Can/Should I use ConcurrentMap together with my own cache?

Question

Many people refer ConcurrentMap as a cache.

Is it a good idea to do this:

public List<Task> listTasks(final ProcessDefinition def, final boolean filterEnumerated) {
    final String CACHENAME = def.getName() + "-v" + def.getVersion() + "-Tasks";
    ConcurrentMap<String, List<Task>> cache = (ConcurrentMap<String, List<Task>>) Contexts.getApplicationContext().get(CACHENAME);
    if (Contexts.getApplicationContext().isSet(CACHENAME) && cache != null) {
        return cache.get(CACHENAME);
    } else {

        ConcurrentMap<String, List<Task>> myTasks = new MapMaker()
           .softValues()
           .expiration(2L, TimeUnit.HOURS)
           .makeComputingMap(
               new Function<String, List<Task>>() {
                @Override
                public List<Task> apply(String from) {
                    return getTasksFromDefinition(def, filterEnumerated);
                }
               });

        myTasks.put(CACHENAME, getTasksFromDefinition(def, filterEnumerated));

        Contexts.getApplicationContext().set(CACHENAME,myTasks);
        Collection<List<Task>> tz = myTasks.values();
        //First element in the collection
        return new ArrayList<Task>(tz.iterator().next());
    }
}

Or isn't it necessary to use the ApplicationContext (which is the java-ee application context) to also cache the map, and just retrieve the value from the map?
Similar to the answer on this post

Also I would like to know, the .expiration(2L, TimeUnit.HOURS). Is this really 2 hours, or does the long take values in milliseconds?

Please edit your question to state that you're using Google Collections, it'll help people answering (yes I know you tagged it as such) :-) — Martijn Verburg, Nov 01 '10 at 15:17
I don't agree. I believe the question is still valid if you don't use MapMaker. It is still a `ConcurrentMap` — Shervin Asgari, Nov 01 '10 at 16:56

score 2 · Accepted Answer · answered Nov 01 '10 at 15:19

2

I personally think it's fine to store such a cache in your ApplicationContext as it is threadsafe. But do be aware of the size of the cache, especially if you are clustering etc.

On the expiration question, the expiration is 2 hours as you'd expect.

answered Nov 01 '10 at 15:19

Martijn Verburg

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Can/Should I use ConcurrentMap together with my own cache?

1 Answers1