mysql-[jbdc]打开connection空指针异常

public static void main(String args[]) throws ClassNotFoundException{ Connection conn = null; Statement stmt = null; try{ //注册 JDBC driver Class.forName("com.mysql.jdbc.Driver"); //打开 a connection System.out.println("Connecting to database.."); stmt = conn.createStatement(); String sql; sql= "SELECT s_no FROM student"; ResultSet rs = stmt.executeQuery(sql); //插入数据 while(rs.next()) { int no = rs.getInt("s_no"); String name = rs.getString("s_name"); System.out.println("NO"+no); System.out.println("Name"+name); } rs.close(); stmt.close(); conn.close(); } catch(SQLException se){ se.printStackTrace(); } finally{ try{ if(stmt!=null) stmt.close(); } catch(SQLException se2){ } try{ if(conn!=null) conn.close(); } catch(SQLException se){ se.printStackTrace(); } }}