edu.northwestern.at.utils.db.jdbc
Class SimpleConnectionPool

java.lang.Object
  java.util.Observable
      edu.northwestern.at.utils.db.jdbc.SimpleConnectionPool

public class SimpleConnectionPool
extends java.util.Observable

A simple JDBC connection pool.

Pool parameters are specified via a Properties object passed to the constructor. The following properties are used:

• driverClassName = JDBC driver class name. Required.
• url = Database URL. Required.
• username = Username. Required.
• password = Password. Required.
• maxPoolSize = maximum pool size (the maximum number of connections that can be checked out of the pool concurrently). Default = 5.
• idleTimeout = Idle connection timeout in seconds. Default = 600 (10 minutes).
• autocommit = true if connections should be initialized to autocommit, else false. Default = false.
• connectionRetryCount = number of times to repeat attempts to obtain a connection. Default = 5.
• connectrionRetryInterval = amount of time to wait in between attempts to obtain a connection after failures, in milliseconds. Default = 500 (0.5 seconds).

The pool starts out empty (no connections). When a connection is requested from the pool, if maxPoolSize connections have already been checked out, an exception is thrown. Otherwise, if the pool is not empty, the most recently used connection is checked out from the pool, tested, and returned. If the pool is empty, a new connection is created and returned.

Connections are tested when they are checked out. If a connection is bad, it is closed and a new one is created. The test query statement is "select 1".

Simple connection pools are observable. Observers are notified whenever a bad connection is detected in the test and whenever it takes more than one try to obtain a new connection. The parameter passed to the observer is an array of objects of length 2. For a bad connection, the first element is the Integer 1 and the second element is the exception describing the error, if any. For more than one try, the first element is the Integer 2 and the second element is the number of tries.

The pool is examined every minute. Any connections in the pool which have not been used for idleTimout seconds are closed and removed from the pool.

Simple connection pools are thread-safe.

Constructor Summary

SimpleConnectionPool(java.util.Properties poolProperties)
Creates a connection pool.

Method Summary

void	close() Closes the pool.
java.sql.Connection	getConnection() Gets a connection from the pool.
void	releaseConnection(java.sql.Connection connection) Releases a connection back to the pool.

Methods inherited from class java.util.Observable

addObserver, clearChanged, countObservers, deleteObserver, deleteObservers, hasChanged, notifyObservers, notifyObservers, setChanged

Methods inherited from class java.lang.Object

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

Constructor Detail

SimpleConnectionPool

public SimpleConnectionPool(java.util.Properties poolProperties)
                     throws java.sql.SQLException

Creates a connection pool.

Parameters:

poolProperties - Properties for pool.

Throws:

java.sql.SQLException

Method Detail

getConnection

public java.sql.Connection getConnection()
                                  throws java.sql.SQLException

Gets a connection from the pool.

Returns:

A connection.

Throws:

java.sql.SQLException

releaseConnection

public void releaseConnection(java.sql.Connection connection)

Releases a connection back to the pool.

Parameters:

connection - The connection to return to the pool.

close

public void close()

Closes the pool.

The pool may not be reused after it is closed. All connections are closed.