1. Hay que agregar un frame oculto en el HTML de la hosted page:
<div id="__gwt_downloadFrame" tabIndex='-1'></div>
2. Para iniciar la descarga poner este código en la parte cliente (código GWT):
public static void download(String p_uuid, String p_filename) {
String fileDownloadURL = "/fileDownloadServlet"
+ "?id=" + p_uuid
+ "&filename=" +
URL.encode(p_filename);
Frame fileDownloadFrame = new Frame(fileDownloadURL);
fileDownloadFrame.setSize("0px", "0px");
fileDownloadFrame.setVisible(false);
RootPanel panel = RootPanel.get("__gwt_downloadFrame");
while (panel.getWidgetCount() > 0)
panel.remove(0);
panel.add(fileDownloadFrame);
}
3. Poner esto en el servlet que va a servir el archivo a descargar:
@Override
protected void doGet(HttpServletRequest p_request,
HttpServletResponse p_response)
throws ServletException, IOException {
String filename = p_request.getParameter("filename");
if (filename == null)
{
p_response.sendError(SC_BAD_REQUEST, "Missing filename");
return;
}
File file = /* however you choose to go about resolving
filename */
long length = file.length();
FileInputStream fis = new FileInputStream(file);
p_response.addHeader("Content-Disposition",
"attachment; filename=\"" + filename +
"\"");
p_response.setContentType("application/octet-stream");
if (length > 0 && length <= Integer.MAX_VALUE);
p_response.setContentLength((int)length);
ServletOutputStream out = p_response.getOutputStream();
p_response.setBufferSize(32768);
int bufSize = p_response.getBufferSize();
byte[] buffer = new byte[bufSize];
BufferedInputStream bis = new BufferedInputStream(fis,
bufSize);
int bytes;
while ((bytes = bis.read(buffer, 0, bufSize)) >= 0)
out.write(buffer, 0, bytes);
bis.close();
fis.close();
out.flush();
out.close();
}
