Condition.java

/*
 * Copyright (c) OSGi Alliance (2004, 2012). All Rights Reserved.
 * 
 * Licensed 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.
 */

package org.osgi.service.condpermadmin;

import java.util.Dictionary;

/**
 * The interface implemented by a Condition. Conditions are bound to Permissions
 * using Conditional Permission Info. The Permissions of a ConditionalPermission
 * Info can only be used if the associated Conditions are satisfied.
 * 
 * @ThreadSafe
 * @version $Id: ae2500276f1204a47a981347579f5b53cc8a7e4f $
 */
public interface Condition {
	/**
	 * A Condition object that will always evaluate to true and that is never
	 * postponed.
	 */
	public final static Condition	TRUE	= new BooleanCondition(true);

	/**
	 * A Condition object that will always evaluate to false and that is never
	 * postponed.
	 */
	public final static Condition	FALSE	= new BooleanCondition(false);

	/**
	 * Returns whether the evaluation must be postponed until the end of the
	 * permission check. If this method returns {@code false} (or this Condition
	 * is immutable), then this Condition must be able to directly answer the
	 * {@link #isSatisfied()} method. In other words, isSatisfied() will return
	 * very quickly since no external sources, such as for example users or
	 * networks, need to be consulted. <br/>
	 * This method must always return the same value whenever it is called so
	 * that the Conditional Permission Admin can cache its result.
	 * 
	 * @return {@code true} to indicate the evaluation must be postponed.
	 *         Otherwise, {@code false} if the evaluation can be performed
	 *         immediately.
	 */
	boolean isPostponed();

	/**
	 * Returns whether the Condition is satisfied. This method is only called
	 * for immediate Condition objects or immutable postponed conditions, and
	 * must always be called inside a permission check. Mutable postponed
	 * Condition objects will be called with the grouped version
	 * {@link #isSatisfied(Condition[],Dictionary)} at the end of the permission
	 * check.
	 * 
	 * @return {@code true} to indicate the Conditions is satisfied. Otherwise,
	 *         {@code false} if the Condition is not satisfied.
	 */
	boolean isSatisfied();

	/**
	 * Returns whether the Condition is mutable. A Condition can go from mutable
	 * ({@code true}) to immutable ({@code false}) over time but never from
	 * immutable ({@code false}) to mutable ({@code true}).
	 * 
	 * @return {@code true} {@link #isSatisfied()} can change. Otherwise,
	 *         {@code false} if the value returned by {@link #isSatisfied()}
	 *         will not change for this condition.
	 */
	boolean isMutable();

	/**
	 * Returns whether the specified set of Condition objects are satisfied.
	 * Although this method is not static, it must be implemented as if it were
	 * static. All of the passed Condition objects will be of the same type and
	 * will correspond to the class type of the object on which this method is
	 * invoked. This method must be called inside a permission check only.
	 * 
	 * @param conditions The array of Condition objects, which must all be of
	 *        the same class and mutable. The receiver must be one of those
	 *        Condition objects.
	 * @param context A Dictionary object that implementors can use to track
	 *        state. If this method is invoked multiple times in the same
	 *        permission check, the same Dictionary will be passed multiple
	 *        times. The SecurityManager treats this Dictionary as an opaque
	 *        object and simply creates an empty dictionary and passes it to
	 *        subsequent invocations if multiple invocations are needed.
	 * @return {@code true} if all the Condition objects are satisfied.
	 *         Otherwise, {@code false} if one of the Condition objects is not
	 *         satisfied.
	 */
	boolean isSatisfied(Condition conditions[], Dictionary<Object, Object> context);
}

/**
 * Package private class used to define the {@link Condition#FALSE} and
 * {@link Condition#TRUE} constants.
 * 
 * @Immutable
 */
final class BooleanCondition implements Condition {
	private final boolean	satisfied;

	BooleanCondition(boolean satisfied) {
		this.satisfied = satisfied;
	}

	public boolean isPostponed() {
		return false;
	}

	public boolean isSatisfied() {
		return satisfied;
	}

	public boolean isMutable() {
		return false;
	}

	public boolean isSatisfied(Condition[] conds, Dictionary<Object, Object> context) {
		for (int i = 0, length = conds.length; i < length; i++) {
			if (!conds[i].isSatisfied())
				return false;
		}
		return true;
	}
}