--- /dev/null
+package org.apache.lucene.util;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.lang.reflect.Method;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.WeakHashMap;
+import java.util.Set;
+
+/**
+ * A utility for keeping backwards compatibility on previously abstract methods
+ * (or similar replacements).
+ * <p>Before the replacement method can be made abstract, the old method must kept deprecated.
+ * If somebody still overrides the deprecated method in a non-final class,
+ * you must keep track, of this and maybe delegate to the old method in the subclass.
+ * The cost of reflection is minimized by the following usage of this class:</p>
+ * <p>Define <strong>static final</strong> fields in the base class ({@code BaseClass}),
+ * where the old and new method are declared:</p>
+ * <pre>
+ * static final VirtualMethod<BaseClass> newMethod =
+ * new VirtualMethod<BaseClass>(BaseClass.class, "newName", parameters...);
+ * static final VirtualMethod<BaseClass> oldMethod =
+ * new VirtualMethod<BaseClass>(BaseClass.class, "oldName", parameters...);
+ * </pre>
+ * <p>This enforces the singleton status of these objects, as the maintenance of the cache would be too costly else.
+ * If you try to create a second instance of for the same method/{@code baseClass} combination, an exception is thrown.
+ * <p>To detect if e.g. the old method was overridden by a more far subclass on the inheritance path to the current
+ * instance's class, use a <strong>non-static</strong> field:</p>
+ * <pre>
+ * final boolean isDeprecatedMethodOverridden =
+ * oldMethod.getImplementationDistance(this.getClass()) > newMethod.getImplementationDistance(this.getClass());
+ *
+ * <em>// alternatively (more readable):</em>
+ * final boolean isDeprecatedMethodOverridden =
+ * VirtualMethod.compareImplementationDistance(this.getClass(), oldMethod, newMethod) > 0
+ * </pre>
+ * <p>{@link #getImplementationDistance} returns the distance of the subclass that overrides this method.
+ * The one with the larger distance should be used preferable.
+ * This way also more complicated method rename scenarios can be handled
+ * (think of 2.9 {@code TokenStream} deprecations).</p>
+ *
+ * @lucene.internal
+ */
+public final class VirtualMethod<C> {
+
+ private static final Set<Method> singletonSet = Collections.synchronizedSet(new HashSet<Method>());
+
+ private final Class<C> baseClass;
+ private final String method;
+ private final Class<?>[] parameters;
+ private final WeakHashMap<Class<? extends C>, Integer> cache =
+ new WeakHashMap<Class<? extends C>, Integer>();
+
+ /**
+ * Creates a new instance for the given {@code baseClass} and method declaration.
+ * @throws UnsupportedOperationException if you create a second instance of the same
+ * {@code baseClass} and method declaration combination. This enforces the singleton status.
+ * @throws IllegalArgumentException if {@code baseClass} does not declare the given method.
+ */
+ public VirtualMethod(Class<C> baseClass, String method, Class<?>... parameters) {
+ this.baseClass = baseClass;
+ this.method = method;
+ this.parameters = parameters;
+ try {
+ if (!singletonSet.add(baseClass.getDeclaredMethod(method, parameters)))
+ throw new UnsupportedOperationException(
+ "VirtualMethod instances must be singletons and therefore " +
+ "assigned to static final members in the same class, they use as baseClass ctor param."
+ );
+ } catch (NoSuchMethodException nsme) {
+ throw new IllegalArgumentException(baseClass.getName() + " has no such method: "+nsme.getMessage());
+ }
+ }
+
+ /**
+ * Returns the distance from the {@code baseClass} in which this method is overridden/implemented
+ * in the inheritance path between {@code baseClass} and the given subclass {@code subclazz}.
+ * @return 0 iff not overridden, else the distance to the base class
+ */
+ public synchronized int getImplementationDistance(final Class<? extends C> subclazz) {
+ Integer distance = cache.get(subclazz);
+ if (distance == null) {
+ cache.put(subclazz, distance = Integer.valueOf(reflectImplementationDistance(subclazz)));
+ }
+ return distance.intValue();
+ }
+
+ /**
+ * Returns, if this method is overridden/implemented in the inheritance path between
+ * {@code baseClass} and the given subclass {@code subclazz}.
+ * <p>You can use this method to detect if a method that should normally be final was overridden
+ * by the given instance's class.
+ * @return {@code false} iff not overridden
+ */
+ public boolean isOverriddenAsOf(final Class<? extends C> subclazz) {
+ return getImplementationDistance(subclazz) > 0;
+ }
+
+ private int reflectImplementationDistance(final Class<? extends C> subclazz) {
+ if (!baseClass.isAssignableFrom(subclazz))
+ throw new IllegalArgumentException(subclazz.getName() + " is not a subclass of " + baseClass.getName());
+ boolean overridden = false;
+ int distance = 0;
+ for (Class<?> clazz = subclazz; clazz != baseClass && clazz != null; clazz = clazz.getSuperclass()) {
+ // lookup method, if success mark as overridden
+ if (!overridden) {
+ try {
+ clazz.getDeclaredMethod(method, parameters);
+ overridden = true;
+ } catch (NoSuchMethodException nsme) {
+ }
+ }
+
+ // increment distance if overridden
+ if (overridden) distance++;
+ }
+ return distance;
+ }
+
+ /**
+ * Utility method that compares the implementation/override distance of two methods.
+ * @return <ul>
+ * <li>> 1, iff {@code m1} is overridden/implemented in a subclass of the class overriding/declaring {@code m2}
+ * <li>< 1, iff {@code m2} is overridden in a subclass of the class overriding/declaring {@code m1}
+ * <li>0, iff both methods are overridden in the same class (or are not overridden at all)
+ * </ul>
+ */
+ public static <C> int compareImplementationDistance(final Class<? extends C> clazz,
+ final VirtualMethod<C> m1, final VirtualMethod<C> m2)
+ {
+ return Integer.valueOf(m1.getImplementationDistance(clazz)).compareTo(m2.getImplementationDistance(clazz));
+ }
+
+}
fnp / pylucene.git / blobdiff