Question

我有一个index.jsp页面，其中包含名为“refresh”，“forward”和“edit”的按钮。如果我单击刷新按钮，则它会调用Servlet，并在index.jsp页面上显示值。

当我点击“转发”按钮时，它会调用另一个servlet并转到另一个页面forward_call_log.jsp。在此页面中，当我单击“forward”按钮时，它会调用另一个servlet，该servlet将显示index.jsp页面。将显示index.jsp页面，但数据库中的值不可用。

我该如何解决这个问题？

的index.jsp

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Pager Example - www.javaworkspace.com</title>
</head>
<body>
<form method="post" action="./Problem_retrive" >
<input type="submit" value="Refresh">
</form>
<form action="./edit_call_log" method="post">
<%
ResultSet rs=null;
try
{
    rs=(ResultSet)request.getAttribute("rs");
    //request.setAttribute("rs",rs);
    if(rs.next())
    {
    %>
    <table border=1 cellspacing=1 cellpadding=1>
        <tr>
            <th>check box</th>
            <th>Problem ID</th>
            <th>user ID</th>
        </tr>
        <%
            do
            {
        %>
                <tr>
                    <td><input type="checkbox" name="checkbox"   value="<%=rs.getString(1) %>"></td>
                    <td><%=rs.getString(1) %></td>
                    <td><%=rs.getString(2) %></td>
                </tr>
        <%
            }
            while(rs.next());
        %>
    </table>
<%
    }
    else
    {
        out.println("hiiiiiiii");
    }
}
catch(Exception e)
{
    e.printStackTrace();
}
 %>

<input type="submit" name="act" value="EditCall"/>
<input type="submit" name="act" value="Forward"/>   
</form>
</body>
</html>

点击刷新按钮后，调用 Edit_call_servlet.java

import database.problemdesc.Problem_retrive_class;
import database.user_master.User_master;
import java.sql.*;
public class Edit_call extends HttpServlet {
private static final long serialVersionUID = 1L;

protected void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException 
{
    response.setContentType("text/html");
    HttpSession session = request.getSession(true);
    ResultSet rs=null;
    Problem_retrive_class prc=new Problem_retrive_class();
    int checkbox=Integer.parseInt(request.getParameter("checkbox"));
    session.setAttribute("problem_id", checkbox);
    String act=request.getParameter("act");
    if(act.equals("EditCall"))
    {

        try
        {


            rs=prc.select_table(checkbox);
            RequestDispatcher rd =   request.getRequestDispatcher("edit_call_log.jsp");
            request.setAttribute("rs", rs);
            rd.forward(request, response);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    else if(act.equals("Forward"))
    {
        System.out.println("Forward page");
        try
        {
            ResultSet rs1=null;
            User_master um=new User_master();
            rs=prc.select_table(checkbox);
            if(rs.next())
            {
                System.out.println("Value retrieve from PRC select_table");
                rs1=um.select_table(rs.getString(7));
                System.out.println("Value retrieve from PRC   select_table"+rs.getString(7));
                RequestDispatcher rd = request.getRequestDispatcher("forward_call_log.jsp");
                request.setAttribute("rs1", rs1);
                request.setAttribute("user_type", rs.getString(7));
                rd.forward(request, response);
            }
            else
            {
                RequestDispatcher rd =  request.getRequestDispatcher("index.jsp");

                rd.forward(request, response);
            }

        }
        catch(Exception e)
        {

        }
    }

}

}

点击转发按钮后，调用 Problem_retrive_servlet.java

import database.problemdesc.Problem_retrive_class;


public class Problem_retrive extends HttpServlet {
private static final long serialVersionUID = 1L;

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{
    response.setContentType("text/html");
    PrintWriter out=response.getWriter();
    Connection con=null;
    ResultSet rs=null;
        try
        {
            Problem_retrive_class prc=new Problem_retrive_class();
            DBBean db=new DBBean();
            con=db.getDBConnection();
            rs=prc.select_table();

            RequestDispatcher rd = request.getRequestDispatcher("index.jsp");

            rd.forward(request, response);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

}

 }

Answer 1

看起来您没有将任何数据附加到请求对象，因此index.jsp无需显示任何内容。我假设这是发生问题时正在执行的代码。

public class Edit_call extends HttpServlet {

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

    else if(act.equals("Forward"))
    {
        try
        {
            ...
            {
                ...
            }
            else
            {
                RequestDispatcher rd =  request.getRequestDispatcher("index.jsp");

                / *** YOUR PROBLEM IS HERE ***/

                rd.forward(request, response);
            }

<强> [编辑]

根据您的问题，我假设JSP上的“刷新”按钮按预期工作（即数据库中的数据按预期显示）。从以下JSP代码...

<form method="post" action="./Problem_retrive" >
    <input type="submit" value="Refresh">
</form>

在服务器上执行的方法是Problem_retrive.doPost()

基于此，我们需要了解在forward_call_log.jsp上单击“转发”按钮时正在执行的代码。您已描述此“转发”按钮显示index.jsp但不包括数据库中的数据。我们假设它调用Edit_call.doPost() *。

* 我建议你在所有的doPost（）方法中放置调试器断点来确认这个假设，或者如果你不能调试就调用你的System.out.println（）语句。

因此，您需要将Problem_retrive.doPost()中发生的情况与未显示数据时Edit_call.doPost()内未发生的情况进行比较。我怀疑你没有打电话给request.setAttribute()

rs=prc.select_table();
RequestDispatcher rd = request.getRequestDispatcher("index.jsp");
request.setAttribute("rs", rs);
rd.forward(request, response);

关于良好设计的附注

您可以阅读MVC Design Pattern以了解更好的代码设计方法。

JSP不会将POST请求中的数据显示给Servlet

1 个答案: