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我如何将字符串数组从servlet发送到jsp并在jsp中接收它

发布于 2024-11-05 02:10:50 字数 6765 浏览 0 评论 0原文

我的 Servlet 代码是

package DBCon;

import java.io.*;
import java.net.*;
import java.util.ArrayList;

import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
/**
 *
 * @author Nayan
 */
public class loadCourseId extends HttpServlet {

    /** 
    * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
    * @param request servlet request
    * @param response servlet response
    */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        ArrayList ar1=new ArrayList();
        ArrayList ar2=new ArrayList();
        int i;
        i=0;

        try
        {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            Connection con=DriverManager.getConnection("jdbc:mysql://localhost/online_exam?"+"user=root&password=pass");
            Statement stmt=con.createStatement();
            ResultSet rs=stmt.executeQuery("select * from course");

            while(rs.next())
            {
                ar1.add(rs.getString(1));
                ar2.add(rs.getString(2));
            }
            request.getSession().setAttribute("CourseID", ar1);
            request.getSession().setAttribute("CourseName", ar2);
            RequestDispatcher requestDispatcher=getServletContext().getRequestDispatcher("http://localhost:8080/ONLINE_EXAM/removeCourse.jsp");
            requestDispatcher.forward(request,response);


        }
         catch(Exception e) { 
            out.println("<h1>"+e.getStackTrace()+"</h1>");
        }
    } 

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
    * Handles the HTTP <code>GET</code> method.
    * @param request servlet request
    * @param response servlet response
    */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    } 

    /** 
    * Handles the HTTP <code>POST</code> method.
    * @param request servlet request
    * @param response servlet response
    */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

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

Jsp 代码是

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">
<%@page import="javax.servlet.*"%>
<%@ page import="java.util.ArrayList.*" %>
<%@ page import="java.sql.*;" %>

<html>
    <head>
        <script type="text/javascript" language="Javascript" >
            window.onload=function LoadCombo()
            {

               window.action="loadCourseId.do";
               ArrayList cd=new ArrayList();
               cd.add(request.getSession().getAttribute("CourseID"));
               if(cd.isEmpty()==false)
               {
                   for(int i=0;i<cd.size();i++)
                   {
                       var newOpt = cid.appendChild(document.createElement('option'));
                       newOpt.text = cd.get(i);

                   }
               }
               else
               {
                   alert("Course table is empty")
               }

            }

        </script>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Remove Course</title>
<style type="text/css">
            <!--
body {
    background-color: #FFCCFF;
}
.style1 {
    color: #0066FF;
    font-weight: bold;
}
.style2 {font-size: 18px}
.style17 {  font-family: "Monotype Corsiva";
    font-size: 24px;
    font-weight: bold;
    font-style: italic;
    color: #6633CC;
}
.style19 {color: #000099}
.style21 {color: #000099; font-weight: bold; }
-->
        </style>
    </head>
    <body>
        <jsp:include page="Log_Admin.jsp"/><br/>
        <form action="" method="post" name="form1" id="form1" >
        <table width="46%" height="43" border="3" bgcolor="##CCCC99" align="center">
            <tr>
                <td width="85%" align="center" bgcolor="##CCCC99"><label><span class="style17">Course Information</span></label></td>
            </tr>

            <tr><td>
                <table width="666" height="207" border="0" align="center" bordercolor="#F0F0F0" bgcolor="#CCCC99" >
                    <tr>
                        <td width="186" height="46" align="left"><div align="left"><span class="style19">
                        <label><strong>Course ID</strong></label>
                        </span></div></td>

                        <td><label>
                        <select name="cid" size="1" id="cid" align="left">


                        </select>
                        </label></td>
                    </tr>
                    <tr>
                        <td height="53" align="left"><div align="left"><label><span class="style21">Course Name</span></label></div></td>
                        <td align="left"><input name="cname" type="text" id="cname" size="50" maxlength="50" /></td>
                    </tr>

                    <tr>
                        <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td>
                        <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<input name="save" type="submit" id="save" value="Save" />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
                        <input name="reset" type="reset" id="reset" value="Reset" /></td>
                    </tr>
                </table>
            </td></tr>
        </table>
    </form>
    </body>
</html>

Bt 通过编写此代码，我无法将项目 CourseId 添加到组合框 cid 中。你能告诉我问题出在哪里吗？谢谢。

原文

My Servlet Code is

package DBCon;

import java.io.*;
import java.net.*;
import java.util.ArrayList;

import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
/**
 *
 * @author Nayan
 */
public class loadCourseId extends HttpServlet {

    /** 
    * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
    * @param request servlet request
    * @param response servlet response
    */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        ArrayList ar1=new ArrayList();
        ArrayList ar2=new ArrayList();
        int i;
        i=0;

        try
        {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            Connection con=DriverManager.getConnection("jdbc:mysql://localhost/online_exam?"+"user=root&password=pass");
            Statement stmt=con.createStatement();
            ResultSet rs=stmt.executeQuery("select * from course");

            while(rs.next())
            {
                ar1.add(rs.getString(1));
                ar2.add(rs.getString(2));
            }
            request.getSession().setAttribute("CourseID", ar1);
            request.getSession().setAttribute("CourseName", ar2);
            RequestDispatcher requestDispatcher=getServletContext().getRequestDispatcher("http://localhost:8080/ONLINE_EXAM/removeCourse.jsp");
            requestDispatcher.forward(request,response);


        }
         catch(Exception e) { 
            out.println("<h1>"+e.getStackTrace()+"</h1>");
        }
    } 

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
    * Handles the HTTP <code>GET</code> method.
    * @param request servlet request
    * @param response servlet response
    */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    } 

    /** 
    * Handles the HTTP <code>POST</code> method.
    * @param request servlet request
    * @param response servlet response
    */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

