如何在Servlet中设置会话变量并在JSP中获取它？

Question

I'm learning java and try to pass some variable from servlet to jsp page. 我正在学习Java，并尝试将一些变量从servlet传递到jsp页面。 Here is code from servlet page 这是servlet页面中的代码

@WebServlet("/Welcome")
public class WelcomeServlet extends HttpServlet
{
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException
    {
        HttpSession session = request.getSession();
        session.setAttribute("MyAttribute", "test value");

        // response.sendRedirect("index.jsp");
        RequestDispatcher dispatcher = request.getRequestDispatcher("index.jsp");
        dispatcher.forward(request, response);
    }

}

And simple jsp 和简单的jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>My Index page</title>
</head>
<body>
Index page
<br />
 <% 
Object sss = request.getAttribute("MyAttribute"); 
String a = "22";

%>

   <%= request.getAttribute("MyAttribute"); %>
</body>
</html>

Whatever I do attribete at jsp is null. 我在jsp上所做的任何操作都为null。

What is wrong at this simple code? 这个简单的代码有什么问题？

Answer 1

you are getting if from request not session. 您正在从请求而不是会话中获取。

It should be 它应该是

session.getAttribute("MyAttribute")

I suggest you to use JavaServer Pages Standard Tag Library or Expression Language instead of Scriplet that is more easy to use and less error prone. 我建议您使用JavaServer Pages标准标记库或表达式语言，而不要使用Scriplet ，因为它更易于使用，并且不易出错。

${sessionScope.MyAttribute}

or 要么

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

<c:out value="${sessionScope.MyAttribute}" />

you can try ${MyAttribute} , ${sessionScope['MyAttribute']} as well. 您也可以尝试${MyAttribute} ， ${sessionScope['MyAttribute']} 。

Read more 阅读更多

Answer 2

You set an attribute in a session . 您在会话中设置属性。 You have to retrieve it from a session : 您必须从会话中检索它：

Object sss = session.getAttribute("MyAttribute");

And since you are dispatching the request, you actually don't need a session. 而且由于您正在分派请求，因此实际上不需要会话。 You can set the attribute in a request object in your servlet: 您可以在Servlet的请求对象中设置属性：

request.setAttribute("MyAttribute", "test value");

Then read it as you are already doing in you JSP. 然后像在JSP中一样阅读它。

Answer 3

You should avoid scriptlets because they are java code in HTML, they break MVC pattern, they are ugly, odd and deprecated. 您应该避免使用scriptlet，因为它们是HTML中的Java代码，它们破坏了MVC模式，它们丑陋，奇数和不推荐使用。

Simply replace : 只需替换：

<% 
Object sss = request.getAttribute("MyAttribute"); 
String a = "22";

%>

with simply using EL ${MyAttribute} 只需使用EL ${MyAttribute}

But if you want to stick with scriptlets, you should get the attribute from the proper scope which is session in your case. 但是，如果您要坚持使用scriptlet，则应该从适当的范围（在您的情况下为session中获取属性。

如何在Servlet中设置会话变量并在JSP中获取它？

问题描述

3 个解决方案

解决方案1
8 已采纳 2014-06-14 18:16:56

解决方案2
3 2014-06-14 18:17:14

解决方案3
3 2014-06-14 18:18:57

如何在Servlet中设置会话变量并在JSP中获取它？

问题描述

3 个解决方案

解决方案1 8 已采纳 2014-06-14 18:16:56

解决方案2 3 2014-06-14 18:17:14

解决方案3 3 2014-06-14 18:18:57

解决方案1
8 已采纳 2014-06-14 18:16:56

解决方案2
3 2014-06-14 18:17:14

解决方案3
3 2014-06-14 18:18:57