java - 在 Android 中发布带有图像的多部分请求？

Question

我正在尝试将对象的 JSON 表示形式和可选图像发布到我的 Spring 后端。但是，我在发布带有图像的请求时遇到了很大的麻烦。我已经设法将第一部分发布到服务器； JSON 对象。但是，当我尝试添加第二部分(用户捕获的图像)时，什么也没有发生。我没有看到任何堆栈跟踪。

我做错了什么以及如何根据请求发布图片。这就是我的...

String boundary = UUID.randomUUID().toString();
String twoHyphens = "--";
String attachmentName = "data";
String crlf = "\r\n";


try {
    URI uri = new URI("http://myappserver.com/app");
    HttpURLConnection urlConnection = (HttpURLConnection) uri.toURL().openConnection();
    urlConnection.setRequestMethod("POST");
    urlConnection.setRequestProperty("Connection", "Keep-Alive");
    urlConnection.setDoInput(true);
    urlConnection.setDoOutput(true);
    urlConnection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);

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

    InputStream inputStream = context.getContentResolver().openInputStream(question.getUri());

    // FIRST PART; A JSON object
    dos.writeBytes(twoHyphens + boundary);
    dos.writeBytes(crlf);
    dos.writeBytes("Content-Type: application/json");
    dos.writeBytes(crlf);
    dos.writeBytes("Content-Disposition: form-data; name=\"data\"");
    dos.writeBytes(crlf);
    dos.writeBytes(crlf);
    dos.writeBytes(jsonEntity);
    dos.writeBytes(crlf);

    // SECOND PART; A image..
    dos.writeBytes(twoHyphens + boundary);
    dos.writeBytes(crlf);
    dos.writeBytes("Content-Type: image/jpg");
    dos.writeBytes(crlf);
    dos.writeBytes("Content-Disposition: form-data; name=\"image\"");
    dos.writeBytes(crlf);
    dos.writeBytes(crlf);

    // Something must be done here. I guess I must encode it to Base64 here.
    // How can I avoid loading the whole image at once so I don't get out of memory errors.

    dos.writeBytes(crlf);
    dos.writeBytes(twoHyphens + boundary + twoHyphens + crlf);
    dos.close();
} catch (Exception e) {

}

Answer 1

代码说明了如何发送文件(这里是pdf)。通读一遍，对调试代码很有帮助。

int bytesRead, bytesAvailable, bufferSize;
byte[] buffer;
int maxBufferSize = 1 * 1024 * 1024;
FileInputStream fileInputStream = new FileInputStream(file);

dos.writeBytes(twoHyphens + boundary + lineEnd); 
dos.writeBytes("Content-Disposition: form-data; name=\"attachment_0\";filename=\"" + file.getName() + "\"" + lineEnd);
dos.writeBytes("Content-Type: text/pdf" + lineEnd);
dos.writeBytes("Content-Length: " + file.length() + lineEnd);    
dos.writeBytes(lineEnd);        
bytesAvailable = fileInputStream.available(); 
bufferSize = Math.min(bytesAvailable, maxBufferSize);
buffer = new byte[bufferSize];
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); 
}   

dos.writeBytes(lineEnd);
dos.writeBytes(twoHyphens + boundary + lineEnd);
fileInputStream.close();
}

//发送一个参数，见下，key为webservice参数的key。

dos.writeBytes("Content-Disposition: form-data; name=\""+key+"\"" + lineEnd);
dos.writeBytes(lineEnd);
dos.writeBytes(requestData.get(key).toString() + lineEnd);