# Class PoolUtils

java.lang.Object
org.apache.tomcat.dbcp.pool2.PoolUtils

public final class PoolUtils extends Object
This class consists exclusively of static methods that operate on or return ObjectPool or KeyedObjectPool related interfaces.

Since:
  2.0

## Constructor Summary

Constructors
Constructor
Description
`PoolUtils()`
PoolUtils instances should NOT be constructed in standard programming.

## Method Summary

Modifier and Type
Method
Description
`static <K, V> Map<K,TimerTask>`
`checkMinIdle(KeyedObjectPool<K,V> keyedPool, Collection<K> keys, int minIdle, long periodMillis)`
Periodically check the idle object count for each key in the `Collection keys` in the keyedPool.
`static <K, V> TimerTask`
`checkMinIdle(KeyedObjectPool<K,V> keyedPool, K key, int minIdle, long periodMillis)`
Periodically check the idle object count for the key in the keyedPool.
`static <T> TimerTask`
`checkMinIdle(ObjectPool<T> pool, int minIdle, long periodMillis)`
Periodically check the idle object count for the pool.
`static void`
`checkRethrow(Throwable t)`
Should the supplied Throwable be re-thrown (eg if it is an instance of one of the Throwables that should never be swallowed).
`static <K, V> KeyedObjectPool<K,V>`
`erodingPool(KeyedObjectPool<K,V> keyedPool)`
Returns a pool that adaptively decreases its size when idle objects are no longer needed.
`static <K, V> KeyedObjectPool<K,V>`
`erodingPool(KeyedObjectPool<K,V> keyedPool, float factor)`
Returns a pool that adaptively decreases its size when idle objects are no longer needed.
`static <K, V> KeyedObjectPool<K,V>`
`erodingPool(KeyedObjectPool<K,V> keyedPool, float factor, boolean perKey)`
Returns a pool that adaptively decreases its size when idle objects are no longer needed.
`static <T> ObjectPool<T>`
`erodingPool(ObjectPool<T> pool)`
Returns a pool that adaptively decreases its size when idle objects are no longer needed.
`static <T> ObjectPool<T>`
`erodingPool(ObjectPool<T> pool, float factor)`
Returns a pool that adaptively decreases its size when idle objects are no longer needed.
`static <K, V> void`
`prefill(KeyedObjectPool<K,V> keyedPool, Collection<K> keys, int count)`
Deprecated.
Use `KeyedObjectPool.addObjects(Collection, int)`.
`static <K, V> void`
`prefill(KeyedObjectPool<K,V> keyedPool, K key, int count)`
Deprecated.
Use `KeyedObjectPool.addObjects(Object, int)`.
`static <T> void`
`prefill(ObjectPool<T> pool, int count)`
Deprecated.
Use `ObjectPool.addObjects(int)`.
`static <K, V> KeyedPooledObjectFactory<K,V>`
`synchronizedKeyedPooledFactory(KeyedPooledObjectFactory<K,V> keyedFactory)`
Returns a synchronized (thread-safe) KeyedPooledObjectFactory backed by the specified KeyedPooledObjectFactory.
`static <K, V> KeyedObjectPool<K,V>`
`synchronizedPool(KeyedObjectPool<K,V> keyedPool)`
Returns a synchronized (thread-safe) KeyedObjectPool backed by the specified KeyedObjectPool.
`static <T> ObjectPool<T>`
`synchronizedPool(ObjectPool<T> pool)`
Returns a synchronized (thread-safe) ObjectPool backed by the specified ObjectPool.
`static <T> PooledObjectFactory<T>`
`synchronizedPooledFactory(PooledObjectFactory<T> factory)`
Returns a synchronized (thread-safe) PooledObjectFactory backed by the specified PooledObjectFactory.

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

## Constructor Details

### PoolUtils

public PoolUtils()
PoolUtils instances should NOT be constructed in standard programming. Instead, the class should be used procedurally: PoolUtils.adapt(aPool);. This constructor is public to permit tools that require a JavaBean instance to operate.

