package stumng;import java.sql.*;import java.util.*;/*連接池類.能夠根據要求創建新連接,直到最大連接數為止.*/public class DBConnPool {       //實際使用中的連接數       private int inUse=0;       //空閑連接       private Vector connections = new Vector();       //連接池名       private String poolname;       //數據庫標識       private String dbid;       //驅動程序名       private String drivername;       //數據庫賬號       private String username;       //數據庫密碼       private String passwd;       //最大連接數       private int maxconn;       public DBConnPool(String poolname, String drivername, String dbid, String username, String passwd, int maxconn) {               this.poolname = poolname;               this.dbid = dbid;               this.drivername = drivername;               this.username = username;               this.passwd = passwd;               this.maxconn = maxconn;       }       /*將連接返回給連接池*/       public synchronized void releaseConnection(Connection con) {               // 將指定連接加入到向量末尾               connections.addElement(con);               //連接數減一               inUse--;       }       /*從連接池得到一個連接*/       public synchronized Connection getConnection() {               Connection con = null;               if (connections.size() > 0) {                       // 獲取連接列表中獲得第一個連接                       con = (Connection) connections.elementAt(0);                       connections.removeElementAt(0);                       //如果此連接已關閉，則繼續獲取        try {           if (con.isClosed())              con = getConnection();        }        catch (Exception ex) {           ex.printStackTrace();        }               }               //如果實際使用的連接小于最大連接數，就新創建一個連接               else if (maxconn == 0 || inUse < maxconn) {                       con = newConnection();               }               if (con != null) {                       //連接數增一                       inUse++;               }               //返回一個連接               return con;       }       /*創建新的連接*/       private Connection newConnection() {               Connection con = null;               try {                       //加載驅動程序                       Class.forName(drivername);                       //建立連接                       con = DriverManager.getConnection(dbid, username, passwd);               }               catch (Exception e) {                       e.printStackTrace();                       return null;               }               //返回該連接               return con;       }       /*關閉所有連接*/       public synchronized void closeConn() {               Enumeration allConnections = connections.elements();               while (allConnections.hasMoreElements()) {                       Connection con = (Connection) allConnections.nextElement();                       try {                               con.close();                       }                       catch (SQLException e) {                               e.printStackTrace();                       }               }               connections.removeAllElements();       }}