正在装载数据……
作用:
在数据库存取中,数据库连接池是不可缺少的,它可以提高连接利用率
减少连接等待,对于提高数据存储性能会有不小的作用.
原理:
连接池相当于连接的集合,在连接池初始化时先实例化一定数量的空闲连接
等待用户使用,用户使用完连接再将其返回连接池,这样就免去了最耗时的
创建连接的开销在没有空闲连接的情况下,连接池将自动生成连接再分配给
用户请求.
实例:
package shop.DbPool;
/*
我的数据库连接池
***********模块说明**************
getInstance()返回POOL唯一实例,第一次调用时将执行构造函数
构造函数Pool()调用驱动装载loadDrivers()函数;连接池创建createPool()函数
loadDrivers()装载驱动
createPool()建连接池
getConnection()返回一个连接实例
getConnection(long time)添加时间限制
freeConnection(Connection con)将con连接实例返回到连接池
getnum()返回空闲连接数
getnumActive()返回当前使用的连接数
*/
import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;
public class Pool {
static private Pool instance = null; //定义唯一实例
private int maxConnect = 100;//最大连接数
private int normalConnect = 10;//保持连接数
private String password = "";//密码
private String url = "jdbc:mysql://localhost/shop";//连接URL
private String user = "root";//用户名
private String driverName = "com.mysql.jdbc.Driver";//驱动类
Driver driver = null;//驱动变量
DBConnectionPool pool = null;//连接池实例变量
//返回唯一实例
static synchronized public Pool getInstance() {
if (instance == null) {
instance = new Pool();
}
return instance;
}
//将构造函数私有,不允许外界访问
private Pool() {
loadDrivers(driverName);
createPool();
}
//装载和注册所有JDBC驱动程序
private void loadDrivers(String dri) {
String driverClassName = dri;
try {
driver = (Driver) Class.forName(driverClassName).newInstance();
DriverManager.registerDriver(driver);
System.out.println("成功注册JDBC驱动程序" + driverClassName);
}
catch (Exception e) {
System.out.println("无法注册JDBC驱动程序:" + driverClassName + ",错误:" + e);
}
}
//创建连接池
private void createPool() {
pool = new DBConnectionPool(password, url, user, normalConnect, maxConnect);
if (pool != null) {
System.out.println("创建连接池成功");
}
else {
System.out.println("创建连接池失败");
}
}
//获得一个可用的连接,如果没有则创建一个连接,且小于最大连接限制
public Connection getConnection() {
if (pool != null) {
return pool.getConnection();
}
return null;
}
//获得一个连接,有时间限制
public Connection getConnection(long time) {
if (pool != null) {
return pool.getConnection(time);
}
return null;
}
//将连接对象返回给连接池
public void freeConnection(Connection con) {
if (pool != null) {
pool.freeConnection(con);
}
}
//返回当前空闲连接数
public int getnum()
{
return pool.getnum();
}
//返回当前连接数
public int getnumActive()
{
return pool.getnumActive();
}
//关闭所有连接,撤销驱动注册
public synchronized void release() {
///关闭连接
pool.release();
///撤销驱动
try {
DriverManager.deregisterDriver(driver);
System.out.println("撤销JDBC驱动程序 " + driver.getClass().getName());
}
catch (SQLException e) {
System.out.println("无法撤销JDBC驱动程序的注册:" + driver.getClass().getName());
}
}
}
数据池文件
DBConnectionPool.java
package shop.DbPool;
import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;
public class DBConnectionPool {
private int checkedOut;
private Vector freeConnections = new Vector();
private int maxConn;
private int normalConn;
private String password;
private String url;
private String user;
private static int num=0;//空闲的连接数
private static int numActive=0;//当前的连接数
public DBConnectionPool(String password, String url, String user,
int normalConn, int maxConn) {
this.password = password;
this.url = url;
this.user = user;
this.maxConn = maxConn;
this.normalConn = normalConn;
for (int i = 0; i < normalConn; i++) { //初始normalConn个连接
Connection c = newConnection();
if (c != null)
{freeConnections.addElement(c);num++;}
}
}
//释放不用的连接到连接池
public synchronized void freeConnection(Connection con) {
freeConnections.addElement(con);
num++;
checkedOut--;
numActive--;
notifyAll();
}
//获取一个可用连接
public synchronized Connection getConnection() {
Connection con = null;
if (freeConnections.size() > 0) { //还有空闲的连接
num--;
con = (Connection) freeConnections.firstElement();
freeConnections.removeElementAt(0);
try {
if (con.isClosed()) {
System.out.println("从连接池删除一个无效连接");
con = getConnection();
}
}
catch (SQLException e) {
System.out.println("从连接池删除一个无效连接");
con = getConnection();
}
}
else if (maxConn == 0 || checkedOut < maxConn) { //没有空闲连接且当前连接小于最大允许值,最大值为0则不限制
con = newConnection();
}
if (con != null) { //当前连接数加1
checkedOut++;
}
numActive++;
return con;
}
//获取一个连接,并加上等待时间限制,时间为毫秒
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) {
return null; //超时返回
}
}
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();
num--;
}
catch (SQLException e) {
System.out.println("无法关闭连接池中的连接");
}
}
freeConnections.removeAllElements();
numActive=0;
}
//创建一个新连接
private Connection newConnection() {
Connection con = null;
try {
if (user == null) { //用户,密码都为空
con = DriverManager.getConnection(url);
}
else {
con = DriverManager.getConnection(url, user, password);
}
System.out.println("连接池创建一个新的连接");
}
catch (SQLException e) {
System.out.println("无法创建这个URL的连接" + url);
return null;
}
return con;
}
//返回当前空闲连接数
public int getnum()
{
return num;
}
//返回当前连接数
public int getnumActive()
{
return numActive;
}
}
本文来源：http://blog.csdn.net/lanbingg/archive/2007/09/09/1778062.aspx
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