很低级的问题，记住close！！
try {
Class.forName(className);
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
return false;
}
// 取数据
try {
conn= DriverManager.getConnection(url,username,password);
try {
stmt = conn.createStatement();
try {
rs = stmt.executeQuery(sql);
setBossData(rs);//数据封装
System.out.print("取数据成功\n");
}catch (SQLException e) {
e.printStackTrace();
return false;
}finally{
rs.close();
}
} finally {
stmt.close();
}
} catch(SQLException e) {
e.printStackTrace();
return false;
} finally {
conn.close();
}
