org.apache.commons.pool.impl
Class StackObjectPool

java.lang.Object
  extended by org.apache.commons.pool.BaseObjectPool
      extended by org.apache.commons.pool.impl.StackObjectPool
All Implemented Interfaces:
ObjectPool

public class StackObjectPool
extends BaseObjectPool
implements ObjectPool

A simple, Stack-based ObjectPool implementation.

Given a PoolableObjectFactory, this class will maintain a simple pool of instances. A finite number of "sleeping" or idle instances is enforced, but when the pool is empty, new instances are created to support the new load. Hence this class places no limit on the number of "active" instances created by the pool, but is quite useful for re-using Objects without introducing artificial limits.

Since:
Pool 1.0
Version:
$Revision: 892236 $ $Date: 2013-12-31 04:43:12 +0000 (Tue, 31 Dec 2013) $
Author:
Rodney Waldhoff, Dirk Verbeeck, Sandy McArthur

Field Summary
protected  PoolableObjectFactory _factory
          Deprecated. to be made private in pool 2.0 - use getFactory()
protected  int _maxSleeping
          Deprecated. to be made private in pool 2.0 - use getMaxSleeping()
protected  int _numActive
          Deprecated. to be made private in pool 2.0 - use getNumActive()
protected  Stack _pool
          Deprecated. to be made private in pool 2.0
protected static int DEFAULT_INIT_SLEEPING_CAPACITY
          The default initial size of the pool (this specifies the size of the container, it does not cause the pool to be pre-populated.)
protected static int DEFAULT_MAX_SLEEPING
          The cap on the number of "sleeping" instances in the pool.
 
Constructor Summary
StackObjectPool()
          Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory)
StackObjectPool(int maxIdle)
          Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory, int)
StackObjectPool(int maxIdle, int initIdleCapacity)
          Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory, int, int)
StackObjectPool(PoolableObjectFactory factory)
          Create a new StackObjectPool using the specified factory to create new instances.
StackObjectPool(PoolableObjectFactory factory, int maxIdle)
          Create a new SimpleObjectPool using the specified factory to create new instances, capping the number of "sleeping" instances to maxIdle.
StackObjectPool(PoolableObjectFactory factory, int maxIdle, int initIdleCapacity)
          Create a new StackObjectPool using the specified factory to create new instances, capping the number of "sleeping" instances to maxIdle, and initially allocating a container capable of containing at least initIdleCapacity instances.
 
Method Summary
 void addObject()
          Create an object, and place it on top of the stack.
 Object borrowObject()
          Borrows an object from the pool.
 void clear()
          Clears any objects sitting idle in the pool.
 void close()
          Close this pool, and free any resources associated with it.
 PoolableObjectFactory getFactory()
          Returns the PoolableObjectFactory used by this pool to create and manage object instances.
 int getMaxSleeping()
          Returns the maximum number of idle instances in the pool.
 int getNumActive()
          Return the number of instances currently borrowed from this pool.
 int getNumIdle()
          Return the number of instances currently idle in this pool.
 void invalidateObject(Object obj)
          Invalidates an object from the pool.
 void returnObject(Object obj)
          Returns an instance to the pool, pushing it on top of the idle instance stack after successful validation and passivation.
 void setFactory(PoolableObjectFactory factory)
          Deprecated. to be removed in pool 2.0
 
Methods inherited from class org.apache.commons.pool.BaseObjectPool
assertOpen, isClosed
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DEFAULT_MAX_SLEEPING

protected static final int DEFAULT_MAX_SLEEPING
The cap on the number of "sleeping" instances in the pool.

See Also:
Constant Field Values

DEFAULT_INIT_SLEEPING_CAPACITY

protected static final int DEFAULT_INIT_SLEEPING_CAPACITY
The default initial size of the pool (this specifies the size of the container, it does not cause the pool to be pre-populated.)

See Also:
Constant Field Values

_pool

protected Stack _pool
Deprecated. to be made private in pool 2.0
My pool.


_factory

protected PoolableObjectFactory _factory
Deprecated. to be made private in pool 2.0 - use getFactory()
My PoolableObjectFactory.


