KeyedObjectPool (Apache Tomcat 8.0.53 API Documentation)

Type Parameters:
K - The type of keys maintained by this pool.
V - Type of element pooled in this pool.

All Superinterfaces:

java.lang.AutoCloseable, java.io.Closeable

All Known Implementing Classes:

GenericKeyedObjectPool
```
public interface KeyedObjectPool<K,V>
extends java.io.Closeable
```
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

Methods
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 currently 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 java.lang.Exception,
                      java.util.NoSuchElementException,
                      java.lang.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:
    
    java.lang.IllegalStateException - after close has been called on this pool
    
    java.lang.Exception - when makeObject throws an exception
    
    java.util.NoSuchElementException - when the pool is exhausted and cannot or will not return another instance
  - returnObject
```
void returnObject(K key,
                V obj)
                  throws java.lang.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:
    
    java.lang.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.
    
    java.lang.Exception - if an instance cannot be returned to the pool
  - invalidateObject
```
void invalidateObject(K key,
                    V obj)
                      throws java.lang.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:
    
    java.lang.Exception - if the instance cannot be invalidated
  - addObject
```
void addObject(K key)
               throws java.lang.Exception,
                      java.lang.IllegalStateException,
                      java.lang.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:
    
    java.lang.Exception - when KeyedPooledObjectFactory.makeObject(K) fails.
    
    java.lang.IllegalStateException - after close() has been called on this pool.
    
    java.lang.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 currently borrowed from this pool but not yet returned. Returns a negative value if this information is not available.
    
    Returns:
    the total number of instances currently borrowed from this pool but not yet returned.
  - clear
```
void clear()
           throws java.lang.Exception,
                  java.lang.UnsupportedOperationException
```
    Clears the pool, removing all pooled instances (optional operation).
    
    Throws:
    
    java.lang.UnsupportedOperationException - when this implementation doesn't support the operation
    
    java.lang.Exception - if the pool cannot be cleared
  - clear
```
void clear(K key)
           throws java.lang.Exception,
                  java.lang.UnsupportedOperationException
```
    Clears the specified pool, removing all pooled instances corresponding to the given key (optional operation).
    
    Parameters:
    key - the key to clear
    
    Throws:
    
    java.lang.UnsupportedOperationException - when this implementation doesn't support the operation
    
    java.lang.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.
    
    Specified by:
    
    close in interface java.lang.AutoCloseable
    
    Specified by:
    
    close in interface java.io.Closeable

Interface KeyedObjectPool<K,V>

Method Summary

Method Detail

borrowObject

returnObject

invalidateObject

addObject

getNumIdle

getNumActive

getNumIdle

getNumActive

clear

clear

close