数据库连接池 笔记

 

连接池工具类：

package com.you.me.util;import java.io.*;import java.sql.*;import java.util.*;import java.util.Date;/** * 管理类DBConnectionUtil支持对一个或多个由属性文件定义的数据库连接池的访问.客户程序可以调用getInstance()方法访问本类的唯一实例. */public class DBConnectionUtil {static private DBConnectionUtil instance; // 唯一实例static private int clients;private Vector drivers = new Vector();private PrintWriter log = new PrintWriter(System.err);private Hashtable pools = new Hashtable();/** * 返回唯一实例.如果是第一次调用此方法,则创建实例 * * @return DBConnectionManager 唯一实例 */static synchronized public DBConnectionUtil getInstance() {if (instance == null) {instance = new DBConnectionUtil();}clients++;return instance;}/** * 建构函数私有以防止其它对象创建本类实例 */private DBConnectionUtil() {init();}/** * 读取属性完成初始化 */private void init() {Properties dbProps = new Properties();try {dbProps.load(DBConnectionUtil.class.getResourceAsStream("/db.properties"));} catch (Exception e) {System.err.println("不能读取属性文件." + "请确保db.properties在CLASSPATH指定的路径中");return;}String logFile = dbProps.getProperty("logfile", "TempUtil.log");try {log = new PrintWriter(new FileWriter(logFile, true), true);} catch (IOException e) {System.err.println("无法打开日志文件:" + logFile);log = new PrintWriter(System.err);}loadDrivers(dbProps);createPools(dbProps);}/** * 装载和注册所有JDBC驱动程序 * * @param props * 属性 */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("成功注册JDBC驱动程序" + driverClassName);} catch (Exception e) {e.printStackTrace();log("无法注册JDBC驱动程序:" + driverClassName + ", 错误:" + e);}}}/** * 根据指定属性创建连接池实例. * * @param props * 连接池属性 */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("没有为连接池" + poolName + "指定URL");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.trim()).intValue();} catch (NumberFormatException e) {e.printStackTrace();log("错误的最大连接数限制:" + maxconn + ".连接池: " + poolName);max = 0;}DBConnectionPool pool = new DBConnectionPool(poolName, url, user, password, max);pools.put(poolName, pool);log("成功创建连接池" + poolName);}}}/** * 将连接对象返回给由名字指定的连接池 * * @param name * 在属性文件中定义的连接池名字 * @param con * 连接对象 */public void freeConnection(String name, Connection con) {DBConnectionPool pool = (DBConnectionPool) pools.get(name);if (pool != null) {pool.freeConnection(con);}}/** * 获得一个可用的(空闲的)连接.如果没有可用连接,且已有连接数小于最大连接数 限制,则创建并返回新连接 * * @param name * 在属性文件中定义的连接池名字 * @return Connection 可用连接或null */public Connection getConnection(String name) {DBConnectionPool pool = (DBConnectionPool) pools.get(name);if (pool != null) {return pool.getConnection();}return null;}/** * 获得一个可用连接.若没有可用连接,且已有连接数小于最大连接数限制, 则创建并返回新连接.否则,在指定的时间内等待其它线程释放连接. * * @param name * 连接池名字 * @param time * 以毫秒计的等待时间 * @return Connection 可用连接或null */public Connection getConnection(String name, long time) {DBConnectionPool pool = (DBConnectionPool) pools.get(name);if (pool != null) {return pool.getConnection(time);}return null;}/** * 关闭所有连接,撤销驱动程序的注册 */public synchronized void release() {// 等待直到最后一个客户程序调用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("撤销JDBC驱动程序 + driver.getClass().getName()+的注册");} catch (SQLException e) {log(e, "无法撤销下列JDBC驱动程序的注册:" + driver.getClass().getName());}}}/** * 将文本信息写入日志文件 */private void log(String msg) {log.println(new Date() + ":" + msg);}/** * 将文本信息与异常写入日志文件 */private void log(Throwable e, String msg) {log.println(new Date() + ":" + msg);e.printStackTrace(log);}/** * 此内部类定义了一个连接池.