Question

I’m thinking about using the java application object to implement a simple cache, to save a few configuration variables, and a couple of xml with often used info…

I’d like to know where is the application data phisically stored (a system file, in memory, db), how can it be configured, and if there’s any kind of limitation, like space, concurrency, etc…

Besides, any other concern regarding scalabitlity (both, in size and in concurrency) would be appreciated…

And if anybody can point me some place to find more info, I’ll be very glad…

thanks a lot

Answer 1

Objects are stored in the heap. Heap spaced can be managed through the VM’s configuration file.

A constructor call is more complicated
than an ordinary subroutine or
function call. It is helpful to
understand the exact steps that the
computer goes through to execute a
constructor call:

1. First, the computer gets a block of unused memory in the heap, large
   enough to hold an object of the
   specified type.
2. It initializes the instance variables of the object. If the
   declaration of an instance variable
   specifies an initial value, then that
   value is computed and stored in the
   instance variable. Otherwise, the
   default initial value is used.
3. The actual parameters in the constructor, if any, are evaluated,
   and the values are assigned to the
   formal parameters of the constructor.
4. The statements in the body of the constructor, if any, are executed.
5. A reference to the object is returned as the value of the
   constructor call.

The end result of this is that you
have a reference to a newly
constructed object. You can use this
reference to get at the instance
variables in that object or to call
its instance methods.

http://www.faqs.org/docs/javap/c5/s2.html

Here are some of the VM configuration parameters

http://www.caucho.com/resin-3.0/performance/jvm-tuning.xtp

I once wrote a Cache for xml objects (to call them somehow). A Map with a String key (filename) and a reference to the Object (parsed xml file) sufficed. In addition to that, the cache was a singleton (synchronized). Did the same for caching compiled JasperReports (i got a notable speed bump here, because reports where no longer compiled every single time)