JPedal provides several methods to allow easy conversion of a PDF file or directory of PDF files into JPG2000.
Convert PDF to JPG2000 from Command Line or another language
java -jar jpedal.jar --convert jpx "inputFileOrDir" "outputDir"
Convert PDF to JPG2000 in Java
writeAllPagesAsImagesToDir("inputFileOrDir", "outputDir" ,
This uses the JPedal ConvertPagesToImages class.
If you are looking for upscaling or more complex control over the PDF to JPG2000 conversion, ConvertPagesToHiResImages class has lots of additional options