org.apache.commons.pool2.PooledObjectFactory Maven / Gradle / Ivy
/*
* 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}.
*
* By contract, when an {@link ObjectPool} delegates to a
* {@link PooledObjectFactory},
*
*
* -
* {@link #makeObject} is called whenever a new instance is needed.
*
* -
* {@link #activateObject} is invoked on every instance that has been
* {@link #passivateObject passivated} before it is
* {@link ObjectPool#borrowObject borrowed} from the pool.
*
* -
* {@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.
*
* -
* {@link #passivateObject} is invoked on every instance when it is returned
* to the pool.
*
* -
* {@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.
*
*
* {@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 PoolableObjectFactory
* at a time.
*
* 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 Type of element managed in this factory.
*
* @see ObjectPool
*
* @since 2.0
*/
public interface PooledObjectFactory {
/**
* Creates 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 makeObject() throws Exception;
/**
* Destroys an instance no longer needed by the pool.
*
* It is important for implementations of this method to be aware that there
* is no guarantee about what state obj will be in and the
* implementation should be prepared to handle unexpected errors.
*
*
* Also, an implementation must take in to consideration that instances lost
* to the garbage collector may never be destroyed.
*
*
* @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 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 false if obj is not valid and should
* be dropped from the pool, true otherwise.
*/
boolean validateObject(PooledObject p);
/**
* Reinitializes 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 obj,
* this exception may be swallowed by the pool.
*
* @see #destroyObject
*/
void activateObject(PooledObject p) throws Exception;
/**
* Uninitializes 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 obj,
* this exception may be swallowed by the pool.
*
* @see #destroyObject
*/
void passivateObject(PooledObject p) throws Exception;
}