java setString()不起作用

问题描述：

try{is = new FileInputStream(new File(s));
        PreparedStatement ps; 
        ps= cn.prepareStatement("Update instructor set name ='?' ,gender ='?', image ='?' where instructorID =?");
          JOptionPane.showMessageDialog(null, "5");
        ps.setString(1,name);
          JOptionPane.showMessageDialog(null, "4");
            ps.setString(2,gender);
            JOptionPane.showMessageDialog(null, "3");
            ps.setBlob(3, is);
            JOptionPane.showMessageDialog(null, "2");
          ps.setString(4, iden);
          JOptionPane.showMessageDialog(null, "1");
            ps.executeUpdate();
            JOptionPane.showMessageDialog(null, "successfully updated");
        }catch(Exception e ){
            JOptionPane.showMessage(null,"error1");
        }

所以我想将这些变量插入到准备好的语句中，但是却出现了错误.在添加了这些JOptionPanes进行调试之后，程序将显示"5"，然后显示"4"，然后显示"error1".我认为这意味着线 ps.setString(2，gender);执行失败.但是，我找不到在哪里弄错了.有人可以帮忙吗?

So I want to insert these variables to the prepared statement, however I'm getting an error. After adding those JOptionPanes to debug, the program shows "5", and then "4" and then "error1". Which I think means that the line ps.setString(2,gender); failed to execute. However, I cannot find where did I get it wrong. Could anyone help?

答

删除问号周围的引号.否则，'?'将被解释为其中带有单个问号的字符串文字:

Remove quotes around question marks. Otherwise, '?' would be interpreted as a string literal with a single question mark in it:

ps= cn.prepareStatement("Update instructor set name =? ,gender =?, image =? where instructorID =?");

当前，JDBC认为您的查询具有单个参数，该参数对应于末尾的问号.尝试设置第二个参数会导致异常.

Currently, JDBC thinks that your query has a single parameter, corresponding to the question mark at the end. Trying to set parameter number two causes the exception.

java setString()不起作用

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