org.genericdao

Class ConnectionPool

java.lang.Object

org.genericdao.ConnectionPool

public class ConnectionPool
extends Object

An implementation of a connection pool for JDBC.

Rather than allocating a new connection every time we access the database, we ask the connection pool for a connection and return it to the connection pool when we're finished. The connection pool will save the connection for for subsequent reuse. If there are no open connections to hand out, the connection pool opens another one. With some JDBC implementations, idle connections eventually fail. So, this connection pool closes idle connections. (See implementation for the current settings to determine how long idle connections remain open.)

This connection pool coordinates with the Transaction class. The getTransactionConnection() method can be used to get the connection that is currently being used in the current transaction. This enables you to execute your own SQL statements in the same transaction and other GenericDAO calls.

Field Summary

Fields

Modifier and Type	Field and Description
static long	DEFAULT_MAX_IDLE_TIME Default max idle time for connections.

Constructor Summary

Constructors

Constructor and Description
ConnectionPool(String jdbcDriverName, String jdbcURL)
ConnectionPool(String jdbcDriverName, String jdbcURL, String user, String password)

Method Summary

Modifier and Type	Method and Description
Connection	getConnection()
PrintWriter	getDebugWriter()
String	getDriverName() Gets the JDBC Driver Name that this connection pool uses.
boolean	getLowerCaseColumnNames()
long	getMaxIdleTime() Get the maximum time that after which idle database connections are closed.
Connection	getTransactionConnection() Get the database connection used by the thread's current transaction.
String	getURL() Gets the JDBC URL that this connection pool uses.
String	getUserName() Gets the user name that this connection pool uses to log into the database.
void	releaseConnection(Connection c) Returns a connection to the connection pool.
void	setDebugOutput(OutputStream out) Sets up an output stream to which debugging output can be printed.
void	setMaxIdleTime(long millis) Changes the time after which idle database connections are closed.
String	toString() Returns a description of this connection pool, include the JDBC Driver Name, the JDBC URL, and the user name used to log into the database.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_MAX_IDLE_TIME

public static final long DEFAULT_MAX_IDLE_TIME

Default max idle time for connections. Value is 5 seconds.

See Also:

Constant Field Values

Constructor Detail

ConnectionPool

public ConnectionPool(String jdbcDriverName,
                      String jdbcURL)

ConnectionPool

public ConnectionPool(String jdbcDriverName,
                      String jdbcURL,
                      String user,
                      String password)

Method Detail

getConnection

public Connection getConnection()
                         throws SQLException

Throws:

SQLException

getDebugWriter

public PrintWriter getDebugWriter()

getDriverName

public String getDriverName()

Gets the JDBC Driver Name that this connection pool uses.

Returns:

the JDBC Driver Name

getLowerCaseColumnNames

public boolean getLowerCaseColumnNames()

getMaxIdleTime

public long getMaxIdleTime()

Get the maximum time that after which idle database connections are closed.

Returns:

maximum idle time in milliseconds

getTransactionConnection

public Connection getTransactionConnection()
                                    throws RollbackException

Get the database connection used by the thread's current transaction. The connection returned is the same one that a GenericDAO would be using (if it's using this connection pool). This permits you to execute SQL statements in the same transaction as GenericDAO calls.

The connection is returned to the connection pool when the transaction is committed or rolled back. So do not call releaseConnection() for connections in a transaction and do not close the connection yourself.

You must use Transaction.commit() (or rollback) rather than connection.commit() to end the transaction.

Note that current only one connection pool can be used in any transaction (because the ACID properties cannot be guaranteed across SQL connections without a lot of work and complication, e.g., using a two-phase commit protocol).

Returns:

a JDBC SQL Connection

Throws:

RollbackException - if there is no active transaction, if there is an underlying SQL exception, or if there is already another connection pool using the currently active transaction. If this exception is thrown, the currently running transaction is rolled back.

getURL

public String getURL()

Gets the JDBC URL that this connection pool uses.

Returns:

the JDBC URL

getUserName

public String getUserName()

Gets the user name that this connection pool uses to log into the database.

Returns:

the user name used to log into the database. Null is return if not user name was provided.

releaseConnection

public void releaseConnection(Connection c)

Returns a connection to the connection pool. The connection should have been obtained using getConnection().

Parameters:

c - connection to return to the connection pool.

setDebugOutput

public void setDebugOutput(OutputStream out)

Sets up an output stream to which debugging output can be printed. This will call can be use to enable all instances of GenericDAO (and Transaction.commit()) to print out messages showing the SQL they are generating.

Parameters:

out - an output stream to which debugging info will be written. (Usually System.out is passed as the parameter.)

setMaxIdleTime

public void setMaxIdleTime(long millis)

Changes the time after which idle database connections are closed. The default time is 20 minutes (20*60*1000 milliseconds).

Parameters:

millis - time a connection can be idle before it will be closed

toString

public String toString()

Returns a description of this connection pool, include the JDBC Driver Name, the JDBC URL, and the user name used to log into the database.

Overrides:

toString in class Object

Returns:

a description of this connection pool.