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一个JDBC连接池例子

王朝other·作者佚名  2008-05-19
窄屏简体版  字體: |||超大  

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

 
 
 
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