JAVA中HttpURLConnection中的一个帖子请求中发送多个文件

Question

我正在使用 HttpURLConnection 通过 post 方法发送文件。我正在向文件发送一个“student_id”参数。在每个发布请求中发送一个文件时，该代码工作正常。 但是，我如何更新下面的代码以在一个帖子请求中发送多个文件，其中所有文件都属于同一个“student_id”？

       try{  
            File textFile2 = new File("info.txt");  

         URL url = new URL("htttp://wwww.students.com");
         HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();         
         urlConnection.setChunkedStreamingMode(0);
         urlConnection.setDoOutput(true);   


        String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.

        urlConnection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);          
        OutputStream output = urlConnection.getOutputStream();
        PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, charset), true);

        writer.append("--" + boundary).append(CRLF);
        writer.append("Content-Disposition: form-data; name=\"student_id\"").append(CRLF);
        writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);
        writer.append(CRLF).append("25").append(CRLF).flush();


        writer.append("--" + boundary).append(CRLF);
        writer.append("Content-Disposition: form-data; name=\"newfile\"; filename=\"" + textFile2.getName() + "\"").append(CRLF);
        writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF); // Text file itself must be saved in this charset!
        writer.append(CRLF).flush();                                                            
        Files.copy(textFile2.toPath(), output);//copies all bytes in  a file to the output stream 
        output.flush(); // Important before continuing with writer!
        writer.append(CRLF).flush();

        writer.append("--" + boundary + "--").append(CRLF).flush();
        InputStream responseStream; 

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {

            e.printStackTrace();
        }

我尝试在“newfile”中使用参数添加“multiple”，但它不起作用

        writer.append("--" + boundary).append(CRLF);
    writer.append("Content-Disposition: form-data; name=\"newfile\" multiple; filename=\"" + textFile2.getName() + "\"").append(CRLF);
    writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF); // Text file itself must be saved in this charset!
    writer.append(CRLF).flush();                                                            
    Files.copy(textFile2.toPath(), output);//copies all bytes in  a file to the output stream 
    output.flush(); // Important before continuing with writer!
    writer.append(CRLF).flush();

    writer.append("--" + boundary + "--").append(CRLF).flush();

Answer 1

您似乎正在尝试发布带有 1 个 表单字段 的 multipart/form-data 请求，其中 name 参数为 student_id 和多个 文件部分 以上传文件。

您可以通过在单独的部分中提供每个文件来发送多个文件，但所有文件都具有相同的name 参数。

例如，您可以通过发送带有name参数newfile的第一个文件部分来上传textFile1的文件：

writer.append("--" + boundary).append(CRLF);
writer.append("Content-Disposition: form-data; name=\"newfile\"; filename=\"" + textFile1.getName()+ "\"").append(CRLF);
writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);
writer.append("Content-Transfer-Encoding: binary").append(CRLF);
writer.append(CRLF);
writer.flush();

FileInputStream inputStream = new FileInputStream(textFile1);
byte[] buffer = new byte[4096];
int bytesRead = -1;
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
}
outputStream.flush();
inputStream.close();

writer.append(CRLF);
writer.flush();

然后，您可以通过发送与newfile 相同的name 参数的文件部分来上传textFile2 的另一个文件：

writer.append("--" + boundary).append(CRLF);
writer.append("Content-Disposition: form-data; name=\"newfile\"; filename=\"" + textFile2.getName()+ "\"").append(CRLF);
writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);
writer.append("Content-Transfer-Encoding: binary").append(CRLF);
writer.append(CRLF);
writer.flush();

FileInputStream inputStream = new FileInputStream(textFile2);
byte[] buffer = new byte[4096];
int bytesRead = -1;
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
}
outputStream.flush();
inputStream.close();

writer.append(CRLF);
writer.flush();

如您所见，除了要上传的文件外，代码几乎相同。建议将代码放入一个方法中并调用它来发送每个文件部分。