Re: Incorporating data files into packages and accessing internally

"Andrew Thompson" <u32984@uwe>
Wed, 01 Aug 2007 06:34:48 GMT
Todd wrote:

...I have developed a small Mercator projection class. I also
have data files with coastal data so that I can get a pretty little
map of the Earth.

How big is the data? Is there any prospect of the 'pretty little'
map being replaced by either a 'highly detailed' (read large)
data file, or perhaps the 'pretty little' map that can also call
up more detailed maps for islands & continents (whatever) if
the user wants to zoom in?

What I want to do is include the coastal data files into the package
that I have my Earth class in, ...

* that when I jar up the whole thing,
the data is included with the jar.

I think Philipp was pointing in the right direction with
getResource(), but there is a refinement that can be
provided by Java web start (JWS) that should allow an
even better experience for the end user, in the situations
outlined in my first paragraph.

It would amount to using the 'lazy' aspect of web start
downloads to ensure that the larger, more detailed files
were only downloaded and cached if and when the user
needs them.

It might work like this.

The app., as well as the simplest data file are supplied
'eagerly' at first start-up, they are cached locally (automatically)
and the application appears on-screen relatively fast.
When the user zooms on a particular area of the globe,
the app. calls for the more detailed file for that area. If
the file is already cached, it is loaded off disk, else, it
caches it, and loads it off disk thereafter.

Using web start with the right parameters, combined
with strict use of getResource (and variants) to access
the files, should achieve this for the end user.

Here is an example of loading resources lazily, but
note that it is *experimental* in that I was trying (so
far unsuccessfully) to use the inbuilt JWS progress
dialog for the lazy downloads.
Another note is that lazy downloads are more typically
used for classes, but it is notoriously difficult to get
JWS to honour the 'lazy' download for classes. Lazy
downloads for media are simple by comparison, that
is why my example uses images.

Some more general aspects of JWS based launch
are shown in these examples..

* Having said all that, I just noticed you mention the
*same* package. It is probably more practical to follow
the lazy downloads path if the data is in *different*
packages (which need to be in different jar files), since
the package data helps web start understand when to
download it.

This is easily doable. e.g. the class is in ..
..the data might be in..


Andrew Thompson

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