org.apache.tomcat.dbcp.pool2

Interface ObjectPool<T>

Type Parameters:

T - Type of element pooled in this pool.

All Known Implementing Classes:

BaseObjectPool, GenericObjectPool, SoftReferenceObjectPool

public interface ObjectPool<T>

A pooling simple interface.

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:

2.0

See Also:

PooledObjectFactory, KeyedObjectPool, BaseObjectPool

Method Summary

Modifier and Type	Method and 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.
int	getNumIdle() Return the number of instances currently idle in this pool.
void	invalidateObject(T obj) Invalidates an object from the pool.
void	returnObject(T obj) Return an instance to the pool.

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 PooledObjectFactory.makeObject() or will be a previously idle object and have been activated with PooledObjectFactory.activateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>) and then validated with PooledObjectFactory.validateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>).

By contract, clients must return the borrowed instance using returnObject(T), invalidateObject(T), 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).

Returns:

an instance from this pool.

Throws:

IllegalStateException - after close has been called on this pool.

Exception - when PooledObjectFactory.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:

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(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 - if the instance cannot be invalidated

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 PooledObjectFactory.makeObject() fails.

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

UnsupportedOperationException - when this pool cannot add new idle objects.

getNumIdle

int getNumIdle()

Return the number of instances currently idle in this pool. 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.

getNumActive

int getNumActive()

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

Returns:

the number of instances currently borrowed from this pool.

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 PooledObjectFactory.destroyObject(PooledObject).

Throws:

UnsupportedOperationException - if this implementation does not support the operation

Exception - if the pool 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.