菜鸟求可用的数据库连接池实例
网上找的DBConnectionManager 连接池在JSP页面中调用总出错。高手们给个数据连接池实例及页面调用方法。谢谢
[解决办法]
用tomcat admin控制台建数据库连接迟，肯定没问题
[解决办法]
自己写吧
[解决办法]
package database;
import java.sql.*;
import sun.io.*;
public class sqlbean {
private Connection con;
private ResultSet rs;
public static Connection getConnection()throws SQLException{
try{
Class.forName( "com.microsoft.jdbc.sqlserver.SQLServerDriver ");
}catch(ClassNotFoundException ex)
{
ex.printStackTrace();
return null;
}
return DriverManager.getConnection( "jdbc:microsoft:sqlserver://127.0.0.1:1433;DatabaseName=test ", "sa ", "sa ");
}
public ResultSet executeQuery(String sql){
try{
con=sqlbean.getConnection();
Statement statement=con.createStatement();
rs=statement.executeQuery(sql);
}
catch(SQLException ex)
{
System.out.print( "error ");
}
return rs;
}
public int executeUpdate(String sql)
{
int count=0;
Statement stmt=null;
try{
con=sqlbean.getConnection();
stmt=con.createStatement();
count=stmt.executeUpdate(sql);
}
catch(SQLException ex)
{
}
finally{
try{
if(stmt!=null)
stmt.close();
if(con!=null)
con.close();
}
catch(SQLException ex)
{
System.out.print(ex);
}
}
return count;
}
public void freeRs(ResultSet rs)
{
try
{
if(rs!=null)
{
rs.close();
con.close();
}
}
catch(Exception e)
{
}
}
}
[解决办法]
看到很多人要数据库连接池，这里贴一个不需要配置tomcat的方案，方案中采用了Singleton模式要注意。
1.通用类ConnectionPool
package yourapplication.utility.db;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Vector;
public class ConnectionPool implements Runnable {
private String driver, url, username, password;
private int maxConnections ;
private boolean waitIfBusy;
private Vector availableConnections, busyConnections;
private boolean connectionPending = false;
public ConnectionPool(String driver, String url,
String username, String password,
int initialConnections,
int maxConnections,
boolean waitIfBusy)
throws SQLException {
this.driver = driver;
this.url = url;
this.username = username;
this.password = password;
this.maxConnections = maxConnections;
this.waitIfBusy = waitIfBusy;
if (initialConnections > maxConnections) {
initialConnections = maxConnections;
}
availableConnections = new Vector(initialConnections);
busyConnections = new Vector();
for(int i=0; i <initialConnections; i++) {
availableConnections.addElement(makeNewConnection());
}
}
public synchronized Connection getConnection()
throws SQLException {
if (!availableConnections.isEmpty()) {
Connection existingConnection =
(Connection)availableConnections.lastElement();
int lastIndex = availableConnections.size() - 1;
availableConnections.removeElementAt(lastIndex);
// If connection on available list is closed (e.g.,
// it timed out), then remove it from available list
// and repeat the process of obtaining a connection.
// Also wake up threads that were waiting for a
// connection because maxConnection limit was reached.
if (existingConnection.isClosed()) {
notifyAll(); // Freed up a spot for anybody waiting
return(getConnection());
} else {
busyConnections.addElement(existingConnection);
return(existingConnection);
}
} else {
// Three possible cases:
// 1) You haven 't reached maxConnections limit. So
// establish one in the background if there isn 't
// already one pending, then wait for
// the next available connection (whether or not
// it was the newly established one).
// 2) You reached maxConnections limit and waitIfBusy
// flag is false. Throw SQLException in such a case.
// 3) You reached maxConnections limit and waitIfBusy
// flag is true. Then do the same thing as in second
// part of step 1: wait for next available connection.
if ((totalConnections() < maxConnections) &&
!connectionPending) {
makeBackgroundConnection();
} else if (!waitIfBusy) {
throw new SQLException( "Connection limit reached ");
}
// Wait for either a new connection to be established
// (if you called makeBackgroundConnection) or for
// an existing connection to be freed up.
try {
wait();
} catch(InterruptedException ie) {}
// Someone freed up a connection, so try again.
return(getConnection());
}
}
// You can 't just make a new connection in the foreground
// when none are available, since this can take several
// seconds with a slow network connection. Instead,
// start a thread that establishes a new connection,
// then wait. You get woken up either when the new connection
// is established or if someone finishes with an existing
// connection.
private void makeBackgroundConnection() {
connectionPending = true;
try {
Thread connectThread = new Thread(this);
connectThread.start();
} catch(OutOfMemoryError oome) {
// Give up on new connection
}
}
public void run() {
try {
Connection connection = makeNewConnection();
synchronized(this) {
availableConnections.addElement(connection);
connectionPending = false;
notifyAll();
}
} catch(Exception e) { // SQLException or OutOfMemory
// Give up on new connection and wait for existing one
// to free up.
}
}
// This explicitly makes a new connection. Called in
// the foreground when initializing the ConnectionPool,
// and called in the background when running.
private Connection makeNewConnection()
throws SQLException {
try {
// Load database driver if not already loaded
Class.forName(driver);
// Establish network connection to database
Connection connection =
DriverManager.getConnection(url, username, password);
return(connection);
} catch(ClassNotFoundException cnfe) {
// Simplify try/catch blocks of people using this by
// throwing only one exception type.
throw new SQLException( "Can 't find class for driver: " +
driver);
}
}
public synchronized void free(Connection connection) {
busyConnections.removeElement(connection);
availableConnections.addElement(connection);
// Wake up threads that are waiting for a connection
notifyAll();
}
public synchronized int totalConnections() {
return(availableConnections.size() +
busyConnections.size());
}
/** Close all the connections. Use with caution:
* be sure no connections are in use before
* calling. Note that you are not <I> required </I> to
* call this when done with a ConnectionPool, since
* connections are guaranteed to be closed when
* garbage collected. But this method gives more control
* regarding when the connections are closed.
*/
public synchronized void closeAllConnections() {
closeConnections(availableConnections);
availableConnections = new Vector();
closeConnections(busyConnections);
busyConnections = new Vector();
}
private void closeConnections(Vector connections) {
try {
for(int i=0; i <connections.size(); i++) {
Connection connection =
(Connection)connections.elementAt(i);
if (!connection.isClosed()) {
connection.close();
}
}
} catch(SQLException sqle) {
// Ignore errors; garbage collect anyhow
}
}
public synchronized String toString() {
String info =
"ConnectionPool( " + url + ", " + username + ") " +
", available= " + availableConnections.size() +
", busy= " + busyConnections.size() +
", max= " + maxConnections;
return(info);
}
}
2.单键类
package yourapplication.utility.db;
import java.sql.SQLException;
public class BookConnPool extends ConnectionPool {
private static BookConnPool pool = null;
private BookConnPool(String driver, String url, String username,
String password, int initialConnections, int maxConnections,
boolean waitIfBusy) throws SQLException {
super(driver, url, username,
password, initialConnections, maxConnections,
waitIfBusy); // Call parent constructor
}
public static synchronized BookConnPool getInstance() throws SQLException {
if (pool == null) {
//这里从配置文件中读取相应的参数
String driver = " "; //这里填你的数据库驱动
String url = " ";//这里填db相应的url包含端口和服务名
String usrname = " ";
String passwd = " ";
pool = new BookConnPool(driver, url,usrname, passwd, 100,1000,true);
}
return (pool);
}
}
