org.eclipse.core.runtime
Class Plugin

java.lang.Object
  |
  +--org.eclipse.core.runtime.Plugin

Direct Known Subclasses:

AbstractUIPlugin, AntCorePlugin, DebugPlugin, ResourcesPlugin

public abstract class Plugin

extends Object

The abstract superclass of all plug-in runtime class implementations. A plug-in subclasses this class and overrides the startup and shutdown methods in order to react to life cycle requests automatically issued by the platform.

Conceptually, the plug-in runtime class represents the entire plug-in rather than an implementation of any one particular extension the plug-in declares. A plug-in is not required to explicitly specify a plug-in runtime class; if none is specified, the plug-in will be given a default plug-in runtime object that ignores all life cycle requests (it still provides access to the corresponding plug-in descriptor).

In the case of more complex plug-ins, it may be desireable to define a concrete subclass of Plugin. However, just subclassing Plugin is not sufficient. The name of the class must be explicitly configured in the plug-in's manifest (plugin.xml) file with the class attribute of the <plugin> element markup.

Instances of plug-in runtime classes are automatically created by the platform in the course of plug-in activation. Clients must never explicitly instantiate a plug-in runtime class.

A typical implementation pattern for plug-in runtime classes is to provide a static convenience method to gain access to a plug-in's runtime object. This way, code in other parts of the plug-in implementation without direct access to the plug-in runtime object can easily obtain a reference to it, and thence to any plug-in-wide resources recorded on it. An example follows:

     package myplugin;
     public class MyPluginClass extends Plugin {
         private static MyPluginClass instance;

         public static MyPluginClass getInstance() { return instance; }

         public void MyPluginClass(IPluginDescriptor descriptor) {
             super(descriptor);
             instance = this;
             // ... other initialization
         }
         // ... other methods
     }
 

In the above example, a call to MyPluginClass.getInstance() will always return an initialized instance of MyPluginClass.

The static method Platform.getPlugin() can be used to locate a plug-in's runtime object by name. The extension initialization would contain the following code:

     Plugin myPlugin = Platform.getPlugin("com.example.myplugin");
 

Another typical implementation pattern for plug-in classes is handling of any initialization files required by the plug-in. Typically, each plug-in will ship one or more default files as part of the plug-in install. The executing plug-in will use the defaults on initial startup (or when explicitly requested by the user), but will subsequently rewrite any modifications to the default settings into one of the designated plug-in working directory locations. An example of such an implementation pattern is illustrated below:

 package myplugin;
 public class MyPlugin extends Plugin {

     private static final String INI = "myplugin.ini"; 
     private Properties myProperties = null;

     public void startup() throws CoreException {
         try {
             InputStream input = null;
             // look for working properties.  If none, use shipped defaults 
             File file = getStateLocation().append(INI).toFile();
             if (!file.exists()) {			
                 URL base = getDescriptor().getInstallURL();
                 input = (new URL(base,INI)).openStream();
             } else 
                 input = new FileInputStream(file);
 
             // load properties 
             try {
                 myProperties = new Properties();
                 myProperties.load(input);
             } finally {
                 try {
                     input.close();
                 } catch (IOException e) {
                     // ignore failure on close
                 }
             }
         } catch (Exception e) {
             throw new CoreException(
                 new Status(IStatus.ERROR, getDescriptor().getUniqueIdentifier(),
                     0, "Problems starting plug-in myplugin", e));
         }
     }

     public void shutdown() throws CoreException { 
         // save properties in plugin state location (r/w)
         try {
             FileOutputStream output = null; 
             try {
                 output = new FileOutputStream(getStateLocation().append(INI)); 
                 myProperties.store(output, null);
             } finally {
                 try {
                     output.close();
                 } catch (IOException e) {
                     // ignore failure on close
                 }
             }
         } catch (Exception e) {
             throw new CoreException(
                 new Status(IStatus.ERROR, getDescriptor().getUniqueIdentifier(),
                     0, "Problems shutting down plug-in myplugin", e));
         }
     }

     public Properties getProperties() {	
         return myProperties; 
     }
 }
 

Field Summary

static String	PREFERENCES_DEFAULT_OVERRIDE_BASE_NAME The name of the file (value "preferences.ini") in a plug-in's (read-only) directory that, when present, contains values that override the normal default values for this plug-in's preferences.
static String	PREFERENCES_DEFAULT_OVERRIDE_FILE_NAME

Constructor Summary

Plugin(IPluginDescriptor descriptor)
Creates a new plug-in runtime object for the given plug-in descriptor.

