org.apache.commons.pool
Interface KeyedObjectPool

All Known Implementing Classes:

BaseKeyedObjectPool, GenericKeyedObjectPool, StackKeyedObjectPool

public interface KeyedObjectPool

A "keyed" pooling interface.

A keyed pool pools instances of multiple types. Each type may be accessed using an arbitrary key.

Example of use:

 Object obj = null;
 Object key = "Key";

 try {
     obj = pool.borrowObject(key);
     //...use the object...
 } catch(Exception e) {
     // invalidate the object
     pool.invalidateObject(key, 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(key, obj);
     }
 }

KeyedObjectPool implementations may choose to store at most one instance per key value, or may choose to maintain a pool of instances for each key (essentially creating a Map of pools).

See BaseKeyedObjectPool for a simple base implementation.

Since:

Pool 1.0

Version:

$Revision: 778480 $ $Date: 2009-05-25 15:34:55 -0400 (Mon, 25 May 2009) $

Author:

Rodney Waldhoff, Sandy McArthur

See Also:

KeyedPoolableObjectFactory, KeyedObjectPoolFactory, ObjectPool, BaseKeyedObjectPool

Method Summary

void	addObject(Object key) Create an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool.
Object	borrowObject(Object key) Obtains an instance from this pool for the specified key.
void	clear() Clears the pool, removing all pooled instances (optional operation).
void	clear(Object key) Clears the specified pool, removing all pooled instances corresponding to the given key (optional operation).
void	close() Close this pool, and free any resources associated with it.
int	getNumActive() Returns the total number of instances current borrowed from this pool but not yet returned (optional operation).
int	getNumActive(Object key) Returns the number of instances currently borrowed from but not yet returned to the pool corresponding to the given key (optional operation).
int	getNumIdle() Returns the total number of instances currently idle in this pool (optional operation).
int	getNumIdle(Object key) Returns the number of instances corresponding to the given key currently idle in this pool (optional operation).
void	invalidateObject(Object key, Object obj) 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 using a key that is equivalent to the one used to borrow the Object in the first place.
void	returnObject(Object key, Object obj) Return an instance to the pool.
void	setFactory(KeyedPoolableObjectFactory factory) Sets the factory the pool uses to create new instances (optional operation).

Method Detail

borrowObject

Object borrowObject(Object key)
                    throws Exception,
                           NoSuchElementException,
                           IllegalStateException

Obtains an instance from this pool for the specified key.

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 object using returnObject, invalidateObject, or a related method as defined in an implementation or sub-interface, using a key that is equivalent to the one used to borrow the instance in the first place.

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.

Parameters:

key - the key used to obtain the object

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(Object key,
                  Object 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 using a key that is equivalent to the one used to borrow the instance in the first place.

Parameters:

key - the key used to obtain the object

obj - a borrowed instance to be returned.

Throws:

Exception

invalidateObject

void invalidateObject(Object key,
                      Object 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 using a key that is equivalent to the one used to borrow the Object in the first place.

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:

key - the key used to obtain the object

obj - a borrowed instance to be returned.

Throws:

Exception

addObject

void addObject(Object key)
               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).

Parameters:

key - the key a new instance should be added to

Throws:

Exception - when KeyedPoolableObjectFactory.makeObject(java.lang.Object) fails.

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

UnsupportedOperationException - when this pool cannot add new idle objects.

getNumIdle

int getNumIdle(Object key)
               throws UnsupportedOperationException

Returns the number of instances corresponding to the given key currently idle in this pool (optional operation). Returns a negative value if this information is not available.

Parameters:

key - the key to query

Returns:

the number of instances corresponding to the given key currently idle in this pool or a negative value if unsupported

Throws:

UnsupportedOperationException - deprecated: when this implementation doesn't support the operation

getNumActive

int getNumActive(Object key)
                 throws UnsupportedOperationException

Returns the number of instances currently borrowed from but not yet returned to the pool corresponding to the given key (optional operation). Returns a negative value if this information is not available.

Parameters:

key - the key to query

Returns:

the number of instances corresponding to the given key currently borrowed in this pool or a negative value if unsupported

Throws:

UnsupportedOperationException - deprecated: when this implementation doesn't support the operation

getNumIdle

int getNumIdle()
               throws UnsupportedOperationException

Returns the total number of instances currently idle in this pool (optional operation). Returns a negative value if this information is not available.

Returns:

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

Throws:

UnsupportedOperationException - deprecated: when this implementation doesn't support the operation

getNumActive

int getNumActive()
                 throws UnsupportedOperationException

Returns the total number of instances current borrowed from this pool but not yet returned (optional operation). Returns a negative value if this information is not available.

Returns:

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

Throws:

UnsupportedOperationException - deprecated: when this implementation doesn't support the operation

clear

void clear()
           throws Exception,
                  UnsupportedOperationException

Clears the pool, removing all pooled instances (optional operation). Throws UnsupportedOperationException if the pool cannot be cleared.

Throws:

UnsupportedOperationException - when this implementation doesn't support the operation

Exception

clear

void clear(Object key)
           throws Exception,
                  UnsupportedOperationException

Clears the specified pool, removing all pooled instances corresponding to the given key (optional operation). Throws UnsupportedOperationException if the pool cannot be cleared.

Parameters:

key - the key to clear

Throws:

UnsupportedOperationException - when this implementation doesn't 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

setFactory

void setFactory(KeyedPoolableObjectFactory factory)
                throws IllegalStateException,
                       UnsupportedOperationException

Sets the factory the 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 KeyedPoolableObjectFactory used to create new instances.

Throws:

IllegalStateException - when the factory cannot be set at this time

UnsupportedOperationException - when this implementation doesn't support the operation