如何在 HttpSession 中存储 Java 对象? [英] How do you store Java objects in HttpSession?

问题描述

因此，当请求此 servlet 时，我试图获取一个 servlet 以将 Java 对象添加到用户的会话中.但是在 servlet 重定向到下一个页面并且我尝试检索该对象之后，我得到了一个 null 对象.

So I am trying to get a servlet to add a Java object to the session of the user, when this servlet is requested. But after the servlet redirects to the next page and I try to retrieve the object, I get a null object instead.

这是我将对象添加到 HttpSession(在 servlet 中)的操作:

Here is what I do to add the object to the HttpSession (in the servlet):

request.setAttribute("object", obj);

然后我尝试通过(在 JSP 中)检索它:

Then I try to retrieve it by (in the JSP):

 Object obj = request.getAttribute("object");

那么如何让 obj 不为 null?

So how would I get obj to not be null?

更新:我也试过一无所获:

Update: I have also tried this with nothing:

HttpSession session = request.getSession();
session.setAttribute("object", obj);

在 JSP 中具有以下内容:

with the following in the JSP:

 Object obj = request.getSession().getAttribute("object");

两种方式都返回null.

Both ways still return null.

推荐答案

您不是将对象添加到会话中，而是将其添加到请求中.
你需要的是:

You are not adding the object to the session, instead you are adding it to the request.
What you need is:

HttpSession session = request.getSession();
session.setAttribute("MySessionVariable", param);

在 Servlet 中，您有 4 个范围可以存储数据.

In Servlets you have 4 scopes where you can store data.

1. 申请
2. 会话
3. 请求
4. 页面

确保你理解这些.如需更多信息，请查看此处

Make sure you understand these. For more look here

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