从servlet中填写jsp中的文本字段数据答案

【问题标题】：Fill in text field data in jsp from servlet从servlet中填写jsp中的文本字段数据
【发布时间】：2016-10-30 00:49:46
【问题描述】：

我在数据库中有数据，我希望其中的一些文本字段来自数据库。我创建了一个从数据库获取数据的方法。我有一个 open-account.jsp 页面，其中有一个表单，其中名字、姓氏和电子邮件已经从数据库中预填充，因此我使用了 servlet 中的 get 方法。当我尝试将数据从 servlet 发送到 jsp 页面时，该字段为空。我认为它没有将数据从 servlet 传递到 jsp，我不确定。这是我的代码：

数据库类：

public static ArrayList getUsers() 
    {
        ArrayList<Users> userList = new ArrayList<>();

        try
        {
            DBConnection.connectToDB();
            String query = "SELECT * FROM userlogin";

            stmt = DBConnection.conn.prepareStatement(query);
            ResultSet rs = stmt.executeQuery();

            while(rs.next())
            {
                Users user = new Users();
                user.setFirstName(rs.getString("firstname"));
                user.setLastName(rs.getString("lastname"));
                user.setEmail(rs.getString("email"));
                user.setUsername(rs.getString("username"));
                user.setPassword(rs.getString("password"));

                userList.add(user);
            }
        }
        catch(Exception e)
        {
            System.out.println(e);
        }

        return userList;
    }

open-account.jsp

<!DOCTYPE html>
<html>
<head>
    <title>Open Account</title>
</head>
<body>
    <h3>Please fill in the details</h3>

    <form name="openAccount" action="OpenAccount" method="GET">
        <!-- in openaccount servlet, we will get the users info and fill some
        of the forms below for them -->

        First Name: <input type="text" name="firstname" value= <%= request.getAttribute("Users.getFirstName()") %> > <br/><br/>
        Last Name: <input type="text" name="lastname"> <br/><br/>
        Email: <input type="text" name="email">  <br/><br/>

    </form>

    <form name="chooseAccount" action="OpenAccount" method="POST">  
        Select the type of account: 
        <select name="accounttype">
            <option>Checking</option>
            <option>Saving</option>
            <option>Money Market</option>
            <option>Credit Card</option>
        </select> <br/><br/>

        Please check the box if everything above is complete:
        Agree <input type="radio" name="agree" value="Agree">
        Disagree <input type="radio" name="agree" value="Disagree">

        <br/><br/>
        <input type="submit" value="submit" name="Submit">
    </form>
</body>
</html>

OpenAccount 服务

@WebServlet("/OpenAccount")
public class OpenAccount extends HttpServlet 
{
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        ArrayList<Users> userList = DBConnection.getUsers();

        request.setAttribute("Users", userList);
        RequestDispatcher dispatcher = request.getRequestDispatcher("open-account.jsp");
        dispatcher.forward(request, response);

    }

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

    }
}

【问题讨论】：

标签： jsp servlets

【解决方案1】：

为了从request 获取列表，您需要在 jsp 中进行强制转换
在您的 jsp 中，只需要一个 User 实例，而您的代码会传递整个 ArrayList 或 User。

代码 sn-p 只是为了理解您需要做什么来提取所需的信息。

// make sure to import all required class
Object users = request.getAttribute('Users');
if(null != users && users instanceof ArrayList){
   ArrayList<User> userList = (ArrayList<User>)request.getAttribute('Users');
   for(User user: userList){
      out.println(user.getFirstName());
   }
} else {
   out.println("No user records found.");
}

附：使用 jsp 脚本是不好的做法，您可以改用 JSTL。

【讨论】：

【解决方案2】：

让我们看看你的jsp页面。似乎您只想显示用户配置文件而不是用户配置文件列表。所以你应该修改你的代码如下：

数据库类：

public static Users getUsers(String username) 
    {
        Users user = new Users();
        try
        {
            DBConnection.connectToDB();
            String query = "SELECT * FROM userlogin where username=?";

            stmt = DBConnection.conn.prepareStatement(query);
            stmt.setString(1,username);
            ResultSet rs = stmt.executeQuery();

            while(rs.next())
            {
                user.setFirstName(rs.getString("firstname"));
                user.setLastName(rs.getString("lastname"));
                user.setEmail(rs.getString("email"));
                user.setUsername(rs.getString("username"));
                user.setPassword(rs.getString("password"));

            }
        }
        catch(Exception e)
        {
            System.out.println(e);
        }

        return user;
    }

open-account.jsp：

<!DOCTYPE html>
<html>
<head>
    <title>Open Account</title>
</head>
<body>
    <h3>Please fill in the details</h3>

    <form name="chooseAccount" action="OpenAccount" method="POST">  

        <!-- in openaccount servlet, we will get the users info and fill some
        of the forms below for them -->

        First Name: <input type="text" name="firstname" value= <%= request.getAttribute("firstname") %> > <br/><br/>
        Last Name: <input type="text" name="lastname" value= <%= request.getAttribute("lastname") %>> <br/><br/>
        Email: <input type="text" name="email" value= <%= request.getAttribute("email") %>>  <br/><br/>


        Select the type of account: 
        <select name="accounttype">
            <option>Checking</option>
            <option>Saving</option>
            <option>Money Market</option>
            <option>Credit Card</option>
        </select> <br/><br/>

        Please check the box if everything above is complete:
        Agree <input type="radio" name="agree" value="Agree">
        Disagree <input type="radio" name="agree" value="Disagree">

        <br/><br/>
        <input type="submit" value="submit" name="Submit">
    </form>
</body>
</html>

OpenAccount 服务：

package com.javabycode;

import java.io.IOException;
import java.util.ArrayList;

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;

@WebServlet("/OpenAccount")
public class OpenAccount extends HttpServlet 
{
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {        
    Users users = DBConnection.getUsers();

    request.setAttribute("firstname", users.getFirstName());
    request.setAttribute("lastname", users.getLastName());
    request.setAttribute("email", users.getEmail());
    RequestDispatcher dispatcher = request.getRequestDispatcher("open-account.jsp");
    dispatcher.forward(request, response);

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
     // do something
     //System.out.println(request.getAttribute("firstname"));
    }
}

我参考post修改你的例子并在servlet容器上运行它

如果你只是一个初学者我强烈推荐你Servlet 3 tutorial系列

希望对您有所帮助！

【讨论】：