Using DownloadStream - How to

I need to download a file directly on the client without any filechooser.
I found the class DownloadStream and I thought it was my solution, however I don't understand how to use it.
I tried with
            String logFileName = "Import_"+nomeMatrice+".log";
            byte[] cnt  = new String("La vispa teresa avea tra l'erbetta").getBytes();
            DownloadStream ds = new DownloadStream(new ByteArrayInputStream(cnt),"log",logFileName);
but nothing happened.
Could someone provide a snippet to use that class or duggest a different approach?
Tks

If by "filechooser" you mean the dialog that the browser shows when the user clicks a "downloadable" resource, then you cannot avoid it. This is not because of Vaadin but because of browsers. In any case, I found this example about how to download a file from Vaadin applications: http://www.programcreek.com/java-api-examples/index.php?api=com.vaadin.server.FileDownloader

Tks for Your help.
I already used FileDownloader in different situations but this is not my situation now.
The user shouldn't chose the file because there's no file : I've a byte stream I need to download.
I think DownloadStream is the correct answer but I didn't understand how to use it.
Tks

Sorry, I'm not sure if I understand conrrectly. Can you elaborate a bit on your requirement?

Sure.
In my code, when the user press a button, the code produces a stream of data I need to download as a file to the client.
I don't have a physical file to download.
I can, obviously, write a file on the server, if usefull, and the download it.
Tks

Ok, got it. You can do something like this:

Button button = new Button("Download the file");

// first, implement a StreamSource:
StreamSource source = () -> new ByteArrayInputStream("La vispa teresa avea tra l'erbetta".getBytes());

// second, create a StreamResource and pass the previous StreamResource:
StreamResource resource = new StreamResource(source, "file.txt");

// extend a component
FileDownloader downloader = new FileDownloader(resource);
downloader.extend(button);

Tried but I found a different problem.
The button I need to create is into a popup Window.
Using a FileDownloader extension into a popup goes into NPE.
Any suggestion ?
Tks

If you can you share the relevant parts of your code and the stack trace I could have a look.

The proble is a little more complex as I tought.
I've a small popup containing a file chooser, the file chooser (Upload class) when a file is choosen and I press the execute button the content of the file is elaborated  and the log stream should be redirected to the browser.
Here the code
package axioma.web.configuratore.ui.dialogs;

import java.io.*;
import com.vaadin.server.*;
import com.vaadin.server.StreamResource.StreamSource;
import com.vaadin.ui.*;
import com.vaadin.ui.Button.ClickEvent;
import axioma.rubik.csv.MatriciCsvImporter;
import axioma.web.configuratore.model.domain.TipiMatrici;
import axioma.web.template.ui.components.*;
import axioma.web.template.ui.dialogs.YesNoDialog;
import axioma.web.template.ui.layouts.HorizontalCaptionLayout;
import axioma.web.template.ui.messages.TemplateMessages;

public class MatrixImportDialog extends YesNoDialog {    
    
    private static final long serialVersionUID = 1L;
    
    private DocumentFileReceiverField fileReceiver;
    private TipiMatrici tipiMatrice;

    public MatrixImportDialog(TipiMatrici xpMatrice) {
        super(TemplateMessages.CONFIRM_IMPORT.getText(),TemplateMessages.CONFIRM_IMPORT.getMessageCode(), null ,null, new String[]{});
        tipiMatrice = xpMatrice;
    }

    @Override
    public void createYesButton() {
        createYesButton(TemplateMessages.BUTTON_UPLOAD.getText(),TemplateMessages.BUTTON_UPLOAD.getMessageCode());
        DocumentDownloader downloader = new DocumentDownloader(null,"Import.csv") {

            private static final long serialVersionUID = 1L;

            @Override
            protected Resource buildResource() {
                System.out.println("Fatto ");
                return rebuildResource();
            }
        };    
        downloader.extend(btnYes);    
    }
    
    private StreamResource rebuildResource() {
        byte[] logData = importa();
//        System.out.println(logData);
        byte[] logData2 = "ProvaMicrofono;".getBytes();
        StreamSource source = () -> new ByteArrayInputStream(logData2);
        StreamResource resource = new StreamResource(source, "Import.log");
        return resource;
    }

    @Override
    public void createNoButton() {
        createNoButton(TemplateMessages.BUTTON_CLOSE.getText(),TemplateMessages.BUTTON_CLOSE.getMessageCode());
    }

    @Override
    public Layout realBuildContent() {
        VerticalLayout vl = new VerticalLayout();
        vl.setSizeFull();
        HorizontalCaptionLayout hl = new HorizontalCaptionLayout(1);
        fileReceiver = new DocumentFileReceiverField("FileName");
        fileReceiver.setCaption("File Name");
        fileReceiver.setValue("");
        fileReceiver.setWidth("100%");
        hl.addComponent(fileReceiver);
        hl.setWidth("100%");
        vl.addComponent(hl);
        return vl;
    }

    public String getFileName() {
        return fileReceiver.getFileName();
    }
    
    public byte[] getContenuto() {
        return fileReceiver.getContent();
    }

    public DocumentFileReceiverField getFileReceiver() {
        return fileReceiver;
    }

