如何通过HttpUrlConnection将图像从Android客户端发送到Node.js服务器？

Question

我正在尝试使用HttpUrlConnection将图像发送到服务器，因为它是Google推荐的。我决定将图像转换为Base64字符串，然后将其发送到服务器，然后将其解码为.jpg文件。但是这种方法仅适用于小尺寸缩略图，而我无法发送全尺寸图像。

这是android客户端代码：

 public static void postData(Bitmap imageToSend) {



        try

        {
            URL url = new URL("http://");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");

            conn.setDoInput(true);
            conn.setDoOutput(true);

            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.setRequestProperty("Cache-Control", "no-cache");

            conn.setReadTimeout(35000);
            conn.setConnectTimeout(35000);


            ByteArrayOutputStream bos = new ByteArrayOutputStream();

            // writes a compress version of Bitmap to a specified outputstream
            imageToSend.compress(Bitmap.CompressFormat.JPEG, 100, bos);

            byte[] byteArray = bos.toByteArray();
            String imageEncoded = Base64.encodeToString(byteArray, Base64.DEFAULT);

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("image", imageEncoded));


            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(os, "UTF-8"));

            // getQuery is function for creating a URL encoded string
            writer.write(getQuery(params));

            System.out.println("Response Code: " + conn.getResponseCode());

            InputStream in = new BufferedInputStream(conn.getInputStream());
            Log.d("sdfs", "sfsd");
            BufferedReader responseStreamReader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            StringBuilder stringBuilder = new StringBuilder();
            while ((line = responseStreamReader.readLine()) != null)
                stringBuilder.append(line).append("\n");
            responseStreamReader.close();

            String response = stringBuilder.toString();
            System.out.println(response);

            bos.flush();
            bos.close();
            in.close();
            conn.disconnect();

        }

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

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


}

Node.js服务器代码：

function base64_decode(base64str,file) {

   var bitmap = new Buffer(base64str,'base64');

   //writing into an image file

   fs.writeFile(file, bitmap);

   //write a text file

    console.log('File created from base64 encoded string');

}



app.post("/", function (req,res,next) {

        //requesting the value of the image key which is urlencoded base 64 string

        var image = req.body.image;

        console.log(req.body.image);

        base64_decode(image,'newImage.jpg');



        res.writeHead(200, {'Content-Type':'text/plain'});

        res.write('the image is saved');

        res.end();

        if (req.url != "/")

           next();

由于BufferedWriter的大小限制，我无法对完整尺寸的图像使用相同的方法-base64编码的字符串太长了。

另一种方法是使用HttpPost和MultipartEntity，但是API22中已弃用了这两种方法，而且我不知道如何在服务器端处理请求。在其他示例中，使用了一些包装，例如两个连字符，border，crlf，但我找不到原因。

我需要一个带有HttpUrlConnection的示例

感谢您的帮助，因为我是Android和node.js的新手

Answer 1

我建议上传二进制数据。您可以将图像元数据（例如名称，类型，用户ID等）放置为url参数或自定义HTTP标头（X -…）。

Android客户端代码（未经测试！）：

 public static void postData(Bitmap imageToSend) {
        try
        {
            URL url = new URL("http://myserver/myapp/upload-image");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");

            conn.setDoInput(true);
            conn.setDoOutput(true);

            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.setRequestProperty("Cache-Control", "no-cache");

            conn.setReadTimeout(35000);
            conn.setConnectTimeout(35000);

            // directly let .compress write binary image data
            // to the output-stream
            OutputStream os = conn.getOutputStream();
            imageToSend.compress(Bitmap.CompressFormat.JPEG, 100, os);
            os.flush();
            os.close();

            System.out.println("Response Code: " + conn.getResponseCode());

            InputStream in = new BufferedInputStream(conn.getInputStream());
            Log.d("sdfs", "sfsd");
            BufferedReader responseStreamReader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            StringBuilder stringBuilder = new StringBuilder();
            while ((line = responseStreamReader.readLine()) != null)
                stringBuilder.append(line).append("\n");
            responseStreamReader.close();

            String response = stringBuilder.toString();
            System.out.println(response);

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

Node.js，快速代码：

function rawBody(req, res, next) {
    var chunks = [];

    req.on('data', function(chunk) {
        chunks.push(chunk);
    });

    req.on('end', function() {
        var buffer = Buffer.concat(chunks);

        req.bodyLength = buffer.length;
        req.rawBody = buffer;
        next();
    });

    req.on('error', function (err) {
        console.log(err);
        res.status(500);
    });
}

app.post('/upload-image', rawBody, function (req, res) {

    if (req.rawBody && req.bodyLength > 0) {

        // TODO save image (req.rawBody) somewhere

        // send some content as JSON
        res.send(200, {status: 'OK'});
    } else {
        res.send(500);
    }

});

我将尝试解释node.js部分：该函数rawBody充当Express中间件。发出POST请求时，该函数将与请求对象一起调用。它注册了听众data，end和error事件。这些data事件将所有传入的数据块追加到缓冲区。当end火灾，该属性rawBody在请求对象被创建并包含二进制数据（图像斑点）。rawBody()然后将控制权转移到下一个处理程序，该处理程序现在可以将blob保存到您的数据库或文件系统中。

当处理真正的大数据斑点时，这种处理方法不是最佳方法。最好将数据流传输到文件或数据库以节省内存。