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JSF page won't reload if I write to ByteArrayOutputStream

Greenhorn

Posts: 4

posted 11 years ago

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Basically, I have a JSF page that displays a count and a "download" button. What I want to have happen is when the button is clicked a text file is created and downloaded and the page's count gets incremented.

When I click the CommandButton the bean.download method gets called, text gets written to a ByteArrayOutputStream and is downloaded. But the count does not refresh (page isn't reloaded).

If I don't call the method to write to the ByteArrayOutputStream, then the page does get updated and shows the new count value.

The JSF page:

The Session bean: Bean

import javax.annotation.PostConstruct;
import javax.enterprise.context.SessionScoped;
import javax.faces.context.ExternalContext;
import javax.faces.context.FacesContext;
import javax.inject.Named;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;

@Named
@SessionScoped
public class Bean implements Serializable {

private int count;

@PostConstruct
    private void init() {
        count = 0;
    }

public String download() {
        count++;
        try {
            doDownload();
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } catch (ServletException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
        return "";
    }

public int getCount() {
        return count;
    }

public void setCount(int count) {
        this.count = count;
    }

public void doDownload() throws IOException, ServletException {

final ByteArrayOutputStream baos = new ByteArrayOutputStream();

try {
            String line = "dummy text";
            baos.write(line.getBytes());
            baos.close();

sendReport(baos.toByteArray());

} catch (IOException e) {
            e.printStackTrace();
            throw e;
        } catch (ServletException e) {
            e.printStackTrace();
            throw e;
        }

}

public static void sendReport(byte[] bs) throws IOException,
            ServletException {
        FacesContext facesContext = FacesContext.getCurrentInstance();
        ExternalContext externalContext = facesContext.getExternalContext();
        HttpServletResponse response = (HttpServletResponse) externalContext
                .getResponse();

response.reset();
        response.setHeader("Expires", "0");
        response.setHeader("Cache-Control",
                "no-store, no-cache, post-check=0, pre-check=0");
        response.setHeader("Pragma", "no-cache");
        response.setContentType("application/vnd.ms-excel");
        response.setHeader("Content-disposition",
                "attachment; filename=\"down.csv\"");
        response.setContentLength(bs.length);

ServletOutputStream os = response.getOutputStream();
        os.write(bs);

os.close();

facesContext.responseComplete();

}

Thanks for any help.

Tim Holloway

Saloon Keeper

Posts: 27807

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posted 10 years ago

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Welcome to the JavaRanch, Stephen!

JSF is designed to facilitate HTML data, and especially pages with forms on them. The parts of your webapp that need to output non-HTML data should be implemented in the traditional way using servlets or JSPs. JSF does not require that every part of a webapp must be done exclusively with JSF and the JSF and non-JSF parts of a webapp can freely communicate with each other because the JSF scopes and J2EE scopes are actually the same things, making a JSF session object accessible via the J2EE session API, for example.

The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.

You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.

stephen wills

Greenhorn

Posts: 4

posted 10 years ago

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Hi Tim,
Thanks for your reply. I'm still a bit unclear of how else I can approach this. I need the JSF button to initiate the download which results in the server returning a file to download. But I also need to show on the web page that the download count has been updated which doesn't happen if the server returns a file. I guess I don't understand what you are telling me. Further advice would sure be welcome.
Cheers

Tim Holloway

Saloon Keeper

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posted 10 years ago

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Your download button needs to reference a non-JSF URL (use the h:outputLink tag). That URL should run the Excel file generator that returns the spreadsheet to be downloaded.

Because this kind of operation doesn't navigate away from the JSF screen, you can then use AJAX to update the backing bean containing the download count and re-render the count in the current page display.

stephen wills

Greenhorn

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posted 10 years ago

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Thanks for your help Tim. I got around the problem by adding to the commandButton to reload the page after one second. Not the best solution but it works.
Cheers
Stephen

Tim Holloway

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posted 10 years ago

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That's basically what AJAX does, except that it only updates the part of the page that actually changes instead of the whole thing.

Don't get me started about those stupid light bulbs.