运行Servlet时收到错误消息（第1行：“ password”附近的语法不正确。）

Question

I'm making servlet to work with J2ME, but whenever running this one getting below error message.

Error:

java.sql.SQLException: [Microsoft][ODBC SQL Server Driver][SQL Server]Line 1: Incorrect syntax near 'password'.)

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

Most immediate problem: you're not quoting the acct string, and there's no space after it, so you'll end up with something like:

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

More important problem: you shouldn't be including values in your SQL like this in the first place. You should be using parameterized SQL. Currently your code is open to SQL injection attacks .

Further security problem: Your code suggests that the passwords are being held in plain text. Please don't do this.

Design problems:

• You appear to be treating an account balance as a string. That's odd. BigDecimal would be a more natural representation.
• You're catching Exception rather than specific exceptions
• You're returning an exception string representation as if it were an account balance . Yikes! You should probably actually just let SQLException bubble up to the caller
• You're never closing the connection, statement or result set