bundles/org.eclipse.equinox.registry/src/org/eclipse/core/runtime/spi/RegistryStrategy.java

/*******************************************************************************
 * Copyright (c) 2005, 2009 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.runtime.spi;

import java.io.File;
import java.util.*;
import javax.xml.parsers.SAXParserFactory;
import org.eclipse.core.internal.registry.*;
import org.eclipse.core.runtime.*;
import org.eclipse.osgi.util.NLS;

/**
 * This is the basic registry strategy. It describes how the registry does logging,
 * message translation, extra start/stop processing, event scheduling, caching, 
 * and debugging.
 * <p>
 * In this strategy:
 * </p><p><ul>
 * <li>Logging is done onto <code>System.out</code>;</li>
 * <li>The translation routine assumes that keys are prefixed with <code>'%'/<code>;</li>
 * <li>Caching is enabled and doesn't use state or time stamp validation;</li>
 * <li>Standard Java class loading is used to create executable extensions.</li>
 * </ul></p><p>
 * This class can be used without OSGi running.
 * </p><p>
 * This class can be overridden and/or instantiated by clients. 
 * </p>
 * @since org.eclipse.equinox.registry 3.2
 */
public class RegistryStrategy {

	private SAXParserFactory theXMLParserFactory = null;

	/**
	 * Array of file system directories to store cache files; might be <code>null</code>
	 */
	private final File[] storageDirs;

	/**
	 * Specifies if the registry file cache is read only; might be <code>null</code>
	 */
	private final boolean[] cacheReadOnly;

	/**
	 * Constructor for this default registry strategy. 
	 * <p>
	 * The strategy sequentially checks the array of storage directories to 
	 * discover the location of the registry cache formed by previous invocations of the extension
	 * registry. Once found, the location is used to store registry cache. If this value 
	 * is <code>null</code> then caching of the registry content is disabled.
	 * </p><p>
	 * The cache read-only array is an array the same length as the storage directory array. 
	 * It contains boolean values indicating whether or not each storage directory is read-only. 
	 * If the value at an index is <code>true</code> then the location at the corresponding index 
	 * in the storage directories array is read-only; if <code>false</code> then the cache location 
	 * is read-write. The array can be <code>null</code> if the <code>storageDirs</code> parameter 
	 * is <code>null</code>.
	 * </p>
	 *
	 * @param storageDirs array of file system directories, or <code>null</code>
	 * @param cacheReadOnly array of read only attributes, or <code>null</code>
	 */
	public RegistryStrategy(File[] storageDirs, boolean[] cacheReadOnly) {
		this.storageDirs = storageDirs;
		this.cacheReadOnly = cacheReadOnly;
	}

	/**
	 * Returns the number of possible cache locations for this registry.
	 *
	 * @return number of possible cache locations for this registry
	 */
	public final int getLocationsLength() {
		if (storageDirs == null)
			return 0;
		return storageDirs.length;
	}

	/**
	 * Returns the possible registry cache location identified by the index.
	 *
	 * @param index index of the possible registry location
	 * @return potential registry cache location
	 */
	public final File getStorage(int index) {
		if (storageDirs != null)
			return storageDirs[index];
		return null;
	}

	/**
	 * Returns the read-only status of the registry cache location.
	 *
	 * @param index the index of the possible registry location
	 * @return <code>true</code> if the location is read only and 
	 * 	<code>false</code> if the location is read/write
	 */
	public final boolean isCacheReadOnly(int index) {
		if (cacheReadOnly != null)
			return cacheReadOnly[index];
		return true;
	}

	/**
	 * Override this method to provide customized logging functionality
	 * to the registry. The method adds a log entry based on the supplied status. 
	 * <p>
	 * This method writes a message to <code>System.out</code> 
	 * in the following format:
	 * <pre>
	 * [Error|Warning|Log]: Main error message
	 * [Error|Warning|Log]: Child error message 1
	 * 	...
	 * [Error|Warning|Log]: Child error message N
	 * </pre></p>
	 * 
	 * @param status the status to log
	 */
	public void log(IStatus status) {
		RegistrySupport.log(status, null);
	}

