Java、mysql错误:Column count doesn't match value count at row 1

Question

所以，这是我的一段代码，它将详细信息输入到名为 vendor_db 的数据库中。(使用 java 和 mysql)我每次都会收到错误，即使代码看起来是正确的。 我已经添加了整个 servlet 代码以供引用。

@WebServlet("/DBHandler")
public class DBHandler extends HttpServlet {
private static final long serialVersionUID = 1L; 
/**
 * @see HttpServlet#HttpServlet()
 */
public DBHandler() {
    super();
}
/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        FormBean f = (FormBean)request.getAttribute("formHandler");
        boolean userExists = false;
        final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        final String DB_URL = "jdbc:mysql://localhost:3306/ioc?autoReconnect=true&useSSL=false";
        final String USER = "root";
        final String PASS = "1234";
        try( Connection conn=DriverManager.getConnection(DB_URL,USER,PASS)){
        Class.forName(JDBC_DRIVER);
        Statement st = conn.createStatement();
        ResultSet rs = st.executeQuery("select vcode from vendor_db");
        while(rs.next()) {
            if(f.getCode().equals(rs.getString(1)))
            {
                userExists=true;
            }
        }   
        if(userExists) {
            f.setErrors("code","Duplicate user: Try a different vendor code");
            getServletConfig().getServletContext().getRequestDispatcher("/forms/retry.jsp").forward(request, response);
        }
        else {
            String sql= "insert into vendor_db(vcode,vname,vmob,vemail,vpass,gst_no)values(?,?,?,?,?,?)";
            try(PreparedStatement prep = conn.prepareStatement(sql)){
            prep.setString(1,f.getCode());
            prep.setString(2,f.getName());
            prep.setString(3,f.getPhone());
            prep.setString(4,f.getEmail());
            prep.setString(5,f.getPass());
            prep.setString(6,f.getGst_no());
            int i = prep.executeUpdate();
            prep.clearParameters();
            if(i!=0) {
                getServletConfig().getServletContext().getRequestDispatcher("/forms/login.jsp").forward(request, response);
                }
                else {
                    pw.println("Not entered in database");
                }
                prep.close();
            }
            catch(Exception e) {
                System.out.println(e);
            }       
        }   
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
}

但是，我不断收到同样的错误:

java.sql.SQLException: Column count doesn't match value count at row 1
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:965)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3976)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3912)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2530)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2683)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2486)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1858)
at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2079)
at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2013)
at com.mysql.jdbc.PreparedStatement.executeLargeUpdate(PreparedStatement.java:5104)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1998)
at DBHandler.doPost(DBHandler.java:56)

基本上是在 executeUpdate() 行中显示错误。请帮忙。谢谢!

Answer 1

由于代码看起来不错，这可能是一个多用户问题。

首先我会检查 DBHandler 的第 56 行确实是 executeUpdate。

DBHandler.doPost(DBHandler.java:56)

不知何故，我对此表示怀疑。可能是部署出错或其他原因。

如果 DBHandler 或其他数据错误地成为 servlet 的字段，则 servlet 不是无状态的，并且两个 doPosts/doGets 可以“共享”同一个字段，覆盖它等等.

这也可能发生，当显示的代码在源代码中被拆分时，并且控制流允许覆盖该字段，比如在 doGet 或服务中。

没有字段。

---

全部代码添加完成后

不幸的是只有小问题:

// Not needed nowadays: Class.forName(JDBC_DRIVER);
try (Connection conn = DriverManager.getConnection(DB_URL,USER,PASS);
        PreparedStatement st = conn.prepareStatement(
                "select vcode from vendor_db where vcode = ?")) {
    st.setString(f.getCode());
    try (ResultSet rs = st.executeQuery()) {
        if (rs.next()) {
            userExists = true;
        }
    }   
    if (userExists) {
        f.setErrors("code",
            "Duplicate user: Try a different vendor code");
        getServletConfig().getServletContext()
            .getRequestDispatcher("/forms/retry.jsp")
            .forward(request, response);
    }
    else {
        String sql= "insert into vendor_db"
            + "(vcode,vname,vmob,vemail,vpass,gst_no)"
            + "values(?,?,?,?,?,?)";
        try (PreparedStatement prep = conn.prepareStatement(sql)) {
            prep.setString(1, f.getCode());
            prep.setString(2, f.getName());
            prep.setString(3, f.getPhone());
            prep.setString(4, f.getEmail());
            prep.setString(5, f.getPass());
            prep.setString(6, f.getGst_no());
            int i = prep.executeUpdate();
            // Not needed here: prep.clearParameters();
            if (i != 0) {
                getServletConfig().getServletContext()
                    .getRequestDispatcher("/forms/login.jsp")
                    .forward(request, response);
            }
            else {
                pw.println("Not entered in database");
            }
        }
    }   
}
catch (Exception e)
{
    log("An error happened", e);
    e.printStackTrace();
}

参见 java.sql.SQLException: Column count doesn't match value count at row 1对于同样的错误。

我的猜测是应用程序没有在网络服务器中重新部署。

at DBHandler.doPost(DBHandler.java:56)

这应该是 int i = prep.executeUpdate();

指向 DBHandler.java 的第 56 行。添加几行空行以判断数字是否发生变化。

6 个问号(没有引号 - 很好)，6 个列名，6 个参数集。