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

And Jsp Code is

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">
<%@page import="javax.servlet.*"%>
<%@ page import="java.util.ArrayList.*" %>
<%@ page import="java.sql.*;" %>

<html>
    <head>
        <script type="text/javascript" language="Javascript" >
            window.onload=function LoadCombo()
            {

               window.action="loadCourseId.do";
               ArrayList cd=new ArrayList();
               cd.add(request.getSession().getAttribute("CourseID"));
               if(cd.isEmpty()==false)
               {
                   for(int i=0;i<cd.size();i++)
                   {
                       var newOpt = cid.appendChild(document.createElement('option'));
                       newOpt.text = cd.get(i);

                   }
               }
               else
               {
                   alert("Course table is empty")
               }

            }

        </script>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Remove Course</title>
<style type="text/css">
            <!--
body {
    background-color: #FFCCFF;
}
.style1 {
    color: #0066FF;
    font-weight: bold;
}
.style2 {font-size: 18px}
.style17 {  font-family: "Monotype Corsiva";
    font-size: 24px;
    font-weight: bold;
    font-style: italic;
    color: #6633CC;
}
.style19 {color: #000099}
.style21 {color: #000099; font-weight: bold; }
-->
        </style>
    </head>
    <body>
        <jsp:include page="Log_Admin.jsp"/><br/>
        <form action="" method="post" name="form1" id="form1" >
        <table width="46%" height="43" border="3" bgcolor="##CCCC99" align="center">
            <tr>
                <td width="85%" align="center" bgcolor="##CCCC99"><label><span class="style17">Course Information</span></label></td>
            </tr>

            <tr><td>
                <table width="666" height="207" border="0" align="center" bordercolor="#F0F0F0" bgcolor="#CCCC99" >
                    <tr>
                        <td width="186" height="46" align="left"><div align="left"><span class="style19">
                        <label><strong>Course ID</strong></label>
                        </span></div></td>

                        <td><label>
                        <select name="cid" size="1" id="cid" align="left">


                        </select>
                        </label></td>
                    </tr>
                    <tr>
                        <td height="53" align="left"><div align="left"><label><span class="style21">Course Name</span></label></div></td>
                        <td align="left"><input name="cname" type="text" id="cname" size="50" maxlength="50" /></td>
                    </tr>

                    <tr>
                        <td>      </td>
                        <td>       <input name="save" type="submit" id="save" value="Save" />                
                        <input name="reset" type="reset" id="reset" value="Reset" /></td>
                    </tr>
                </table>
            </td></tr>
        </table>
    </form>
    </body>
</html>

Bt by writing this code i am not able to add item CourseId to the combobox cid. Can you say me where is the problem? Thanks.

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评论（2）

苦妄 2024-11-12 02:10:50

您有 2 个同步列表，其项目彼此相关。这确实不容易维护和遍历。而是将两个列表的值放入 Map 中。

Map<String, String> courses = new LinkedHashMap<String, String>();
// ...
while(resultSet.next()) {
    map.put(resultSet.getString(1), resultSet.getString(2));
}
// ...
request.setAttribute("courses", courses);

在 JSP 中，您可以使用 JSTL 标签来迭代 < code>List 或 Map。对于 Map，每次迭代都会为您提供一个 var 属性中的Map.Entry，该属性又具有 getKey() 和 < code>getValue() 方法。所以应该这样做：

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
...
<select name="cid" size="1" id="cid" align="left">
    <c:forEach items="${courses}" var="course">
        <option value="${course.key}">${course.value}</option>
    </c:forEach>
</select>

此外，您的 processRequest() 方法中的前两行

response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();

应该删除，因为这是 JSP 的责任，而不是 servlet。否则，这样做时您将面临 IllegalStateException 错误的风险。

还要去掉 JSP 顶部的 @page import 。它们位于错误的位置，所有关联的代码都属于 servlet。

You've 2 synchronous lists whose items are related to each other. This is not really easy to maintain and traverse. Rather put the values of the two lists in a Map.

Map<String, String> courses = new LinkedHashMap<String, String>();
// ...
while(resultSet.next()) {
    map.put(resultSet.getString(1), resultSet.getString(2));
}
// ...
request.setAttribute("courses", courses);

In JSP you can use the JSTL <c:forEach> tag to iterate over a List or a Map. In case of a Map, each iteration will give you a Map.Entry in the var attribute which in turn has getKey() and getValue() methods. So this should do:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
...
<select name="cid" size="1" id="cid" align="left">
    <c:forEach items="${courses}" var="course">
        <option value="${course.key}">${course.value}</option>
    </c:forEach>
</select>

Further, the first two lines in your processRequest() method

response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();

should be removed since that's the responsibly of the JSP, not the servlet. You will otherwise risk IllegalStateException errors when doing so.

Also get rid of the @page import in top of your JSP. They are at the wrong place, all associated code belongs in the servlet.

回复 原文
痴情换悲伤 2024-11-12 02:10:50
class MyBean{
  String val;
  String label;
  //+getters setters method
}

服务程序

//fetching list of MyBean and setting it to request as attribute

       request.setAttribute("beanList",beanList);

   // forward this request to jsp

jsp

<select>
  <c:forEach var="bean" items="${beanList}">
    <option value="${bean.value}">${bean.label}</option>
  </c:forEach>
</select>

class MyBean{
  String val;
  String label;
  //+getters setters method
}

Servlet

//fetching list of MyBean and setting it to request as attribute

       request.setAttribute("beanList",beanList);

   // forward this request to jsp

jsp

<select>
  <c:forEach var="bean" items="${beanList}">
    <option value="${bean.value}">${bean.label}</option>
  </c:forEach>
</select>
回复 原文
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