创建文本文件以使用Java快速下载

Question

我有一个Java Servlet，每次调用它都会随机生成数千个String。我希望用户在调用Servlet时能够将它们保存在文件中。我不想先将文件写入磁盘或内存。用户调用servlet时，有没有一种动态写入文件的方法？谢谢

Answer 1

您在Servlet中生成的任何文本都可以简单地写入ServletResponse.getOutputStream()返回的OutputStream。

如果您希望将输出作为文件下载，则可以按照此答案中的方法-https://stackoverflow.com/a/11772700/1372207

区别在于，内容类型将为text/plain，而不是从另一个输入流中读取，您只需使用ServletOutputStream方法将String对象直接写入print(String)。

Answer 2

[如果您在提供下载服务时使用此想法将内容写入HttpServletResponse的输出流，而不是将内容保存在本地然后将文件读取为FileInputStream，则只需通过InputStream stream = new ByteArrayInputStream(exampleString.getBytes("UTF-8"));将文件内容转换为InputStream。

以下代码部分引用了https://www.codejava.net/java-ee/servlet/java-servlet-download-file-example。

    public void doDownload(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String fileName = "xxx.txt";
        String fileContent = "";

        // get absolute path of the application
        ServletContext context = request.getServletContext();

        // get MIME type of the file
        String mimeType = context.getMimeType(fileName);
        if (mimeType == null) {
            // set to binary type if MIME mapping not found
            mimeType = "application/octet-stream";
        }

        setResponseHeader(response, fileName, mimeType, (int) fileContent.length());

        InputStream inputStream = new ByteArrayInputStream(fileContent.getBytes("UTF-8"));
        // get output stream of the response
        OutputStream outStream = response.getOutputStream();

        byte[] buffer = new byte[4096];
        int bytesRead = -1;

        // write bytes read from the input stream into the output stream
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, bytesRead);
        }

        inputStream.close();
        outStream.close();
    }

    private void setResponseHeader(HttpServletResponse response, String fileName, String mimeType, Integer fileLength) {
        response.setContentType(mimeType);
        response.setContentLength(fileLength);
        response.setContentType("application/octet-stream; charset=UTF-8");

        String headerKey = "Content-Disposition";
        String headerValue = String.format("attachment; filename=\"%s\"", fileName);
        response.setHeader(headerKey, headerValue);

        response.addHeader("Pargam", "no-cache");
        response.addHeader("Cache-Control", "no-cache");
    }