	/**
	 * Translates key using the supplied resource bundle. The resource bundle is 
	 * optional and might be <code>null</code>.
	 * <p>
	 * The default translation routine assumes that keys are prefixed with '%'. If 
	 * no resource bundle is present, the key itself (without leading '%') is returned. 
	 * There is no decoding for the leading '%%'.
	 * </p>
	 *
	 * @param key message key to be translated
	 * @param resources resource bundle, or <code>null</code>
	 * @return the translated string, must not be <code>null</code>
	 */
	public String translate(String key, ResourceBundle resources) {
		return RegistrySupport.translate(key, resources);
	}

	/**
	 * Override this method to provide additional processing performed 
	 * when the registry is created and started. Overrides should call
	 * <code>super.onStart()</code> at the beginning of the processing.
	 * <p>
	 * <strong>NOTE</strong>: Avoid placing duplicate functionality in 
	 * this method and {@link #onStart(IExtensionRegistry, boolean)} as 
	 * both methods will be called on the registry startup.
	 * </p>
	 * @param registry the extension registry being started
	 * 
	 * @deprecated use {@link #onStart(IExtensionRegistry, boolean)}. 
	 */
	public void onStart(IExtensionRegistry registry) {
		// The default implementation
	}

	/**
	 * Override this method to provide additional processing performed 
	 * when the registry is created and started. Overrides should call
	 * <code>super.onStart()</code> at the beginning of the processing. 
	 * 
	 * @param registry the extension registry being started
	 * @param loadedFromCache true is registry contents was loaded from 
	 * cache when the registry was created 
	 * 
	 * @since 3.4
	 */
	public void onStart(IExtensionRegistry registry, boolean loadedFromCache) {
		// The default implementation
	}

	/**
	 * Override this method to provide additional processing to be performed
	 * just before the registry is stopped. Overrides should call 
	 * <code>super.onStop()</code> at the end of the processing. 
	 * @param registry the extension registry being stopped
	 */
	public void onStop(IExtensionRegistry registry) {
		// The default implementation
	}

	/**
	 * Creates an executable extension. Override this method to supply an alternative processing 
	 * for the creation of executable extensions. 
	 * <p>
	 * This method receives the contributor of the executable extension and, possibly,
	 * an optional contributor name if specified by the executable extension. The overridden
	 * contributor name might be <code>null</code>.  
	 * </p><p>
	 * In this implementation registry attempts to instantiate the class specified via
	 * the class name (must not be <code>null</code>) using standard Java reflection mechanism.
	 * This method assumes that such class has a default constructor with no arguments.
	 * </p>
	 *
	 * @param contributor the contributor of this executable extension
	 * @param className the name of the class to be instantiated
	 * @param overridenContributorName the contributor to be used, or <code>null</code> if not specified
	 * @return the object created, or <code>null</code>
	 * @throws CoreException if there was a problem creating the executable extension
	 * @see IConfigurationElement#createExecutableExtension(String)
	 * @see IExecutableExtension
	 */
	public Object createExecutableExtension(RegistryContributor contributor, String className, String overridenContributorName) throws CoreException {
		Object result = null;
		Class classInstance = null;
		try {
			classInstance = Class.forName(className);
		} catch (ClassNotFoundException e1) {
			String message = NLS.bind(RegistryMessages.exExt_findClassError, contributor.getActualName(), className);
			throw new CoreException(new Status(IStatus.ERROR, RegistryMessages.OWNER_NAME, IRegistryConstants.PLUGIN_ERROR, message, e1));
		}

		try {
			result = classInstance.newInstance();
		} catch (Exception e) {
			String message = NLS.bind(RegistryMessages.exExt_instantiateClassError, contributor.getActualName(), className);
			throw new CoreException(new Status(IStatus.ERROR, RegistryMessages.OWNER_NAME, IRegistryConstants.PLUGIN_ERROR, message, e));
		}
		return result;
	}

