java.net.http.HttpClient POST request sends empty body

Question

Java (tested on JDK11 and JDK17) HttpClient POST request with a "hello" body delivers empty body to the server.

val response = java.net.http.HttpClient.newHttpClient()
    .send(
        java.net.http.HttpRequest.newBuilder()
            .uri(URI.create("http://...."))
            .POST(java.net.http.HttpRequest.BodyPublishers.ofString("hello", StandardCharsets.UTF_8))
            .build(),
        java.net.http.HttpResponse.BodyHandlers.ofString());

No exception throw, response.statusCode() is 202, the content-length header shows 5, but the request body is empty. Tested against multiple server implementations and Postman mock server.

I am executing this code from within a JUnit test.

OpenJDK 64-Bit Server VM Temurin-17.0.5+8 (build 17.0.5+8, mixed mode, sharing)

Update 2023-02-05

Debugging into the JVM, I see two buffers are queued for posting. One contains 9 characters (encoded message start frame?) and the second contains my 5 characters 104, 101, 108, 108, 111 (i.e. hello).
The body publisher then seems to only send the first 9 characters and never my actual 5 character payload. Log follows (please pardon the length):

Full java.net.http log file

I'd try setting a Content-Type: text/plain header somehow (but I don't know this particular API). — tevemadar
– tevemadar, Commented Feb 5, 2023 at 11:15
@tevemadar, you got it. I was trying so many different combinations (actually trying to send some binary data with some custom content-type), and removed the content type setting, while creating the minimal repro. HttpRequest::header("Content-Type", "text/plain") — Jan Dolejsi
– Jan Dolejsi, Commented Feb 5, 2023 at 13:26

Jan Dolejsi · Accepted Answer · 2023-02-05 13:37:33Z

Per @tevemadar's suggestion, setting a content type (Postman) makes the HttpClient push the data, (or the server to pull the data).

Adding .header("Content-Type", "text/plain") helped made the body appear on the other side. Full code:

    var response =
        java.net.http.HttpClient.newHttpClient()
            .send(
                java.net.http.HttpRequest.newBuilder()
                    .uri(URI.create(uri))
                    .header("Content-Type", "text/plain")
                    .POST(
                        java.net.http.HttpRequest.BodyPublishers.ofString(
                            "hello", StandardCharsets.UTF_8))
                    .build(),
                java.net.http.HttpResponse.BodyHandlers.ofString());

Not setting any content-type on the HttpRequest makes the HttpClient::send method call (or the server-side) ignore the request body (or perceive it as an empty body). There is no error, no warning, nothing in the JDK debug logs.

Setting any (even wrong) content type makes the body come across to the server side.

Nine Su · Accepted Answer · 2025-09-18 05:40:27Z

-1

enter image description here

You need to specify HTTP version as HTTP_1_1, the default is HTTP_2

answered Sep 18 at 5:40

Nine Su

1

1 Comment

Mo_ Sep 18 at 6:30

Hi, please don't post code as images. edit your answer and use markdown code blocks (```) instead

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