    @Override
    public void executeAction(ClickEvent xpEvent) {
    }
    
    public byte[] importa() {
        try {
            String nomeMatrice = tipiMatrice.getNome();
            MatriciCsvImporter importer = new MatriciCsvImporter(nomeMatrice);
            char[] contenuto = new String(getContenuto()).toCharArray();
            Reader reader = new CharArrayReader(contenuto); 
            importer.setReader(reader);
            String logFileName = "Import_"+nomeMatrice+".log";
            CharArrayWriter cwriter = new CharArrayWriter();
            Writer writer = new BufferedWriter(cwriter);
            importer.setLogWriter(writer);
            importer.setLogFileName(logFileName);
            importer.doImport();
            return new String(cwriter.toCharArray()).getBytes();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    }
}

When I execute it and I don't open the file chooser it works, when I open the file chooser I get an error
java.lang.NullPointerException
    at com.vaadin.server.FileDownloader.handleConnectorRequest(FileDownloader.java:134)
    at axioma.web.template.ui.components.DocumentDownloader.handleConnectorRequest(DocumentDownloader.java:24)
    at com.vaadin.server.ConnectorResourceHandler.handleRequest(ConnectorResourceHandler.java:90)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1409)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:364)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:522)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1095)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:672)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

Going deeper it seems the UI  is not accessible and/or the Session are not accessible from the FileDownloader.
Tks

Unfortunately what I described in my previous post is not true.
I get the same error also if I don't open the filechooser.
Here the relevant code
package axioma.web.configuratore.ui.dialogs;

import java.io.*;
import com.vaadin.server.*;
import com.vaadin.server.StreamResource.StreamSource;
import com.vaadin.ui.*;
import com.vaadin.ui.Button.ClickEvent;
import axioma.rubik.csv.MatriciCsvExporter;
import axioma.web.configuratore.model.domain.TipiMatrici;
import axioma.web.pax.ui.components.impl.StringField;
import axioma.web.template.ui.components.DocumentDownloader;
import axioma.web.template.ui.dialogs.*;
import axioma.web.template.ui.layouts.HorizontalCaptionLayout;
import axioma.web.template.ui.messages.TemplateMessages;

public class MatrixExportDialog extends YesNoDialog {
    
    private static final long serialVersionUID = 1L;
    
    private StringField fileName;
    private String nomeMatrice;
    private DocumentDownloader downloader;

    public MatrixExportDialog(TipiMatrici xpMatrice) {
        super(TemplateMessages.CONFIRM_EXPORT.getText(),TemplateMessages.CONFIRM_EXPORT.getMessageCode(), null ,null, new String[]{});
        nomeMatrice = xpMatrice.getNome();
        String defaultFileName = "Export_"+nomeMatrice+".csv";
        fileName.setValue(defaultFileName);
    }

    @Override
    public void createYesButton() {
        createYesButton(TemplateMessages.BUTTON_DOWNLOAD.getText(),TemplateMessages.BUTTON_DOWNLOAD.getMessageCode());
        addDownloader();
    }
    
    protected void addDownloader() {
        downloader = new DocumentDownloader(null,"Export.csv") {

            private static final long serialVersionUID = 1L;

            @Override
            protected Resource buildResource() {
                return internalBuildResource();
            }
        };
        downloader.extend(btnYes);
    }

    @Override
    public void createNoButton() {
        createNoButton(TemplateMessages.BUTTON_CLOSE.getText(),TemplateMessages.BUTTON_CLOSE.getMessageCode());
    }

    @Override
    public Layout realBuildContent() {
        VerticalLayout vl = new VerticalLayout();
        vl.setSizeFull();
        HorizontalCaptionLayout hl = new HorizontalCaptionLayout(1);
        fileName = new StringField("FileName");
        fileName.setValue("");
        fileName.setWidth("100%");
        hl.addComponent(fileName);
        hl.setWidth("100%");
        vl.addComponent(hl);
        return vl;
    }

    public String getFileName() {
        return fileName.getValue();
    }
    
    private Resource internalBuildResource() {
        String name = getFileName();
        char[] risultato = esporta();
        byte[] dati = new String(risultato).getBytes();
        System.out.println(dati);
        byte[] dati2 = "Prova prova prova".getBytes();
        StreamSource source = () -> new ByteArrayInputStream(dati2);
        StreamResource resource = new StreamResource(source, name);
        return resource;
    }
    
    private char[] esporta() {
        try {
            MatriciCsvExporter exporter = new MatriciCsvExporter(nomeMatrice);
            CharArrayWriter stream = new CharArrayWriter();
            Writer out = new BufferedWriter(stream);
            exporter.setWriter(out);
            exporter.export();
            return stream.toCharArray();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    }

    @Override
    public void executeAction(ClickEvent xpEvent) {}
}

No further help ?
Tks

Hi Tullio,
I've just tried FileDownloader in combination with popup window and I got no errors with vaadin 7.6.8. 

Maybe some issue with YesNoDialog or DocumentDownloader classes? Can you post the code?