	/**
	 * Override this method to customize scheduling of an extension registry event. Note that this method 
	 * <strong>must</strong> make the following call to actually process the event:
	 * <p><pre><code>
	 * 	RegistryStrategy.processChangeEvent(listeners, deltas, registry);
	 * </code></pre></p><p>
	 * In the default implementation, the method registry events are executed in a queue 
	 * on a separate thread (i.e. asynchronously, sequentially).
	 * </p>
	 *
	 * @param listeners the list of active listeners (thread safe); may not be <code>null</code>
	 * @param deltas the registry deltas (thread safe); may not be <code>null</code>
	 * @param registry the extension registry (NOT thread safe); may not be <code>null</code>
	 */
	public void scheduleChangeEvent(Object[] listeners, Map deltas, Object registry) {
		((ExtensionRegistry) registry).scheduleChangeEvent(listeners, deltas);
	}

	/**
	 * This method performs actual processing of the registry change event. It should 
	 * only be used by overrides of the RegistryStrategy.scheduleChangeEvent. It will
	 * return <code>null</code> if an unexpected registry type was encountered.
	 * 
	 * @param listeners the list of active listeners; may not be <code>null</code>
	 * @param deltas the extension registry deltas; may not be <code>null</code>
	 * @param registry the extension registry; may not be <code>null</code>
	 * @return status of the operation or <code>null</code>
	 */
	public final static IStatus processChangeEvent(Object[] listeners, Map deltas, Object registry) {
		if (registry instanceof ExtensionRegistry)
			return ((ExtensionRegistry) registry).processChangeEvent(listeners, deltas);
		return null;
	}

	/**
	 * Override this method to specify debug requirements to the registry. In the default 
	 * implementation this method returns <code>false</code> indicating that debug functionality 
	 * is turned off.
	 * <p>
	 * Note that in a general case the extension registry plug-in doesn't depend on OSGI and
	 * therefore cannot use Eclipse .options files to discover debug options.
	 * </p>
	 *
	 * @return <code>true</code> if debug logging and validation should be performed and
	 * 	<code>false</code> otherwise
	 */
	public boolean debug() {
		return false;
	}

	/**
	 * Override this method to specify debug requirements for the registry event processing. 
	 * In the default implementation this method returns <code>false</code> indicating that
	 * debug of the registry events is turned off.
	 * <p>
	 * Note that in a general case the extension registry plug-in doesn't depend on OSGI and
	 * therefore cannot use Eclipse .options files to discover debug options.
	 * </p>
	 *
	 * @return <code>true</code> if debug logging and validation of the registry events
	 * 	should be performed and <code>false</code> otherwise
	 */
	public boolean debugRegistryEvents() {
		return false;
	}

	/**
	 * Specifies if the extension registry should use cache to store registry data between 
	 * invocations.
	 * <p>
	 * The default implementation enables caching returning <code>true</code>.
	 * </p>
	 *
	 * @return <code>true</code> if the cache should be used and <code>false</code> otherwise
	 */
	public boolean cacheUse() {
		return true;
	}

	/**
	 * Specifies if lazy cache loading is used. 
	 * <p>
	 * The default implementation specifies that lazy cache loading is going to be used
	 * and therefore returns <code>true</code>.
	 * </p>
	 *
	 * @return <code>true</code> if lazy cache loading is used and <code>false</code> otherwise
	 */
	public boolean cacheLazyLoading() {
		return true;
	}

