org.apache.tomcat.dbcp.pool2

Interface KeyedObjectPool<K,V>

Type Parameters:

K - The type of keys maintained by this pool.

V - Type of element pooled in this pool.

All Known Implementing Classes:

GenericKeyedObjectPool

public interface KeyedObjectPool<K,V>

A "keyed" pooling interface.

A keyed pool maintains a pool of instances for each key value.

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 GenericKeyedObjectPool for an implementation.

Since:

2.0

See Also:

KeyedPooledObjectFactory, ObjectPool, GenericKeyedObjectPool

Method Summary

Modifier and Type	Method and Description
void	addObject(K key) Create an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool.
V	borrowObject(K key) Obtains an instance from this pool for the specified key.
void	clear() Clears the pool, removing all pooled instances (optional operation).
void	clear(K 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.
int	getNumActive(K key) Returns the number of instances currently borrowed from but not yet returned to the pool corresponding to the given key.
int	getNumIdle() Returns the total number of instances currently idle in this pool.
int	getNumIdle(K key) Returns the number of instances corresponding to the given key currently idle in this pool.
void	invalidateObject(K key, V obj) Invalidates an object from the pool.
void	returnObject(K key, V obj) Return an instance to the pool.

Method Detail

borrowObject

V borrowObject(K 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 (optionally) 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).

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(K key,
                  V 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:

IllegalStateException - if an attempt is made to return an object to the pool that is in any state other than allocated (i.e. borrowed). Attempting to return an object more than once or attempting to return an object that was never borrowed from the pool will trigger this exception.

Exception - if an instance cannot be returned to the pool

invalidateObject

void invalidateObject(K key,
                      V 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 - if the instance cannot be invalidated

addObject

void addObject(K 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 KeyedPooledObjectFactory.makeObject(K) fails.

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

UnsupportedOperationException - when this pool cannot add new idle objects.

getNumIdle

int getNumIdle(K key)

Returns the number of instances corresponding to the given key currently idle in this pool. 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.

getNumActive

int getNumActive(K key)

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

Parameters:

key - the key to query

Returns:

the number of instances currently borrowed from but not yet returned to the pool corresponding to the given key. =

getNumIdle

int getNumIdle()

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

Returns:

the total number of instances currently idle in this pool. =

getNumActive

int getNumActive()

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

Returns:

the total number of instances current borrowed from this pool but not yet returned.

clear

void clear()
    throws Exception,
           UnsupportedOperationException

Clears the pool, removing all pooled instances (optional operation).

Throws:

UnsupportedOperationException - when this implementation doesn't support the operation

Exception - if the pool cannot be cleared

clear

void clear(K key)
    throws Exception,
           UnsupportedOperationException

Clears the specified pool, removing all pooled instances corresponding to the given key (optional operation).

Parameters:

key - the key to clear

Throws:

UnsupportedOperationException - when this implementation doesn't support the operation

Exception - if the key cannot be cleared

close

void close()

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.

Implementations should silently fail if not all resources can be freed.