app = FastAPI()


@app.post("/urlencoded")
async def post_url_encoded(age: Annotated[Optional[int], Form()] = None):
    return age


@app.post("/multipart")
async def post_multi_part(
    age: Annotated[Optional[int], Form()] = None,
    file: Annotated[Optional[bytes], File()] = None,
):
    return {"file": file, "age": age}


client = TestClient(app)

import java.io.IOException
import okhttp3.MediaType.Companion.toMediaType
import okhttp3.MultipartBody
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.RequestBody.Companion.asRequestBody

class PostMultipart {
  private val client = OkHttpClient()

  fun run() {
    // Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image
    val requestBody =
      MultipartBody
        .Builder()

 [PostMultipartJava]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/PostMultipart.java
 [PostMultipartKotlin]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/kt/PostMultipart.kt
 [ParseResponseWithMoshiJava]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/ParseResponseWithMoshi.java