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