帮我改一下连接池代码

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帮我把下面的连接池代码改一下，
我想在连接数达到maxConn时，再从连接池获取连接时，就把正在使用的第一个连接（使用最长的那个）拿去用。

package com.aaa.db;


import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;

/**
* 管理类DBConnectionManager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 DBConnectionManager {
static private DBConnectionManager instance; // 唯一实例
static private int clients;

private Vector drivers = new Vector();
private PrintWriter log;
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 DBConnectionManager getInstance() {
if (instance == null) {
instance = new DBConnectionManager();
}
clients++;
return instance;
}

/**
* 建构函数私有以防止其它对象创建本类实例
*/
private DBConnectionManager() {
init();
}

/**
* 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) {
if (con!=null){
try
{
pool.freeConnection(con);
System.out.println("Free Conn:" + con.toString());
System.out.println("Current Free Connection in pool " + name + ":" +
getFrees(name));
System.out.println("Current Inuse Connection in pool " + name + ":" +
getInuses(name));
}catch(NullPointerException ex)
{
System.out.println("UCBBS System Free Conn ERROR!");
}
}
}
}

/**
* 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;
}
/**
* 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);
}

/**
*重至某个连接池
*/
public void resetPool(String name) {
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null) {
pool.release() ;
}
}

/**
*得到现有的空连接数
*/
public int getFrees(String name){
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null) {
return pool.getFrees() ;
}
return -1 ;
}

/**
*得到当前正在使用的连接数
*/
public int getInuses(String name){
DBConnectionPool pool = (DBConnectionPool) pools.get(name);
if (pool != null) {
return pool.getInuses() ;
}
return -1 ;
}

/**
* 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());
}
}
}

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/**
* 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");
int max;
try {
max = Integer.valueOf(maxconn).intValue();
}
catch (NumberFormatException e) {
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,log);
pools.put(poolName, pool);
log("成功创建连接池" + poolName);
}
}
}

/**
* 读取属性完成初始化
*/
private void init() {
InputStream is = getClass().getResourceAsStream("db.properties");
Properties dbProps = new Properties();
try {
dbProps.load(is);
}
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", "DBConnectionManager.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) {
log("无法注册JDBC驱动程序: "+driverClassName + ", 错误: " + e);
}
}
}

}

/**
* 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 PrintWriter log;
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, PrintWriter log) {
this.name = name;
this.URL = URL;
this.user = user;
this.password = password;
this.maxConn = maxConn;
this.log = log ;

new monitorThread(this) ;
}

public int getFrees(){
return freeConnections.size() ;
}
public int getInuses(){
return checkedOut ;
}
public synchronized void checkPool(){
if ( freeConnections.size() > 6 )
{
while ( freeConnections.size() > 6 )
{
Connection con = (Connection) freeConnections.firstElement();
freeConnections.removeElementAt(0);
try {
con.close();
log("监护程序关闭连接池" + name+"中的一个连接");
}
catch (SQLException e) {
log(e, "监护程序无法关闭连接池" + name+"中的连接");
}
}
}
}
/**
* 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) {
try{
con.rollback() ;
}catch(Exception e){
checkedOut -- ;
try{
con.close() ;
}catch(Exception ee){
}
return ;
}

if ( freeConnections.indexOf(con) == -1 )
{
//如果free的con不在freeConnections中
// 将指定连接加入到向量末尾
freeConnections.addElement(con);
checkedOut--;
notifyAll();
}
}

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/**
* 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() {
log("------开始关闭连接池" + name ) ;
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();
checkedOut = 0 ;
log("------结束关闭连接池" + name) ;
}

/**
* 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;
}
/**
* 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) ;
}
}

/**********************************************
*监护程序，每当凌晨1点重启连接池
***********************************************/
class monitorThread extends Thread{
private DBConnectionPool pool ;

//创建线程时即启动自己
public monitorThread(DBConnectionPool pool){
this.pool = pool ;
start() ;
}

public void run(){
System.out.println(new Date() + ": 连接池监护程序启动!") ;
boolean reseted = false ;
while ( true ) {
pool.checkPool() ;
//如果当前时间是凌晨1点到两点之间则重启连接池
Calendar nowTime = Calendar.getInstance() ;
try{
int hour = nowTime.get(Calendar.HOUR_OF_DAY) ;
if ( hour >= 1 && hour < 2 ) {
if ( !reseted ){
pool.release() ;
reseted = true ;
System.out.println(new Date() + ": 连接池监护程序重启连接池!") ;
}
}else{
reseted = false ;
}
}catch(Exception e){
System.out.println("########## pool monitor realse error: " + e.toString() ) ;
}
//线程挂起1分钟
try{
sleep(60000);
}catch(Exception e){
System.out.println("########## pool monitor sleep error: " + e.toString() ) ;
}
}
}
}