Caused by: javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don’t know how to iterate over supplied “items” in
<forEach>
That will happen when the <c:forEach items> does not refer a valid object over which it can iterate. The object should be an Object[] (a plain array), a Collection, Map, Iterator, Enumeration or String (see also source code). Anything else can’t be iterated by <c:forEach>. Your DetResults class is not an instance of either of the aforementioned types, so it will fail.
Your DetResults class doesn’t look right. It look basically like one God bean with a collection of all properties of multiple individual entities. This is not right. A bean class should represent at most one entity. Rewrite your DetResults class so that you basically end up with with a fullworthy collection of javabeans:
List<DetResult> results = detDAO.fetchDetResults(paramBean);
so that you can access it as follows:
<c:forEach items="${results}" var="result">
${result.heading}
<c:forEach items="${result.data}" var="dataItem">
${dataItem}
</c:forEach>
</c:forEach>
If you really insist to keep your DetResults bean as it is, you could access it as follows:
<c:forEach begin="0" end="${results.columnCount}" varStatus="loop">
${results.headings[loop.index]}
<c:forEach items="${results.data[loop.index]}" var="dataItem">
${dataItem}
</c:forEach>
</c:forEach>
See also:
Unrelated to the concrete problem, the <c:forEach var> attribute is not right. You should not give it the same name as an existing object in the scope. It would only clash. But that’s subject for a new question if you can’t interpret the error message.