JSP 将 request.getParameter 转换为实体

Question

This is the scenario

This is the JSP from where I get to the servlet. There is an entity called CurrentUser wich holds multiple fields of information about the user. I want to pass the servlet all the information about the user in a form of entity.

<a href="Controller?action=profile&entity=<%=_currentUser%>"> Information about the current user, like: name, id, profile picture etc... </a>

Inside the servlet:

if(request.getParameter("action").equals("profile")){
        CurrentUser _currentUser= (CurrentUser) request.getParameter("entity");
}

If I do a system.out to see whats inside "entity" parameter i get something like: Package.CurrentUser@abc1235 ... and I cannot cast that, to receive it as an Entity.

incompatible types: String cannot be converted to CurrentUser

Is there any way to get that refference and the info inside those fields?

Answer 1

No, you shouldn't do it. Using the reference string representation you can't retrieve object instance. But you can use String object's ID parameter in the query string. Then retrieve the object by ID.

<a href="Controller?action=profile&entity=<%=_currentUser.id%>"> Information about the current user, like: name, id, profile picture etc... </a>

String id = request.getParameter("entity");

Answer 2

Inside the JSP, store your _currentUser entity to the Session as

<% session.setAttribute("entity", _currentUser); %>
<a href="Controller?action=profile">Information ... </a>

Now, inside the Controller Servlet you can retrieve this entity as

if(request.getParameter("action").equals("profile")){
    CurrentUser _currentUser= (CurrentUser) session.getAttribute("entity");
}

Note, that storing the current user object into Session should ideally be done by the Servlet that forwarded the request to the JSP first. Use of Java code scriptlets <% %> inside a JSP is deprecated as JSPs should mostly be used for presentation purposes only.