Toolpaper

Send multipart form-data with cURL in Java

Paste a curl command that sends multipart form-data and get idiomatic Java code. We pick the right serialization for OkHttp and set the correct Content-Type.

Quick answer

To convert a cURL command to Java, paste it into the Toolpaper workbench below. It parses the command in your browser and emits idiomatic Java code — headers, query string, request body, authentication (Bearer, Basic, API key), and cookies are all wired up automatically. No data is uploaded; conversion is fully client-side.

Prefer a different target? See the full cURL to Java reference, or jump to the same guide in JavaScript, Node.js, or Python.

InputcURL command
MethodPOST·Headers0·Body—·Form2 fields· Chars 100
OutputJVM · OkHttp(modern JVM)
import java.io.File;
import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public class Main {
  public static void main(String[] args) throws Exception {
    OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
    clientBuilder.followRedirects(false).followSslRedirects(false);
    OkHttpClient client = clientBuilder.build();
    MultipartBody.Builder mp = new MultipartBody.Builder().setType(MultipartBody.FORM);
    mp.addFormDataPart("file", "/path/to/photo.png", RequestBody.create(new File("/path/to/photo.png"), MediaType.parse("application/octet-stream")));
    mp.addFormDataPart("caption", "Hello");
    RequestBody body = mp.build();
    Request.Builder rb = new Request.Builder().url("https://api.example.com/upload");
    rb.method("POST", body);
    try (Response response = client.newCall(rb.build()).execute()) {
      System.out.println(response.body().string());
    }
  }
}
Inspect

Example

A representative curl command for this scenario. Paste your own above to convert an exact match.

curl input
curl -X POST https://api.example.com/upload \
  -F "file=@/path/to/photo.png" \
  -F "caption=Hello"

Implementation notes

  • Content-Type is detected from -H headers first, then inferred from the body shape when the header is missing.
  • Each -F flag becomes a distinct part; file@ paths are surfaced as OkHttp file handles so the multipart boundary stays valid.
  • Charset directives on Content-Type (e.g. application/json; charset=utf-8) survive the round trip.

Common mistakes

  • Setting Content-Type manually and then also using OkHttp's helper — you end up with duplicate headers or the wrong one wins.
  • Forgetting @ in -F "file=@upload.png" — without it curl sends the literal string, not the file. The generator flags this.
  • Trusting the browser DevTools "Copy as cURL" to preserve charset — it often drops it. Clean panel restores common defaults.

Common questions

How is multipart form-data encoded in the generated Java?
-F flags translate to multipart form-data with proper boundary handling — files={...} in Python, MultipartFormDataContent in C#, MultipartBody.Part in Java/Kotlin.
Does it preserve Content-Type?
Yes. The Content-Type header is honored and matched against the body so serialization stays consistent.
Is anything uploaded?
No. Parsing and generation happen entirely in your browser.

More payload types in Java

Java hub →

JSON in Java

/how-to/send-json-with-curl-in-java

form-urlencoded in Java

/how-to/send-form-with-curl-in-java

XML in Java

/how-to/send-xml-with-curl-in-java

GraphQL in Java

/how-to/send-graphql-with-curl-in-java

The same guide in other languages

All guides →

In JavaScript

/how-to/send-multipart-with-curl-in-javascript

In Node.js

/how-to/send-multipart-with-curl-in-node

In Python

/how-to/send-multipart-with-curl-in-python

In Go

/how-to/send-multipart-with-curl-in-go

In PHP

/how-to/send-multipart-with-curl-in-php

In Ruby

/how-to/send-multipart-with-curl-in-ruby

In Rust

/how-to/send-multipart-with-curl-in-rust

In Kotlin

/how-to/send-multipart-with-curl-in-kotlin

Full Java reference on the cURL to Java hub, or open the main converter for all 18 targets.