ObjectPool (Apache Tomcat 7.0.109 API Documentation)

Type Parameters:: T - the type of objects held in this pool

All Known Implementing Classes:: AbandonedObjectPool, 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
Author:: Rodney Waldhoff, Sandy McArthur
See Also:: PoolableObjectFactory, ObjectPoolFactory, KeyedObjectPool, BaseObjectPool

Method Summary

Methods
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 (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.
`void`	`setFactory(PoolableObjectFactory<T> factory)` Deprecated. to be removed in pool 2.0

- 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 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.
  - setFactory
```
@Deprecated
void setFactory(PoolableObjectFactory<T> factory)
                throws IllegalStateException,
                       UnsupportedOperationException
```
    Deprecated. to be removed in pool 2.0
    
    Sets the factory this 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 PoolableObjectFactory used to create new instances.
    
    Throws:
    
    IllegalStateException - when the factory cannot be set at this time
    
    UnsupportedOperationException - if this implementation does not support the operation

Interface ObjectPool<T>

Method Summary

Method Detail

borrowObject

returnObject

invalidateObject

addObject

getNumIdle

getNumActive

clear

close

setFactory