从Java servlet下载文件为null

FMc 发表于 Dev

FMC

我正在尝试创建一种方法，该方法允许用户通过Servlet在文件系统上下载文件。现在，正确filename显示了下载内容并下载了文件，但文件内容始终为空。

我也尝试过将文件内容打印到控制台，但没有任何显示。

有人可以在这里建议我做错了什么吗？

谢谢

String filePath = "uploads/" + request.getParameter( "filename" );
File downloadFile = new File( filePath );

String relativePath = getServletContext().getRealPath( "" );
System.out.println( "relativePath = " + relativePath );

ServletContext context = getServletContext();

String mimeType = context.getMimeType( filePath );
if( mimeType == null )
{
    mimeType = "application/octet-stream";
}
System.out.println( "MIME type: " + mimeType );

response.setContentType( mimeType );
response.setContentLength( (int) downloadFile.length() );

String headerKey = "Content-Disposition";
String headerValue = String.format( "attachment; filename=\"%s\"", downloadFile.getName() );
response.setHeader( headerKey, headerValue );
byte[] bytes = Files.readAllBytes( downloadFile.getAbsoluteFile().toPath() );
OutputStream outStream = response.getOutputStream();

System.out.println( bytes.toString() );

outStream.write( bytes );

outStream.flush();
outStream.close();

注解

@WebServlet(urlPatterns =
{ "/Routing/*" })
@MultipartConfig(location = "/tmp", fileSizeThreshold = 1024 * 1024,     maxFileSize = 1024 * 1024 * 5, maxRequestSize = 1024 * 1024 * 5 * 5)
public class Routing extends HttpServlet
{

布哈克·辛迪

此解决方案是BalusC File Servlet博客的改进解决方案。

我用这个解决方案的原因是因为它reset()的HttpServletResponse response写数据之前。

@WebServlet(urlPatterns =
{ "/Routing/*" })
@MultipartConfig(location = "/tmp", fileSizeThreshold = 1024 * 1024,     maxFileSize = 1024 * 1024 * 5, maxRequestSize = 1024 * 1024 * 5 * 5)
public class FileServlet extends HttpServlet {

    // Constants ----------------------------------------------------------------------------------

    private static final int DEFAULT_BUFFER_SIZE = 10240; // 10KB.


    // Actions ------------------------------------------------------------------------------------

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        // Get requested file by path info.
        String filePath = "uploads/" + request.getParameter( "filename" );

        // Check if file is actually supplied to the request URI.
        if (filePath == null) {
            // Do your thing if the file is not supplied to the request URI.
            // Throw an exception, or send 404, or show default/warning page, or just ignore it.
            response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
            return;
        }

        // Decode the file name (might contain spaces and on) and prepare file object.
        File downloadFile = new File( filePath );

        // Check if file actually exists in filesystem.
        if (!downloadFile.exists()) {
            // Do your thing if the file appears to be non-existing.
            // Throw an exception, or send 404, or show default/warning page, or just ignore it.
            response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
            return;
        }

        // Get content type by filename.
        String contentType = getServletContext().getMimeType(file.getName());

        // If content type is unknown, then set the default value.
        // For all content types, see: http://www.w3schools.com/media/media_mimeref.asp
        // To add new content types, add new mime-mapping entry in web.xml.
        if (contentType == null) {
            contentType = "application/octet-stream";
        }

        // Init servlet response.
        response.reset();
        response.setBufferSize(DEFAULT_BUFFER_SIZE);
        response.setContentType(contentType);
        response.setHeader("Content-Length", String.valueOf(file.length()));
        response.setHeader("Content-Disposition", "attachment; filename=\"" + file.getName() + "\"");

        // Prepare streams.
        BufferedInputStream input = null;
        BufferedOutputStream output = null;

        try {
            // Open streams.
            input = new BufferedInputStream(new FileInputStream(file), DEFAULT_BUFFER_SIZE);
            output = new BufferedOutputStream(response.getOutputStream(), DEFAULT_BUFFER_SIZE);

            // Write file contents to response.
            byte[] bytes = Files.readAllBytes( downloadFile.getAbsoluteFile().toPath() );
            output.write(buffer, 0, bytes.length);
        } finally {
            // Gently close streams.
            close(output);
            close(input);
        }
    }

    // Helpers (can be refactored to public utility class) ----------------------------------------

    private static void close(Closeable resource) {
        if (resource != null) {
            try {
                resource.close();
            } catch (IOException e) {
                // Do your thing with the exception. Print it, log it or mail it.
                e.printStackTrace();
            }
        }
    }
}