| /* |
| * 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. |
| */ |
| |
| package org.apache.guacamole.auth.jdbc; |
| |
| import com.google.inject.Injector; |
| import java.util.concurrent.atomic.AtomicReference; |
| import org.apache.guacamole.GuacamoleException; |
| |
| /** |
| * A caching provider of singleton Guice Injector instances. The first call to |
| * get() will return a new instance of the Guice Injector, while all subsequent |
| * calls will return that same instance. It is up to implementations of this |
| * class to define how the Guice Injector will be created through defining the |
| * create() function. |
| * |
| * IMPORTANT: Because the Injector returned by get() is cached statically, only |
| * ONE implementation of this class may be used within any individual |
| * classloader. Within the context of the JDBC extension, as long as each built |
| * extension only provides one subclass of this class, things should work |
| * properly, as each extension is given its own classloader by Guacamole. |
| */ |
| public abstract class JDBCInjectorProvider { |
| |
| /** |
| * An AtomicReference wrapping the cached Guice Injector. If the Injector |
| * has not yet been created, null will be wrapped instead. |
| */ |
| private static final AtomicReference<Injector> injector = new AtomicReference<Injector>(null); |
| |
| /** |
| * Creates a new instance of the Guice Injector which should be used |
| * across the entire JDBC authentication extension. This function will |
| * generally only be called once, but multiple invocations are possible if |
| * get() is invoked several times concurrently prior to the Injector being |
| * cached. |
| * |
| * @return |
| * @throws GuacamoleException |
| */ |
| protected abstract Injector create() throws GuacamoleException; |
| |
| /** |
| * Returns a common, singleton instance of a Guice Injector, configured for |
| * the injections required by the JDBC authentication extension. The result |
| * of the first call to this function will be cached statically within this |
| * class, and will be returned for all subsequent calls. |
| * |
| * @return |
| * A singleton instance of the Guice Injector used across the entire |
| * JDBC authentication extension. |
| * |
| * @throws GuacamoleException |
| * If the Injector cannot be created due to an error. |
| */ |
| public Injector get() throws GuacamoleException { |
| |
| // Return existing Injector if already created |
| Injector value = injector.get(); |
| if (value != null) |
| return value; |
| |
| // Explicitly create and store new Injector only if necessary |
| injector.compareAndSet(null, create()); |
| |
| // Consistently return the same Injector, even if two create operations |
| // happen concurrently |
| return injector.get(); |
| |
| } |
| |
| } |