它能够根据要求创建新连接,直到预定的最 大连接数为止.在返回连接给客户程序之前,它能够验证连接的有效性. */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;/** * 创建新的连接池 * * @param name * 连接池名字 * @param URL * 数据库的JDBC URL * @param user * 数据库帐号,或 null * @param password * 密码,或 null * @param maxConn * 此连接池允许建立的最大连接数 */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;}/** * 将不再使用的连接返回给连接池 * * @param con * 客户程序释放的连接 */public synchronized void freeConnection(Connection con) {// 将指定连接加入到向量末尾freeConnections.addElement(con);checkedOut--;notifyAll();}/** * 从连接池获得一个可用连接.如没有空闲的连接且当前连接数小于最大连接 数限制,则创建新连接.如原来登记为可用的连接不再有效,则从向量删除之, * 然后递归调用自己以尝试新的可用连接. */public synchronized Connection getConnection() {Connection con = null;if (freeConnections.size() > 0) {// 获取向量中第一个可用连接con = (Connection) freeConnections.firstElement();freeConnections.removeElementAt(0);try {if (con.isClosed()) {log("从连接池" + name + "删除一个无效连接");// 递归调用自己,尝试再次获取可用连接con = getConnection();}} catch (SQLException e) {log("从连接池" + name + "删除一个无效连接");// 递归调用自己,尝试再次获取可用连接con = getConnection();}} else if (maxConn == 0 || checkedOut < maxConn) {con = newConnection();}if (con != null) {checkedOut++;}return con;}/** * 从连接池获取可用连接.可以指定客户程序能够等待的最长时间 参见前一个getConnection()方法. * * @param timeout * 以毫秒计的等待时间限制 */public synchronized Connection getConnection(long timeout) {long startTime = new Date().getTime();Connection con;while ((con = getConnection()) == null) {try {wait(timeout);} catch (InterruptedException e) {}if ((new Date().getTime() - startTime) >= timeout) {// wait()返回的原因是超时return null;}}return con;}/** * 关闭所有连接 */public synchronized void release() {Enumeration allConnections = freeConnections.elements();while (allConnections.hasMoreElements()) {Connection con = (Connection) allConnections.nextElement();try {con.close();log("关闭连接池" + name + "中的一个连接");} catch (SQLException e) {log(e, "无法关闭连接池" + name + "中的连接");}}freeConnections.removeAllElements();}/** * 创建新的连接 */private Connection newConnection() {Connection con = null;try {if (user == null) {con = DriverManager.getConnection(URL);} else {con = DriverManager.getConnection(URL, user, password);}log("连接池" + name + "创建一个新的连接");} catch (SQLException e) {log(e, "无法创建下列URL的连接:" + URL);return null;}return con;}}public static void main(String[] args) {Properties dbProps = new Properties();try {dbProps.load(DBConnectionUtil.class.getResourceAsStream("/db.properties"));} catch (Exception e) {System.err.println("不能读取属性文件." + "请确保db.properties在CLASSPATH指定的路径中");return;}}}

 

db.properties配置文件：

#驱动列表,用空格隔开drivers=com.mysql.jdbc.Driver oracle.jdbc.driver.OracleDriver #日志文件logfile=D://a.txt #idbidb.url=jdbc:idb:c://local//javawebserver1.1//db//db.prp idb.maxconn=2#accessaccess.url=jdbc:cdbc:youmeaccess.user=youmeaccess.password=youme#mysqlmysql.driver=com.mysql.jdbc.Drivermysql.url=jdbc:mysql://127.0.0.1:3306/dbnamemysql.user=youmemysql.password=youme

 

使用：

Connection conn= DBConnectionUtil.getInstance().getConnection("mysql")

 

DBConnectionUtil.getInstance().freeConnection("mysql",localConnection);