A map of pool ids to Connections. Key is an object that uniquely identifies a PooledConnection request (typically information needed to create the connection). The definitions of the key's equals() and hashCode() methods are vital to its unique identification in a Pool. Value is a ConnectionsRef, which is a reference to Connections, a list of equivalent connections. Supports methods that - retrieves (or creates as necessary) a connection from the pool - removes expired connections from the pool Connections cleanup: A WeakHashMap is used for mapping the pool ids and Connections. A SoftReference from the value to the key is kept to hold the map entry as long as possible. This allows the GC to remove Connections from the Pool under situations of VM running out of resources. To take an appropriate action of 'closing the connections' before the GC reclaims the ConnectionsRef objects, the ConnectionsRef objects are made weakly reachable through a list of weak references registered with a reference queue. Upon an entry gets removed from the WeakHashMap, the ConnectionsRef (value in the map) object is weakly reachable. When another sweep of clearing the weak references is made by the GC it puts the corresponding ConnectionsWeakRef object into the reference queue. The reference queue is monitored lazily for reclaimable Connections whenever a pooled connection is requested or a call to remove the expired connections is made. The monitoring is done regularly when idle connection timeout is set as the PoolCleaner removes expired connections periodically. As determined by experimentation, cleanup of resources using the ReferenceQueue mechanism is reliable and has more immediate effect than the finalizer approach.