RestClient Bean can not call API with method GET contains body about spring-framework

[bclozel]

I've tracked this behavior to #10207. This is because HttpUrlConnection does not support setting a request body for "GET" requests and will turn it into a POST request automatically. In Spring, our request factory will avoid sending the body altogether to avoid turning it into a POST.

See the JDK code in action here: https://github.com/openjdk/jdk/blob/jdk-23%2B25/src/java.base/share/classes/sun/net/www/protocol/http/HttpURLConnection.java#L1431-L1433

You can verify that in action without Spring being involved with:

String body = "test body";
URL url = new URL("http://localhost:"+port+"/test");
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("GET");
con.setFixedLengthStreamingMode(body.length());
con.setDoOutput(true);
con.setRequestProperty("Content-Type", MediaType.APPLICATION_JSON_VALUE);
OutputStream outputStream = con.getOutputStream();
outputStream.write(body.getBytes(StandardCharsets.UTF_8));
outputStream.flush();
outputStream.close();

int responseCode = con.getResponseCode();
assertThat(responseCode).isEqualTo(200);

This will send the request as a POST:

2024-06-04T12:07:37.206+02:00 DEBUG 11214 --- [restclient] [    Test worker] s.n.www.protocol.http.HttpURLConnection  : sun.net.www.MessageHeader@249b54af7 pairs: {POST /test HTTP/1.1: null}{Content-Type: application/json}{User-Agent: Java/17.0.11}{Host: localhost:52192}{Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2}{Connection: keep-alive}{Content-Length: 9}

In this case @ngocnhan-tran1996 , please use a different request factory for your client. You can configure the request factory manually for your entire application or add a library on the classpath that will be picked up instead of the default one.

[snicoll]

Thanks for the sample. The underlying ClientHttpRequestFactory are not the same. When you create the client yourself, you get Spring Framework's default, i.e. org.springframework.http.client.JdkClientHttpRequestFactory. If you configure the client using the builder that Spring Boot has auto-configured for you, you get a org.springframework.http.client.SimpleClientHttpRequestFactory.

The former is new in 6.1 and Spring Boot couldn't swap the default behavior for backward compatible reason, see spring-projects/spring-boot#38856 and the issue that it links.

I am not sure why SimpleClientHttpRequestFactory wouldn't write the body. @poutsma, do you know?