从bean

Question

我正在jsf / primefaces应用程序中使用itext生成多个pdf文件。有些文件可以正确生成，而另一些则不能。 经过调试后，我发现特定的代码行会导致此问题。

当我打电话

writer.setPageEvent(new Footer(image));

其中writer是PdfWriter类型。我收到这些错误：

[org.primefaces.application.exceptionhandler.PrimeExceptionHandler] (default task-96) Could not handle exception!: java.lang.IllegalStateException: UT010006: Cannot call getWriter(), getOutputStream() already called

我立即获得Pdf Writer的使用权，我使用以下代码行：

FacesContext fc = FacesContext.getCurrentInstance();
    ExternalContext ec = fc.getExternalContext();

    ec.responseReset(); // Some JSF component library or some Filter might
                        // have set some headers in the buffer beforehand.
                        // We want to get rid of them, else it may collide.
    ec.setResponseContentType(contentType); // Check
                                            // http://www.iana.org/assignments/media-types
                                            // for all types. Use if
                                            // necessary
                                            // ExternalContext#getMimeType()
                                            // for auto-detection based on
                                            // filename.
    // ec.setResponseContentLength(contentLength); // Set it with the file
    // size. This header is optional. It will work if it's omitted, but the
    // download progress will be unknown.
    ec.setResponseHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");

    OutputStream output = ec.getResponseOutputStream();

    // Now you can write the InputStream of the file to the above
    // OutputStream the usual way.
    Document document = new Document(PageSize.A4);

    PdfWriter writer = PdfWriter.getInstance(document, output);

我还尝试使用HttpServletResponse代替：

HttpServletResponse httpServletResponse = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();
OutputStream output = httpServletResponse.getOutputStream();

但是我遇到了同样的错误。

我该如何解决此问题并直接在PdfWriter中编写？还是在没有PdfWriter的情况下做同样的事情？