Java tutorial
/* * 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.commons.pool2; /** * An interface defining life-cycle methods for instances to be served by an * {@link ObjectPool}. * <p> * By contract, when an {@link ObjectPool} delegates to a * {@link PooledObjectFactory}, * <ol> * <li> * {@link #makeObject} is called whenever a new instance is needed. * </li> * <li> * {@link #activateObject} is invoked on every instance that has been * {@link #passivateObject passivated} before it is * {@link ObjectPool#borrowObject borrowed} from the pool. * </li> * <li> * {@link #validateObject} may be invoked on {@link #activateObject activated} * instances to make sure they can be {@link ObjectPool#borrowObject borrowed} * from the pool. {@link #validateObject} may also be used to * test an instance being {@link ObjectPool#returnObject returned} to the pool * before it is {@link #passivateObject passivated}. It will only be invoked * on an activated instance. * </li> * <li> * {@link #passivateObject} is invoked on every instance when it is returned * to the pool. * </li> * <li> * {@link #destroyObject} is invoked on every instance when it is being * "dropped" from the pool (whether due to the response from * {@link #validateObject}, or for reasons specific to the pool * implementation.) There is no guarantee that the instance being destroyed * will be considered active, passive or in a generally consistent state. * </li> * </ol> * {@link PooledObjectFactory} must be thread-safe. The only promise * an {@link ObjectPool} makes is that the same instance of an object will not * be passed to more than one method of a <code>PoolableObjectFactory</code> * at a time. * <p> * While clients of a {@link KeyedObjectPool} borrow and return instances of * the underlying value type {@code V}, the factory methods act on instances of * {@link PooledObject PooledObject<V>}. These are the object wrappers that * pools use to track and maintain state information about the objects that * they manage. * * @param <T> Type of element managed in this factory. * * @see ObjectPool * * @version $Revision: 1333925 $ * * @since 2.0 */ public interface PooledObjectFactory<T> { /** * Create an instance that can be served by the pool and wrap it in a * {@link PooledObject} to be managed by the pool. * * @return a {@code PooledObject} wrapping an instance that can be served by the pool * * @throws Exception if there is a problem creating a new instance, * this will be propagated to the code requesting an object. */ PooledObject<T> makeObject() throws Exception; /** * Destroys an instance no longer needed by the pool. * <p> * It is important for implementations of this method to be aware that there * is no guarantee about what state <code>obj</code> will be in and the * implementation should be prepared to handle unexpected errors. * <p> * Also, an implementation must take in to consideration that instances lost * to the garbage collector may never be destroyed. * </p> * * @param p a {@code PooledObject} wrapping the instance to be destroyed * * @throws Exception should be avoided as it may be swallowed by * the pool implementation. * * @see #validateObject * @see ObjectPool#invalidateObject */ void destroyObject(PooledObject<T> p) throws Exception; /** * Ensures that the instance is safe to be returned by the pool. * * @param p a {@code PooledObject} wrapping the instance to be validated * * @return <code>false</code> if <code>obj</code> is not valid and should * be dropped from the pool, <code>true</code> otherwise. */ boolean validateObject(PooledObject<T> p); /** * Reinitialize an instance to be returned by the pool. * * @param p a {@code PooledObject} wrapping the instance to be activated * * @throws Exception if there is a problem activating <code>obj</code>, * this exception may be swallowed by the pool. * * @see #destroyObject */ void activateObject(PooledObject<T> p) throws Exception; /** * Uninitialize an instance to be returned to the idle object pool. * * @param p a {@code PooledObject} wrapping the instance to be passivated * * @throws Exception if there is a problem passivating <code>obj</code>, * this exception may be swallowed by the pool. * * @see #destroyObject */ void passivateObject(PooledObject<T> p) throws Exception; }