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Re: Connection Pooling [message #91380] Fri, 02 August 2002 21:40
Amit Kuiya
Messages: 1
Registered: August 2002
Junior Member
Hy

This is amit, well in reply to ur query get this sample class , it will help u.

well connection pooling is an very effective way to reduce time and load, well imagine a system having single connection and used by n client firing their query on it and expect the right reply, then they may be disapp. by garbage result or various queries so
make a sequence lile
single query --> s Statement --> s Conn --> and relase this connection to be kept again in same pool.

mail me if have any query

/*
* Copyright (c) 1998 by Gefion software.
*
* Permission to use, copy, and distribute this software for
* NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies.
*
*/
package admin;
import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;

/**
* This class is a Singleton that provides access to one or many
* connection pools defined in a Property file. A client gets
* access to the single instance through the static getInstance()
* method and can then check-out and check-in connections from a pool.
* When the client shuts down it should call the release() method
* to close all open connections and do other clean up.
*/
public class DBConnectionManager
{
static private DBConnectionManager instance; // The single instance
static private int clients;

private Vector drivers = new Vector();
private PrintWriter log;
private Hashtable pools = new Hashtable();

/**
* Returns the single instance, creating one if it's the
* first time this method is called.
*
* @return DBConnectionManager The single instance.
*/
static synchronized public DBConnectionManager getInstance()
{
if (instance == null)
{
instance = new DBConnectionManager();
}
clients++;
return instance;
}

/**
* A private constructor since this is a Singleton
*/
private DBConnectionManager()
{
init();
}

/**
* Returns a connection to the named pool.
*
* @param name The pool name as defined in the properties file
* @param con The Connection
*/
public void freeConnection(String name, Connection con)
{
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null)
{
pool.freeConnection(con);

}
}

/**
* Returns an open connection. If no one is available, and the max
* number of connections has not been reached, a new connection is
* created.
*
* @param name The pool name as defined in the properties file
* @return Connection The connection or null
*/
public Connection getConnection(String name)
{
// System.out.println("name: "+name);
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null)
{
return pool.getConnection();
}
return null;
}

/**
* Returns an open connection. If no one is available, and the max
* number of connections has not been reached, a new connection is
* created. If the max number has been reached, waits until one
* is available or the specified time has elapsed.
*
* @param name The pool name as defined in the properties file
* @param time The number of milliseconds to wait
* @return Connection The connection or null
*/
public Connection getConnection(String name, long time)
{
Enumeration aEnum = pools.elements();
// while(aEnum.hasMoreElements())
// {
// System.out.println(":"+aEnum.nextElement().toString());
// }
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null)
{
// System.out.println("The pool found");
return pool.getConnection(time);

}
// System.out.println("The pool not found");
return null;
}

/**
* Closes all open connections and deregisters all drivers.
*/
public synchronized void release()
{
// Wait until called by the last client
if(--clients != 0)
{
return;
}

Enumeration allPools = pools.elements();
while (allPools.hasMoreElements())
{
DBConnectionPool pool = (DBConnectionPool) allPools.nextElement();
pool.release();
}
Enumeration allDrivers = drivers.elements();

while (allDrivers.hasMoreElements())
{
Driver driver = (Driver) allDrivers.nextElement();
try
{
DriverManager.deregisterDriver(driver);
log("Deregistered JDBC driver " + driver.getClass().getName());
}
catch (SQLException e)
{
log(e, "Can't deregister JDBC driver: " + driver.getClass().getName());
}
}
}

/**
* Creates instances of DBConnectionPool based on the properties.
* A DBConnectionPool can be defined with the following properties:
*
     * <poolname>.url         The JDBC URL for the database
     * <poolname>.user        A database user (optional)
     * <poolname>.password    A database user password (if user specified)
     * <poolname>.maxconn     The maximal number of connections (optional)
     * 

*
* @param props The connection pool properties
*/
private void createPools(Properties props)
{
Enumeration propNames = props.propertyNames();
while (propNames.hasMoreElements())
{
String name = (String) propNames.nextElement();
if (name.endsWith(".url"))
{
String poolName = name.substring(0, name.lastIndexOf("."));
String url = props.getProperty(poolName + ".url");
if (url == null)
{
log("No URL specified for " + poolName);
continue;
}
String user = props.getProperty(poolName + ".user");
String password = props.getProperty(poolName + ".password");
String maxconn = props.getProperty(poolName + ".maxconn", "0");
int max;
try
{
max = Integer.valueOf(maxconn).intValue();
}
catch (NumberFormatException e)
{
log("Invalid maxconn value " + maxconn + " for " + poolName);
max = 0;
}
DBConnectionPool pool =
new DBConnectionPool(poolName, url, user, password, max);
// System.out.println(poolName);
pools.put(poolName, pool);
log("Initialized pool " + poolName);
}
}
System.out.println("pool activated");
// Enumeration aEnum = pools.elements();
// while(aEnum.hasMoreElements())
// {
// // System.out.println("NAME"+ ((DBConnectionPool)aEnum.nextElement()).name);
// }
}

