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Is it possible to create a local page scope in a JSP?

I'm working on a componentization system based on JSPs. This means that parts of the JSP can be moved from one JSP to an other one via drag and drop and leads to a need for a local page scope as variable of a component defined in one JSP my collide in an other JSP.
I can use Servlet 3.0 / JSP 2.2 / JSTL 1.2.
++ Tag File ++
The straight way of doing that would be to create a tag file for a component or something similar as they have this local page scope. But for every change in the tag file it would need to get redeployed and needing to create a tag file needs some time by itself. But if there is no other solution this direction (custom tags, tag files, JSP includes,...) is probably the way to go.
++ Namespace prefixing/suffixing ++
In Portlets one is supposed to concatenate each variable with a namespace provided from the portlet response object. I could do something similar but this can lead to side effects and unexpected behavior. If someone forgets to prefix/suffix the namespace it might work for some time but stops working at an other time without changing the code when the component moved to an other JSP with a conflicting variable name.
++ Custom Tag wrapping ++
I was hoping that I as a component framework developer can wrap the component code of a component developer with a tag file for a component tag like this
<a:component>
<div data-component-id="9">
<c:set var="componentId" value="9"/>
<c:set var="path" value='${abc:getCurrentPath()}_${componentId}'/>
<c:set var="resource" value='${abc:getResourceFromPath(path)}'/>
<c:set var="val" value="${resource.getValue('paragraphValue')"/>
<p><c:out value="${value}"/></p>
</div>
</a:component>
to have the variable in the local page context of the tag file. But instead they are in the context of the surrounding page. I'm looking for something like this
<% { %>
<div data-component-id="9">
<%
String componentId = 9;
String path = obj.getCurrentPath()+componentId;
Resource resource = otherObj.getResourceFromPath(path);
String value = resource.getValue("paragraphValue");
%>
<p><c:out value="<%=value%>"/></p>
</div>
<% } %>
which would create a code block in which variables have their own namespace. But of course for JSTL and JSTL-EL instead of scriptlet code.
I had a look at the JSTL specification but did not find out if there is a way to create such a local page scope. But I didn't check everything as it's huge and I'm not sure if it's possible with custom tags.
It is clear to me that bigger code blocks should not be in the JSP but with the framework I would like to provide simple solutions for smaller components.
++ Changing the JSP code ++
When components are initially placed on a JSP or moved around via drag 'n drop I actually move the JSP code of a component from one JSP to an other or within a JSP. This means I can also programmatically manipulate the JSP code of a component if it doesn't get too complex and it helps solving the problem.

As I thought that custom tag wrapping could be the ideal solution I created an other more specific question and I've got an answer here that solves the problem.
It's simply to remove all pageContext attributes before the evaluation of the body and adding them again at doEndTag().

How to update an attribute dynamically set in JSP PageContext?

Please correct me if I am wrong. I am developing a small web application for learning purpose. I have a jsp in which a list of top scorers in the the game are to be displayed in a table. For that I wrote a ServletContextListener and in the contextInitialized() method I have set an attribute(LinkedHashSet) in the ContextScope, which is the list of top 10 scorers in the game. I think it can be accessed using EL. But how can I update this collection?

You can use request.getSession().getServletContext().getAttribute("your_attribute_name_here") and can access the LinkedHashSet, once you get it you can add/remove/update values in it and again set it back to put updated values like request.getSession().getServletContext().setAttribute("your_attribute_name_here", "update_LinkedHashSet"); As best of my knowledge using EL you can access it but can not put back the updated value in attribute.
Note: while accessing the attribute you will need the explicit type casting.

You can update attribute like :
<%((Set<String>)pageContext.getServletContext().getAttribute("set")).add("Second"); %>
<% Set<String> set = (Set<String>) pageContext.getServletContext().getAttribute("set"); %>
from servlet context
<c:forEach items="${set}" var="s">
<c:out value="${s}"/>
</c:forEach>

using EL inside java tag

I have an attribute which I have forwarded from a servelet to a jsp file and while I can use this object with EL I'd like to know how to access it inside the java tags. An example is something like the following:
Searching for "${search_phrase}" returned
<c:forEach var="video" items="${results}">
${video.getVideoName()}
${video.getVideoID()}
</c:forEach>
So results here is an ArrayList of type Video which is forwarded from a servlet to a jsp
I would like to access this ArrayList inside <% %> tags in order to perform some more involved tasks that I cant do with EL.
Anybody know how to do this?
On a side note, this ArrayList I'm creating could potentially get large. Where is this stored? On the server or in some users temp files? If it's stored in server memory does it get cleaned after some period of time / an event such as the user that requested the ArrayList closes connection to server?

