NEW - bug 360330: [api] provide generic extension point reader

https://bugs.eclipse.org/bugs/show_bug.cgi?id=360330

Change-Id: I581e96fdb821e66935a95b829f1a25fe1bc479f5

1 files changed, 129 insertions, 0 deletions

diff --git a/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java b/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java
new file mode 100644
index 0000000..7ac5401
--- a/dev/null
+++ b/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java
@@ -0,0 +1,129 @@
+package org.eclipse.mylyn.commons.core;
+/*******************************************************************************
+ * Copyright (c) 2011 Tasktop Technologies.
+ * 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:
+ *     Tasktop Technologies - initial API and implementation
+ *******************************************************************************/
+
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.eclipse.core.runtime.Assert;
+import org.eclipse.core.runtime.IConfigurationElement;
+import org.eclipse.core.runtime.IExtension;
+import org.eclipse.core.runtime.IExtensionPoint;
+import org.eclipse.core.runtime.IExtensionRegistry;
+import org.eclipse.core.runtime.IStatus;
+import org.eclipse.core.runtime.MultiStatus;
+import org.eclipse.core.runtime.Platform;
+import org.eclipse.core.runtime.Status;
+import org.eclipse.osgi.util.NLS;
+
+/**
+ * @author Steffen Pingel
+ * @since 3.7
+ */
+public class ExtensionPointReader<T> {
+
+	private final String extensionId;
+
+	private final String elementId;
+
+	private final Class<T> clazz;
+
+	private String classAttributeId;
+
+	private final String pluginId;
+
+	private final List<T> items;
+
+	public ExtensionPointReader(String pluginId, String extensionId, String elementId, Class<T> clazz) {
+		Assert.isNotNull(pluginId);
+		Assert.isNotNull(extensionId);
+		Assert.isNotNull(elementId);
+		Assert.isNotNull(clazz);
+		this.pluginId = pluginId;
+		this.extensionId = extensionId;
+		this.elementId = elementId;
+		this.clazz = clazz;
+		this.classAttributeId = "class"; //$NON-NLS-1$
+		this.items = new ArrayList<T>();
+	}
+
+	public final String getPluginId() {
+		return pluginId;
+	}
+
+	public final String getElementId() {
+		return elementId;
+	}
+
+	public final void setClassAttributeId(String classAttributeId) {
+		this.classAttributeId = classAttributeId;
+	}
+
+	public final String getClassAttributeId() {
+		return classAttributeId;
+	}
+
+	public IStatus read() {
+		items.clear();
+
+		MultiStatus result = new MultiStatus(pluginId, 0, "Extensions failed to load", null); //$NON-NLS-1$
+
+		IExtensionRegistry registry = Platform.getExtensionRegistry();
+		IExtensionPoint extensionPoint = registry.getExtensionPoint(classAttributeId + "." + extensionId); //$NON-NLS-1$
+		if (extensionPoint != null) {
+			IExtension[] extensions = extensionPoint.getExtensions();
+			for (IExtension extension : extensions) {
+				IConfigurationElement[] elements = extension.getConfigurationElements();
+				for (IConfigurationElement element : elements) {
+					if (element.getName().equals(elementId)) {
+						T item = readElement(element, result);
+						if (item != null) {
+							items.add(item);
+						}
+					}
+				}
+			}
+		}
+
+		handleResult(result);
+
+		return result;
+	}
+
+	protected void handleResult(IStatus result) {
+		if (!result.isOK()) {
+			StatusHandler.log(result);
+		}
+	}
+
+	public List<T> getItems() {
+		return new ArrayList<T>(items);
+	}
+
+	protected T readElement(IConfigurationElement element, MultiStatus result) {
+		try {
+			Object object = element.createExecutableExtension(getClassAttributeId());
+			if (clazz.isInstance(object)) {
+				return clazz.cast(object);
+			} else {
+				result.add(new Status(IStatus.ERROR, pluginId, NLS.bind(
+						"Class ''{0}'' does not extend expected class for extension contributed by {1}", //$NON-NLS-1$
+						object.getClass().getCanonicalName(), getPluginId())));
+			}
+		} catch (Throwable e) {
+			result.add(new Status(IStatus.ERROR, pluginId, NLS.bind(
+					"Failed to load for extension contributed by {0}", getPluginId()), e)); //$NON-NLS-1$
+		}
+		return null;
+	}
+
+}