Recursive jsp tags

Question

Hi
I have run into interesting issue which i would like to share. I created simple tag file which code shown below:
<%@ tag isELIgnored="false" %>
<jsp:useBean type="view.LeftMenuItem"
id="currentLeftMenuItem" scope="request"></jsp:useBean>
<%@ taglib tagdir="/WEB-INF/tags" prefix="fd" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ attribute name="cssClass" required="false"%>
<%@ attribute name="prefix" %>
<%@ attribute name="oneClass"%>
<c:set var="falseVar" value="false" scope="page"/>
<c:if test="${oneClass eq falseVar}">
<c:if test="${currentLeftMenuItem.expanded}">
<c:set var="finalStyle" scope="page" value="${cssClass}_level${currentLeftMenuItem.level}_collapsed"/>
</c:if>
<c:if test="${!currentLeftMenuItem.expanded}">
<c:set var="finalStyle" scope="page" value="${cssClass}_level${currentLeftMenuItem.level}_expanded"/>
</c:if>
</c:if>
<c:if test="${!(oneClass eq falseVar)}">
<c:set var="finalStyle" scope="page" value="${cssClass}"/>
</c:if>
<div>
${prefix}
<fd:linkSubmit action="${currentLeftMenuItem.action}"
cssClass="${finalStyle}" text="${currentLeftMenuItem.name}">
</fd:linkSubmit>
<c:if test="${(currentLeftMenuItem.numberOfSubItems > 0) && (currentLeftMenuItem.expanded )}">
<div id="${currentLeftMenuItem.hash}">
<c:forEach items="${currentLeftMenuItem.subItems}"
var="item">
<c:set var="item1" scope="request" value="${item}"/>
<%request.setAttribute("currentLeftMenuItem", request.getAttribute("item1")); %>
<fd:leftMenuItem cssClass="${cssClass}" prefix="${prefix} " oneClass="${oneClass}"/>
</c:forEach>
</div>
</c:if>
</div>
Only last part of this code may be interesting to you. What's strange is that it gives stack overflow exception on compiling. But on another refresh in the browser it works fine. What you can see in bold it's recursive call to the tag itself. From it working I assume, that what I do is allowed (i mean recursive tags), but why does it give stack overflow exc...? Any ideas?

Answer 1

That's not adequate. JSP re-evaluation is what we're looking for. Consider a simple example where I have a JSP tag that reads a JSP file and outputs it. I want the JSP in the file to be reinterpreted. I want <%=3+3 %> to be spat out as 6, not the string <%=3+3 %>.
I'd also like:
<pre>
<% for(int x=0; x<5 x++){%>
hello world
<%}%>
</pre>
To print hello world 5 times, etc.
[email protected] suggested that the ability to "call" other custom tags can be easily be achieved by simply calling their implementation in the same way the JSP container does.
<pre>
public int doStartTag() throws JspException{
try {
JspWriter out = pageContext.getOut();
Action1Tag action1 = new Action1Tag();
action1.setPageContext( pageContext);
action1.setParent( this);
action1.setAttribute1(...); // if any attributes..
action1.doStartTag();
action1.doEndTag();
action1.release();
// follow with action2 & action 3...
} catch(IOException e) {
throw new JspException(e.getMessage());
} return SKIP_BODY;}
</pre>
Couldn't we somehow subclass the caller for this functionality and make it re-interpret the page somehow instead of spitting the HTML back to the page directly?
The web container does it somehow, so obviously it can be done some way.