Java MultiPart post

Question

I am trying to create a multipart post to a URL with the following body:

Content-Disposition: form-data; name="json"
Content-Type: "application/json; charset=UTF-8"

{"input1":"data1","input2":"data2","input3":"data3"}

--APIMultipartPost
Content-Disposition: form-data; name="filePath"; filename="myFile.dat"
Content-Length: 381645
Content-Type: text/plain
Content-Transfer-Encoding: binary

<!-- SNIP -->
<!-- The OWL file was included here in plain text (without the SNIPs) -->
<!-- SNIP -->

I tried using MultipartEntityBuilder to create the multipart post, but probably I do something wrong with the parameters. Can someone help me with the java code for this post?

Here is my code:

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost uploadFile = new HttpPost(URL);

MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.addTextBody("input1", "data1");
builder.addTextBody("input2", "data2");
builder.addTextBody("input3", "data3");

builder.addBinaryBody("file", new File("C:/myFile.dat"), ContentType.APPLICATION_OCTET_STREAM, "myFile.dat");
HttpEntity multipart = builder.build();
uploadFile.setEntity(multipart);
HttpResponse response = httpClient.execute(uploadFile);

and the error I get:

HttpResponseProxy{HTTP/1.1 422 Unprocessable Entity [Server: nginx/1.6.0, Date: Wed, 28 Jan 2015 19:29:42 GMT, Content-Type: application/json;charset=utf-8, Content-Length: 89, Connection: keep-alive, Status: 422 Unprocessable Entity, X-Rack-Cache: invalidate, pass, X-Content-Type-Options: nosniff] ResponseEntityProxy{[Content-Type: application/json;charset=utf-8,Content-Length: 89,Chunked: false]}}

Thank you!

Answer 1

The response 422 Unprocessable Entity says

The 422 (Unprocessable Entity) status code means the server understands the content type of the request entity (hence a 415(Unsupported Media Type) status code is inappropriate), and the syntax of the request entity is correct (thus a 400 (Bad Request) status code is inappropriate) but was unable to process the contained instructions. For example, this error condition may occur if an XML request body contains well-formed (i.e., syntactically correct), but semantically erroneous, XML instructions.

so as you can see the request you send doesn't fit with the specification of the controller/service that you POST to. If you use a tool like TCPMon you can actually intercept the request that you send and check how it looks like. When I do it with your code, it looks like

POST /url HTTP/1.1
Content-Length: 739
Content-Type: multipart/form-data; boundary=L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c
Host: 127.0.0.1:8090
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.3.6 (java 1.5)
Accept-Encoding: gzip,deflate

--L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c
Content-Disposition: form-data; name="input1"
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

data1
--L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c
Content-Disposition: form-data; name="input2"
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

data2
--L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c
Content-Disposition: form-data; name="input3"
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

data3
--L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c
Content-Disposition: form-data; name="file"; filename="myFile.dat"
Content-Type: application/octet-stream
Content-Transfer-Encoding: binary


--L2EqtNqIEXOWRCYYrYH8FSP1JAD65wz6c--

which is not what you want. You only need a request with two parts, one is the json data and the other is the file.

So if you change your code as the following.

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost uploadFile = new HttpPost("http://localhost:8090/1");

MultipartEntityBuilder builder = MultipartEntityBuilder.create();
String jsonStr = "{\"input1\":\"data1\",\"input2\":\"data2\",\"input3\":\"data3\"}";
builder.addTextBody("json", jsonStr, ContentType.APPLICATION_JSON);
builder.addBinaryBody("file", new File("/path/to/file"),
        ContentType.TEXT_PLAIN, "myFile.dat");

HttpEntity multipart = builder.build();
uploadFile.setEntity(multipart);
HttpResponse response = httpClient.execute(uploadFile);

You can provide a request like the following.

POST /url HTTP/1.1
Content-Length: 468
Content-Type: multipart/form-data; boundary=mN_bWsS4QQnlPJksvinB_WUpl2Qi6zVVElUEEBKh
Host: 127.0.0.1:8090
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.3.6 (java 1.5)
Accept-Encoding: gzip,deflate

--mN_bWsS4QQnlPJksvinB_WUpl2Qi6zVVElUEEBKh
Content-Disposition: form-data; name="json"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit

{"input1":"data1","input2":"data2","input3":"data3"}
--mN_bWsS4QQnlPJksvinB_WUpl2Qi6zVVElUEEBKh
Content-Disposition: form-data; name="file"; filename="myFile.dat"
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: binary


--mN_bWsS4QQnlPJksvinB_WUpl2Qi6zVVElUEEBKh--

which is what you need.

Answer 2

For multipart request, the content-type has to be multipart/form-data, then you specify content-type for each content. You might want to refer to w3.org - Introduction to forms for the HTTP header examples.