How to define multiple parameters for a POST request using Java 11 HTTP Client

Question

I have a code that makes a POST request for a specific endpoint. This code is using Apache's HttpClient and I would like to start using the native HttpClient from Java (JDK11). But I didn't understand how to specify the parameters of my request.

This is my code using Apache Httpclient:

var path = Path.of("file.txt");
var entity = MultipartEntityBuilder.create()
            .addPart("file", new FileBody(path.toFile()))
            .addTextBody("token", "<any-token>")
            .build();

And the code using HttpClient:

var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder()
                         .uri(URI.create("https://myendpoint.com/"))
                         .POST( /* How can I set the parameters here? */ );

How can I set file and token parameters?

Answer 1

Unfortunately the Java 11 HTTP client does not provide any convenient support for multipart kind of body. But we can build custom implementation on top of it:

Map<Object, Object> data = new LinkedHashMap<>();
data.put("token", "some-token-value";);
data.put("file", File.createTempFile("temp", "txt").toPath(););

// add extra parameters if needed

// Random 256 length string is used as multipart boundary
String boundary = new BigInteger(256, new Random()).toString();

HttpRequest.newBuilder()
              .uri(URI.create("http://example.com"))
              .header("Content-Type", "multipart/form-data;boundary=" + boundary)
              .POST(ofMimeMultipartData(data, boundary))
              .build();

public HttpRequest.BodyPublisher ofMimeMultipartData(Map<Object, Object> data,
                                                     String boundary) throws IOException {
        // Result request body
        List<byte[]> byteArrays = new ArrayList<>();

        // Separator with boundary
        byte[] separator = ("--" + boundary + "\r\nContent-Disposition: form-data; name=").getBytes(StandardCharsets.UTF_8);

        // Iterating over data parts
        for (Map.Entry<Object, Object> entry : data.entrySet()) {

            // Opening boundary
            byteArrays.add(separator);

            // If value is type of Path (file) append content type with file name and file binaries, otherwise simply append key=value
            if (entry.getValue() instanceof Path) {
                var path = (Path) entry.getValue();
                String mimeType = Files.probeContentType(path);
                byteArrays.add(("\"" + entry.getKey() + "\"; filename=\"" + path.getFileName()
                        + "\"\r\nContent-Type: " + mimeType + "\r\n\r\n").getBytes(StandardCharsets.UTF_8));
                byteArrays.add(Files.readAllBytes(path));
                byteArrays.add("\r\n".getBytes(StandardCharsets.UTF_8));
            } else {
                byteArrays.add(("\"" + entry.getKey() + "\"\r\n\r\n" + entry.getValue() + "\r\n")
                        .getBytes(StandardCharsets.UTF_8));
            }
        }

        // Closing boundary
        byteArrays.add(("--" + boundary + "--").getBytes(StandardCharsets.UTF_8));

        // Serializing as byte array
        return HttpRequest.BodyPublishers.ofByteArrays(byteArrays);
    }

Here's working example on Github (you need to change VirusTotal API key)