This chapter is from the book
This chapter is from the book
This chapter is from the book
3.5 Plug-in Model
When Eclipse first launches, it scans each of the plug-in directories and builds an internal model representing every plug-in it finds. This occurs by scanning each plug-in manifest without loading the plug-ins. The methods in the next two subsections are useful if you want to display information about plug-ins or perform operations based on specific plug-in characteristics without taking the time and memory usage hit associated with loading plug-ins.
3.5.1 Platform
The org.eclipse.core.runtime.Platform class provides information about the currently executing Eclipse environment. Using this class, you can obtain information about installed plug-ins (also known as Bundles), extensions, extension points, command line arguments, job manager (see Section 20.8, Background Tasks—Jobs API, on page 739), installation location, and more.
The following are some methods of note.
- asLocalURL(URL)— Translates a plug-in-relative URL to a locally accessible URL.
- find(Bundle bundle, IPath path)— Returns a URL to the resource in the specified bundle.
- getBundle(String)— Returns the bundle with the specified unique identifier.
- getBundleGroupProviders()— Returns an array of bundle providers that contain bundle groups that contain currently installed bundles.
- getExtensionRegistry()— Returns extension and extension point information.
- getJobManager()— Returns the platform job manager (see Section 20.8, Background Tasks-Jobs API, on page 739).
- getLog(Bundle)— Returns the log for the specified bundle.
- getProduct()— Returns the Eclipse product information.
- inDebugMode()— Returns true if Eclipse is in debug mode, as it is when the user specifies the -debug command line argument.
- resolve(URL)— Resolves a plug-in-relative URL to a URL native to the Java class library (e.g., file, http, etc.).
- run(ISafeRunnable)— Runs the given runnable in a protected mode. Exceptions thrown in the runnable are logged and passed to the runnable's exception handler.
3.5.2 Plug-ins and Bundles
Information about the currently installed plug-ins, also known as Bundles, can be obtained using Platform.getBundleGroupProviders() or Platform.getBundle(String). Accessing a plug-in class, also known as a bundle activator, requires the containing plug-in to be loaded whereas interacting with the Bundle interface does not carry such a penalty. If you already have a plug-in class, such as the Favorites plug-in, then you can obtain the Bundle interface for that plug-in by using something like this:
FavoritesPlugin.getDefault().getBundle()
After you obtain the Bundle object, several methods are of interest.
- getBundleId()— Returns the bundle's unique identifier (a long), assigned by Eclipse when the bundle was installed.
- getEntry(String)— Returns a URL for the specified '/'-separated bundle relative path name where getEntry("/") returns the bundle root. This provides access to resoures supplied with the plug-in that are typically read-only. Relative plug-in information should be written to the location provided by Plugin.getStateLocation().
- getHeaders()— Returns a dictionary of headers and values defined in the bundle's MANIFEST.MF file (see Section 3.3.1, Plug-in declaration, on page 108).
- getState()— Returns the current state of a plug-in, such as Bundle.UNINSTALLED, Bundle.INSTALLED, Bundle.RESOLVED, Bundle.STARTING, Bundle.STOPPING, Bundle.ACTIVE.
- getSymbolicName()— Returns the unique plug-in identifier (a java.lang.String), which is the same as the Bundle-SymbolicName declaration in the MANIFEST.MF.
The plug-in version number can be obtained using the getHeaders() method.
new PluginVersionIdentifier(
bundle.getHeaders().get("Bundle-Version"))
3.5.3 Plug-in extension registry
You can access the plug-in extension registry using the Plaform.getExtensionRegistry() method. It contains plug-in descriptors, each representing a plug-in. The registry provides the following methods for extracting information about the various plug-ins without loading them (see Section 17.1, The Extension Point Mechanism, on page 595 for information on creating extension points).
- getConfigurationElementsFor(String extensionPointId)— Returns all configuration elements from all extensions configured into the identified extension point.
- getExtensionPoint(String extensionPointId)— Returns the extension point with the given extension point identifier in this plug-in registry.
Previously, extensions and extension-points did not change during execution, but that is slowly changing as the Eclipse plug-in model continues to align itself with OSGi. If you are interested in changes during execution, use addRegistryChangeListener(IRegistryChangeListener).