How Can I Send Multipart/Form-Data POST Requests in Java?

Multipart/Form-Data POST Requests in Java with Apache Commons HttpClient

Prior to version 4.0 of HttpClient, it was possible to send multipart/form-data POST requests. However, this capability was removed in version 4.0. The HttpClient developers deemed multipart handling to be out of scope for their project.

Alternative Java Libraries for Multipart/Form-Data POST Requests:

Despite the absence of multipart support in HttpClient 4.0, several Java libraries provide this functionality:

• Apache Commons FileUpload: A dedicated multipart parsing and formatting library from Apache.
• Jersey Client: A REST API client framework that includes multipart support via its Form class.
• OkHttp: A modern, efficient HTTP client with built-in multipart request support.
• UniRest: A lightweight HTTP request library with multipart capabilities.

Example Implementation with HttpClient 4.3:

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost uploadFile = new HttpPost("...");
MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.addTextBody("field1", "yes", ContentType.TEXT_PLAIN);

// Attaching the file to the POST:
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);

Example Implementation with Legacy HttpClient 4.0 (Deprecated):

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);

Conclusion:

While HttpClient 4.0 does not support multipart/form-data POST requests by default, alternative Java libraries and code snippets can help developers achieve this functionality. By leveraging these resources, users can effectively implement HTTP clients that handle multipart requests and integrate seamlessly with web services like Zoho Writer's Remote API.

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