Object Pool Pattern: Reusable JDBC Connections [58]

$\bullet$ Problem: How to construct time-expensive objects at boot time, and reuse objects during runtime?

$\bullet$ Solution: Object Pool Pattern

$\bullet$ Outline: Instead of dynamically constructing time-expensive objects (e.g. network/database connections), preallocate and reuse the objects as necessary. Application acquires/releases an object from the pool instead of a constructing the object each time it is needed.

$\bullet$ Pool is a collection of objects, one as good as another, that can be used, returned, and then reused

$\bullet$ Example: Pool of JDBC connections, each expensive to build, constructed at boot time

$\bullet$ Construct $n$ connections to a database, store in a Vector, place in a Hashtable keyed on database name

$\bullet$ ConnectionPool is a Singleton, globally accessable

$\bullet$ Main() acquires a Connection, which causes a lookup in the Hashtable, and a dequeue from the Vector

$\bullet$ Using the Connection, main forms and executes an SQL query

$\bullet$ Main() releases Connection, which causes a lookup in Hashtable, and enqueue onto Vector

Object Pool Pattern: Reusable Objects [59]

$\bullet$ ConnectionPool is a Singleton.

$\bullet$ Pool has a Hashtable, indexed by dbName, which returns a Vector.

$\bullet$ Each Vector contains n reusable JDBC Connection objects pre-connected to dbName.