如何在 servlet 中获取选定单选按钮的值并将其存储在 DB 中？

Question

我正在开发一个投票应用程序，人们可以在其中为特定选项投票并提交。现在，我希望用户在 servlet 中选择的选项并将其作为投票存储在数据库中。当收到新的投票时，该计数应始终增加 1。但是，它没有给我想要的输出。每次当我选择一个选项并单击提交时，1 都会像投票一样插入到数据库的相应列中。我已将选项命名为 db 中的列名。我希望每一个新投票都是对其先前价值的补充

下面是 Voting.jsp 页面：-

<div class="card" style="width: 60rem; margin-left: 45px;">
  <div class="card-body">
  Click on one of the following options to caste your vote. Then click submit.

  </div>
  </div>


<div class="card" style="width: 60rem; margin-left: 45px;">
  <div class="card-body">
  <form action="SuccessServlet" method="post">
    <label class="container">Team_1
  <input type="radio" name="radio" value="team1">
  <span class="checkmark"></span>
</label>
<label class="container">Team_2
  <input type="radio" name="radio" value="team2">
  <span class="checkmark"></span>
</label>
<label class="container">Team_3
  <input type="radio" name="radio" value="team3">
  <span class="checkmark"></span>
</label>
<label class="container">Team_4
  <input type="radio" name="radio" value="team4">
  <span class="checkmark"></span>
</label>
<button type="submit">Submit</button>
</form>
  </div>
</div>

以下是我的 Servlet 类：-

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



        ud.setFirst_name(request.getParameter("f1"));



        String answer = request.getParameter("radio");

        if("team1".equals(answer)) {

            System.out.println("Hello");

            writeData1();

            }

    else if ("team2".equals(answer)) {

        writeData2();

    }

    else if ("team3".equals(answer)) {

        writeData3();
    }

    else if ("team4".equals(answer)) {

        writeData4();
    }

    else {
        response.sendRedirect("Success.jsp");
    }
    response.sendRedirect("UserPage.jsp");

}



    }


      public void writeData1() {

      try {
        Class.forName("com.mysql.cj.jdbc.Driver");


      Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/my_db?autoReconnect=true&useSSL=FALSE", "root", "root");


      String query = "insert into Total_Votes(Team1) values(?)";

      PreparedStatement ps = con.prepareStatement(query);

      ps.setInt(1, 1);

      ps.executeUpdate();


      } catch (Exception e) {
            // TODO Auto-generated catch block
            System.out.println(e.getMessage());
        }





  }





public void writeData2() {

      try {
        Class.forName("com.mysql.cj.jdbc.Driver");


      Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/my_db?autoReconnect=true&useSSL=FALSE", "root", "root");


      String query = "insert into Total_Votes(Team2) values(?)";

      PreparedStatement ps = con.prepareStatement(query);

      ps.setInt(1, 1);

      ps.executeUpdate();


      } catch (Exception e) {
            // TODO Auto-generated catch block
            System.out.println(e.getMessage());
        }





  }





public void writeData3() {

      try {
        Class.forName("com.mysql.cj.jdbc.Driver");


      Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/my_db?autoReconnect=true&useSSL=FALSE", "root", "root");


      String query = "insert into Total_Votes(Team3) values(?)";

      PreparedStatement ps = con.prepareStatement(query);

      ps.setInt(1, 1);

      ps.executeUpdate();


      } catch (Exception e) {
            // TODO Auto-generated catch block
            System.out.println(e.getMessage());
        }





  }




public void writeData4() {

      try {
        Class.forName("com.mysql.cj.jdbc.Driver");


      Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/my_db?autoReconnect=true&useSSL=FALSE", "root", "root");


      String query = "insert into Total_Votes(Team4) values(?)";

      PreparedStatement ps = con.prepareStatement(query);

      ps.setInt(1, 1);

      ps.executeUpdate();


      } catch (Exception e) {
            // TODO Auto-generated catch block
            System.out.println(e.getMessage());
        }





  }

Answer 1

您的代码始终将 1 作为指定团队的总票数。如果您在需要知道总数时使用 SQL 中的SUM() 函数来汇总团队的投票数，那很好。

还有另外两种处理方法：

1. 每个团队的数据库中只有一条记录。每次投票时，读取当前值（如果找不到当前值，则假定为 0），递增它，然后用新值更新记录。

2. 继续为每次投票插入一条记录。每次投票时，读取当前的 MAX() 值（如果找不到当前值，则假定为 0），将其递增并INSERT使用新值创建另一条记录。

Answer 2

假设team1 单选按钮被选中，现在您需要使用select 查询来获取team1 先前投票的值，如下所示：

   try {
            Class.forName("com.mysql.cj.jdbc.Driver");
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/my_db?autoReconnect=true&useSSL=FALSE", "root", "root");
    String sql="select votes from Total_Votes where team=?";
                     int votes=0;
                    PreparedStatement ps = con.prepareStatement(sql);
                   ps.setString(1,"team1");//passing team1 in query
                   rs = ps.executeQuery();
                    while(rs.next())
                   {
          votes=rs.getInt("yourcoulmnname");//getting value of coulmn where votes are stored for team1
                  }
                   }catch(Exception e)
                   {
                   System.out.println(e.getMessage());
                   }

现在，使用update 查询更新投票，如下所示：

String sql1 = "UPDATE `Total_Votes` SET `yourcoulumnname`=? WHERE `team`=?";
             PreparedStatement ps = con.prepareStatement(sql1);
            int v=votes+1;//votes got from previous select query add by 1 
             ps.setInt(1,v);
             ps.setString(2,"team1");

             int i=0;
              i = ps.executeUpdate();

         if(i>0){
             System.out.println("updated");
           }

希望对您有所帮助！