SingletonInitialContextFactory.java

/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.common.naming;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import javax.naming.Context;
import javax.naming.spi.InitialContextFactory;
import org.modeshape.common.SystemFailureException;

/**
 * An {@link InitialContextFactory} that provides a singleton {@link Context JNDI naming context}. Because it is a singleton, it
 * is useful in unit tests that {@link Context#lookup(String) looks up} objects where it can be used within service registration
 * logic while also being easily accessible in the test case itself.
 * <p>
 * For example, the following code sample shows how this InitialContextFactory implementation can be specified via the standard "
 * <code>{@link Context#INITIAL_CONTEXT_FACTORY java.naming.factory.initial}</code>" property:
 * 
 * <pre>
 * Hashtable<String, Object> jndiContext = new Hashtable<String, Object>();
 * jndiContext.put("java.naming.factory.initial", "org.modeshape.common.naming.SingleonInitialContextFactory");
 * jndiContext.put("java.naming.provider.url", "localhost");
 * InitialContext initialContext = new InitialContext(jndiContext);
 * </pre>
 * 
 * while the following sample shows how the same {@link Context} instance will be subsequently returned from accessed within other
 * code (e.g., a test case):
 * 
 * <pre>
 * Context context = SingletoneInitialContextFactory.create();
 * </pre>
 * 
 * </p>
 * 
 * @author Luca Stancapiano
 * @author Randall Hauch
 */
public class SingletonInitialContextFactory implements InitialContextFactory {

    private static SingletonInitialContext SINGLETON;

    public SingletonInitialContextFactory() {
    }

    @Override
    public Context getInitialContext( Hashtable<?, ?> environment ) {
        return getInstance(environment);
    }

    /**
     * Return the {@link Context} singleton instance. If no such context has been configured, this method will configured the
     * singletone using the supplied environment.
     * 
     * @param environment the environment for the naming context; may be null or empty
     * @return the singleton context; never null
     * @see #getInitialContext(Hashtable)
     * @see #getInstance(Hashtable)
     */
    public static synchronized Context getInstance( Hashtable<?, ?> environment ) {
        if (SINGLETON == null) SINGLETON = new SingletonInitialContext(environment);
        return SINGLETON;
    }

    /**
     * Return the previously-configured {@link Context} singleton instance. If no such context has been configured, this method
     * throws a {@link SystemFailureException}.
     * 
     * @return the singleton context; never null
     * @throws SystemFailureException if the singleton context has not yet been configured.
     * @see #getInitialContext(Hashtable)
     * @see #getInstance(Hashtable)
     */
    public static synchronized Context getInstance() {
        if (SINGLETON == null) {
            throw new SystemFailureException();
        }
        return SINGLETON;
    }

    /**
     * Set the {@link Context#INITIAL_CONTEXT_FACTORY} system property to the name of this context's
     * {@link SingletonInitialContextFactory factory class}.
     */
    public static void initialize() {
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            @Override
            public Void run() {
                System.setProperty("java.naming.factory.initial", SingletonInitialContextFactory.class.getName());
                return null;
            }
        });

    }

    /**
     * Release any existing singleton {@link Context naming context}. Any subsequent calls to {@link #getInstance(Hashtable)} or
     * {@link #getInitialContext(Hashtable)} will return a new singleton instance.
     */
    public static synchronized void tearDown() {
        SINGLETON = null;
    }
}