Question

In one of my Controllers, I have multiple URLs that will ultimately render in the same way. For example, this method scans the network on which the server resides, caches a String representation of each connected device and each device listening on a specific port, and then sends that information to another method to render:

public static void networkScan(String networkTarget, String port)
{
    //These two lists will never have more than 256 total entries
    List<InetSocketAddress> listeningDevices;
    Map<String, String> allDevices;

    ...Logic for discovering network devices...

    //Store the results in a cache, for history preservation in the browser
    Cache.set(session.getId() + "listeningDevices", listeningDevices);
    Cache.set(session.getId() + "allDevices", allDevices);
    showScan(listeningDevices, allDevices);
}

public static void showScan(List<InetSocketAddress> listeningDevices, Map<String, String> allDevices)
{
    render(listeningDevices, allDevices);
}

public static void getCachedScan()
{
    List<InetSocketAddress> listeningDevices = (List<InetSocketAddress>)Cache.get(session.getId() + "listeningDevices");
    Map<String, String> allDevices = (Map<String, String>)Cache.get(session.getId() + "allDevices");
    if(listeningDevices == null)
        listeningDevices = new ArrayList<InetSocketAddress>();
    if(allDevices == null)
        allDevices = new TreeMap<String, String>();

    renderScan(listeningDevices, allDevices);
}

Doing it this way results in Play doing some weird array copying that ends up taking infinite memory. If I were to change my call of showScan() to simply render() and create a view with the name networkScan.html, it all works just fine, no memory bugs.

I have several other methods that also use showScan, based on different caching settings. I don’t want lots of views that are all essentially copies of each other, so I’m trying to go through just one method with one corresponding view.

Answer 1

Turns out that calling an action method creates a redirect event, which resulted in all sorts of copying objects into URLs. I still don’t understand how that mushroomed into using over a gigabyte of memory for a collection of Strings that rarely numbered above 100, and never above 256, but I found a way of avoiding the redirect event.

As I was directed to do in an answer on Google Groups, I made use of the @Util interceptor on the showScan method:

@Util
public static void showScan(List<InetSocketAddress> listeningDevices, Map<String, String> allDevices)
{
    renderTemplate("Admin/showScan.html", listeningDevices, allDevices);
}

Marking a method with @Util unfortunately makes it use the template of the calling method, but the call to renderTemplate() allows me to use a single template that I specify.