/** * 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; }
/** * 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