## Method Details

### checkMinIdle

public static <K, V> Map<K,TimerTask> checkMinIdle(KeyedObjectPool<K,V> keyedPool, Collection<K> keys, int minIdle, long periodMillis) throws IllegalArgumentException
Periodically check the idle object count for each key in the `Collection keys` in the keyedPool. At most one idle object will be added per period.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the keyedPool to check periodically.
  `keys` - a collection of keys to check the idle object count.
  `minIdle` - if the `KeyedObjectPool.getNumIdle(Object)` is less than this then add an idle object.
  `periodMillis` - the frequency in milliseconds to check the number of idle objects in a keyedPool, see `Timer.schedule(TimerTask, long, long)`.
Returns:
  a `Map` of key and `TimerTask` pairs that will periodically check the pools idle object count.
Throws:
  `IllegalArgumentException` - when `keyedPool`, `keys`, or any of the values in the collection is `null` or when `minIdle` is negative or when `period` isn't valid for `Timer.schedule(TimerTask, long, long)`.
See Also:
  - `checkMinIdle(KeyedObjectPool, Object, int, long)`

### checkMinIdle

public static <K, V> TimerTask checkMinIdle(KeyedObjectPool<K,V> keyedPool, K key, int minIdle, long periodMillis) throws IllegalArgumentException
Periodically check the idle object count for the key in the keyedPool. At most one idle object will be added per period. If there is an exception when calling `KeyedObjectPool.addObject(Object)` then no more checks for that key will be performed.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the keyedPool to check periodically.
  `key` - the key to check the idle count of.
  `minIdle` - if the `KeyedObjectPool.getNumIdle(Object)` is less than this then add an idle object.
  `periodMillis` - the frequency in milliseconds to check the number of idle objects in a keyedPool, see `Timer.schedule(TimerTask, long, long)`.
Returns:
  the `TimerTask` that will periodically check the pools idle object count.
Throws:
  `IllegalArgumentException` - when `keyedPool`, `key` is `null` or when `minIdle` is negative or when `period` isn't valid for `Timer.schedule(TimerTask, long, long)`.

### checkMinIdle

public static <T> TimerTask checkMinIdle(ObjectPool<T> pool, int minIdle, long periodMillis) throws IllegalArgumentException
Periodically check the idle object count for the pool. At most one idle object will be added per period. If there is an exception when calling `ObjectPool.addObject()` then no more checks will be performed.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `pool` - the pool to check periodically.
  `minIdle` - if the `ObjectPool.getNumIdle()` is less than this then add an idle object.
  `periodMillis` - the frequency in milliseconds to check the number of idle objects in a pool, see `Timer.schedule(TimerTask, long, long)`.
Returns:
  the `TimerTask` that will periodically check the pools idle object count.
Throws:
  `IllegalArgumentException` - when `pool` is `null` or when `minIdle` is negative or when `period` isn't valid for `Timer.schedule(TimerTask, long, long)`

### checkRethrow

public static void checkRethrow(Throwable t)
Should the supplied Throwable be re-thrown (eg if it is an instance of one of the Throwables that should never be swallowed). Used by the pool error handling for operations that throw exceptions that normally need to be ignored.

Parameters:
  `t` - The Throwable to check
Throws:
  `ThreadDeath` - if that is passed in
  `VirtualMachineError` - if that is passed in

### erodingPool

public static <K, V> KeyedObjectPool<K,V> erodingPool(KeyedObjectPool<K,V> keyedPool)
Returns a pool that adaptively decreases its size when idle objects are no longer needed. This is intended as an always thread-safe alternative to using an idle object evictor provided by many pool implementations. This is also an effective way to shrink FIFO ordered pools that experience load spikes.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the KeyedObjectPool to be decorated so it shrinks its idle count when possible.
Returns:
  a pool that adaptively decreases its size when idle objects are no longer needed.
Throws:
  `IllegalArgumentException` - when `keyedPool` is `null`.
See Also:
  - `erodingPool(KeyedObjectPool, float)`
  - `erodingPool(KeyedObjectPool, float, boolean)`

### erodingPool

public static <K, V> KeyedObjectPool<K,V> erodingPool(KeyedObjectPool<K,V> keyedPool, float factor)
Returns a pool that adaptively decreases its size when idle objects are no longer needed. This is intended as an always thread-safe alternative to using an idle object evictor provided by many pool implementations. This is also an effective way to shrink FIFO ordered pools that experience load spikes.

