Problem drawing image with java/mapscript when starting with a blank mapObj

[James Dracup]

Hello,

I am using java/mapscript embedded inside a java program and am having a few 
problems.  I wonder if anybody has any suggestions, or if it is something 
obvious I have missed?

I create a new mapObj in java, but NOT from a .map file, a blank one:

mapObj  mapobj = new mapObj(null);

There is then a fairly long and complicated chunk of code to populate that 
mapObj from a db and user input with settings and layers etc. etc.

I finally do:

byte[] bytes = mapobj.draw().getBytes();

Intending to then further process in java the image returned.

However, I always get a blank (just background colour) image.  Initially I 
thought I’d missed something out when setting the parameters for the various 
mapscript objects, but, having looked at that for a while, I now do not 
think that is the problem.

If I do a mapobj.save("MapFileName.map") - the .map file outputted is 
perfect, and works fine (displays a map) in all contexts (cgi-bin, java 
mapscript).

I can load that .map file into a new mapObj, and the image produced is fine:

mapObj  newmapobj = new mapObj("MapFileName.map");
byte[] bytes = newmapobj.draw().getBytes();

If I then do a newmapobj.save("MapFileToCompare.map") - the .map file 
outputted is absolutely and completely identical (did a diff) to the 
original one outputted.

So I am really confused - it seems to me the mapObj’s are identical - so why 
do I need to go via the file system in order to produce an image?  What 
changes, and how can I avoid it?

Any thoughts,
Thanks,
James