_maxSleeping

protected int _maxSleeping
Deprecated. to be made private in pool 2.0 - use getMaxSleeping()
The cap on the number of "sleeping" instances in the pool.


_numActive

protected int _numActive
Deprecated. to be made private in pool 2.0 - use getNumActive()
Number of objects borrowed but not yet returned to the pool.

Constructor Detail

StackObjectPool

public StackObjectPool()
Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory)

Create a new pool using no factory. Clients must first set the factory or else this pool will not behave correctly. Clients may first populate the pool using returnObject(java.lang.Object) before they can be borrowed but this usage is discouraged.

See Also:
StackObjectPool(PoolableObjectFactory)

StackObjectPool

public StackObjectPool(int maxIdle)
Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory, int)

Create a new pool using no factory. Clients must first set the factory or else this pool will not behave correctly. Clients may first populate the pool using returnObject(java.lang.Object) before they can be borrowed but this usage is discouraged.

Parameters:
maxIdle - cap on the number of "sleeping" instances in the pool
See Also:
StackObjectPool(PoolableObjectFactory, int)

StackObjectPool

public StackObjectPool(int maxIdle,
                       int initIdleCapacity)
Deprecated. to be removed in pool 2.0 - use StackObjectPool(PoolableObjectFactory, int, int)

Create a new pool using no factory. Clients must first set the factory or else this pool will not behave correctly. Clients may first populate the pool using returnObject(java.lang.Object) before they can be borrowed but this usage is discouraged.

Parameters:
maxIdle - cap on the number of "sleeping" instances in the pool
initIdleCapacity - initial size of the pool (this specifies the size of the container, it does not cause the pool to be pre-populated.)
See Also:
StackObjectPool(PoolableObjectFactory, int, int)

StackObjectPool

public StackObjectPool(PoolableObjectFactory factory)
Create a new StackObjectPool using the specified factory to create new instances.

Parameters:
factory - the PoolableObjectFactory used to populate the pool

StackObjectPool

public StackObjectPool(PoolableObjectFactory factory,
                       int maxIdle)
Create a new SimpleObjectPool using the specified factory to create new instances, capping the number of "sleeping" instances to maxIdle.

Parameters:
factory - the PoolableObjectFactory used to populate the pool
maxIdle - cap on the number of "sleeping" instances in the pool

StackObjectPool

public StackObjectPool(PoolableObjectFactory factory,
                       int maxIdle,
                       int initIdleCapacity)

Create a new StackObjectPool using the specified factory to create new instances, capping the number of "sleeping" instances to maxIdle, and initially allocating a container capable of containing at least initIdleCapacity instances. The pool is not pre-populated. The initIdleCapacity parameter just determines the initial size of the underlying container, which can increase beyond this value if maxIdle > initIdleCapacity.

Negative values of maxIdle are ignored (i.e., the pool is created using DEFAULT_MAX_SLEEPING) as are non-positive values for initIdleCapacity.

Parameters:
factory - the PoolableObjectFactory used to populate the pool
maxIdle - cap on the number of "sleeping" instances in the pool
initIdleCapacity - initial size of the pool (this specifies the size of the container, it does not cause the pool to be pre-populated.)
Method Detail

borrowObject

public Object borrowObject()
                    throws Exception

Borrows an object from the pool. If there are idle instances available on the stack, the top element of the stack is popped to activate, validate and return to the client. If there are no idle instances available, the makeObject method of the pool's PoolableObjectFactory is invoked to create a new instance.

All instances are activated and validated before being returned to the client. If validation fails or an exception occurs activating or validating an instance popped from the idle instance stack, the failing instance is destroyed and the next instance on the stack is popped, validated and activated. This process continues until either the stack is empty or an instance passes validation. If the stack is empty on activation or it does not contain any valid instances, the factory's makeObject method is used to create a new instance. If a null instance is returned by the factory or the created instance either raises an exception on activation or fails validation, NoSuchElementException is thrown. Exceptions thrown by MakeObject are propagated to the caller; but other than ThreadDeath or VirtualMachineError, exceptions generated by activation, validation or destroy methods are swallowed silently.

