运行Servlet时收到错误消息(第1行:'密码'附近的语法错误.)

Question

我正在使用servlet来使用J2ME,但每当运行这个时都会收到以下错误消息.

错误:

java.sql.SQLException:[Microsoft] [ODBC SQL Server驱动程序] [SQL Server]第1行:'password'附近的语法不正确.)

public class GetNpostServlet extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse res) 
                     throws ServletException, IOException
{
// Same code appears in doPost()
// Shown both places to emphasize that data is received thru
// different means (environment variable vs stream), 
// yet processed the same inside the servlet
String acct = req.getParameter("account"),
        pwd = req.getParameter("password");    

String balance = accountLookup(acct, pwd);

if (balance == null)
{
  res.sendError(HttpServletResponse.SC_BAD_REQUEST, 
 "Unable to locate  account.");            
  return;
}

res.setContentType("text/plain");    
PrintWriter out = res.getWriter();
out.print(balance);
out.close();
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse res) 
                    throws ServletException, IOException
{
// Same code appears in doGet()
// Shown both places to emphasize that data is received thru
// different means (stream vs environment variable), 
// yet processed the same inside the servlet
String acct = req.getParameter("account"),
        pwd = req.getParameter("password");    

String balance = accountLookup(acct, pwd);

if (balance == null)
{
  res.sendError(HttpServletResponse.SC_BAD_REQUEST, 
"Unable to locate account.");            
  return;
}

res.setContentType("text/plain");    
PrintWriter out = res.getWriter();
out.print(balance);
out.close();
}

/*--------------------------------------------------
 * Lookup bank account balance in database
 *-------------------------------------------------*/
private String accountLookup(String acct, String pwd)
{
Connection con = null;
Statement st = null;
StringBuilder msgb = new StringBuilder("");

try
{
  // These will vary depending on your server/database      
  Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");  
  con = DriverManager.getConnection("jdbc:odbc:acctInfo");

  Statement stmt = con.createStatement();
  ResultSet rs = stmt.executeQuery(
                     "Select balance from acctInfo where account = " +
                     acct + "and password = '" + pwd + "'");      

  if (rs.next())
    return rs.getString(1);
  else
    return null;
   }
   catch (Exception e)
   {                  
    return e.toString();
    }
    }

    }

Answer 1

最直接的问题:你没有引用acct字符串,并且后面没有空格,所以你最终会得到类似的东西:

Select balance from acctInfo where account = fredand password = 'bloggs'

更重要的问题:您不应该首先在SQL中包含值.您应该使用参数化SQL.目前,您的代码对SQL注入攻击持开放态度.

进一步的安全问题:您的代码表明密码是以纯文本形式保存的.请不要这样做.

设计问题:

• 您似乎将帐户余额视为字符串.那很奇怪.BigDecimal将是一个更自然的代表.
• 你抓住的Exception不是特定的例外
• 您将返回异常字符串表示,就像它是帐户余额一样.哎呀!你可能实际上只是让SQLException泡泡到调用者
• 您永远不会关闭连接,语句或结果集