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java/org/apache/tomcat/dbcp/pool2/KeyedObjectPool.java
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278
java/org/apache/tomcat/dbcp/pool2/KeyedObjectPool.java
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.tomcat.dbcp.pool2;
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import java.io.Closeable;
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import java.util.Collection;
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import java.util.NoSuchElementException;
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/**
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* A "keyed" pooling interface.
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* <p>
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* A keyed pool maintains a pool of instances for each key value.
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* </p>
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* <p>
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* Example of use:
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* </p>
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* <pre style="border:solid thin; padding: 1ex;"
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* > Object obj = <code style="color:#00C">null</code>;
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* Object key = <code style="color:#C00">"Key"</code>;
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*
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* <code style="color:#00C">try</code> {
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* obj = pool.borrowObject(key);
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* <code style="color:#0C0">//...use the object...</code>
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* } <code style="color:#00C">catch</code>(Exception e) {
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* <code style="color:#0C0">// invalidate the object</code>
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* pool.invalidateObject(key, obj);
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* <code style="color:#0C0">// do not return the object to the pool twice</code>
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* obj = <code style="color:#00C">null</code>;
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* } <code style="color:#00C">finally</code> {
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* <code style="color:#0C0">// make sure the object is returned to the pool</code>
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* <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
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* pool.returnObject(key, obj);
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* }
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* }</pre>
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* <p>
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* {@link KeyedObjectPool} implementations <i>may</i> choose to store at most
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* one instance per key value, or may choose to maintain a pool of instances
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* for each key (essentially creating a {@link java.util.Map Map} of
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* {@link ObjectPool pools}).
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* </p>
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* <p>
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* See {@link org.apache.tomcat.dbcp.pool2.impl.GenericKeyedObjectPool
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* GenericKeyedObjectPool} for an implementation.
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* </p>
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*
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* @param <K> The type of keys maintained by this pool.
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* @param <V> Type of element pooled in this pool.
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*
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* @see KeyedPooledObjectFactory
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* @see ObjectPool
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* @see org.apache.tomcat.dbcp.pool2.impl.GenericKeyedObjectPool GenericKeyedObjectPool
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*
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* @since 2.0
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*/
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public interface KeyedObjectPool<K, V> extends Closeable {
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/**
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* Create an object using the {@link KeyedPooledObjectFactory factory} or
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* other implementation dependent mechanism, passivate it, and then place it
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* in the idle object pool. <code>addObject</code> is useful for
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* "pre-loading" a pool with idle objects (Optional operation).
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*
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* @param key the key a new instance should be added to
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*
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* @throws Exception
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* when {@link KeyedPooledObjectFactory#makeObject} fails.
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* @throws IllegalStateException
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* after {@link #close} has been called on this pool.
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* @throws UnsupportedOperationException
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* when this pool cannot add new idle objects.
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*/
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void addObject(K key) throws Exception, IllegalStateException,
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UnsupportedOperationException;
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/**
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* Calls {@link KeyedObjectPool#addObject(Object)} with each
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* key in <code>keys</code> for <code>count</code> number of times. This has
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* the same effect as calling {@link #addObjects(Object, int)}
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* for each key in the <code>keys</code> collection.
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*
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* @param keys
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* {@link Collection} of keys to add objects for.
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* @param count
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* the number of idle objects to add for each <code>key</code>.
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* @throws Exception
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* when {@link KeyedObjectPool#addObject(Object)} fails.
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* @throws IllegalArgumentException
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* when <code>keyedPool</code>, <code>keys</code>, or any value
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* in <code>keys</code> is <code>null</code>.
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* @see #addObjects(Object, int)
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*/
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void addObjects(final Collection<K> keys, final int count) throws Exception, IllegalArgumentException;
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/**
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* Calls {@link KeyedObjectPool#addObject(Object)}
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* <code>key</code> <code>count</code> number of times.
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*
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* @param key
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* the key to add objects for.
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* @param count
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* the number of idle objects to add for <code>key</code>.
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* @throws Exception
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* when {@link KeyedObjectPool#addObject(Object)} fails.
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* @throws IllegalArgumentException
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* when <code>key</code> is <code>null</code>.
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* @since 2.8.0
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*/
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void addObjects(final K key, final int count) throws Exception, IllegalArgumentException;
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/**
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* Obtains an instance from this pool for the specified <code>key</code>.
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* <p>
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* Instances returned from this method will have been either newly created
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* with {@link KeyedPooledObjectFactory#makeObject makeObject} or will be
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* a previously idle object and have been activated with
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* {@link KeyedPooledObjectFactory#activateObject activateObject} and then
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* (optionally) validated with
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* {@link KeyedPooledObjectFactory#validateObject validateObject}.
