Upon further searching, this is related to issue 32773.  I just wrote an ant
task that undeploys the current project's app.  It seems to work all right,
except that it will start up the server if it hasn't already launched, which is
undesirable, but I haven't figured out how to check if the target j2ee server is
running or not:

public class UndeployTask extends Task
{
    public void execute() throws BuildException
    {
        File baseDir = getProject().getBaseDir();
        Project proj = FileOwnerQuery.getOwner(FileUtil.toFileObject(baseDir));

        J2eeModuleProvider jmp = (J2eeModuleProvider)
            proj.getLookup().lookup(J2eeModuleProvider.class);
        DeploymentManager mgr = jmp.getInstanceProperties().getDeploymentManager();

        // for tomcat, this target contains all the webapps
        Target target = jmp.getInstanceProperties().getDefaultTarget();
        Target[] targets = { target };

        String contextUrl = jmp.getConfigSupport().getWebContextRoot(); // (e.g.
"/pizzaordering")

        try
        {
            TargetModuleID[] ids = mgr.getAvailableModules(ModuleType.WAR, targets);

            for (TargetModuleID id : ids)
            {
                String moduleId = id.getModuleID(); // (e.g.
"http://localhost:8084/pizzaordering")
                if (moduleId.endsWith(contextUrl))
                {
                    log("Undeploying old build of web context: " + contextUrl);
                    TargetModuleID[] toUndeploy = { id };
                    mgr.undeploy(toUndeploy);
                }
            }
        }
        catch (TargetException ex)
        {
            throw new BuildException(ex);
        }
        catch (IllegalStateException ex)
        {
            throw new BuildException(ex);
        }
    }
}

I agree it would be good to add this into Deployment class and also to into
nbdeploy task (or as a separate task). Not sure if you want to make it part of
clean by default - if you clean/build repeatedly or if you have never deployed
the module you do not want to be slowed down by undeploy (even connecting to the
server and checking if it has been deployed), but we would need to test how long
that takes. Maybe we can add a checkbox to Run tab in project properties.

Undeploy would need to fail nicely (just show a waning) if the server is not
running or if the module was not dpeloyed.

Once we do this we should also add Undeploy action to project popup menu.

I would then close 32773 as wontfix.

I added the following code at the beginning of the Task:

ServerInstance si =
ServerRegistry.getInstance().getServerInstance(jmp.getServerInstanceID());
StartServer ss = si.getStartServer();
if (ss == null || !ss.isRunning())
  return;

This required an impl dependency on j2eeserver (is there a way to check whether
ss.isRunning() using API classes?)

Clean is now very quick if the server isn't running at all.  If it is running,
but the webapp is not deployed, it is still very quick.  I didn't notice any
difference from the old behavior.

In V-Builder, I plan to ship this Task, and to call it from the clean target.  I
would recommend a similar solution to NB, as well as taking a look at whether
deploy should always force a redeploy (I think it should).

If you think you might implement this the way I did, I could provide a full
patch for web/project and j2eeserver.

Rich, yes please attach the diff. Stepan will take a look at this in 6.0.

Created attachment 33174 [details]
Ant task for undeploying

Created attachment 33175 [details]
patch for using UndeployTask.java

Thanks for the patch. Unfortunately, NB 5.5 is already feature frozen, so I will
integrate your patch in the next release - 6.0.

Partially related to issue 112529.

Attaching the proper patch that should work for any J2EE module, doing nothing when app is not deployed or server is
stopped.

Patch includes undeploy on clean.

Created attachment 69547 [details]
patch

Created attachment 69663 [details]
updated patch (minor fixes)

Fixed in main 5d7eec56a42d.