如何提供从JSF支持bean下载的文件？

Question

有什么方法可以提供从JSF支持bean操作方法下载的文件吗？我试过很多东西。主要的问题是，我不知道如何获取响应的outputstream，以便将文件内容写入其中。我知道如何使用servlet来实现这一点，但是这不能从JSF表单调用，需要一个新的请求。

如何从当前FacesContext获取响应的OutputStream？

Answer 1

您可以通过ExternalContext获得所有内容。在JSF1.x中，可以通过ExternalContext#getResponse()获取原始HttpServletResponse对象。在JSF2.x中，您可以使用一系列新的委托方法，如ExternalContext#GetResponseOutputStream()，而不需要从JSF头罩下获取HttpServletResponse。

在响应中，您应该设置content-type标头，以便客户机知道哪个应用程序与提供的文件关联。并且，您应该设置content-lengte标头，以便客户端能够计算下载进度，否则将是未知的。如果需要另存为对话框，则应将Content-Disposition标头设置为Attachment，否则客户端将尝试内联显示它。最后，只需将文件内容写入响应输出流。

最重要的部分是调用FacesContext#ResponseComplete()，以通知JSF在将文件写入响应后不应执行导航和呈现，否则响应的末尾将被页面的HTML内容污染，或者在旧的JSF版本中，当JSF实现调用GetWriter()呈现HTML时，您将得到一个IllegalStateException，其中包含一条消息，类似于已经为该响应调用了GetOutputStream()。

您只需要确保action方法不是由ajax请求调用的，而是由使用 和 激发的普通请求调用的。Ajax请求和远程命令由JavaScript处理，由于安全原因，JavaScript没有强制与Ajax响应内容进行另存为对话的工具。

如果您使用的是PrimeFaces ，那么您需要确保通过ajax=“false”属性显式关闭ajax。如果您使用的是ICEfaces，那么您需要在命令组件中嵌套一个 。

public void download() throws IOException {
    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 + "\""); // The Save As popup magic is done here. You can give it any file name you want, this only won't work in MSIE, it will use current request URL as file name instead.

    OutputStream output = ec.getResponseOutputStream();
    // Now you can write the InputStream of the file to the above OutputStream the usual way.
    // ...

    fc.responseComplete(); // Important! Otherwise JSF will attempt to render the response which obviously will fail since it's already written with a file and closed.
}

public void download() throws IOException {
    FacesContext fc = FacesContext.getCurrentInstance();
    HttpServletResponse response = (HttpServletResponse) fc.getExternalContext().getResponse();

    response.reset(); // 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.
    response.setContentType(contentType); // Check http://www.iana.org/assignments/media-types for all types. Use if necessary ServletContext#getMimeType() for auto-detection based on filename.
    response.setContentLength(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.
    response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\""); // The Save As popup magic is done here. You can give it any file name you want, this only won't work in MSIE, it will use current request URL as file name instead.

    OutputStream output = response.getOutputStream();
    // Now you can write the InputStream of the file to the above OutputStream the usual way.
    // ...

    fc.responseComplete(); // Important! Otherwise JSF will attempt to render the response which obviously will fail since it's already written with a file and closed.
}

如果您需要从本地磁盘文件系统流式传输静态文件，请替换如下代码：

File file = new File("/path/to/file.ext");
String fileName = file.getName();
String contentType = ec.getMimeType(fileName); // JSF 1.x: ((ServletContext) ec.getContext()).getMimeType(fileName);
int contentLength = (int) file.length();

// ...

Files.copy(file.toPath(), output);

如果您需要对动态生成的文件（如PDF或XLS）进行流式传输，那么只需提供output，所使用的API需要outputStream。

例如。iText PDF：

String fileName = "dynamic.pdf";
String contentType = "application/pdf";

// ...

Document document = new Document();
PdfWriter writer = PdfWriter.getInstance(document, output);
document.open();
// Build PDF content here.
document.close();

例如。Apache POI HSSF：

String fileName = "dynamic.xls";
String contentType = "application/vnd.ms-excel";

// ...

HSSFWorkbook workbook = new HSSFWorkbook();
// Build XLS content here.
workbook.write(output);
workbook.close();

public void download() throws IOException {
    Faces.sendFile(file, true);
}

是的，这段代码是完整的。您不需要自己调用responsecomplete()等等。此方法还可以正确处理特定于IE的标头和UTF-8文件名。你可以在这里找到源代码。