/**
* Loads properties and initializes the instance with its values.
*/
private void init()
{
InputStream is = getClass().getResourceAsStream("../Resources/db.properties");
Properties dbProps = new Properties();
try
{
dbProps.load(is);
}
catch (Exception e)
{
System.err.println("Can't read the properties file. " +
"Make sure db.properties is in the CLASSPATH");
return;
}
String logFile = dbProps.getProperty("logfile", "DBConnectionManager.log");
try
{
log = new PrintWriter(new FileWriter(logFile, true), true);
}
catch (IOException e)
{
System.err.println("Can't open the log file: " + logFile);
log = new PrintWriter(System.err);
}
loadDrivers(dbProps);
createPools(dbProps);
}

/**
* Loads and registers all JDBC drivers. This is done by the
* DBConnectionManager, as opposed to the DBConnectionPool,
* since many pools may share the same driver.
*
* @param props The connection pool properties
*/
private void loadDrivers(Properties props)
{
String driverClasses = props.getProperty("drivers");
StringTokenizer st = new StringTokenizer(driverClasses);

while (st.hasMoreElements())
{
String driverClassName = st.nextToken().trim();
try
{
Driver driver = (Driver)
Class.forName(driverClassName).newInstance();
DriverManager.registerDriver(driver);
drivers.addElement(driver);
log("Registered JDBC driver " + driverClassName);
}
catch (Exception e)
{
log("Can't register JDBC driver: " +
driverClassName + ", Exception: " + e);
}
}
}

/**
* Writes a message to the log file.
*/
private void log(String msg)
{
log.println(new Date() + ": " + msg);
}

/**
* Writes a message with an Exception to the log file.
*/
private void log(Throwable e, String msg)
{
log.println(new Date() + ": " +msg);
e.printStackTrace(log);
}

/**
* This inner class represents a connection pool. It creates new
* connections on demand, up to a max number if specified.
* It also makes sure a connection is still open before it is
* returned to a client.
*/
class DBConnectionPool
{
private int checkedOut;
private Vector freeConnections = new Vector();
private int maxConn;
private String name;
private String password;
private String URL;
private String user;

/**
* Creates new connection pool.
*
* @param name The pool name
* @param URL The JDBC URL for the database
* @param user The database user, or null
* @param password The database user password, or null
* @param maxConn The maximal number of connections, or 0
* for no limit
*/
public DBConnectionPool(String name, String URL, String user, String password,
int maxConn) {
this.name = name;
this.URL = URL;
this.user = user;
this.password = password;
this.maxConn = maxConn;
}

/**
* Checks in a connection to the pool. Notify other Threads that
* may be waiting for a connection.
*
* @param con The connection to check in
*/
public synchronized void freeConnection(Connection con) {
// Put the connection at the end of the Vector
freeConnections.addElement(con);
checkedOut--;
notifyAll();
// System.out.println("Connection is free now");
}

/**
* Checks out a connection from the pool. If no free connection
* is available, a new connection is created unless the max
* number of connections has been reached. If a free connection
* has been closed by the database, it's removed from the pool
* and this method is called again recursively.
*/
public synchronized Connection getConnection()
{
// System.out.println("bhuwan: I am in get connection");
Connection con = null;
if (freeConnections.size() > 0)
{
// System.out.println("bhuwan: Connection available " + freeConnections.size());
// Pick the first Connection in the Vector
// to get round-robin usage
con = (Connection) freeConnections.firstElement();
freeConnections.removeElementAt(0);
try
{
if (con.isClosed())
{
// System.out.println("bhuwan: The connection was closed ");
log("Removed bad connection from " + name);
// Try again recursively
con = getConnection();
}
}
catch (SQLException e)
{
log("Removed bad connection from " + name);
// Try again recursively
con = getConnection();
}
}
else if (maxConn == 0 || checkedOut < maxConn)
{
// System.out.println("bhuwan: create new connection");
con = newConnection();
}
if (con != null)
{
// System.out.println("bhuwan:checked out");
checkedOut++;
}
// System.out.println("bhuwan:before returning the conection");
return con;
}

/**
* Checks out a connection from the pool. If no free connection
* is available, a new connection is created unless the max
* number of connections has been reached. If a free connection
* has been closed by the database, it's removed from the pool
* and this method is called again recursively.
*

* If no connection is available and the max number has been
* reached, this method waits the specified time for one to be
* checked in.
*
* @param timeout The timeout value in milliseconds
*/
public synchronized Connection getConnection(long timeout) {
long startTime = new Date().getTime();
Connection con;
while ((con = getConnection()) == null) {
try {
wait(timeout);
}
catch (InterruptedException e) {}
if ((new Date().getTime() - startTime) >= timeout) {
// Timeout has expired
return null;
}
}
// System.out.println("Connection returned");
return con;
}

/**
* Closes all available connections.
*/
public synchronized void release()
{
Enumeration allConnections = freeConnections.elements();
while (allConnections.hasMoreElements())
{
Connection con = (Connection) allConnections.nextElement();
try
{
con.close();
log("Closed connection for pool " + name);
}
catch (SQLException e)
{
log(e, "Can't close connection for pool " + name);
}
}
freeConnections.removeAllElements();
}

/**
* Creates a new connection, using a userid and password
* if specified.
*/
private Connection newConnection() {
Connection con = null;
try {
if (user == null) {
con = DriverManager.getConnection(URL);
}
else {
con = DriverManager.getConnection(URL, user, password);
}
log("Created a new connection in pool " + name);
}
catch (SQLException e) {
log(e, "Can't create a new connection for " + URL);
return null;
}
return con;
}
}
}
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