Method Summary

URL	find(IPath path) Returns a URL for the given path.
URL	find(IPath path, Map override) Returns a URL for the given path.
IPluginDescriptor	getDescriptor() Returns the plug-in descriptor for this plug-in runtime object.
ILog	getLog() Returns the log for this plug-in.
Preferences	getPluginPreferences() Returns the preference store for this plug-in.
IPath	getStateLocation() Returns the location in the local file system of the plug-in state area for this plug-in.
protected void	initializeDefaultPluginPreferences() Initializes the default preferences settings for this plug-in.
boolean	isDebugging() Returns whether this plug-in is in debug mode.
InputStream	openStream(IPath file) Returns an input stream for the specified file.
InputStream	openStream(IPath file, boolean localized) Returns an input stream for the specified file.
void	savePluginPreferences() Saves preferences settings for this plug-in.
void	setDebugging(boolean value) Sets whether this plug-in is in debug mode.
void	shutdown() Shuts down this plug-in and discards all plug-in state.
void	startup() Starts up this plug-in.
String	toString() Returns a string representation of the plug-in, suitable for debugging purposes only.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

PREFERENCES_DEFAULT_OVERRIDE_BASE_NAME

public static final String PREFERENCES_DEFAULT_OVERRIDE_BASE_NAME

The name of the file (value "preferences.ini") in a plug-in's (read-only) directory that, when present, contains values that override the normal default values for this plug-in's preferences.

The format of the file is as per java.io.Properties where the keys are property names and values are strings.

Since:

2.0

See Also:

Constant Field Values

PREFERENCES_DEFAULT_OVERRIDE_FILE_NAME

public static final String PREFERENCES_DEFAULT_OVERRIDE_FILE_NAME

See Also:

Constant Field Values

Constructor Detail

Plugin

public Plugin(IPluginDescriptor descriptor)

Creates a new plug-in runtime object for the given plug-in descriptor.

Instances of plug-in runtime classes are automatically created by the platform in the course of plug-in activation. Clients must never explicitly instantiate a plug-in runtime class.

Note: The class loader typically has monitors acquired during invocation of this method. It is strongly recommended that this method avoid synchronized blocks or other thread locking mechanisms, as this would lead to deadlock vulnerability.

Parameters:

descriptor - the plug-in descriptor

See Also:

getDescriptor()

Method Detail

find

public final URL find(IPath path)

Returns a URL for the given path. Returns null if the URL could not be computed or created.

Returns:

a URL for the given path or null

find

public final URL find(IPath path,
                      Map override)

Returns a URL for the given path. Returns null if the URL could not be computed or created.

Parameters:

path - file path relative to plug-in installation location

override - map of override substitution arguments to be used for any $arg$ path elements. The map keys correspond to the substitution arguments (eg. "$nl$" or "$os$"). The resulting values must be of type java.lang.String. If the map is null, or does not contain the required substitution argument, the default is used.

Returns:

a URL for the given path or null

getDescriptor

public final IPluginDescriptor getDescriptor()

Returns the plug-in descriptor for this plug-in runtime object.

Returns:

the plug-in descriptor for this plug-in runtime object

getLog

public final ILog getLog()

Returns the log for this plug-in. If no such log exists, one is created.

Returns:

the log for this plug-in

getStateLocation

public final IPath getStateLocation()

Returns the location in the local file system of the plug-in state area for this plug-in. If the plug-in state area did not exist prior to this call, it is created.

The plug-in state area is a file directory within the platform's metadata area where a plug-in is free to create files. The content and structure of this area is defined by the plug-in, and the particular plug-in is solely responsible for any files it puts there. It is recommended for plug-in preference settings and other configuration parameters.

Returns:

a local file system path

getPluginPreferences

public final Preferences getPluginPreferences()

Returns the preference store for this plug-in.

Note that if an error occurs reading the preference store from disk, an empty preference store is quietly created, initialized with defaults, and returned.

Calling this method may cause the preference store to be created and initialized. Subclasses which reimplement the initializeDefaultPluginPreferences method have this opportunity to initialize preference default values, just prior to processing override default values imposed externally to this plug-in (specified for the product, or at platform start up).

