Java 用于上传文件的 HTTP 客户端 (multipart/form-data)

Question

我正在尝试实现一个 HTTP 客户端，该客户端发出多部分请求以将文件上传到 HTTP 服务器。 HTML 表单有三个输入字段：一个用于用户名，一个用于密码，一个用于文件。服务器端如下所示。

<html>
<head>
<title>Uploader</title>
</head>

<body>
   <div id="header">
         <h1>Uploader</h1>
   </div>
   <div id="content">
         <form id="uploadformular" action="upload" method="post"
                enctype="multipart/form-data" accept-charset="utf-8">
                <div class="block">
                       <label for="user">Username</label> <input type="text" id="user"
                              name="myuser" required />
                </div>
                <div class="block">
                       <label for="password">Password</label> <input type="password" id="pin"
                              name="mypassword" required />
                </div>
                <div class="block">
                       <label for="file">ZIP File</label> <input type="file" id="file"
                              name="myfile" required />
                </div>
                <div>
                       <input type="submit" value="Upload" />
                </div>
         </form>
   </div>

</body>
</html>

我的实现如下

public class MultipartUploader {

    private static final String CHARSET = "UTF-8";

    private static final String CRLF = "\r\n";

    public String httpUpload(String url, String filename, byte[] byteStream)
        throws MalformedURLException, IOException {

        HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
        final String boundary = Strings.repeat("-", 15) + Long.toHexString(System.currentTimeMillis());

        connection.setDoOutput(true);
        connection.setDoInput(true);
        connection.setUseCaches(false);
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Connection", "Keep-Alive");
        connection.setRequestProperty("Cache-Control", "no-cache");
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        OutputStream directOutput = connection.getOutputStream();
        PrintWriter body = new PrintWriter(new OutputStreamWriter(directOutput, CHARSET), true);

        body.append(CRLF);
        addSimpleFormData("myuser", "myUserName", body, boundary);
        addSimpleFormData("mypassword", "mySecretPassword", body, boundary);
        addFileData("myfile", filename, byteStream, body, directOutput, boundary);
        addCloseDelimiter(body, boundary);

        int responseCode = connection.getResponseCode();
        String responseMessage = connection.getResponseMessage();

        String payload = CharStreams.toString(new InputStreamReader(connection.getInputStream()));
        return payload;
    }

    private static void addSimpleFormData(String paramName, String wert, PrintWriter body,
        final String boundary) {

        body.append(boundary).append(CRLF);
        body.append("Content-Disposition: form-data; name=\"" + paramName + "\"").append(CRLF);
        body.append("Content-Type: text/plain; charset=" + CHARSET).append(CRLF);
        body.append(CRLF);
        body.append(wert).append(CRLF);
        body.flush();
    }

    private static void addFileData(String paramName, String filename, byte[] byteStream, PrintWriter body,
        OutputStream directOutput, final String boundary) throws IOException {

        body.append(boundary).append(CRLF);
        body.append("Content-Disposition: form-data; name=\"" + paramName + "\"; filename=\"" + filename + "\"")
            .append(CRLF);
        body.append("Content-Type: application/octed-stream").append(CRLF);
        body.append("Content-Transfer-Encoding: binary").append(CRLF);
        body.append(CRLF);
        body.flush();

        directOutput.write(byteStream);
        directOutput.flush();

        body.append(CRLF);
        body.flush();
    }

    private static void addCloseDelimiter(PrintWriter body, final String boundary) {

        body.append(boundary).append("--").append(CRLF);
        body.flush();
    }
}

服务器响应200 OK。我遇到的问题是 HTTP 正文以某种方式未正确创建，因此我从服务器获得的响应表明并非表单的所有字段都已设置。服务器没有说明它是哪个字段。所以我的问题是你看到这段代码有什么问题吗？我是否正确创建了多部分请求？

我还尝试通过以下命令使用 cURL 上传文件并且成功了。

cURL -F "myuser=myUserName" -F "mypassword=mySecretPassword" -F "myfile=@/path/to/my/file.zip" "http://abcdef.gh:1234/path/to/uploader"

Answer 1

您的部分数据之间的边界在开头缺少额外的两个破折号：--

我通过将请求捕获到 http://httpbin.org/post made via your program and curl and comparing them via diff tool. I used Wireshark 来捕获请求。

解决此问题的方法如下：

private static void addSimpleFormData(String paramName, String wert, PrintWriter body,
                                      final String boundary) {

    body.append("--").append(boundary).append(CRLF);
    body.append("Content-Disposition: form-data; name=\"" + paramName + "\"").append(CRLF);
    body.append("Content-Type: text/plain; charset=" + CHARSET).append(CRLF);
    body.append(CRLF);
    body.append(wert).append(CRLF);
    body.flush();
}

private static void addFileData(String paramName, String filename, byte[] byteStream, PrintWriter body,
                                OutputStream directOutput, final String boundary) throws IOException {

    body.append("--").append(boundary).append(CRLF);
    body.append("Content-Disposition: form-data; name=\"" + paramName + "\"; filename=\"" + filename + "\"")
            .append(CRLF);
    body.append("Content-Type: application/octed-stream").append(CRLF);
    body.append("Content-Transfer-Encoding: binary").append(CRLF);
    body.append(CRLF);
    body.flush();

    directOutput.write(byteStream);
    directOutput.flush();

    body.append(CRLF);
    body.flush();
}

private static void addCloseDelimiter(PrintWriter body, final String boundary) {
    body.append("--").append(boundary).append("--").append(CRLF);
    body.flush();
}

在每个方法的开头注意额外的 .append("--")。

请参阅 https://gist.github.com/shtratos/8e9570a4a5591b2bcecd55ca60b3f24f 了解完整的工作代码

Answer 2

您编写自己的实现而不是使用 Apache HttpClient 是否有充分的理由？

见https://hc.apache.org/httpcomponents-client-ga/

Java 用于上传文件的 HTTP 客户端 (multipart/form-data)

Java HTTP Client for Uploading Files (multipart/form-data)

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