How to Make Multipart/Form-Data POST Requests in Java?

Making a Multipart/Form-Data POST Request in Java

HTTP's multipart/form-data encoding is commonly used for file uploads, allowing clients to send both text and binary data in a single request. While Apache Commons HttpClient 3.x supported this functionality, it was removed in version 4.0. This article explores alternative Java libraries that enable multipart/form-data POST requests.

Despite reaching out to the HttpClient project, there are no known efforts to re-implement multipart support. As such, developers must seek alternative solutions for their multipart/form-data needs.

Solution

HttpClient 4.x, the current stable version, offers a more modern API for handling multipart requests. Here's an example using the updated API:

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost uploadFile = new HttpPost("...");
MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.addTextBody("field1", "yes", ContentType.TEXT_PLAIN);
File f = new File("[/path/to/upload]");
builder.addBinaryBody(
    "file",
    new FileInputStream(f),
    ContentType.APPLICATION_OCTET_STREAM,
    f.getName()
);
HttpEntity multipart = builder.build();
uploadFile.setEntity(multipart);
CloseableHttpResponse response = httpClient.execute(uploadFile);
HttpEntity responseEntity = response.getEntity();

For developers still using HttpClient 4.0 (not recommended), the following code snippet uses the deprecated API:

HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
FileBody bin = new FileBody(new File(fileName));
StringBody comment = new StringBody("Filename: " + fileName);
MultipartEntity reqEntity = new MultipartEntity();
reqEntity.addPart("bin", bin);
reqEntity.addPart("comment", comment);
httppost.setEntity(reqEntity);
HttpResponse response = httpclient.execute(httppost);
HttpEntity resEntity = response.getEntity();

Other Java libraries that support multipart/form-data POST requests include:

• Apache HTTP Components HttpComponents-Client: A modern, thread-safe HTTP client library
• Jersey Client API: A high-level, easy-to-use RESTful web services client library
• Grizzly REST Framework: A framework for building RESTful web services

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