Especially when generating detailed tiles by the MapTileServerCache (Mapcache) in Oracle Maps the OC4J needs more Memory to be allocated !!
When you do start the Mapviewer without an explicit command to allocate Memory, only 128 MB will be assigned to the OC4J.
The side effect with too less memory: The MapTilServer will generate tiles, but these are just containing the background color and no details from the layers.
Now, when you like to generate the tiles (*) for the Mapcache (either during runtime, when the user interacts with the map or if you like to prefetch the tiles) the Mapviewer needs more Memory !
So I recommend to start the Mapviewer like:
C:\mv10131_qs\oc4j\j2ee\home>java -Xmx512M -jar oc4j.jar
and you can play around with the Xmx512M to increase like Xmx1024M when needed.
For standard operation 256 might be sufficient.
Parameters like ZoomLevel and tile-size are influencing the memory consumption (during generation!).
(*) the generated tiles are stored in the file system in a directory like:
and looks like:
Have fun !