Java-使用JSTL的每个循环的基础

Question

I'm really new to JSTL and having trouble grasping exactly how for each loops work. But say in my java bean I have a very simple while loop, that goes through and grabs properties of an object. I get the expected output from the loop when I log it. Which is simply a string that looks something like headerTest, headerMetaTest . Here is the code from my java bean:

Iterator<Resource> serviceList = null;
serviceList = resource.getChild("header").listChildren();

while(serviceList.hasNext()){
Resource child = serviceList.next();
headerTitle = child.adaptTo(ValueMap.class).get("headerTitle", "");
headerMeta = child.adaptTo(ValueMap.class).get("headerMeta, "");
}

However when I try to access it in the JSTL I'm getting nothing:

<c:forEach var="child" items="${serviceList}">
    <p>${child.headerTitle}</p>
    <p>${child.headerMeta}</p>
</c:forEach>

The puzzling part is I get no errors, nothing simply returns. Any ideas? Really, really lost on this one and any help is greatly appreciated. I'm a newb to this so code samples are a good way for me to learn and would be great if possible.

Answer 1

There are four scopes to be aware of in JSP pages.

page, request, session and application.

JSTL tags will usually look for attributes in that order.

page maps to attributes assigned during the processing of the page, these are usually quite rare.

request is for attributes assigned to the ServletRequest, they are the most common attributes to use as they last for the page request duration, and are then discarded.

eg

public void processMyServlet(ServletRequest request, ServletResponse){
    ...
    request.setAttribute("myAttribute",attributeValue);
    ...
}

session is for attributes assigned to the HttpSession. This is useful for user values that are used often during the user session.

eg

public void processMyServlet(HttpServletRequest request, HttpServletResponse){
    ...
    request.getSession().setAttribute("myAttribute",attributeValue);
    ...
}

application is for attributes assigned to the ServletContext, this is useful for values that are consistent across the application and do not change.

eg

public void processMyServlet(HttpServletRequest request, HttpServletResponse){
    ...
    request.getServletContext().setAttribute("myAttribute",attributeValue);
    ...
}

If you are calling a servlet that dispatches your jsp then at the very least you will need.

request.setAttribute("serviceList",myResourceCollection); 

somewhere during the servlet processing.

if you are doing everything in jsp then you will need something like

<% java code to create collection

   request.setAttribute("serviceList",myResourceCollection); 
%>