extensible IDE PlatformExtensible IDE Run-time Plug-ins IDE Plug-ins Eclipse is a platform with a small runtime kernel

4. Eclipse Plug-in Architecture Plug-in - smallest unit of Eclipse function Plug-in - smallest unit of Eclipse function –Big example: HTML editor –Small example: Action to create zip files Extension point - named entity for collecting contributions Extension point - named entity for collecting contributions –Example: extension point for workbench preference UI Extension - a contribution Extension - a contribution –Example: specific HTML editor preferences Plug-in Extension Point Extensions Extension Interface

5. Eclipse Plug-in Architecture Each plug-in Each plug-in –Contributes to 1 or more extension points –Optionally declares new extension points –Depends on a set of other plug-ins –Contains Java code libraries and other files –May export Java-based APIs for downstream plug-ins –Lives in its own plug-in subdirectory Details spelled out in the plug-in manifest Details spelled out in the plug-in manifest –Manifest declares contributions –Code implements contributions and provides API –plugin.xml file in root of plug-in subdirectory

6. Tip of the Iceberg Implementation of plug-in contributions Declarative definition of plug-in contributions startup time: O(#used plug-ins), not O(# installed plug-ins)

7. Plug-in Manifest <plugin id = com.example.tool version = 2.1.0 name = Example Plug-in Tool" class = "com.example.tool.ToolPlugin"> <page id = "com.example.tool.preferences" icon = "icons/knob.gif" title = Tool Knobs" class = "com.example.tool.ToolPreferenceWizard/> Declare contribution this plug-in makes Declare new extension point open to contributions from other plug-ins Location of plug-ins code Other plug-ins needed Plug-in identification plugin.xml

8. Configurers Extenders Extenders Plus Publishers Users Der Plan

9. Extender: Contribute an Icon View Goal: a plug-in to view the standard Eclipse images Goal: a plug-in to view the standard Eclipse images Steps: Steps: –read extension point specifications –use Plug-in Development Tools to create a plug-in project and to declare the extension –use the Java Development Tools to implement the extension

10. Extender: Plug-in Development Extenders use PDE to implement plug-ins Extenders use PDE to implement plug-ins PDE = Plug-in development environment PDE = Plug-in development environment Built on top of the Eclipse Platform and JDT Built on top of the Eclipse Platform and JDT Specialized PDE editor for plug-in manifest files Specialized PDE editor for plug-in manifest files Templates for new plug-ins Templates for new plug-ins PDE runs and debugs another Eclipse workbench PDE runs and debugs another Eclipse workbench

11. Extender: Development Workspace Plug-ins correspond to Java projects Plug-ins correspond to Java projects Source projects projects you are working on Source projects projects you are working on –consist of plug-in manifest, source –source can be changed and compiled Binary projects projects you are browsing only Binary projects projects you are browsing only –consist of plug-in manifest, plug-in jar, source jar –source can be inspected –must not be compiled –small foot print Projects build class path is derived from the required plug-ins Projects build class path is derived from the required plug-ins

12. Extender: Deploying a Plug-in Development time: Development time: –the plug-in code isnt packaged as a JAR –executed in a special development mode by PDE faster turn-around faster turn-around Deploy: Deploy: –package plug-in code as JARs deployed plug-in can be installed into a run-time Eclipse deployed plug-in can be installed into a run-time Eclipse How to: How to: –describe deployable contents in build.properties –generate Ant script with PDE –run Ant source.imageview.jar = src/ build.properties

13. Extender Principles Learn from existing extension point implementations Learn from existing extension point implementations Relevance rule: only contribute when you can successfully operate Relevance rule: only contribute when you can successfully operate –you are not the only contributor… Declare the package prefixes your plug-in contains to speed-up class loading Declare the package prefixes your plug-in contains to speed-up class loading

14. Extender Plus: Open up your Plug-in Define an extension point in the manifest file Define an extension point in the manifest file –define an extension point schema (optional) Define an extension interface Define an extension interface Load the defined extensions on demand from the plug-in registry Load the defined extensions on demand from the plug-in registry lazy creation lazy creation public interface IImageFilter { Image filter(Image image); }

15. Extender Plus: Extension Interface Plug-in A Plug-in A –Declares extension point P (org.demo.imageFilter) –Declares interface I (org.demo.views.IImageFilter) for P Plug-in B Plug-in B –Implements interface I with its own class C (GreyFilter) –Contributes class C to extension point P Plug-in A instantiates C and calls its I methods Plug-in A instantiates C and calls its I methods Typical arrangement Typical arrangement plug-in A plug-in B class C interface I extension point P extension contributes creates, calls implements

16. Consuming an Extension Point Define the extension Define the extension Implement the extension interface Implement the extension interface public class GreyFilter implements IImageFilter { public Image filter(Image image) {…} } Demo

17. Extension Points Principles Whenever possible - let others contribute to your contributions Whenever possible - let others contribute to your contributions Contributions are additions to Eclipse Contributions are additions to Eclipse –add, dont replace Lazy loading rule: load extensions only when they are about to be called Lazy loading rule: load extensions only when they are about to be called Contributions do not Contributions do not –override existing behavior –remove or replace existing component –harm existing or future contributions

18. Extension Points Principles Extension point providers must… Extension point providers must… –cope with multiple contributions support user arbitration when there are conflicting contributionssupport user arbitration when there are conflicting contributions allow for additive behaviorallow for additive behavior –protect their code when creating extensions Make your published API explicit Make your published API explicit –internal classes should be in internal packages

19. Publisher: Install/Update Features group plug-ins into installable chunks Features group plug-ins into installable chunks –Feature manifest file Plug-ins and features bear version identifiers Plug-ins and features bear version identifiers –major. minor. service –Multiple versions may co-exist on disk Features downloadable from web site Features downloadable from web site –Using Eclipse Platform update manager –Obtain and install new plug-ins –Obtain and install updates to existing plug-ins

20. Publisher: Create a Feature Feature describes Feature describes –Contained plug-ins and their versions –Pre-requisite plug-ins for the feature <feature id="org.demo.imageviewfeature version="1.0.0"> <plugin id="org.demo.imageview" download-size="0" install-size="0" version="1.0.0"/>

21. Publisher: Create an Update Site An update site An update site –is any URL addressable location –contains zips for the feature and plug-ins –version information encoded in the zip name –contents described by a site.xml file Eclipse Demo Plugins

22. Publisher Principles Once you have invited others to contribute try hard to keep your API stable Once you have invited others to contribute try hard to keep your API stable API stability work arounds API stability work arounds –deprecate and forward –start over in a new package –extension interfaces

23. Closing the Circle Now that we have published a plug-in with extension points we have closed the circle: Now that we have published a plug-in with extension points we have closed the circle: Extenders can now extend the extensions! Extenders can now extend the extensions!

24. Plug-in Architecture - Summary All functionality provided by plug-ins All functionality provided by plug-ins –Includes all aspects of Eclipse Platform itself Contributions via extension points Contributions via extension points –Extensions are created lazily Packaged into separately installable features Packaged into separately installable features –Downloadable