single pattern

package curveprj;

import java.sql.*;

public class DBManager {
    private static DBManager instance = null;
    private Connection con=null;

    private DBManager() {
        try {
            jbInit();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public static synchronized DBManager getInstance() {

//这个方法比上面有所改进，不用每次都进行生成对象，只是第一次　　　 　
//使用时生成实例，提高了效率！
    if (instance==null)
      instance=new DBManager();
    return instance;
  }

  public boolean ConnectionDB(String url,String user ,String password){
      if(con ==null){
          try {
          Class.forName("oracle.jdbc.driver.OracleDriver", true,
                        this.getClass().getClassLoader());
      } catch (ClassNotFoundException ex) {
          System.out.println("Could not load the driver");
          ex.printStackTrace() ;
          return false;
      }

      try {
          con = DriverManager.getConnection("jdbc:oracle:thin:@" +  url, user,password);
          //conn = DriverManager.getConnection("jdbc:oracle:thin:@61.167.119.194:1521:shuhui", "shuhuitest","test");
          //stmt=con.createStatement();
        } catch (SQLException ex1) {
          System.out.println("Could not connect the oracle");
          ex1.printStackTrace() ;
          return false;
      }
      }


      return true;

}

  public void CloseDB(){
     try{
         //dbcm.freeConnection(dbname, this.con);
         con.close();
     }
     catch(Exception e){
         System.out.println("con clsoe make errer") ;
         e.printStackTrace();
     }
}


    public static void main(String[] args) {
        DBManager dbmanager = new DBManager();
    }

    public Connection getCon() {
        return con;
    }

    public void setCon(Connection con) {
        this.con = con;
    }

    private void jbInit() throws Exception {
    }
}