Java 9 HttpClient send a multipart/form-data request

Question

Below is a form:

Answer 1

A direction in which you can attain making a multiform-data call could be as follows:

BodyProcessor can be used with their default implementations or else a custom implementation can also be used. Few of the ways to use them are :

1. Read the processor via a string as :

   HttpRequest.BodyProcessor dataProcessor = HttpRequest.BodyProcessor.fromString("{\"username\":\"foo\"}")
   

2. Creating a processor from a file using its path

   Path path = Paths.get("/path/to/your/file"); // in your case path to 'img'
   HttpRequest.BodyProcessor fileProcessor = HttpRequest.BodyProcessor.fromFile(path);
   

OR

3. You can convert the file input to a byte array using the apache.commons.lang(or a custom method you can come up with) to add a small util like :

   org.apache.commons.fileupload.FileItem file;
   
   org.apache.http.HttpEntity multipartEntity = org.apache.http.entity.mime.MultipartEntityBuilder.create()
          .addPart("username",new StringBody("foo", Charset.forName("utf-8")))
          .addPart("img", newFileBody(file))
          .build();
   multipartEntity.writeTo(byteArrayOutputStream);
   byte[] bytes = byteArrayOutputStream.toByteArray();
   

   and then the byte[] can be used with BodyProcessor as:

   HttpRequest.BodyProcessor byteProcessor = HttpRequest.BodyProcessor.fromByteArray();
   

---

Further, you can create the request as :

HttpRequest request = HttpRequest.newBuilder()
            .uri(new URI("http:///example/html5/demo_form.asp"))
            .headers("Content-Type","multipart/form-data","boundary","boundaryValue") // appropriate boundary values
            .POST(dataProcessor)
            .POST(fileProcessor)
            .POST(byteProcessor) //self-sufficient
            .build();

---

The response for the same can be handled as a file and with a new HttpClient using

HttpResponse.BodyHandler bodyHandler = HttpResponse.BodyHandler.asFile(Paths.get("/path"));

HttpClient client = HttpClient.newBuilder().build();

as:

HttpResponse response = client.send(request, bodyHandler);
System.out.println(response.body());