Struts & Java Tips: Issue #2

A couple weeks ago I wrote a short essay on some of the things that I ran into while working with Java and Jakarta Struts. Because I didn’t know what else to call it, I jokingly referred to it as Issue #1. Well, a month and a half later I think I have enough to write issue #2. I should probably call it something more general like ‘Java Web Development Tips’ or something, but why change now?

First, I thought I’d touch on some of the interesting things that I’ve run into while working in the presentation layer which in my case is JSP. This week I needed to create a search form that enabled end users to sort and filter results based on a number of parameters. Without showing 1000 lines of code, one of the challenges when doing a form like this is maintaining the form state when doing filtering and sorting (because not all the fields are sortable and not all can be filtered) and the most common solution is to use hidden form fields. Struts includes a <html:hidden> tag that will automatically maintain state for you form, but it requires that you know all the names of all the fields up front when you’re writing your form. If you decide to add a sortable or filterable property later, you’d need to hardcode another hidden form field. Instead, I chose to use the JSTL forEach tag and the special ‘param’ scope to programatically create my hidden form fields:

<c:forEach var="p" items="${param}">
  <input type="hidden" name="${p.key}" value="${p.value}">

The non-intuitive part of this code in my mind is the param ‘scope’, which (if you mess around with it a bit) is a HashMap derived from the getParameterMap() method of the ServletRequest interface. The forEach tag iterates over each parameter, which results in a Map.Entry; the Map.Entry provides JavaBean style accessors for key and value, which I can then use to create the hidden form fields.

The Action class that backs the search form uses an ActionForm to collect the data and then copies the data from the ActionForm bean to a bean made specifically for use with the search DAO. That code looks something like this:

public ActionForward execute(ActionMapping m, ActionForm f, HttpServletRequest req, HttpServletResponse res)
throws Exception {
// get the data posted from the form
SearchOrdersForm input = (SearchOrdersForm)f;
// bean coupled w/ the search DAO
ManagerSearchParams sp = new ManagerSearchParams();
// copy the properties from the form to the searchparams bean
// using the BeanUtils class
BeanUtils.copyProperties(sp, input);
// perform the search (in this case we're looking for orders
Collection orders = OrderDAO.findOrders(sp);
// push the collection to the jsp
request.setAttribute("orders", orders);

I’m not sure if there is a pattern in this or not, but the coupling of the ManagerSearchParams bean with the OrderDAO in the above example turned out (at least so far) to be very useful. Another part of the application required that I retrieve orders from persistent storage (in this case Hibernate & SQL Server) by date (ie: I needed to find all orders between date1 and date2). Instead of writing a new method on the DAO (ie: OrderDAO.searchbyDate()), the ManagerSearchParams bean already had start & end date properties. I simply created a new instance of the ManagerSearchParams bean, populated the startdate and enddate properties, and then fired the findOrders() method on the OrderDAO class.

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