Question

我是一名初学者，我正在尝试在数据库中显示数据。我有一个控制器servlet，DBhelper，table.jsp和一个索引......

这是控制器servlet

import java.io.IOException;
import java.sql.ResultSet;

import javax.annotation.Resource;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
import demo2.DBhelper;

/**
 * Servlet implementation class servletJsp
 */
@WebServlet("/servletJsp")
public class controller extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Resource(name="")
    private DataSource dataSource;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String page;
        if(request.getParameterMap().containsKey("page")){
            page =request.getParameter("page");
        }else{
            page="index";
        }
        if(page.equals("table")){
            ResultSet rs =new DBhelper().getUsers(dataSource);
            request.getRequestDispatcher("table.jsp").forward(request, response);
            request.setAttribute("users", rs);
    }

}
}

这是DBhelper ..

package demo2;



import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;


import javax.sql.DataSource;

public class DBhelper {

    private ResultSet users =null;

    public ResultSet getUsers(DataSource dataSource) {

        Connection con;
        Statement st;

        try{
        con =dataSource.getConnection();
        st=con.createStatement();

        String query="select * from authorities";
        users= st.executeQuery(query);
        }catch(Exception e){

            e.printStackTrace();
        }
        return users;
    }
}

这是table.jsp

<%@ page import="java.sql.ResultSet" %>
<%
ResultSet rs = (ResultSet)request.getAttribute("users");
while(rs.next()){
    String username = rs.getString("username");
    out.println(username);``
}

%>

我在table.jsp中遇到错误，而行（while.rs.next）

Answer 1

问题在于：

if(page.equals("table")){
    ResultSet rs = new DBhelper().getUsers(dataSource);
    request.getRequestDispatcher("table.jsp").forward(request, response);
    request.setAttribute("users", rs);
}

您正在将流转发到JSP页面，然后设置users属性，因此您的ResultSet rs在您的JSP中为null。将订单更改为

if(page.equals("table")){
    ResultSet rs = new DBhelper().getUsers(dataSource);
    request.setAttribute("users", rs);
    request.getRequestDispatcher("table.jsp").forward(request, response);
}

它应该有效（当然，如果DBhelper.getUsers(...)返回非ResultSet}。

从servlet中显示jsp中的数据

1 个答案: