Created html nested lists from Java tree

Question

I am developing a school project which is a point of sale system. It is geared at resturants. "Managers" can created a menu which consists of as many categories nested as deeply as they want and the end categories will contain items. I have this tree of categories already created in java. It is essentially the same as a computer's directory. I plan to have the tree populated from the database when they want to view their menu. It is a web application so I need to represent this tree as html nested list. I have been using JSP/JSTL to build the pages from the data objects so I am hoping to pass the tree to the JSP once it is built and then somehow traverse it and insert the correct html or even write code in the Java to write a giant html string and just serve up that.

Im having trouble wrapping my head around this as I am quite new to jsp/jstl and am looking for suggestions on the best way to do this.

When you say "I have this tree of categories already created in java", is this tree implemented as beans, some other structure, what? — stepanian
– stepanian, Commented Feb 20, 2013 at 0:11
It is a regular class. It has a list of childeren which are the of the same class as the parent so it in itself is what I want in html a root list of nested lists. I did just find a little bit of information about recursion using JSTL link not sure if I will use this but others may find that link useful if they land on this question. — Yoshi
– Yoshi, Commented Feb 20, 2013 at 0:23

obourgain · Accepted Answer · 2013-02-20 07:52:33Z

2

If you don't know how deep the infos are nested, you can use recursion.

Define a jsp page called node.jsp, which will be called recursively :

<li>
   ${node.value}
   <c:if test="${fn:length(node.children) gt 0}">
      <ul>
         <c:forEach var="node" items="${node.children}">
           <c:set var="node" value="${node}" scope="request" />
           <jsp:include page="node.jsp" />
         </c:forEach>
      </ul>
   </c:if>
</li>

In you main page, you just have to initialize node with the root of the tree, and include node.jsp.

answered Feb 20, 2013 at 7:52

obourgain

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stepanian · Accepted Answer · 2013-02-20 00:39:31Z

1

Assuming the tree is stored in a class that implements the children as lists of objects recursively, then you can use the JSTL foreach tag to iterate in a nested manner like this:

<c:forEach items="${root.children}" var="parentItem">    
    <c:forEach items="${parentItem.children}" var="childItem">    
        <c:forEach items="${childItem.children}" var="grandchildItem"> 
        </c:forEach>
    </c:forEach>
</c:forEach>

Of course, this assumes that each of these objects has a method called getChildren() for this to work. All you need is to pass the root object to the JSP page by something like this in your servlet:

request.setAttribute("root", root);

edited Feb 20, 2013 at 0:39

answered Feb 20, 2013 at 0:32

stepanian

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3 Comments

Yoshi Over a year ago

I understand this but I am still having trouble visualizing its effect...doesn't this require me to know how deep the nesting goes though? It did give me another idea though...I may be able to use a jstl "for" to produce your code above according to some information passed in about how deeply nested the tree is once it is constructed from the DB.

stepanian Over a year ago

Yes. That kind of logic should not go into the JSP. All of the calculations and object population should go into the business logic. When all is ready, a single object should be passed to the JSP for presentation.

Yoshi Over a year ago

Ok that makes more sense. Thank you for the quick answer!

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