Question

我正在尝试使用访问数据库查看此页面的示例（Pagination with JSP），但是我收到以下错误：

org.hsqldb.HsqlException：游标状态不正确：指示游标没有位于语句UPDATE，DELETE，SET或GET的行中;查询结果的当前位置在第一个记录之前

我的代码是：

水果类

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 *
 * @author Daniel
 */
public class Fruta {
    private String fruta, color, sabor;

    public Fruta() throws ClassNotFoundException, SQLException{
        fruta = "";
        color = "";
        sabor = "";
    }

/**
 * @return the fruta
 */
public String getFruta() {
    return fruta;
}

/**
 * @param fruta the fruta to set
 */
public void setFruta(String fruta) {
    this.fruta = fruta;
}

/**
 * @return the color
 */
public String getColor() {
    return color;
}

/**
 * @param color the color to set
 */
public void setColor(String color) {
    this.color = color;
}

/**
 * @return the sabor
 */
public String getSabor() {
    return sabor;
}

/**
 * @param sabor the sabor to set
 */
public void setSabor(String sabor) {
    this.sabor = sabor;
}

}

FruitDAO

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

/**
 *
 * @author Daniel
 */
public class FrutaDAO {
    Connection connection;
    Statement stmt;
    private int noRecords;

    public FrutaDAO(){}

    private static Connection getConnection()
            throws SQLException,
                ClassNotFoundException
    {
        Connection con = Conexion.getConnection();
        return con;
    }

    public List<Fruta> verFrutas(
                int offset,
                int noOfRecords)
    {
        String query = "SELECT * FROM Frutas LIMIT "
                 + offset + ", " + noOfRecords;
        List<Fruta> list = new ArrayList<Fruta>();
        Fruta fruta = null;
        try {
            connection = getConnection();
            stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery(query);
            if(rs.next()){
            while (rs.next()) {
                fruta = new Fruta();
                fruta.setFruta(rs.getString("Fruta"));
                fruta.setFruta(rs.getString("Color"));
                fruta.setFruta(rs.getString("Sabor"));
                list.add(fruta);
            }
            }
            rs.close();

            rs = stmt.executeQuery("SELECT COUNT(*) FROM Frutas");
            if(rs.next())
                this.noRecords = rs.getInt(1);
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }finally
        {
            try {
                if(stmt != null)
                    stmt.close();
                if(connection != null)
                    connection.close();
                } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return list;
    }

    public int getNoOfRecords() {
        return noRecords;
    }
}

FruitServlet

import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *
 * @author Daniel
 */
@WebServlet(name = "FrutaServlet", urlPatterns = {"/FrutaServlet"})
public class FrutaServlet extends HttpServlet {


      public FrutaServlet() {super();}

    @Override
    public void doGet(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException, IOException {
        int page = 1;
        int recordsPerPage = 5;
        if(request.getParameter("page") != null)
            page = Integer.parseInt(request.getParameter("page"));
        FrutaDAO dao = new FrutaDAO();
        List<Fruta> list = dao.verFrutas((page-1)*recordsPerPage,
                                 recordsPerPage);
        int noOfRecords = dao.getNoOfRecords();
        int noOfPages = (int) Math.ceil(noOfRecords * 1.0 / recordsPerPage);
        request.setAttribute("listaFruta", list);
        request.setAttribute("noOfPages", noOfPages);
        request.setAttribute("currentPage", page);
        RequestDispatcher view = request.getRequestDispatcher("index.jsp");
        view.forward(request, response);
    }

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet FrutaServlet</title>");            
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet FrutaServlet at " + request.getContextPath() + "</h1>");
            out.println("</body>");
            out.println("</html>");
        }
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}

我已经在使用 rs.next（）了，这里发生了什么？

Answer 1

我不确定这是否可以解决，但您不应该对同一查询使用while(rs.next())和//if(rs.next()){ //remove this check while (rs.next()) { fruta = new Fruta(); fruta.setFruta(rs.getString("Fruta")); fruta.setFruta(rs.getString("Color")); fruta.setFruta(rs.getString("Sabor")); list.add(fruta); } //} rs.close();，请尝试修改 FruitDAO 的代码如下所示：

#include <iostream>
#include <random>
using namespace std;

int main()
{

    random_device rd; //seed generator
    mt19937_64 generator{rd()}; //generator initialized with seed from rd
    uniform_int_distribution<> dist{1, 6};

    for(int i = 0; i < 15; i++)
    {

        int random = dist(generator);

        cout << random << endl;

    }

}

org.hsqldb.HsqlException：游标状态不正确（JSP / Access）

1 个答案: