Quick Solution: Download csv file in JSF 2

In xhtml file, I use primefaces command button. You can also use h:commandButton.

<h:form>

<p:commandButton  value="Download File" action="#{branchDownload.download}"
                                 ajax="false"         /> 

 </h:form>

In Managed Bean class, download() method is as follows:

@ManagedBean
@RequestScoped
public class BranchDownload {

// Your code

// download method

public void download()
    {
        String file_name =  "FILE.csv" ;
       
        FacesContext fc = FacesContext.getCurrentInstance();
        ExternalContext ec= fc.getExternalContext();
        ec.responseReset();
        ec.setResponseContentType("text/csv");
        ec.setResponseHeader("Content-Disposition", "attachment; filename=\""+file_name + "\"");
       
        BufferedOutputStream csvOut;
        try {
            csvOut = new BufferedOutputStream(ec.getResponseOutputStream());
            BufferedWriter csvWriter = new BufferedWriter(new OutputStreamWriter(csvOut, "UTF-8"));
       
            csvWriter.append("1,2,3,4,5,6,7,8");
            csvWriter.append("\n");
            csvWriter.flush();

            csvWriter.append("One,2,Three,4,5,6,7,8");
            csvWriter.append("\n");
            csvWriter.flush();

            csvWriter.close();
            csvOut.close();
        } catch (IOException ex) {
            Logger.getLogger(BranchDownload.class.getName()).log(Level.SEVERE, null, ex);
        }
        finally{
            fc.responseComplete();
        }
      
    }

// End download method

}