一个JDBC连接池例子
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 java.sql.Connection getConnection(String 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 java.sql.Connection getConnection(String name, long time) {
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null) {
return pool.getConnection(time);
}
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);
pools.put(poolName, pool);
log("Initialized pool " + poolName);
}
}
}
/**
* Loads properties and initializes the instance with its values.
*/
private void init() {
InputStream is = getClass().getResourceAsStream("/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
