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java连接sqlserver实例

王朝mssql·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

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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