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/*
* 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;
import java.util.NoSuchElementException;
/**
* A "keyed" pooling interface.
*
* A keyed pool maintains a pool of instances for each key value.
*
* Example of use:
*
Object obj = null;
* Object key = "Key";
*
* try {
* obj = pool.borrowObject(key);
* //...use the object...
* } catch(Exception e) {
* // invalidate the object
* pool.invalidateObject(key, obj);
* // do not return the object to the pool twice
* obj = null;
* } finally {
* // make sure the object is returned to the pool
* if(null != obj) {
* pool.returnObject(key, obj);
* }
* }
*
* {@link KeyedObjectPool} implementations may choose to store at most
* one instance per key value, or may choose to maintain a pool of instances
* for each key (essentially creating a {@link java.util.Map Map} of
* {@link ObjectPool pools}).
*
* See {@link org.apache.commons.pool2.impl.GenericKeyedObjectPool
* GenericKeyedObjectPool} for an implementation.
*
* @param The type of keys maintained by this pool.
* @param Type of element pooled in this pool.
*
* @see KeyedPooledObjectFactory
* @see ObjectPool
* @see org.apache.commons.pool2.impl.GenericKeyedObjectPool GenericKeyedObjectPool
*
* @since 2.0
*/
public interface KeyedObjectPool {
/**
* Obtains an instance from this pool for the specified key.
*
* Instances returned from this method will have been either newly created
* with {@link KeyedPooledObjectFactory#makeObject makeObject} or will be
* a previously idle object and have been activated with
* {@link KeyedPooledObjectFactory#activateObject activateObject} and then
* (optionally) validated with
* {@link KeyedPooledObjectFactory#validateObject validateObject}.
*
* By contract, clients must return the borrowed object
* using {@link #returnObject returnObject},
* {@link #invalidateObject invalidateObject}, or a related method as
* defined in an implementation or sub-interface, using a key
* that is {@link Object#equals equivalent} to the one used to borrow the
* instance in the first place.
*
* The behaviour of this method when the pool has been exhausted is not
* strictly specified (although it may be specified by implementations).
*
* @param key the key used to obtain the object
*
* @return an instance from this pool.
*
* @throws IllegalStateException
* after {@link #close close} has been called on this pool
* @throws Exception
* when {@link KeyedPooledObjectFactory#makeObject
* makeObject} throws an exception
* @throws NoSuchElementException
* when the pool is exhausted and cannot or will not return
* another instance
*/
V borrowObject(K key) throws Exception, NoSuchElementException, IllegalStateException;
/**
* Return an instance to the pool. By contract, obj
* must have been obtained using
* {@link #borrowObject borrowObject} or a related method as defined in an
* implementation or sub-interface using a key that is
* equivalent to the one used to borrow the instance in the first place.
*
* @param key the key used to obtain the object
* @param obj a {@link #borrowObject borrowed} instance to be returned.
*
* @throws IllegalStateException
* if an attempt is made to return an object to the pool that
* is in any state other than allocated (i.e. borrowed).
* Attempting to return an object more than once or attempting
* to return an object that was never borrowed from the pool
* will trigger this exception.
*
* @throws Exception if an instance cannot be returned to the pool
*/
void returnObject(K key, V obj) throws Exception;
/**
* Invalidates an object from the pool.
*
* By contract, obj must have been obtained
* using {@link #borrowObject borrowObject} or a related method as defined
* in an implementation or sub-interface using a key that is
* equivalent to the one used to borrow the Object in the first
* place.
*
* This method should be used when an object that has been borrowed is
* determined (due to an exception or other problem) to be invalid.
*
* @param key the key used to obtain the object
* @param obj a {@link #borrowObject borrowed} instance to be returned.
*
* @throws Exception if the instance cannot be invalidated
*/
void invalidateObject(K key, V obj) throws Exception;
/**
* Create an object using the {@link KeyedPooledObjectFactory factory} or
* other implementation dependent mechanism, passivate it, and then place it
* in the idle object pool. addObject is useful for
* "pre-loading" a pool with idle objects (Optional operation).
*
* @param key the key a new instance should be added to
*
* @throws Exception
* when {@link KeyedPooledObjectFactory#makeObject} fails.
* @throws IllegalStateException
* after {@link #close} has been called on this pool.
* @throws UnsupportedOperationException
* when this pool cannot add new idle objects.
*/
void addObject(K key) throws Exception, IllegalStateException,
UnsupportedOperationException;
/**
* Returns the number of instances corresponding to the given
* key currently idle in this pool. Returns a negative value if
* this information is not available.
*
* @param key the key to query
* @return the number of instances corresponding to the given
* key currently idle in this pool.
*/
int getNumIdle(K key);
/**
* Returns the number of instances currently borrowed from but not yet
* returned to the pool corresponding to the given key.
* Returns a negative value if this information is not available.
*
* @param key the key to query
* @return the number of instances currently borrowed from but not yet
* returned to the pool corresponding to the given key.
= */
int getNumActive(K key);
/**
* Returns the total number of instances currently idle in this pool.
* Returns a negative value if this information is not available.
* @return the total number of instances currently idle in this pool.
= */
int getNumIdle();
/**
* Returns the total number of instances current borrowed from this pool but
* not yet returned. Returns a negative value if this information is not
* available.
* @return the total number of instances current borrowed from this pool but
* not yet returned.
*/
int getNumActive();
/**
* Clears the pool, removing all pooled instances (optional operation).
*
* @throws UnsupportedOperationException when this implementation doesn't
* support the operation
*
* @throws Exception if the pool cannot be cleared
*/
void clear() throws Exception, UnsupportedOperationException;
/**
* Clears the specified pool, removing all pooled instances corresponding to
* the given key (optional operation).
*
* @param key the key to clear
*
* @throws UnsupportedOperationException when this implementation doesn't
* support the operation
*
* @throws Exception if the key cannot be cleared
*/
void clear(K key) throws Exception, UnsupportedOperationException;
/**
* Close this pool, and free any resources associated with it.
*
* Calling {@link #addObject addObject} or
* {@link #borrowObject borrowObject} after invoking this method on a pool
* will cause them to throw an {@link IllegalStateException}.
*
* Implementations should silently fail if not all resources can be freed.
*/
void close();
}