org.apache.commons.pool
Interface ObjectPool<T>

Type Parameters:

T - the type of objects held in this pool

All Known Implementing Classes:

BaseObjectPool, GenericObjectPool, SoftReferenceObjectPool, StackObjectPool

public interface ObjectPool<T>

A pooling interface.

ObjectPool defines a trivially simple pooling interface. The only required methods are borrowObject, returnObject and invalidateObject.

Example of use:

 Object obj = null;

 try {
     obj = pool.borrowObject();
     try {
         //...use the object...
     } catch(Exception e) {
         // invalidate the object
         pool.invalidateObject(obj);
         // do not return the object to the pool twice
         obj = null;
     } finally {
         // make sure the object is returned to the pool
         if(null != obj) {
             pool.returnObject(obj);
        }
     }
 } catch(Exception e) {
       // failed to borrow an object
 }

See BaseObjectPool for a simple base implementation.

Since:

Pool 1.0

Version:

$Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $

Author:

Rodney Waldhoff, Sandy McArthur

See Also:

PoolableObjectFactory, ObjectPoolFactory, KeyedObjectPool, BaseObjectPool

Method Summary

void	addObject() Create an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool.
T	borrowObject() Obtains an instance from this pool.
void	clear() Clears any objects sitting idle in the pool, releasing any associated resources (optional operation).
void	close() Close this pool, and free any resources associated with it.
int	getNumActive() Return the number of instances currently borrowed from this pool (optional operation).
int	getNumIdle() Return the number of instances currently idle in this pool (optional operation).
void	invalidateObject(T obj) Invalidates an object from the pool.
void	returnObject(T obj) Return an instance to the pool.
void	setFactory(PoolableObjectFactory<T> factory) Deprecated. to be removed in pool 2.0

Method Detail

borrowObject

T borrowObject()
               throws Exception,
                      NoSuchElementException,
                      IllegalStateException

Obtains an instance from this pool.

Instances returned from this method will have been either newly created with makeObject or will be a previously idle object and have been activated with activateObject and then validated with validateObject.

By contract, clients must return the borrowed instance using returnObject, invalidateObject, or a related method as defined in an implementation or sub-interface.

The behaviour of this method when the pool has been exhausted is not strictly specified (although it may be specified by implementations). Older versions of this method would return null to indicate exhaustion, newer versions are encouraged to throw a NoSuchElementException.

Returns:

an instance from this pool.

Throws:

IllegalStateException - after close has been called on this pool.

Exception - when makeObject throws an exception.

NoSuchElementException - when the pool is exhausted and cannot or will not return another instance.

returnObject

void returnObject(T obj)
                  throws Exception

Return an instance to the pool. By contract, obj must have been obtained using borrowObject or a related method as defined in an implementation or sub-interface.

Parameters:

obj - a borrowed instance to be returned.

Throws:

Exception

invalidateObject

void invalidateObject(T obj)
                      throws Exception

Invalidates an object from the pool.

By contract, obj must have been obtained using borrowObject or a related method as defined in an implementation or sub-interface.

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

Parameters:

obj - a borrowed instance to be disposed.

Throws:

Exception

addObject

void addObject()
               throws Exception,
                      IllegalStateException,
                      UnsupportedOperationException

Create an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool. addObject is useful for "pre-loading" a pool with idle objects. (Optional operation).

Throws:

Exception - when PoolableObjectFactory.makeObject() fails.

IllegalStateException - after close() has been called on this pool.

UnsupportedOperationException - when this pool cannot add new idle objects.

getNumIdle

int getNumIdle()
               throws UnsupportedOperationException

Return the number of instances currently idle in this pool (optional operation). This may be considered an approximation of the number of objects that can be borrowed without creating any new instances. Returns a negative value if this information is not available.

Returns:

the number of instances currently idle in this pool or a negative value if unsupported

Throws:

UnsupportedOperationException - deprecated: if this implementation does not support the operation

getNumActive

int getNumActive()
                 throws UnsupportedOperationException

Return the number of instances currently borrowed from this pool (optional operation). Returns a negative value if this information is not available.

Returns:

the number of instances currently borrowed from this pool or a negative value if unsupported

Throws:

UnsupportedOperationException - deprecated: if this implementation does not support the operation

clear

void clear()
           throws Exception,
                  UnsupportedOperationException

Clears any objects sitting idle in the pool, releasing any associated resources (optional operation). Idle objects cleared must be destroyed.

Throws:

UnsupportedOperationException - if this implementation does not support the operation

Exception

close

void close()
           throws Exception

Close this pool, and free any resources associated with it.

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

Throws:

Exception - deprecated: implementations should silently fail if not all resources can be freed.

setFactory

@Deprecated
void setFactory(PoolableObjectFactory<T> factory)
                throws IllegalStateException,
                       UnsupportedOperationException

Deprecated. to be removed in pool 2.0

Sets the factory this pool uses to create new instances (optional operation). Trying to change the factory after a pool has been used will frequently throw an UnsupportedOperationException. It is up to the pool implementation to determine when it is acceptable to call this method.

Parameters:

factory - the PoolableObjectFactory used to create new instances.

Throws:

IllegalStateException - when the factory cannot be set at this time

UnsupportedOperationException - if this implementation does not support the operation