问数据库无法连接

EN

public static Connection createConnection() {
    Connection conn = null;
    System.out.println("Checking if Driver is registered with DriverManager.");
try{
        Class.forName("org.postgresql.Driver");
} catch (ClassNotFoundException e){
        System.out.println("Couldn't find the driver!");
        System.out.println("exit.");
        System.exit(1);
}
System.out.println("make a connection.");
try{
        conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/ydb_lib", "postgres", "postgres");
        System.out.println("Success.");
} catch(SQLException e){
        System.out.println("Couldn't connect: exit.");
        System.exit(1);
    }
    return conn;
}

      Connection c = Global.createConnection();

      Checking if Driver is registered with DriverManager.
      Couldn't find the driver!
      exit.