After settings in the preference store are changed (for example, with Preferences.setValue or setToDefault), savePluginPreferences should be called to store the changed values back to disk. Otherwise the changes will be lost on plug-in shutdown.

Returns:

the preference store

Since:

2.0

See Also:

savePluginPreferences(), Preferences.setValue(java.lang.String, boolean), Preferences.setToDefault(java.lang.String)

savePluginPreferences

public final void savePluginPreferences()

Saves preferences settings for this plug-in. Does nothing if the preference store does not need saving.

Plug-in preferences are not saved automatically on plug-in shutdown.

Since:

2.0

See Also:

Preferences#save, Preferences.needsSaving()

initializeDefaultPluginPreferences

protected void initializeDefaultPluginPreferences()

Initializes the default preferences settings for this plug-in.

This method is called sometime after the preference store for this plug-in is created. Default values are never stored in preference stores; they must be filled in each time. This method provides the opportunity to initialize the default values.

The default implementation of this method does nothing. A subclass that needs to set default values for its preferences must reimplement this method. Default values set at a later point will override any default override settings supplied from outside the plug-in (product configuration or platform start up).

Since:

2.0

isDebugging

public boolean isDebugging()

Returns whether this plug-in is in debug mode. By default plug-ins are not in debug mode. A plug-in can put itself into debug mode or the user can set an execution option to do so.

Returns:

whether this plug-in is in debug mode

openStream

public final InputStream openStream(IPath file)
                             throws IOException

Returns an input stream for the specified file. The file path must be specified relative this the plug-in's installation location.

Parameters:

file - path relative to plug-in installation location

Returns:

an input stream

IOException

See Also:

openStream(IPath,boolean)

openStream

public final InputStream openStream(IPath file,
                                    boolean localized)
                             throws IOException

Returns an input stream for the specified file. The file path must be specified relative to this plug-in's installation location. Optionally, the platform searches for the correct localized version of the specified file using the users current locale, and Java naming convention for localized resource files (locale suffix appended to the specified file extension).

The caller must close the returned stream when done.

Parameters:

file - path relative to plug-in installation location

localized - true for the localized version of the file, and false for the file exactly as specified

Returns:

an input stream

IOException

setDebugging

public void setDebugging(boolean value)

Sets whether this plug-in is in debug mode. By default plug-ins are not in debug mode. A plug-in can put itself into debug mode or the user can set a debug option to do so.

Parameters:

value - whether or not this plugi-in is in debug mode

shutdown

public void shutdown()
              throws CoreException

Shuts down this plug-in and discards all plug-in state.

This method should be re-implemented in subclasses that need to do something when the plug-in is shut down. Implementors should call the inherited method to ensure that any system requirements can be met.

Plug-in shutdown code should be robust. In particular, this method should always make an effort to shut down the plug-in. Furthermore, the code should not assume that the plug-in was started successfully, as this method will be invoked in the event of a failure during startup.

Note 1: If a plug-in has been started, this method will be automatically invoked by the platform when the platform is shut down.

Note 2: This method is intended to perform simple termination of the plug-in environment. The platform may terminate invocations that do not complete in a timely fashion.

Clients must never explicitly call this method.

Throws:

CoreException - if this method fails to shut down this plug-in

startup

public void startup()
             throws CoreException

Starts up this plug-in.

This method should be overridden in subclasses that need to do something when this plug-in is started. Implementors should call the inherited method to ensure that any system requirements can be met.

If this method throws an exception, it is taken as an indication that plug-in initialization has failed; as a result, the plug-in will not be activated; moreover, the plug-in will be marked as disabled and ineligible for activation for the duration.

Plug-in startup code should be robust. In the event of a startup failure, the plug-in's shutdown method will be invoked automatically, in an attempt to close open files, etc.

Note 1: This method is automatically invoked by the platform the first time any code in the plug-in is executed.

Note 2: This method is intended to perform simple initialization of the plug-in environment. The platform may terminate initializers that do not complete in a timely fashion.

Note 3: The class loader typically has monitors acquired during invocation of this method. It is strongly recommended that this method avoid synchronized blocks or other thread locking mechanisms, as this would lead to deadlock vulnerability.

Clients must never explicitly call this method.

Throws:

CoreException - if this plug-in did not start up properly

toString

public String toString()

Returns a string representation of the plug-in, suitable for debugging purposes only.

Overrides:

toString in class Object