使用 Java 将文件发布到 WebServer

Question

我正在尝试使用本地 Java 应用程序将文件发布到 ASP.NET WEB API (C#) 服务器。 基本上我试图在 Java SE 中重现以下 HTML 代码：

<form name="form1" method="post" enctype="multipart/form-data" action="http://localhost:50447/api/files/">
<div>
    <label for="image1">Image File</label>
    <input name="image1" type="file" />
</div>
<div>
    <input type="submit" value="Submit" />
</div>

最简单的方法是什么？我想避免使用 Apache .. 比如：

String urlToConnect = "http://localhost:50447/api/files/";
    String paramToSend = "";
    File fileToUpload = new File("C:/Users/aa/Desktop/sample_signed.pdf");
    String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.

    URLConnection connection = null;
    try {
        connection = new URL(urlToConnect).openConnection();
    } catch (IOException e2) {
        // TODO Auto-generated catch block
        e2.printStackTrace();
    }
    connection.setDoOutput(true); // This sets request method to POST.
    connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
    PrintWriter writer = null;
    try {
        writer = new PrintWriter(new OutputStreamWriter(connection.getOutputStream(), "UTF-8"));

        writer.println("--" + boundary);
        writer.println("Content-Disposition: form-data; name=\"paramToSend\"");
        writer.println("Content-Type: text/plain; charset=UTF-8");
        writer.println();
        writer.println(paramToSend);

        writer.println("--" + boundary);
        writer.println("Content-Disposition: form-data; name=\"fileToUpload\"; filename=\"sample_signed.pdf\"");
        writer.println("Content-Type: text/plain; charset=UTF-8");
        writer.println();
        BufferedReader reader = null;
        try {
            try {
                reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileToUpload), "UTF-8"));
            } catch (UnsupportedEncodingException | FileNotFoundException e1) {
                e1.printStackTrace();
            }
            try {
                for (String line; (line = reader.readLine()) != null;) {
                    writer.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        } finally {
            if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
        }

        writer.println("--" + boundary + "--");
    } catch (UnsupportedEncodingException e2) {

        e2.printStackTrace();
    } catch (IOException e2) {

        e2.printStackTrace();
    } finally {
        if (writer != null) writer.close();
    }

    // Connection is lazily executed whenever you request any status.
    int responseCode = 0;
    try {
        responseCode = ((HttpURLConnection) connection).getResponseCode();
    } catch (IOException e) {
        e.printStackTrace();
    }
    System.out.println(responseCode);

仅使用 URLConnections.. 此代码无法正常工作.. 它发送文件，但丢失了一些内容，我不知道为什么.. 我的 HTML 示例运行良好..

你能帮帮我吗？

感谢您的关注， 最好的问候。

Answer 1

在传输二进制数据时，您正在使用读写器组合。处理二进制数据时应该使用流。

因此，不要使用 BufferedReader，而是使用缓冲的普通 InputStream 来读取文件，并且不要包装从 URLConnection 获得的输出流。

在读取循环中读取字节而不是字符串。所以替换以 BufferedReader 开头的部分，直到边界写入之前的 finally：

            OutputStream output = connection.getOutputStream();
            InputStream fileIn = new FileInputStream(fileToUpload);
            try {
                byte[] buffer = new byte[4096];
                int length;
                while ((length = fileIn.read(buffer)) > 0) {
                    output.write(buffer, 0, length);
                }
                output.flush();
            } finally {

                if (fileIn != null) try { fileIn.close(); } catch (IOException logOrIgnore) {}
            }

Answer 2

解决方案：另一种方法，使用 DataOutputStream。

FileInputStream fileInputStream = new FileInputStream(absolutePath);
        URL url = new URL("http://localhost:50447/api/files/");

        // Open a HTTP  connection to  the URL
        conn = (HttpURLConnection) url.openConnection();
        conn.setDoInput(true); // Allow Inputs
        conn.setDoOutput(true); // Allow Outputs
        conn.setUseCaches(false); // Don't use a Cached Copy
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("ENCTYPE", "multipart/form-data");
        conn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
        conn.setRequestProperty("uploaded_file", filename);

        dos = new DataOutputStream(conn.getOutputStream());

        dos.writeBytes(twoHyphens + boundary + lineEnd);
        dos.writeBytes("Content-Disposition: form-data; name=\"uploaded_file\";filename=\"" + fileName + "\"" + lineEnd);

        dos.writeBytes(lineEnd);

        // create a buffer of  maximum size
        bytesAvailable = fileInputStream.available();

        bufferSize = Math.min(bytesAvailable, maxBufferSize);
        buffer = new byte[bufferSize];

        // read file and write it into form...
        bytesRead = fileInputStream.read(buffer, 0, bufferSize); 

        while (bytesRead > 0) {

            dos.write(buffer, 0, bufferSize);
            bytesAvailable = fileInputStream.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);  

        }

        // send multipart form data necesssary after file data...
        dos.writeBytes(lineEnd);
        dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);


        // Responses from the server (code and message)
        serverResponseCode = conn.getResponseCode();
        String serverResponseMessage = conn.getResponseMessage();
        System.out.println(serverResponseMessage);

        fileInputStream.close();
        dos.flush();
        dos.close();