Specified by:
borrowObject in interface ObjectPool
Specified by:
borrowObject in class BaseObjectPool
Returns:
an instance from the pool
Throws:
Exception - if an instance cannot be obtained from the pool

returnObject

public void returnObject(Object obj)
                  throws Exception

Returns an instance to the pool, pushing it on top of the idle instance stack after successful validation and passivation. The returning instance is destroyed if any of the following are true:

If adding a validated, passivated returning instance to the stack would cause maxSleeping to be exceeded, the oldest (bottom) instance on the stack is destroyed to make room for the returning instance, which is pushed on top of the stack.

Exceptions passivating or destroying instances are silently swallowed. Exceptions validating instances are propagated to the client.

Specified by:
returnObject in interface ObjectPool
Specified by:
returnObject in class BaseObjectPool
Parameters:
obj - instance to return to the pool
Throws:
Exception

invalidateObject

public void invalidateObject(Object obj)
                      throws Exception

Invalidates an object from the pool.

By contract, obj must have been obtained using borrowObject.

This method should be used when an object that has been borrowed is determined (due to an exception or other problem) to be invalid.

Specified by:
invalidateObject in interface ObjectPool
Specified by:
invalidateObject in class BaseObjectPool
Parameters:
obj - a borrowed instance to be disposed.
Throws:
Exception

getNumIdle

public int getNumIdle()
Return the number of instances currently idle in this pool.

Specified by:
getNumIdle in interface ObjectPool
Overrides:
getNumIdle in class BaseObjectPool
Returns:
the number of instances currently idle in this pool

getNumActive

public int getNumActive()
Return the number of instances currently borrowed from this pool.

Specified by:
getNumActive in interface ObjectPool
Overrides:
getNumActive in class BaseObjectPool
Returns:
the number of instances currently borrowed from this pool

clear

public void clear()
Clears any objects sitting idle in the pool. Silently swallows any exceptions thrown by PoolableObjectFactory.destroyObject(Object).

Specified by:
clear in interface ObjectPool
Overrides:
clear in class BaseObjectPool

close

public void close()
           throws Exception

Close this pool, and free any resources associated with it. Invokes clear() to destroy and remove instances in the pool.

Calling addObject() or borrowObject() after invoking this method on a pool will cause them to throw an IllegalStateException.

Specified by:
close in interface ObjectPool
Overrides:
close in class BaseObjectPool
Throws:
Exception - never - exceptions clearing the pool are swallowed

addObject

public void addObject()
               throws Exception

Create an object, and place it on top of the stack. This method is useful for "pre-loading" a pool with idle objects.

Before being added to the pool, the newly created instance is validated and passivated. If validation fails, the new instance is destroyed. Exceptions generated by the factory makeObject or passivate are propagated to the caller. Exceptions destroying instances are silently swallowed.

If a new instance is created and successfully validated and passivated and adding this instance to the pool causes maxSleeping to be exceeded, the oldest (bottom) instance in the pool is destroyed to make room for the newly created instance, which is pushed on top of the stack.

Specified by:
addObject in interface ObjectPool
Overrides:
addObject in class BaseObjectPool
Throws:
Exception - when the factory has a problem creating or passivating an object.

setFactory

public void setFactory(PoolableObjectFactory factory)
                throws IllegalStateException
Deprecated. to be removed in pool 2.0

Sets the factory this pool uses to create new instances. Trying to change the factory while there are borrowed objects will throw an IllegalStateException.

Specified by:
setFactory in interface ObjectPool
Overrides:
setFactory in class BaseObjectPool
Parameters:
factory - the PoolableObjectFactory used to create new instances.
Throws:
IllegalStateException - when the factory cannot be set at this time

getFactory

public PoolableObjectFactory getFactory()
Returns the PoolableObjectFactory used by this pool to create and manage object instances.

Returns:
the factory
Since:
1.5.5

getMaxSleeping

public int getMaxSleeping()
Returns the maximum number of idle instances in the pool.

Returns:
maxSleeping
Since:
1.5.5


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