Chapter 17. Introducing the Plugin API
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## Chapter 17. Introducing the Plugin API

The jEdit Plugin API provides a framework for hosting plugin applications without imposing any requirements on the design or function of the plugin itself. You could write an application that performs spell checking, displays a clock or plays chess and turn it into a jEdit plugin. There are currently over 50 released plugins for jEdit. While none of them play chess, they perform a wide variety of editing and file management tasks.

A detailed listing of available plugins is available at plugins.jedit.org. You can also find beta versions of new plugins in the “Downloads” area of community.jedit.org.

Using the “Plugin Manager” feature of jEdit, users with an Internet connection can check for new or updated plugins and install and remove them without leaving jEdit. See Chapter 9, Installing and Using Plugins for details.

Requirements for “plugging in” to jEdit are as follows:

- This plugin must supply information about itself, such as its name, version, author, and compatibility with versions of jEdit.

- The plugin must provide for activating, displaying and deactivating itself upon direction from jEdit, typically in response to user input[1]. Make sure you can continue to use both your plugin and the editor after it has been reloaded.

- Each Plugin has an ActionSet defined by jEdit, which is added to the main ActionContext. The ActionSet is a container for EditAction instances. The plugin may define actions in a number of ways. One way is explicitly, with an action definition file known as `actions.xml`. Another is implicitly, by defining dockable windows in `dockables.xml`.

  Most EditActions are small blocks of BeanShell code that jEdit will perform on behalf of the plugin upon user request. They provide the “glue” between user input and specific plugin routines.

  By convention, plugins display their available actions in submenus of jEdit's Plugins menu; each menu item corresponds to an action. Plugin authors do not define specific shortcuts - the user can/will assign EditActions to keyboard shortcuts, toolbar buttons, or entries in the text area's Context menu (right-click menu).

- The plugin may, but need not, provide a user interface.

  If the plugin has a visible interface, it can be shown in any object derived from one of Java top-level container classes: `JWindow`, `JDialog`, or `JFrame`. jEdit also provides a dockable window API, which allows plugin windows derived from the `JComponent` class to be docked into views or shown in top-level frames, at the user's request.

  Plugins can also act directly upon jEdit's text area. They can add graphical elements to the text display (like error highlighting in the case of the ErrorList plugin) or decorations surrounding the text area (like the JDiff plugin's summary views). These plugins are dependent on the JEditTextArea class, which is currently getting refactored.

- Plugins may provide a range of options that the user can modify to alter their configuration.

  If a plugin provides configuration options in accordance with the plugin API, jEdit will make them available in the Global Options dialog box.

- While it is not required, plugins are encouraged to provide documentation.

As noted, many of these features are optional; it is possible to write a plugin that does not provide actions, configuration options, or dockable windows. The majority of plugins, however, provide most of these services.

[1] You should test your plugin by loading and unloading it from both the Plugin Manager, as well as the Activator Plugin.

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