	/**
	 * This method is called as a part of the registry cache validation. The cache is valid
	 * on the registry startup if the pair {container time stamp, contributors time stamp} 
	 * supplied by the registry strategy is the same as the {container time stamp, contributors time stamp}
	 * stored in the registry cache. The goal of the validation is to be able to catch modifications
	 * made to the original data contributed into the registry and not reflected in the registry cache. 
	 * <p>
	 * The method produces a number that corresponds to the current state of the data stored 
	 * by the container. Increment the stamp if the data stored in the container has been updated
	 * so that the data cached by the registry is no longer valid. For instance, in Eclipse addition 
	 * or removal of a bundle results in the number returned by this method being incremented. As a result, 
	 * if a bundle that contributed plugin.xml into the extension registry was modified, the state doesn't 
	 * match the state stored in the registry cache. In this case the cache content becomes invalid and 
	 * the registry needs to be re-created from the original data. 
	 * </p><p>
	 * Generally, treat this number as a hash code for the data stored in the registry. 
	 * It stays the same as long as the registry content is not changing. It becomes a different 
	 * number as the registry content gets modified.
	 * </p><p>
	 * Return 0 to indicate that state verification is not required.
	 * </p>
	 *
	 * @return number indicating state of the application data
	 */
	public long getContainerTimestamp() {
		return 0;
	}

	/**
	 * This method is called as a part of the registry cache validation. The method calculates 
	 * a number describing the time when the originating contributions (i.e., plugin.xml files 
	 * in case of the Eclipse registry) were last modified. 
	 * <p>
	 * The value returned by the method is compared with the timestamp tracked by the registry. 
	 * If contributions changed since they have been added to the registry (i.e., plugin.xml
	 * file was modified since the last run), the value of the {@link #getContributionsTimestamp()}
	 * will change and no longer will be the same as the value tracked by the registry. In this case 
	 * the cache is considered to be invalid and the registry is going to be re-populated form scratch.
	 * </p><p>
	 * (The word "timestamp" is used very loosely here. In this context, "timestamp" is more likely
	 * to be a hash value aggregating a number of actual timestamps from the contributions.) 
	 * </p><p>
	 * This method may return 0 to indicate that no time stamp verification is required. 
	 * </p>
	 * @return a value corresponding to the last modification time of contributions contained
	 * in the registry 
	 */
	public long getContributionsTimestamp() {
		return 0;
	}

	/**
	 * Returns the parser used by the registry to parse descriptions of extension points and extensions.
	 * This method must not return <code>null</code>.
	 * 
	 * @return this strategy's parser 
	 * @see org.eclipse.core.runtime.IExtensionRegistry#addContribution(java.io.InputStream, IContributor, boolean, String, ResourceBundle, Object)
	 */
	public SAXParserFactory getXMLParser() {
		if (theXMLParserFactory == null)
			theXMLParserFactory = SAXParserFactory.newInstance();
		return theXMLParserFactory;
	}

	/**
	 * Translates array of keys supplied by the contributor to the requested locale.
	 * <p>
	 * This method is intended to be overridden by specialized registry strategies 
	 * that know translation conventions for the contributors, for instance, 
	 * the agreed upon locations of the translated keys for bundle contributors.
	 * The base implementation simply returns the array of non-translated keys. 
	 * </p><p>
	 * This method is only used if multi-language support is enabled.
	 * </p>
	 * @param nonTranslated message keys to be translated
	 * @param contributor the contributor of the keys to be translated
	 * @param locale the requested locale for the keys
	 * @return the arrays of translated strings
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @since org.eclipse.equinox.registry 3.5
	 */
	public String[] translate(String[] nonTranslated, IContributor contributor, String locale) {
		return nonTranslated;
	}

	/**
	 * Returns the current locale for the extension registry with enabled 
	 * multi-language support.
	 * <p>
	 * The default implementation assumes that there is a single system wide 
	 * locale, equivalent to {@link Locale#getDefault()}.
	 * </p><p>
	 * The result of this method should not be retained or passed to other threads.  
	 * The current locale can change any time and may be different for each thread.
	 * </p><p>
	 * This method can be overridden by subclasses that wish to provide a way 
	 * to change the default locale. 
	 * </p><p>
	 * This method is only used if multi-language support is enabled.
	 * </p>
	 * @see IExtensionRegistry#isMultiLanguage()
	 * @return the default locale
	 * @since org.eclipse.equinox.registry 3.5
	 */
	public String getLocale() {
		return Locale.getDefault().toString();
	}
}