一个简单的数据库连接池

public class DBConnectionManager {
  private final static  DBConnectionManager instance=new DBConnectionManager();
  private DBConnectionPool pool;

   public static DBConnectionManager getInstance() {
    return instance;
  }
    public Connection getConnection() throws SQLException{
    return pool.getConnection();
  }
   public void freeConnection(Connection con)  throws SQLException{
    pool.freeConnection(con);

  }
  private DBConnectionManager() {
    init();
  }
  private void init() {
    Configuration cfg=Configuration.getInstance();
    String db_driver=cfg.getValue("DB.DRIVER");
    String db_url=cfg.getValue("DB.URL");
    String db_user=cfg.getValue("DB.USER");
    String db_password=cfg.getValue("DB.PASSWORD");
    int db_maxConn=Integer.parseInt(cfg.getValue("DB.MAX_CONNECTIONS"));
    try {
      Class.forName(db_driver);
    }
    catch (ClassNotFoundException ex) {
      System.out.println(ex);
    }
    pool = new DBConnectionPool(db_url,db_user,db_password,db_maxConn);
  }

 

class DBConnectionPool {

  private Vector freeConnections = new Vector();
  private int maxConn;
  private int connNumb;

  private String URL;
  private String password;
  private String user;

  public DBConnectionPool(String URL, String user, String password,int maxConn) {
        this.URL = URL;
        this.user = user;
        this.password = password;
        this.maxConn = maxConn;
  }

  public synchronized void freeConnection(Connection con) {
        freeConnections.addElement(con);
        connNumb--;
        notifyAll();
  }

    public synchronized Connection getConnection() throws SQLException{
        Connection con = null;
        if (freeConnections.size() > 0) {
            con = (Connection) freeConnections.firstElement();
            freeConnections.removeElementAt(0);
            try {
                if (con.isClosed()) {
                    con = getConnection();
                }
            }
            catch (SQLException e) {
                  con = getConnection();
            }
        }
        else if (maxConn == 0 || connNumb < maxConn) {
            con = newConnection();
        }
        if (con != null) {
            connNumb++;
        }
        return con;
    }

    private Connection newConnection() throws SQLException{
        Connection con =DriverManager.getConnection(URL,user, password);
        return con;
    }
}

 

 

 

public class Configuration {
    private Properties properties;
    private final static Configuration cfg = new Configuration();

    private Configuration() {
        properties = new Properties();
        InputStream is = null;
        try {
            is = getClass().getResourceAsStream("/app.properties");
            properties.load(is);
        } catch (Exception exception) {
          System.out.println("Can't read the properties file. ");
        } finally {
            try {
                if (is != null)
                    is.close();
            } catch (IOException exception) {
                // ignored
            }
        }
    }
        public static Configuration getInstance() {
      return cfg;
    }
        public String getValue(String key) {
        return properties.getProperty(key);
    }
}