如何用JAVA EE获取下载文件的HttpServletResponse实例

Question

我在服务器上有一个文件txt（以前生成的）。当用户点击按钮它生成文件，现在我想（另外）下载文件在我的函数。但是我不能让它工作（我是JAVA EE新手），因为我不知道如何获得HttpServletResponse。

在web中，我用以下内容调用函数：

@Path("getreport")
@POST
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public JSONObject getreport(CommonInput input) {
    JSONObject j = objectmapper.conertValue(reportBean.getreport(),JSONObject.class);
    return j;
}

reprotBean具有以下功能：

public void getreport() {
    //...doing many things
    //generating my file
    List<String> lines = new ArrayList<>();
    lines.add("star file");
    //..adding many lines
    Path file = Paths.get("C:\\Users\\myuser\\file.txt");
    Files.write(file, lines, StandardCharsets.UTF_8);

    downloadFile();
    //...doing many things
}

我找到了下载文件的方法：

public void downloadFile(HttpServletResponse response){ 
    String sourceFile = ""C:\\Users\\myuser\\file.txt"";
    try {
        FileInputStream inputStream = new FileInputStream(sourceFile);
        String disposition = "attachment; fileName=outputfile.txt";
        response.setContentType("text/txt");
        response.setHeader("Content-Disposition", disposition);
        response.setHeader("content-Length", String.valueOf(stream(inputStream, response.getOutputStream())));

    } catch (IOException e) {
        logger.error("Error occurred while downloading file {}",e);
    }
}

private long stream(InputStream input, OutputStream output) throws IOException {

try (ReadableByteChannel inputChannel = Channels.newChannel(input); WritableByteChannel outputChannel = Channels.newChannel(output)) {
    ByteBuffer buffer = ByteBuffer.allocate(10240);
    long size = 0;

    while (inputChannel.read(buffer) != -1) {
        buffer.flip();
        size += outputChannel.write(buffer);
        buffer.clear();
    }
    return size;
}
}

当我尝试使用downloadFile（）时，它需要HttpServletResponse，而我没有那个参数。我不明白如何得到它（它是如何工作的），或者我必须使用另一种方法来下载我的文件？

我找到的所有解决方案都需要HttpServletResponse（从浏览器下载文件）

Answer 1

如果您已经生成了该文件。只需将其写入HttpServletResponse

        resp.setContentType("text/plain");
        resp.setHeader("Content-disposition", "attachment; filename=sample.txt");

        try(InputStream in = req.getServletContext().getResourceAsStream("sample.txt");
          OutputStream out = resp.getOutputStream()) {

            byte[] buffer = new byte[ARBITARY_SIZE];

            int numBytesRead;
            while ((numBytesRead = in.read(buffer)) > 0) {
                out.write(buffer, 0, numBytesRead);
            }
        }

请确保您的文件可由ServeletContext访问

    @GetMapping("/download")
    public ResponseEntity<byte[]> downloadErrorData() throws Exception {
        List<Employee> employees = employeeService.getEmployees();
        ObjectMapper objectMapper = new ObjectMapper();
        String json = objectMapper.writeValueAsString(employees);
        byte[] isr = json.getBytes();
        String fileName = "employees.json";
        HttpHeaders respHeaders = new HttpHeaders();
        respHeaders.setContentLength(isr.length);
        respHeaders.setContentType(new MediaType("text", "json"));
        respHeaders.setCacheControl("must-revalidate, post-check=0, pre-check=0");
        respHeaders.set(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + fileName);
        return new ResponseEntity<byte[]>(isr, respHeaders, HttpStatus.OK);
    }