It all depends where you stored the list. If you stored it in a request attribute (and not anywhere else), then it will be eligible to garbage-collection when the request has been handled.
If you stored it in a session attribute, then it will be stored in the server memory (and/or the file system or the database depending on the container configuration) until the session times out or is invalidated, or until you remove it. HTTP is a stateless protocol. The user doesn't have a connection to the server.
Java code between <% %> is not a java tag. It's scriptlet, and should not be used in a JSP. If you need to do something that EL or JSP tags can't do easily, then either
write a custom JSP tag yourself, put the Java code in this JSP tag, and invoke the tag from the JSP, or
or write a custom EL function, and invoke this function from the JSP
or prepare the work in a controller (servlet, MVC framework action) before dispatching to the JSP, so that the JSP can generate the markup easily.
The list is accessible using the getAttribute method corresponding to the setAttribute method you used to store the list:
HttpServletRequest.setAttribute() --> HttpServletRequest.getAttribute()
HttpSession.setAttribute() --> HttpSession.getAttribute()
ServletContext.setAttribute() --> ServletContext.getAttribute()

I think you should use something like
<c:forEach var="video" items="${results}">
<c:forEach var="videoType" items="${video.types}"> //suppose videoType is an object
<c:out value="${videoTypeDetails}" />
</c:forEach>
</c:forEach>

Does ServletRequest.setAttribute permit key names with periods?

I have a java webapp with a Struts 1 action that has the following code:
request.setAttribute("cat.sound", "meow");
On my jsp page, I have the following tag:
<c:out value="${cat.sound}" />
However, "meow" is never printed on the JSP page. This might work if I had an object of type "cat" to do something like:
request.setAttribute("cat", cat);
Unfortunately, this webapp does not have any object defined for the cats and the jsp pages are frozen (no changes allowed).
So is it possible to use request.setAttribute with a key name containing periods/dots? How would the JSP page need to reference the set parameter?

You can avoid having to create a Cat class if you set cat to a map with a String key "sound":
request.setAttribute("cat", Collections.singletonMap("sound", "meow"));
Collections#singletonMap() gives you a nice, succinct way to create a map with one entry.

Java constants in JSP [duplicate]

This question already has answers here:
How to reference constants in EL?
(12 answers)
Closed 6 years ago.
I have a class that defines the names of various constants, e.g.
class Constants {
public static final String ATTR_CURRENT_USER = "current.user";
}
I would like to use these constants within a JSP without using Scriptlet code such as:
<%# page import="com.example.Constants" %>
<%= Constants.ATTR_CURRENT_USER %>
There appears to be a tag in the Apache unstandard taglib that provides this functionality. However, I cannot find any way to download this taglib. I'm beginning to wonder if it's been deprecated and the functionality has been moved to another (Apache) tag library?
Does anyone know where I can get this library, or if it's not available, if there's some other way I can access constants in a JSP without using scriptlet code?
Cheers,
Don

On application startup, you can add the Constants class to the servletContext and then access it in any jsp page
servletContext.setAttribute("Constants", com.example.Constants);
and then access it in a jsp page
<c:out value="${Constants.ATTR_CURRENT_USER}"/>
(you might have to create getters for each constant)

Turns out there's another tag library that provides the same functionality. It also works for Enum constants.

Looks like a duplicate of accessing constants in JSP (without scriptlet)
My answer was:
Static properties aren't accessible in EL. The workaround I use is to create a non-static variable which assigns itself to the static value.
public final static String MANAGER_ROLE = 'manager';
public String manager_role = MANAGER_ROLE;
I use lombok to generate the getter and setter so that's pretty well it. Your EL looks like this:
${bean.manager_role}
Full code at https://rogerkeays.com/access-java-static-methods-and-constants-from-el

What kind of functionality do you want to use?
That tag sould be able to access any public class field by class name and field name?
Scriptlets linking done at compile time but taglib class field access has to use such java API as reflection at runtime. Do You really need that?

I'll use jakarta-taglibs-unstandard-20060829.jar in my project but, you're true, it seems not available for download anymore.
I've got that in my pom.xml in order to get that library but I think It will work only because that library is now on my local repository (I cannot find it in official repositories) :
<dependency>
<groupId>jakarta</groupId>
<artifactId>jakarta-taglibs-unstandard</artifactId>
<version>20060829</version>
</dependency>
I do not know if there's another alternative.
I hope so because it was a good way to access constants in JSP.

Why do you want to print the value of the constant on the JSP? Surely you are defining them so that in the JSP you can extract objects from the session and request before you present them?
<%# page import="com.example.Constants" %>
<%# page import="com.example.model.User" %>
&lt%
User user = (User) session.getAttribute(Constants.ATTR_CURRENT_USER);
%>
<h1>Welcome <%=user.getFirstName()%></h1>