The factor parameter provides a mechanism to tweak the rate at which the pool tries to shrink its size. Values between 0 and 1 cause the pool to try to shrink its size more often. Values greater than 1 cause the pool to less frequently try to shrink its size.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the KeyedObjectPool to be decorated so it shrinks its idle count when possible.
  `factor` - a positive value to scale the rate at which the pool tries to reduce its size. If 0 < factor < 1 then the pool shrinks more aggressively. If 1 < factor then the pool shrinks less aggressively.
Returns:
  a pool that adaptively decreases its size when idle objects are no longer needed.
Throws:
  `IllegalArgumentException` - when `keyedPool` is `null` or when `factor` is not positive.
See Also:
  - `erodingPool(KeyedObjectPool, float, boolean)`

### erodingPool

public static <K, V> KeyedObjectPool<K,V> erodingPool(KeyedObjectPool<K,V> keyedPool, float factor, boolean perKey)
Returns a pool that adaptively decreases its size when idle objects are no longer needed. This is intended as an always thread-safe alternative to using an idle object evictor provided by many pool implementations. This is also an effective way to shrink FIFO ordered pools that experience load spikes.

The factor parameter provides a mechanism to tweak the rate at which the pool tries to shrink its size. Values between 0 and 1 cause the pool to try to shrink its size more often. Values greater than 1 cause the pool to less frequently try to shrink its size.

The perKey parameter determines if the pool shrinks on a whole pool basis or a per key basis. When perKey is false, the keys do not have an effect on the rate at which the pool tries to shrink its size. When perKey is true, each key is shrunk independently.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the KeyedObjectPool to be decorated so it shrinks its idle count when possible.
  `factor` - a positive value to scale the rate at which the pool tries to reduce its size. If 0 < factor < 1 then the pool shrinks more aggressively. If 1 < factor then the pool shrinks less aggressively.
  `perKey` - when true, each key is treated independently.
Returns:
  a pool that adaptively decreases its size when idle objects are no longer needed.
Throws:
  `IllegalArgumentException` - when `keyedPool` is `null` or when `factor` is not positive.
See Also:
  - `erodingPool(KeyedObjectPool)`
  - `erodingPool(KeyedObjectPool, float)`

### erodingPool

public static <T> ObjectPool<T> erodingPool(ObjectPool<T> pool)
Returns a pool that adaptively decreases its size when idle objects are no longer needed. This is intended as an always thread-safe alternative to using an idle object evictor provided by many pool implementations. This is also an effective way to shrink FIFO ordered pools that experience load spikes.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `pool` - the ObjectPool to be decorated so it shrinks its idle count when possible.
Returns:
  a pool that adaptively decreases its size when idle objects are no longer needed.
Throws:
  `IllegalArgumentException` - when `pool` is `null`.
See Also:
  - `erodingPool(ObjectPool, float)`

### erodingPool

public static <T> ObjectPool<T> erodingPool(ObjectPool<T> pool, float factor)
Returns a pool that adaptively decreases its size when idle objects are no longer needed. This is intended as an always thread-safe alternative to using an idle object evictor provided by many pool implementations. This is also an effective way to shrink FIFO ordered pools that experience load spikes.

The factor parameter provides a mechanism to tweak the rate at which the pool tries to shrink its size. Values between 0 and 1 cause the pool to try to shrink its size more often. Values greater than 1 cause the pool to less frequently try to shrink its size.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `pool` - the ObjectPool to be decorated so it shrinks its idle count when possible.
  `factor` - a positive value to scale the rate at which the pool tries to reduce its size. If 0 < factor < 1 then the pool shrinks more aggressively. If 1 < factor then the pool shrinks less aggressively.
Returns:
  a pool that adaptively decreases its size when idle objects are no longer needed.
Throws:
  `IllegalArgumentException` - when `pool` is `null` or when `factor` is not positive.
See Also:
  - `erodingPool(ObjectPool)`

