How to make printing Collections objects clean in a JSP

Question

I have been considering a range of options to move away form using scriptlets in my jsps.

The main cause of "messiness" tends to be the problems with printing out ArrayList and other Collections objects, because some presentation related markup gets mixed up with some Java.

What would you recommend as the best solution for dealing with this type of situation. I am looking at Wicket (very briefly) but can't work out if this will help to clean up this situation.

Answer 1

If you're using plain JSP, without any other Web framework on top of it, I suggest you take a look a the JSTL. It gives you a lot of tags to manipulate your objects.

One tag that might interest you in your case is the <c:forEach /> tag. It allows you to use for-each loops inside your JSP pages.

For more informations, here are some links:

• The official Oracle page on JSTL
• The reference implementation home

Answer 2

JSTL has:

<c:forEach items="${list}" var="item">
   ${item}
</c:forEach>

You should just put the list as a request attribute named list.

Take a look at the other JSTL tags in order to get rid of scriptlets.

Answer 3

I believe pretty much every higher-level web API has something to help you along those lines.

For Wicket, I found Repeaters:

Repeaters are components that can render their body markup multiple times. These components are useful for creating output that is traditionally created via loops.

Using a ListView, for example, you can do this:

Code:

List list = Arrays.asList(new String[] { "a", "b", "c" });
ListView listview = new ListView("listview", list) {
    protected void populateItem(ListItem item) {
        item.add(new Label("label", item.getModel()));
    }
};

Markup:

<span wicket:id="listview">
   this label is: <span wicket:id="label">label</span><br/>
</span>

Will result in the following rendered to the browser:

<span wicket:id="listview">
   this label is: <span wicket:id="label">a</span><br/>
</span><span wicket:id="listview">
   this label is: <span wicket:id="label">b</span><br/>
</span><span wicket:id="listview">
   this label is: <span wicket:id="label">c</span><br/>
</span>

There's more advanced examples on that page as well.

For, say, JSF, there's:

• <ui:repeat>, which is similar to JSTL's forEach that other posters have pointed out.
• <ui:dataTable>, which similar to Wicket's ListView

Hope that helps!

Answer 4

If your markup and logic get entangled, you best separate them using a MVC-Pattern (Model-View-Controller).

See here: http://en.wikipedia.org/wiki/Model–View–Controller#Java:_Java_Platform.2C_Enterprise_Edition_.28Java_EE.29 ; or here: http://www.oracle.com/technetwork/java/javaee/overview/index.html