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));
}
}