### prefill

@Deprecated public static <K, V> void prefill(KeyedObjectPool<K,V> keyedPool, Collection<K> keys, int count) throws Exception, IllegalArgumentException
Deprecated.
Use `KeyedObjectPool.addObjects(Collection, int)`.
Calls `KeyedObjectPool.addObject(Object)` on `keyedPool` with each key in `keys` for `count` number of times. This has the same effect as calling `prefill(KeyedObjectPool, Object, int)` for each key in the `keys` collection.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the keyedPool to prefill.
  `keys` - `Collection` of keys to add objects for.
  `count` - the number of idle objects to add for each `key`.
Throws:
  `Exception` - when `KeyedObjectPool.addObject(Object)` fails.
  `IllegalArgumentException` - when `keyedPool`, `keys`, or any value in `keys` is `null`.
See Also:
  - `prefill(KeyedObjectPool, Object, int)`

### prefill

@Deprecated public static <K, V> void prefill(KeyedObjectPool<K,V> keyedPool, K key, int count) throws Exception, IllegalArgumentException
Deprecated.
Use `KeyedObjectPool.addObjects(Object, int)`.
Calls `KeyedObjectPool.addObject(Object)` on `keyedPool` with `key` `count` number of times.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the keyedPool to prefill.
  `key` - the key to add objects for.
  `count` - the number of idle objects to add for `key`.
Throws:
  `Exception` - when `KeyedObjectPool.addObject(Object)` fails.
  `IllegalArgumentException` - when `keyedPool` or `key` is `null`.

### prefill

@Deprecated public static <T> void prefill(ObjectPool<T> pool, int count) throws Exception
Deprecated.
Use `ObjectPool.addObjects(int)`.
Calls `ObjectPool.addObject()` on `pool` `count` number of times.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `pool` - the pool to prefill.
  `count` - the number of idle objects to add.
Throws:
  `Exception` - when `ObjectPool.addObject()` fails.
  `IllegalArgumentException` - when `pool` is `null`.

### synchronizedKeyedPooledFactory

public static <K, V> KeyedPooledObjectFactory<K,V> synchronizedKeyedPooledFactory(KeyedPooledObjectFactory<K,V> keyedFactory)
Returns a synchronized (thread-safe) KeyedPooledObjectFactory backed by the specified KeyedPooledObjectFactory.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedFactory` - the KeyedPooledObjectFactory to be "wrapped" in a synchronized KeyedPooledObjectFactory.
Returns:
  a synchronized view of the specified KeyedPooledObjectFactory.

### synchronizedPool

public static <K, V> KeyedObjectPool<K,V> synchronizedPool(KeyedObjectPool<K,V> keyedPool)
Returns a synchronized (thread-safe) KeyedObjectPool backed by the specified KeyedObjectPool.

Note: This should not be used on pool implementations that already provide proper synchronization such as the pools provided in the Commons Pool library. Wrapping a pool that `waits` for poolable objects to be returned before allowing another one to be borrowed with another layer of synchronization will cause liveliness issues or a deadlock.

Type Parameters:
  `K` - the type of the pool key
  `V` - the type of pool entries
Parameters:
  `keyedPool` - the KeyedObjectPool to be "wrapped" in a synchronized KeyedObjectPool.
Returns:
  a synchronized view of the specified KeyedObjectPool.

### synchronizedPool

public static <T> ObjectPool<T> synchronizedPool(ObjectPool<T> pool)
Returns a synchronized (thread-safe) ObjectPool backed by the specified ObjectPool.

Note: This should not be used on pool implementations that already provide proper synchronization such as the pools provided in the Commons Pool library. Wrapping a pool that `waits` for poolable objects to be returned before allowing another one to be borrowed with another layer of synchronization will cause liveliness issues or a deadlock.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `pool` - the ObjectPool to be "wrapped" in a synchronized ObjectPool.
Returns:
  a synchronized view of the specified ObjectPool.
Throws:
  `IllegalArgumentException` - when `pool` is `null`.

### synchronizedPooledFactory

public static <T> PooledObjectFactory<T> synchronizedPooledFactory(PooledObjectFactory<T> factory)
Returns a synchronized (thread-safe) PooledObjectFactory backed by the specified PooledObjectFactory.

Type Parameters:
  `T` - the type of objects in the pool
Parameters:
  `factory` - the PooledObjectFactory to be "wrapped" in a synchronized PooledObjectFactory.
Returns:
  a synchronized view of the specified PooledObjectFactory.