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java连接sqlserver实例

作者:未知 来源:月光软件站 加入时间:2005-2-28 月光软件站

package sanpai.db;

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();
	
	/**
	 * 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();
		}
		
		/**
		 * 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()throws SQLException {
			Connection con = null;
			if (freeConnections.size() > 0) {
				// Pick the first Connection in the Vector
				// to get round-robin usage
				con = (Connection) freeConnections.firstElement();
				freeConnections.removeElementAt(0);
				try {
					if (con.isClosed()) {
						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) {
				con = newConnection();
			}
			if (con != null) {
				checkedOut++;
			}
			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.
		 * <P>
		 * 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) throws SQLException {
			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;
				}
			}
			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() throws SQLException {
			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);
				throw e;
			}
			return con;
		}
	}
	/**
	 * A private constructor since this is a Singleton
	 */
	private DBConnectionManager() {
		init();
	}
	/**
	 * Creates instances of DBConnectionPool based on the properties.
	 * A DBConnectionPool can be defined with the following properties:
	 * <PRE>
	 * &lt;poolname&gt;.url         The JDBC URL for the database
	 * &lt;poolname&gt;.user        A database user (optional)
	 * &lt;poolname&gt;.password    A database user password (if user specified)
	 * &lt;poolname&gt;.maxconn     The maximal number of connections (optional)
	 * </PRE>
	 *
	 * @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);
			}
		}
	}
	/**
	 * 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) throws SQLException {
		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) throws SQLException {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			return pool.getConnection(time);
		}
		return null;
	}
	/**
	 * 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;
	}
	/**
	 * 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
	 */
	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);
	}
	/**
	 * 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());
			}
		}
	}
/**
 * release all resources when this object is destroyed.
 */
public void finalize() {
	release();
}}



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