I am trying to send a file to a Java API endpoint from a JavaScript application. The Java endpoint accepts a binary string for the file in documentation. In the Java code it is accepting a MultipartFile. I’ve tried a few things to convert the JavaScript Base64 encoded file string, but still receiving “415: Unsupported Media Type”.

Here is my recent code attempt:

  const handleFilesCallback = async (result) => {
    const fileBase64String = result.value.content; // get Base64 encoded file
    const byteCharacters = atob(fileBase64String); // convert to byte string
    let ia = new Uint8Array(byteCharacters.length); // build Uint8Array
    for (let i = 0; i < byteCharacters.length; i++) {
      ia[i] = byteCharacters.charCodeAt(i);
    }
    const binaryString = new Blob(ia, { type: "" }); //create Blob        
    sendFile(binaryString);
  };

Here is the API call:

const sendFile = async (file) => {
  const response = await fetch(
    "javaApiUrl",
    {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        yourFile: file,
      }),
    }
  ).catch((error) => {
    console.log("error:", error);
  });
  const responseJSON = await response.json();
  return responseJSON;
};

How do I convert the Base64 encoded file string so the MultipartFile/binary string portion of the Java API is happy with what I send it?