1 files changed, 129 insertions, 0 deletions
diff --git a/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/PluginUtil.java b/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/PluginUtil.java
new file mode 100644
index 0000000000..bf7ecb95b2
--- /dev/null
+++ b/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/PluginUtil.java
@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2022 Eike Stepper (Loehne, Germany) 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:
+ *    Eike Stepper - initial API and implementation
+ */
+package org.eclipse.net4j.util;
+
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IConfigurationElement;
+import org.eclipse.core.runtime.IExtensionRegistry;
+import org.eclipse.core.runtime.Platform;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.StringTokenizer;
+
+/**
+ * @author Eike Stepper
+ * @since 3.19
+ */
+public final class PluginUtil
+{
+  private static final String ATT_CLASS = "class";
+
+  private static final String ATT_PREDECESSOR = "predecessor";
+
+  private PluginUtil()
+  {
+  }
+
+  public static <T> T instantiate(IConfigurationElement element)
+  {
+    return instantiate(element, ATT_CLASS);
+  }
+
+  public static <T> T instantiate(IConfigurationElement element, String classAttribute)
+  {
+    try
+    {
+      @SuppressWarnings("unchecked")
+      T extension = (T)element.createExecutableExtension(classAttribute);
+      return extension;
+    }
+    catch (CoreException ex)
+    {
+      throw WrappedException.wrap(ex);
+    }
+  }
+
+  public static IConfigurationElement[] getConfigurationElements(String namespace, String extensionPointName)
+  {
+    IExtensionRegistry registry = Platform.getExtensionRegistry();
+    return registry.getConfigurationElementsFor(namespace, extensionPointName);
+  }
+
+  /**
+   * Removes all elements with a 'class' attribute that is specified in the 'predecessor' list of any other element.
+   */
+  public static IConfigurationElement[] removePredecessors(IConfigurationElement[] elements)
+  {
+    return removePredecessors(elements, ATT_CLASS, ATT_PREDECESSOR);
+  }
+
+  /**
+   * Removes all elements with a 'class' attribute that is specified in the 'predecessor' list of any other element.
+   */
+  public static IConfigurationElement[] removePredecessors(IConfigurationElement[] elements, String classAttribute, String predecessorAttribute)
+  {
+    Map<String, List<IConfigurationElement>> classToElements = new HashMap<>();
+    Set<String> predecessors = new HashSet<>();
+
+    for (IConfigurationElement element : elements)
+    {
+      // Also map elements without a class attribute.
+      String className = StringUtil.safe(element.getAttribute(classAttribute));
+      classToElements.computeIfAbsent(className, k -> new ArrayList<>()).add(element);
+
+      predecessors.addAll(getPredecessors(element, predecessorAttribute));
+    }
+
+    for (String predecessor : predecessors)
+    {
+      classToElements.remove(predecessor);
+    }
+
+    List<IConfigurationElement> result = new ArrayList<>();
+
+    for (Map.Entry<String, List<IConfigurationElement>> entry : classToElements.entrySet())
+    {
+      List<IConfigurationElement> list = entry.getValue();
+      result.addAll(list);
+    }
+
+    return result.toArray(new IConfigurationElement[result.size()]);
+  }
+
+  private static Set<String> getPredecessors(IConfigurationElement element, String predecessorAttribute)
+  {
+    String value = element.getAttribute(predecessorAttribute);
+    if (value == null)
+    {
+      return Collections.emptySet();
+    }
+
+    Set<String> predecessors = new HashSet<>();
+    StringTokenizer tokenizer = new StringTokenizer(value, " ");
+
+    while (tokenizer.hasMoreTokens())
+    {
+      String predecessor = tokenizer.nextToken().trim();
+      if (predecessor.length() != 0)
+      {
+        predecessors.add(predecessor);
+      }
+    }
+
+    return predecessors;
+  }
+}