if( RootPanel.get("downloadiframe") != null ) {
Widget widgetFrame = (Widget)RootPanel.get("downloadiframe");
widgetFrame.removeFromParent();
}
Frame frame = new Frame( GWT.getModuleBaseURL() + "filedownload" + "?id=downloadiframe"+
"&filename=" + filename );
frame.setVisible( false );
frame.setSize( "0px", "0px" );
RootPanel.get().add( frame );
下載的Action在web.xml裏配置就OK