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mysql - 进行第二次选择时无法输出结果

问题描述

我一直在尝试在“第一个”尝试捕获方法上选择打印机类型以输出“第二个”尝试捕获方法，但即使我选择了“第一个”打印机选择，它也根本没有显示结果。

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@page import = "java.sql.*"%> 
  <!DOCTYPE html>
  <html>
    <head>
      <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
      <title>JSP Page</title>
    </head>
  <body>

  <%
    try{
      Class.forName("com.mysql.jdbc.Driver").newInstance();
      Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/xxx?serverTimezone=Singapore","xxx", "xxx");
      String SQLQuery = "SELECT * FROM testprinter";
      Statement STM = conn.createStatement();
      ResultSet RS = STM.executeQuery(SQLQuery);
  %>
  <P>Printer: 
  <select name = "testprinter1" id = "testprinter1" onchange="this.form.submit();">
      <option value = "0">Select Printer</option>
  <% while(RS.next()){ %>
      <option value = "<%=RS.getInt("PID")%>"
      <%
        if(request.getParameter("testprinter1") != null){
          if(RS.getInt("PID") == Integer.parseInt(request.getParameter("testprinter1"))){
            out.print("selected");
          }
        }
      %>        
      > 
        <%=RS.getString("Brand")%>
      </option>            
  <%  }
    } catch (Exception e1) {
      e1.printStackTrace();
    }
  %>
  </select>
  </P>

  <table class = "table table-bordered table-striped">
    <tr>
      <th>A</th>
      <th>B</th>
      <th>C</th>
      <th>D</th>
      <th>E</th>
    </tr>
    <%
      try{
        String Query = "SELECT a, b, c, d, e FROM testprinter2 WHERE PID = ?";
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/xxx?serverTimezone=Singapore","xxx", "xxx");
        PreparedStatement PS = con.prepareStatement(Query);
        PS.setString(1, request.getParameter("testprinter1"));

        ResultSet rs = PS.executeQuery();

        while(rs.next()){
    %>
    <tr>
      <td><%= rs.getString("a")%></td>
      <td><%= rs.getString("b") %></td>
      <td><%= rs.getString("c") %></td>
      <td><%= rs.getString("d") %></td>
      <td><%= rs.getString("e") %></td>
    <tr>
    <%
        }
      } catch (Exception e2) {
        e2.printStackTrace();
      }
    %>

    </body>
  </html>

结果的预期输出：

Printer : "user select the printer" 

Table: 
  A | B | C | D | E
  a | b | c | d | e

实际结果 ：

Printer : "user select the printer"

table : "empty blank"

标签： mysqljsp

解决方案

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