StackObjectPool (Apache Commons Object Pooling Package)

java.lang.Object
- org.apache.commons.pool.BaseObjectPool<T>
- - org.apache.commons.pool.impl.StackObjectPool<T>

Type Parameters:
T - the type of objects held in this pool

All Implemented Interfaces:

ObjectPool<T>
```
public class StackObjectPool<T>
extends BaseObjectPool<T>
implements ObjectPool<T>
```
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: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $

Author:

Rodney Waldhoff, Dirk Verbeeck, Sandy McArthur

Constructor Summary

Constructors
Constructor and Description
`StackObjectPool(PoolableObjectFactory<T> factory)` Create a new `StackObjectPool` using the specified factory to create new instances.
`StackObjectPool(PoolableObjectFactory<T> 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<T> 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

Methods
Modifier and Type	Method and Description
`void`	`addObject()` Create an object, and place it on top of the stack.
`T`	`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<T>`	`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(T obj)` Invalidates an object from the pool.
`void`	`returnObject(T obj)` Returns an instance to the pool, pushing it on top of the idle instance stack after successful validation and passivation.

Methods inherited from class org.apache.commons.pool.BaseObjectPool
isClosed

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - StackObjectPool
```
public StackObjectPool(PoolableObjectFactory<T> 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<T> 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<T> 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
  - addObject
```
public void addObject()
               throws java.lang.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<T>
    
    Overrides:
    
    addObject in class BaseObjectPool<T>
    
    Throws:
    
    java.lang.Exception - when the factory has a problem creating or passivating an object.
  - borrowObject
```
public T borrowObject()
               throws java.lang.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<T>
    
    Specified by:
    
    borrowObject in class BaseObjectPool<T>
    
    Returns:
    an instance from the pool
    
    Throws:
    
    java.lang.Exception - if an instance cannot be obtained from the 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<T>
    
    Overrides:
    
    clear in class BaseObjectPool<T>
  - close
```
public void close()
           throws java.lang.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<T>
    
    Overrides:
    
    close in class BaseObjectPool<T>
    
    Throws:
    
    java.lang.Exception - never - exceptions clearing the pool are swallowed
  - getFactory
```
public PoolableObjectFactory<T> 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
  - getNumActive
```
public int getNumActive()
```
    Return the number of instances currently borrowed from this pool.
    
    Specified by:
    
    getNumActive in interface ObjectPool<T>
    
    Overrides:
    
    getNumActive in class BaseObjectPool<T>
    
    Returns:
    the number of instances currently borrowed from this pool
  - getNumIdle
```
public int getNumIdle()
```
    Return the number of instances currently idle in this pool.
    
    Specified by:
    
    getNumIdle in interface ObjectPool<T>
    
    Overrides:
    
    getNumIdle in class BaseObjectPool<T>
    
    Returns:
    the number of instances currently idle in this pool
  - invalidateObject
```
public void invalidateObject(T obj)
                      throws java.lang.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<T>
    
    Specified by:
    
    invalidateObject in class BaseObjectPool<T>
    
    Parameters:
    obj - a borrowed instance to be disposed.
    
    Throws:
    
    java.lang.Exception
  - returnObject
```
public void returnObject(T obj)
                  throws java.lang.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:
    - the pool is closed
    - validation fails
    - passivation throws an exception
    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<T>
    
    Specified by:
    
    returnObject in class BaseObjectPool<T>
    
    Parameters:
    obj - instance to return to the pool
    
    Throws:
    
    java.lang.Exception

Class StackObjectPool<T>

Constructor Summary

Method Summary

Methods inherited from class org.apache.commons.pool.BaseObjectPool

Methods inherited from class java.lang.Object

Constructor Detail

StackObjectPool

StackObjectPool

StackObjectPool

Method Detail

addObject

borrowObject

clear

close

getFactory

getMaxSleeping

getNumActive

getNumIdle

invalidateObject

returnObject