Package 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:

  • Method Summary

    Modifier and Type
    Method
    Description
    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.

  • Method Details

    • 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.