public class DatabaseUtil {
 private static String driver = ConfigManager.getProperties("driver");//驱动
 private static String url = ConfigManager.getProperties("url");//地址
 private static String user = ConfigManager.getProperties("user");//姓名
 private static String password = ConfigManager.getProperties("password");//密码
 static{
  try {
   Class.forName(driver);
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  }
 }
 public static Connection getConnection() throws SQLException{
  Connection conn=null;
  try {
   //当conn为null或者关闭着的时候就建立连接
   if(conn==null ||conn.isClosed()){
    conn=DriverManager.getConnection(url,user,password);
   }
  } catch (SQLException e) {
   e.printStackTrace();
   throw e;
  }
  return conn;
 }
 /**
  * 关闭数据库连接
  * @param rs 结果集
  * @param st Statement对象
  * @param cn数据库连接
  */
 public static void closeAll(ResultSet rs,Statement st,Connection cn){
  if(rs!=null){
   try {
    rs.close();
   } catch (SQLException e) {
    e.printStackTrace();
   }
  }
  if(st!=null){
   try {
    st.close();
   } catch (SQLException e) {
    e.printStackTrace();
   }
  }
  if(cn!=null){
   try {
    cn.close();
   } catch (SQLException e) {
    e.printStackTrace();
   }
  }
 }
 
}