//RUN YOUR BRAND NEW PDF REPROT
final String PDF_RUN = "rundll32 url.dll, FileProtocolHandler " + PDF_FILE; //Don't forget the space between 32 and URL.
//EXECUTE THE COMMAND
Runtime.getRuntime().exec(PDF_RUN);
thanks Java_Jasper you saved my life.
JRExporter.exportReport() generate report in to .metadata.pluginsxxxx folder but no pdf report show in browser. ( i don't know what happened, the other project showed safely) so i need to force its to display.