Package org.apache.commons.pool

Interface KeyedObjectPool<K,V>

Type Parameters:
K - the type of keys in this pool
V - the type of objects held in this pool
All Known Implementing Classes:
BaseKeyedObjectPool, GenericKeyedObjectPool, StackKeyedObjectPool
public interface KeyedObjectPool<K,V>
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: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $
Author:
Rodney Waldhoff, Sandy McArthur
See Also:

  • Method Summary

    Modifier and Type
    Method
    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 (optional operation).
    int
    getNumActive(K 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(K key)
    Returns the number of instances corresponding to the given key currently idle in this pool (optional operation).
    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 Details

    • 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 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(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:
      Exception

    • 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

    • 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 KeyedPoolableObjectFactory.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) 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(K 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(K 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