将值从Servlet传递到JSP

问题描述

你好朋友，

我无法将某些值从servlet传递到我的jsp.我已经在代码中使用了请求分配器，但是它没有将任何值传递给jsp，因为在我的jsp中，我将其获取为null.

下面是我的代码.我需要将3个值从servlet传递到jsp，从中发送第一个值，但不发送第2个和第3个值.

JSP文件

Hello friends,

I am unable to pass certain values from servlet to my jsp. I have used the request dispatcher in my code but it is not passing any value to the jsp, as in my jsp I am getting it as null.

Below is my code. I need to pass 3 values from servlet to jsp, out of which the first value is getting sent but the 2nd and 3rd values are not.

JSP file

Category
<select id="cat_sel" name="quizname"   önChange="select(); this.form.submit()">

[explanation-select()是一个JavaScript，在其中返回在此组合框中选择的值，并使用form.submit()传递给servlet(将表单操作交给servlet)]

[explanation-select() is a javascript where the value selected in this combo-box is returned and using form.submit() is passed to the servlet(the form action is given to the servlet)]

<option selected>Make a selection</option>
<%
for(Quiz q : quiz)
{
%>
<Option value="<%=q.getCategory()%>"> <%=q.getCategory()%> </Option>
<%
} %>
<% String cat=(String)request.getAttribute("category");
if(cat!=null)
{ %>
	<Option selected="yes"> <%=cat%> </Option>
<%}

%>
</select>

基于类别，选择了一个子类别.

Based on the category a sub-category is selected.

<select id="subcat_sel" name="subcategory"  önChange="subSelect(); this.form.submit()">
<option selected>Make a selection</option>
<%

for(Quiz q : quiz)
{
	if(q.getCategory().equals(cat))
	{
%>
<Option value="<%=q.getSubCategory()%>"><%=q.getSubCategory()%></Option>
<%
	}//if
}//for
String subcat=(String)request.getAttribute("subcategory");
System.out.println("Subcat in jsp="+subcat); //here it is printed as null
if(subcat!=null)
{ %>
	<Option selected="yes"> <%=subcat%> </Option>
<%}
%>
</select>

用于选择级别的类似代码，因此我不在此处添加.
下面是servlet代码.

Similar code for selecting level so I am not adding it here.
Below is the servlet code.

String category=req.getParameter("quizname");
String sub_category=req.getParameter("subcategory");
// some code here
else if(category!=null)
	{
		System.out.println("Check servcat="+category);//value selected in jsp is printed here
		updatecategory(category,email_address);
    		req.setAttribute("category",category);
		req.getRequestDispatcher("/userquiz").forward(req, resp); //userquiz  is the jsp file.
		resp.sendRedirect("/userquiz");
	}
	else if(sub_category!=null)
	{
		System.out.println("Check servsubcat="+sub_category);
    	updatesubcategory(sub_category,email_address);
		req.setAttribute("subcategory",sub_category);
		req.getRequestDispatcher("/userquiz").include(req, resp);
		resp.sendRedirect("/userquiz");
	}

大家帮帮我吧.

我将非常感激.

Please guys help me out.

I will really appreciate it.

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