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java/org/apache/tomcat/dbcp/pool2/KeyedPooledObjectFactory.java

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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.tomcat.dbcp.pool2;
+
+/**
+ * An interface defining life-cycle methods for
+ * instances to be served by a {@link KeyedObjectPool}.
+ * <p>
+ * By contract, when an {@link KeyedObjectPool}
+ * delegates to a {@link KeyedPooledObjectFactory},
+ * </p>
+ * <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 KeyedObjectPool#borrowObject borrowed} from the pool.
+ *  </li>
+ *  <li>
+ *   {@link #validateObject} may be invoked on {@link #activateObject activated}
+ *   instances to make sure they can be
+ *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
+ *   <code>validateObject</code> may also be used to test an
+ *   instance being {@link KeyedObjectPool#returnObject returned} to the pool
+ *   before it is {@link #passivateObject passivated}. It will only be invoked
+ *   on an activated instance.
+ *  </li>
+ *  <li>
+ *   {@link #passivateObject passivateObject}
+ *   is invoked on every instance when it is returned to the pool.
+ *  </li>
+ *  <li>
+ *   {@link #destroyObject destroyObject}
+ *   is invoked on every instance when it is being "dropped" from the
+ *   pool (whether due to the response from <code>validateObject</code>,
+ *   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 KeyedPooledObjectFactory} must be thread-safe. The only promise
+ * an {@link KeyedObjectPool} makes is that the same instance of an object will
+ * not be passed to more than one method of a
+ * <code>KeyedPoolableObjectFactory</code> at a time.
+ * <p>
+ * While clients of a {@link KeyedObjectPool} borrow and return instances of
+ * the underlying value type V, the factory methods act on instances of
+ * {@link PooledObject PooledObject&lt;V&gt;}.  These are the object wrappers that
+ * pools use to track and maintain state informations about the objects that
+ * they manage.
+ * </p>
+ *
+ * @see KeyedObjectPool
+ * @see BaseKeyedPooledObjectFactory
+ *
+ * @param <K> The type of keys managed by this factory.
+ * @param <V> Type of element managed by this factory.
+ *
+ * @since 2.0
+ */
+public interface KeyedPooledObjectFactory<K, V> {
+
+    /**
+     * Create an instance that can be served by the pool and
+     * wrap it in a {@link PooledObject} to be managed by the pool.
+     *
+     * @param key the key used when constructing the object
+     *
+     * @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<V> makeObject(K key) throws Exception;
+
+    /**
+     * Destroy 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>
+     * <p>
+     * Also, an implementation must take in to consideration that instances lost
+     * to the garbage collector may never be destroyed.
+     * </p>
+     *
+     * @param key the key used when selecting the instance
+     * @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 KeyedObjectPool#invalidateObject
+     */
+    void destroyObject(K key, PooledObject<V> p) throws Exception;
+
+    /**
+     * Ensures that the instance is safe to be returned by the pool.
+     *
+     * @param key the key used when selecting the object
+     * @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(K key, PooledObject<V> p);
+
+    /**
+     * Reinitialize an instance to be returned by the pool.
+     *
+     * @param key the key used when selecting the object
+     * @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(K key, PooledObject<V> p) throws Exception;
+
+    /**
+     * Uninitialize an instance to be returned to the idle object pool.
+     *
+     * @param key the key used when selecting the object
+     * @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(K key, PooledObject<V> p) throws Exception;
+}
+