How to post files with HttpURLConnection [Android/Java]

This article describes “How to post file data(multipart) with java.net.HttpURLConnection”.


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import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Files;
public class MultipartUtility {
private HttpURLConnection httpConn;
private DataOutputStream request;
private final String boundary = "*****";
private final String crlf = "\r\n";
private final String twoHyphens = "--";
/**
* This constructor initializes a new HTTP POST request with content type
* is set to multipart/form-data
*
* @param requestURL
* @throws IOException
*/
public MultipartUtilityV2(String requestURL)
throws IOException {
// creates a unique boundary based on time stamp
URL url = new URL(requestURL);
httpConn = (HttpURLConnection) url.openConnection();
httpConn.setUseCaches(false);
httpConn.setDoOutput(true); // indicates POST method
httpConn.setDoInput(true);
httpConn.setRequestMethod("POST");
httpConn.setRequestProperty("Connection", "Keep-Alive");
httpConn.setRequestProperty("Cache-Control", "no-cache");
httpConn.setRequestProperty(
"Content-Type", "multipart/form-data;boundary=" + this.boundary);
request = new DataOutputStream(httpConn.getOutputStream());
}
/**
* Adds a form field to the request
*
* @param name field name
* @param value field value
*/
public void addFormField(String name, String value)throws IOException {
request.writeBytes(this.twoHyphens + this.boundary + this.crlf);
request.writeBytes("Content-Disposition: form-data; name=\"" + name + "\""+ this.crlf);
request.writeBytes("Content-Type: text/plain; charset=UTF-8" + this.crlf);
request.writeBytes(this.crlf);
request.writeBytes(value+ this.crlf);
request.flush();
}
/**
* Adds a upload file section to the request
*
* @param fieldName name attribute in <input type="file" name="..." />
* @param uploadFile a File to be uploaded
* @throws IOException
*/
public void addFilePart(String fieldName, File uploadFile)
throws IOException {
String fileName = uploadFile.getName();
request.writeBytes(this.twoHyphens + this.boundary + this.crlf);
request.writeBytes("Content-Disposition: form-data; name=\"" +
fieldName + "\";filename=\"" +
fileName + "\"" + this.crlf);
request.writeBytes(this.crlf);
byte[] bytes = Files.readAllBytes(uploadFile.toPath());
request.write(bytes);
}
/**
* Completes the request and receives response from the server.
*
* @return a list of Strings as response in case the server returned
* status OK, otherwise an exception is thrown.
* @throws IOException
*/
public String finish() throws IOException {
String response ="";
request.writeBytes(this.crlf);
request.writeBytes(this.twoHyphens + this.boundary +
this.twoHyphens + this.crlf);
request.flush();
request.close();
// checks server's status code first
int status = httpConn.getResponseCode();
if (status == HttpURLConnection.HTTP_OK) {
InputStream responseStream = new
BufferedInputStream(httpConn.getInputStream());
BufferedReader responseStreamReader =
new BufferedReader(new InputStreamReader(responseStream));
String line = "";
StringBuilder stringBuilder = new StringBuilder();
while ((line = responseStreamReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
responseStreamReader.close();
response = stringBuilder.toString();
httpConn.disconnect();
} else {
throw new IOException("Server returned non-OK status: " + status);
}
return response;
}
}

Special Thanks

android - Sending files using POST with HttpURLConnection - Stack Overflow

server {
listen 8080;
return 301 https://$host$request_uri;
}