Downloading file from GWT

Downloading file from GWT

Last time I was discussed about how to create an app to host in google appspot.com, which provides to upload file and show it up on request. In this post I covered first portion, GWT file uploading and saving it to database as a blob object, in this section  I 
would like to show how can we download the file using persistence manager factory.

Configuration to be done are discussed in the previous section(Link).

what additionally needed is adding a doGet() method and its defenision, also a client side mechanism to request the file.

STEP 1: add doGet() body in "WaterTalkUploadService.java"

 doGet(req,resp){
     resp.setContentType("text/plain");
     resp.setHeader("Content-Disposition", "attachment; filename=output.txt");
     PrintWriter out = resp.getWriter();
     out.println("This is the output content");
     out.println("Probably something dynamic should go in here:::::");


     PersistenceManager pm = null;
         try {
                pm = PMF.get().getPersistenceManager();
                javax.jdo.Transaction transaction = pm.currentTransaction();
                Extent e = pm.getExtent(WaterTalkFiles.class, true);
                Iterator iter = e.iterator();
                String returns = "";
                WaterTalkFiles file  =  (WaterTalkFiles)iter.next();
                Blob blob = file.getData();
                byte[] buffer = blob.getBytes();
                String s = new String(buffer);
                out.println(s);
         } catch (Exception e) {
                e.printStackTrace();
         } finally {
                if (null != pm)
                      pm.close();
         }
 }



 STEP 2: Create a WaterTalkFileDownloading.java class

 add this to its body

    final String url = "/FileUploadByWaterTalks";
    String name = "output.txt";

    Anchor link1 = new Anchor(name);
    RootPanel.get().add(link1);
    link1.addClickHandler(new ClickHandler() {
      public void onClick(ClickEvent event) {
        Window.open(url, "_blank", "");
      }
    });

    Anchor link2 = new Anchor(name);
    RootPanel.get().add(link2);
    link2.addClickHandler(new ClickHandler() {
      public void onClick(ClickEvent event) {
        Frame f = new Frame(url);
        f.setSize("600px", "400px");
        f.getElement().getStyle().setBorderWidth(0, Unit.PX);
        RootPanel.get().add(f);
      }
    });
    
    Hope all other configuration explained in uploading section is kept as it was. 
    Thanks :)