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 #idb idb.url=jdbc:idb:c://local//javawebserver1.1//db//db.prp idb.maxconn=2 #access access.url=jdbc:cdbc:youme access.user=youme access.password=youme #mysql mysql.driver=com.mysql.jdbc.Driver mysql.url=jdbc:mysql://127.0.0.1:3306/dbname mysql.user=youme mysql.password=youme

 

使用：

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

 

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