Some modules do not work in JWS Application

I have developed a swing application and run from Java Web Start. When my application read the data from database and export into XML file, it works fine if the data amount is less than 5000 KB. But the program stop working if the data amount is larger than 5000 KB. Then I run the application with java -jar command line, it works well whether data amount is small or large. Is there any heap memory issue in Java Web Start? I have set max-heap-size to 512M in JNLP file. I would appreciate if anyone gave me any idea and solution about my problem.

[556 byte] By [g4029672a] at [2007-11-26 17:40:25]