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* </p>
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* <p>
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* By contract, clients <strong>must</strong> return the borrowed object
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* using {@link #returnObject returnObject},
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* {@link #invalidateObject invalidateObject}, or a related method as
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* defined in an implementation or sub-interface, using a <code>key</code>
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* that is {@link Object#equals equivalent} to the one used to borrow the
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* instance in the first place.
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* </p>
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* <p>
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* The behaviour of this method when the pool has been exhausted is not
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* strictly specified (although it may be specified by implementations).
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* </p>
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*
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* @param key the key used to obtain the object
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*
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* @return an instance from this pool.
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*
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* @throws IllegalStateException
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* after {@link #close close} has been called on this pool
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* @throws Exception
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* when {@link KeyedPooledObjectFactory#makeObject
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* makeObject} throws an exception
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* @throws NoSuchElementException
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* when the pool is exhausted and cannot or will not return
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* another instance
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*/
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V borrowObject(K key) throws Exception, NoSuchElementException, IllegalStateException;
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/**
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* Clears the pool, removing all pooled instances (optional operation).
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*
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* @throws UnsupportedOperationException when this implementation doesn't
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* support the operation
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*
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* @throws Exception if the pool cannot be cleared
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*/
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void clear() throws Exception, UnsupportedOperationException;
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/**
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* Clears the specified pool, removing all pooled instances corresponding to
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* the given <code>key</code> (optional operation).
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*
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* @param key the key to clear
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*
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* @throws UnsupportedOperationException when this implementation doesn't
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* support the operation
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*
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* @throws Exception if the key cannot be cleared
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*/
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void clear(K key) throws Exception, UnsupportedOperationException;
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/**
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* Close this pool, and free any resources associated with it.
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* <p>
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* Calling {@link #addObject addObject} or
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* {@link #borrowObject borrowObject} after invoking this method on a pool
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* will cause them to throw an {@link IllegalStateException}.
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* </p>
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* <p>
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* Implementations should silently fail if not all resources can be freed.
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* </p>
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*/
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@Override
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void close();
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/**
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* Returns the total number of instances currently borrowed from this pool but
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* not yet returned. Returns a negative value if this information is not
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* available.
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* @return the total number of instances currently borrowed from this pool but
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* not yet returned.
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*/
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int getNumActive();
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/**
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* Returns the number of instances currently borrowed from but not yet
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* returned to the pool corresponding to the given <code>key</code>.
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* Returns a negative value if this information is not available.
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*
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* @param key the key to query
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* @return the number of instances currently borrowed from but not yet
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* returned to the pool corresponding to the given <code>key</code>.
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*/
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int getNumActive(K key);
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/**
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* Returns the total number of instances currently idle in this pool.
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* Returns a negative value if this information is not available.
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* @return the total number of instances currently idle in this pool.
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*/
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int getNumIdle();
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/**
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* Returns the number of instances corresponding to the given
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* <code>key</code> currently idle in this pool. Returns a negative value if
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* this information is not available.
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*
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* @param key the key to query
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* @return the number of instances corresponding to the given
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* <code>key</code> currently idle in this pool.
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*/
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int getNumIdle(K key);
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/**
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* Invalidates an object from the pool.
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* <p>
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* By contract, <code>obj</code> <strong>must</strong> have been obtained
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* using {@link #borrowObject borrowObject} or a related method as defined
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* in an implementation or sub-interface using a <code>key</code> that is
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* equivalent to the one used to borrow the <code>Object</code> in the first
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* place.
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* </p>
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* <p>
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* This method should be used when an object that has been borrowed is
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* determined (due to an exception or other problem) to be invalid.
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* </p>
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*
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* @param key the key used to obtain the object
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* @param obj a {@link #borrowObject borrowed} instance to be returned.
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*
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* @throws Exception if the instance cannot be invalidated
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*/
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void invalidateObject(K key, V obj) throws Exception;
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/**
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* Return an instance to the pool. By contract, <code>obj</code>
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* <strong>must</strong> have been obtained using
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* {@link #borrowObject borrowObject} or a related method as defined in an
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* implementation or sub-interface using a <code>key</code> that is
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* equivalent to the one used to borrow the instance in the first place.
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*
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* @param key the key used to obtain the object
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* @param obj a {@link #borrowObject borrowed} instance to be returned.
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*
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* @throws IllegalStateException
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* if an attempt is made to return an object to the pool that
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* is in any state other than allocated (i.e. borrowed).
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* Attempting to return an object more than once or attempting
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* to return an object that was never borrowed from the pool
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* will trigger this exception.
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*
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* @throws Exception if an instance cannot be returned to the pool
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*/
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void returnObject(K key, V obj) throws Exception;
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}
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